So anyway, the first photo shows the roof of my Taurus in beautiful, scenic Fauquier County, Virginia.

Ugly Mag Mount in Beautiful Countryside

Farms, countryside, cattle, horses, even foxes with the view spoiled by the unsightly, ugly cable coming from the magnetic mount antenna on the auto roof top.

I never considered punching a hole in the roof of my Ford Taurus. I don’t have anything against this, but mag antennas have, quite simply, always been around to serve my mobile antenna needs. After years of weathering, it’s time to consider a through hole mount on the old Ford Taurus.

CBs, K-40 and Big Momma

What, on Earth, am I talking about? I am not embarrassed to say I worked in a popular CB Shop in Fairfax, VA during the college years – 1980s. This was a superb experience. I installed CBs and Antennas in vehicles from compact cars to Firebirds to pickups to Tractor Trailers to RVs. I even designed a CB Antenna for someone’s hot air balloon.

The easiest antenna to install was the K-40. However, another popular antenna of the day was the Antenna Specialist “Big Momma” CB aerial. This antenna was once found on every VA State Police car. The key difference between the K-40 and Big Momma twist off mount was the addition of car ground connection whereas the K-40 only connected the coax center conductor. I never quite understood, then, why a base loaded 5 foot whip would need a ground connection. Little did I know I saw my first NMO mount antenna.

New Motorola (NMO) Mounts

Back then I thought the NMO mount was an over designed mount. Who needs the ground connection to the whip? If it is a simple quarter wave or loaded short antenna, you don’t. However, if you use a transformer with one end tied to ground, the NMO is the perfect mount to use.

Indeed, my further research found that NMO is pretty much the defacto mount used in professional applications for antennas of all kinds. One standard threaded connection provides for an unlimited choice of antennas that one can replace as requirements change. Nice.

NMO Through-hole Mount Choices

Current Antenna with various NMO Through Hole Replacements.

Research on the Internet reveals quite a few selections to ponder when considering through hole NMO antenna mounts. Choices include:

• 3/8″ or 3/4″ hole
• Open or shielded cable connection point
• Name brand of cheap knockoff
• Hole Saw or Metal Punch

3/8″ vs. 3/4″ Hole
It is quite clear the traditional installation of NMO uses a 3/4 inch hole. This is precisely what I thought I was going to do. However, I stumbled onto one web site offering a 3/8 inch option and I had to know more.

It seems the 3/8 inch option is primarily used for mounts that must attach to very think metal… 1/8″ or thicker. If I can get a way with a 3/8″ hole in my Taurus I was willing to try it. Let’s compare the advantages of each.

Advantages of 3/4″ NMO through-hole mount include:

• Mount can be drilled and installed from the outside (Cable routing extra of course)
• Seems to be the “way” to do it
• 3/4 inch specialty drills available to drill hole, but not go any deeper

Advantages of 3/8″ NMO through-hole mount include:

• Smaller hole
• Potentially sturdier with smaller hole

Open or Shielded Connection Point
While searching for NMO mounts to consider, I stumbled onto a web site showing an NMO mount with a completely metal enclosed connection area. This is to ensure little RF energy escapes into the human occupied area. Apparently some countries require this. The US does not seem to have such a requirement, but I purchased one of these for review… see below.

Name Brand or ‘other’
One thing that became obvious after reading the forums about NMO mounts is the suggestion to use brand name parts from Laird, Motorola, Larson, etc. The NMO mount is standardized, but the suggestion is quality tolerances may be loose in off-brand parts.

One problem I had while shopping was knowing just what brand parts were being sold. After receipt of my examples, shown below, Laird and Antenex were the primary manufacturers. However, only two of the four vendors said so on their web site and in the sales receipts.

Hole Saw or Metal Punch
No one in the metal industry uses hole saws for small holes like this, however, it appears just about every installer of mobile antennas does. When installing through-hole CB antennas back in the day, the bossman insisted on the use of his metal punch. It did make superb holes requiring very little de-burring.

One clear problem with punches is the need for tool access to both sides of the metal. I can see where busy installers desire top only access and the hole saw is about the only way to get it.

Fortunately Laird and others make a hole saw specifically for use with NMO installation. The good ones have a pilot drill bit followed by a “wood hole saw” like cylinder and, most important, a shoulder that stops the thing from going too far into your vehicle. I did not see such a tool for 3/8″ installation, but you need bottom access for this anyway, so a punch or carefully used drill may be just fine.

Pictures hard to find
One particularly annoying thing with most of the NMO Vendor web sites is the lack of specific pictures for the particular model you are trying to buy. The descriptions were fine, but seeing the thing helps. So for the readers of this web site, here are some pictures of the actual items purchased.

Vendor A – Off brand NMO Mount for 3/8″ or 3/4″ Hole

Unknown manufacturer NMO Mount for 3/8 or 3/4 inch Hole

I’m not really too hip to that bent metal back support as it feels a bit cheap. The main barrel is for the 3/8″ hole, but the metal back support has too small knockout bumps which help center it in a 3/4″ hole.

Vendor B – Antenex (Laird) MABTO NMO Mount for 3/8″ or 3/4″ Hole

Laird Brand NMO Mount for 3/8 inch or 3/4 inch Hole

This unit has a longer barrel for thicker base-plates than the MABO (below). The sales receipt says precisely “Antenex 3/4″ or 3/8″ Hole NMO Antenna Thick Mount MABTO” as did the web site when I purchased it. The Laird bag it came in says this is for a 3/8″ hole. However, the fine print on the bag describes the purpose of the white washer is a centering washer when you use this mount in a 3/4 inch hole.

Vendor C – Laird MBO NMO Mount for 3/4″ Hole and MABO for 3/8″ Mount

Laird Brand NMO Mount for 3/4 inch Hole

This Laird item may be the “classic” NMO mount. It is for the traditional 3/4″ hole. The top component and backing component are actually just one piece. The backing component has a nice centering cylinder milled right into which looks like it will nestle right into the hole and keep it in place. This unified unit feels and seems very solid.

Laird Brand NMO Mount for 3/8 inch Hole

This is also from Laird with the only difference between it and the MABO is the backing piece shape. This one has no 3/4 inch centering ridge milled in it.

Both the MBO and MABO Laird mounts impress me.

Vendor D – Unknown Manufacturer NMO Mount for 3/4″ Hole with FME Connector

Possible Motorola Brand NMO Mount for 3/4 inch Hole with FME Connector

This product contains a 90 degree coaxial connector. The RF energy is obviously well contained. There are only two pieces and the bottom portion is one solid block of metal. I don’t know a lot about the FME connector.

Conclusions

Laird (Antenex) easily won my admiration for quality and function. Vendor mis-information and lack of product specifics forces the buyer to do their own research into product selection. I hope the pictures of actual products above help you select the best NME through-hole for your application.

My final choice is likely between the MBO and MABO. Upon close examination the only real difference between the two is the milled 3/4″ circular “shelf” on the MBO inner foot and the size of the threaded connection between the top and bottom pieces. Many reports from the field suggest the 3/4″ MBO style is “much stronger” than the 3/8″ MABO style, but the folks never seem to have any clue as to why. The outer dimensions of the inside foot for each are identical and, thus, transfer stresses to the metal identically. The cylinder of metal between the two is the same diameter. It’s plainly obvious the 3/8″ unit transfers mechanical stress over a larger surface area of vehicle metal with the smaller hole. I will prototype both onto a scrap piece of metal, show it to some machinists and MEs to get their take on this.

More details to come.

73
John, kx4o

That’s not the point though. If we were to cut off the connector we would surely still see a spark from center conductor to shield. If the cable were near station ground I would expect a spark jump. That large a charge has to go somewhere.

The point is a wire, any wire, with wind blowing on it will build a static charge. We should keep this in mind as we design our antenna systems. Including a DC path to ground is prudent.

I cannot imagine a more teachable YouTube moment. Thanks to the poster for making this video available.

Here is a link to a very old video which explains quite nicely what and how static charge occurs…

http://video.google.com/videoplay?docid=2306375174608358801&hl=en#

73

1. Crimp on connectors have been the norm in industry since at least the 1970s. I’m just ashamed it took me so long to figure this out.

I cannot comment on the mechanical realities of the antenna flying off the roof during rapid changes in speed, but can say I have never seen one do so. I encourage anyone with data to propose their article to this web site

So…

Let’s talk about the electrical conductivity of a standard mount vs. a magnetic mount antenna. Here is a quote from the newsgroups concerning antennas for scanners…

The average mag-mount antenna gets its “ground” from the magnetic attraction between the mount and the metal of the car body. This is nowhere near the quality of a good, solid ground connection to the body. We are relying here on the mount, the paint on the car, and the metal underneath to form a “capacitive ground connection”. (I scared myself with that one !) The smaller in diameter the magnetic mount is, the less effective this is. It is a simple matter of total area covered by the mount.

First while the mag mount antenna does hold itself to the car via magnetic attraction, there is no other direct electrical benefit related to the magnetism. There is no magnetic “coupling.”

The post author correctly identifies the ground connection happens due to the capacitor created between the bottom of the antenna and the metal of the vehicle. The claim this is worse than a direct connection via set screw or other demands verification. Let’s do some math to check this out.

First some assumptions:

• Paint thickness of autos seems to range from 75-200 microns. Add in clear-coat and primer this might grow to 3x or so. I am not a paint guy so I am not at all sure about these figures, but since capacitance is reduced at greater thickness, we will assume 600 microns for our calculations or about 24 mils (1 mil = 1/1000 inch).
• Typical small 2m ham antenna with 3 inch base.
• Braid of coax electrically attached to the foil on the bottom of the antenna. Did you notice that mag mount antennas have electrical foil to make the antenna side of the capacitor?
• We will derive the capacitive reactance of the above details at 50MHz, 144MHz and 440MHz
• Dielectric Constant, K, of clear coat and paint something like 3

Figure 1 shows a simplified model of antenna electrical parameters:

Fig 1 - Currents in and around a magnetic antenna.

• The Radiation Resistance is the thing you want your transmitter to work into.
• The Ohmic loss is the simple resistive loss of the antenna and its inner connections.
• The sum of the Shield Currents exactly equal the current on the inner conductor and flow back to the transmitter on the inside of the outer conductor. If you do not connect the antenna’s ground to the local ground around the antenna, the current will simply flow back on the outside of the outer coax conductor and create havoc for your radio and possibly you.
• This fact applies equally well to ground mounted HF vertical antennas and is why radials are so important.
• Xc is actually part of the resistance from coax shield to ground and adds directly to the overall impedance.
• Keeping every resistance or impedance small with respect to the radiation resistance makes or breaks an antenna’s efficiency.

Calculating Capacitance between Antenna and Metal

The forumla for the capacitance between two conducting plates is:

C = 0.2258 * K * A / d

Where…

• K is the dielectric constant of the material,
• A is the overlapping surface area of the plates in square inches,
• d is the distance between the plates in inches, and
• C is capacitance in pF (pico Farads – 1×10^-12 Farads)

Capacitor Area = pi * r^2 = 3.14159 * 1.5^2 ~ 7 sq. in.

Capacitance(pF) = 0.2258 * 3 * 7 / 0.024

Capacitance(pF) = 198pF

Xc = Capacitive Reactance = 1/(2*pi*f*C)

Results:

• When f = 50MHz => Xc = 16 Ohms
• When f = 144MHz => Xc = 6 Ohms
• When f = 440MHz => Xc < 2 Ohms

This probably represents the worst case where the car’s paint and clear-coat are super thick as assumed above. Let’s redo the calculations for a more probable 8 mils…

Capacitance = 0.2258 * K * A / d

Capacitance(pF) = 0.2258 * 3 * 7 / 0.008

Capacitance(pF) = 593pF

Xc = Capacitive Reactance = 1/(2*pi*f*C)

Results:

• When f = 50MHz => Xc = 5 Ohms
• When f = 144MHz => Xc < 2 Ohms
• When f = 440MHz => Xc < 1 Ohm

The above calculations reveal mag mount antennas do, indeed, provide a very robust AC coupling of the RF shield currents to the metal of the car via capacitive currents.

The impedance presented by the mag-mount/metal interface adds directly to the radiation impedance of the antenna resulting in the final impedance of the antenna approaching 50 ohms… ~36 ohms + Xc. This also directly affects the efficiency of the antenna just like a ground radial system helps a ground mounted vertical.

The post author does understand the area of the mag mount bottom in contact with the car matters with larger being better. He goes on to say…

I am not going to launch into a big tech discussion here, with foot-long words, and math that would give you (and me) a headache. You will just have to take my word for it. And, the really sad part is, the higher the frequency that you monitor, the worse this gets

This is where his understanding breaks from reality. The higher the frequency the better. The math is straight forward; You do not have to take anyone’s word for it. All other things being equal, capacitors conduct better at higher frequencies as the above math shows. There is no need for foot-long words, but full understanding does require doing some math.

What we have shown above is magnetic mount antennas do, indeed, provide a good connection to the metal it is attached to so long as there is a foil bottom attached to the shield of the coax and the area of this bottom is reasonable large. It is true that as the frequency goes down, the mag mount antenna efficiency also goes down. Many CB antennas for 27MHz have much larger bases not only to support the longer whips, but to provide that extra contact area to keep the Xc low.

It can be argued this large capacitor in contact with the metal of the vehicle may well be more effective than trunk lip mounts that make their contact with one or two small set screws dug through the paint to the metal of the trunk lid or gutter. This is, of course, if the trunk lid is made of a conductor… many are not. This is all especially true if high power is applied to the antenna system. The magnetic mount antenna provides the unique advantage of spreading out the ground currents over a large area rather than through the finite points of locking screws.

A properly installed though-hole NMO mount probably beats the mag mount in shield to ground plane connection as its design provides a large direct contact area from shield to hole avoiding the set screw problem.

When shopping for a magnetic mount antenna you might well benefit from a unit that keeps the Capacitive reactance below, say, 10% of the antenna impedance. For a quarter wave antenna of about 36 ohms that means the mag mount impedance should be under 3 ohms. Much depends on the frequency, paint thickness, dielectric constant and area. Armed with the above technique you can comparison shop with better clarity.

With the above method of calculation, you can easily convince yourself that, at least electrically, the magnetic mount antenna works just fine in many situations and provides the added bonus of putting the antenna in the best position without need for a hole in the roof.

What follows is the experiment which provides proof Velocity Factor of Coaxial Cables does not apply to cables used simply as a wire in parallel with another wire.

The Experiment

The two Baluns are an excellent pair to compare. The Coaxial Cable Balun is just two transmission lines tied together one 1/4 wavelength long, the other 3/4 wavelength long. In this case the electric and magnetic fields are entirely within the dielectric material. Thus the velocity factor adjustment should apply. The Pawsey Stub relies entirely on becoming a parallel transmission line with the feedline coax. Its fields are entirely outside the structure of the coax.

I built the two baluns using some RG316 coax. My target frequency for both is 300 MHz. I cut pieces with no corrections applied to see how the frequency changes.

The Coaxial Cable Balun has the following dimensions based on calculations…

• 1/4 wave section = 300m/s / 300 MHz * .25 = 25cm ~ 9.8 inches
• 3/4 wave section = 300m/s / 300 MHz * .75 = 75cm ~ 29.5 inches

I simply cut two pieces of coax to the above lengths and added a third with an SMA connector for the feed line.

Figure 4 shows the Coaxial Cable Balun with a 50 ohm resistance at the balanced feed point.

Fig 4 - Coaxial Cable Balun with 1/4 and 3/4 sections of coax, cut for 300MHz Freespace, in parallel.

With the resistance at the feedpoint, the Balun should show some very obvious frequency dependence on a Return Loss or SWR plot. Because this is the case where Velocity factor does apply, the target frequency of 300 MHz should be lowered by .695 or about 208 MHz. Given that I flayed the coax shield and center, thereby reducing some of the coaxial cable length, the actual frequency should be a little higher.

Figure 5 shows what happens when I connect the Coaxial Cable Balun to the VNA…

Fig 5 - Return Loss of Coaxial Cable Balun from 100 - 500 MHz. Markers M1 and M2 are at 300 and 214 MHz respectively.

Wow the 214 MHz pretty confirms that Velocity Factor is well in play for this style of Balun.

Now let’s try the Pawsey Stub. The only critical dimension is the stub length.

• 1/4 wave section = 300m/s / 300 MHz * .25 = 25cm ~ 9.8 inches

Once again, my trimming slightly shortens the actual electrical length to about 9.2 inches which raises the frequency just a bit. Figure 6 shows my test unit with 50 ohms at the feed point.

Fig 6 - Pawsey Stub Balun with 1/4 of coax, cut for 300MHz Freespace, in alongside the feedline.

What’s the prediction here? If you listen to the web sites which suggest coax cable VF applies, the frequency will be between 210 and 230 MHz. If I am right and this is free space, or very close to free space, then the frequency should be about 300 MHz, or since the connection points on the stub are a little closer together, about 320 MHz. Let’s see the Return Loss plot…

Fig 7 - Return Loss of Split Coax Balun from 100 - 500 MHz. Markers M1 and M2 are at 300 and 322 MHz respectively.

Bulls Eye!!!!

This conclusively proves external stubs, like the Pawsey Stub, should be calculated using free space wavelengths without corrections for Velocity Factor.

The funny thing is, this has been the case in the ARRL Antenna book for many many years. The book never suggests to apply velocity factor to external stub calculations. However, they never say don’t either.

Conclusion
It is a good thing Amateur Radio Operators know about transmission line Velocity Factor specifications. Without this knowledge you would be cutting stubs incorrectly. However, some Amateurs assume that just because a piece of coax is used for a stub, Velocity Factor applies. The key to understanding when it does and when it doesn’t is found by following the electric and magnetic fields. Where are they? Are they inside the coax or outside between pieces of coax? If inside, apply VF. If outside assume freespace.

Measure, but verify…
This experiment relies on some crude cutting of cable lengths and assumed values of Velocity Factor. Potential sources of error include:

• Cable End Trimming – Source for my slight errors above
• Coax Velocity Factor not what the manufacturer says – When you do need to know VF, it might be a bit off especially with lower quality coax
• Freespace not quite freespace – Even the best air gap transmission line has some dielectric material in the fields – VF values of 0.95 are common even with parallel transmission ladder line.

So what does this suggest? If you are going to the trouble to make something as critical as a Balun for your Yagi antenna, electrically measure each cable with your SWR meter or VNA to ensure you are spot on the frequency of choice.

This was an interesting test. I am now so interested in Baluns, I will focus on posts for each type in the near future.

Thanks for reading.

John

VHF and UHF antennas, especially beams, often have balanced feed points. Several methods exist to connect unbalanced coax to the dipole element: gamma, t-match, etc. Some VHF/UHF Balun options use tuned stub or shunt topologies to achieve the unbalanced to balanced goal; Methods include the Pawsey Stub, Split Coax Balun and Coaxial Cable Balun. Each of these requires specific lengths of conductors based on multiples of 1/4 wavelength at the design frequency.

When calculating 1/4 wavelengths, however, it seems the amateur radio community has lost the collective knowledge of when Velocity Factor (VF) of Coaxial Cable Dielectric Material applies. Indeed despite the decades of college texts and ARRL Antenna books showing otherwise, the idea Velocity Factor always applies to coaxial cable length calculations when used as nothing more than a wire stub in a Balun seems to have gone viral on the Internet.

The web site of G0KSC provides innovative new approaches to Yagi-Uda design. The author provides focus on the topic of Baluns on his Creating a Balun web page.

The topic of baluns is vast so let’s just focus on the ones for VHF/UHF antennas. Most often these are tuned assemblies using some combination of coax and/or wire stubs at specific lengths.

G0KSC highlights several Baluns on his web page:

• 1:1 Coaxial Cable Balun I have never seen before using 1/4 and 3/4 wavelengths of coax. This is similar to the 4:1 Balun we have seen for decades in the literature.
• 1:1 Pawsey Stub – a method using a 1/4 wavelength wire off the coax center conductor and tied a 1/4 wavelength back.

One comment made on the web site concerns velocity factor of coax. Certainly the Coaxial Cable Balun has this effect which requires shortening wavelength dependent coax pieces. The author also claims the Pawsey Stub requires the same adjustment for velocity factor. The electric and magnetic fields for the Pawsey Stub are outside the realm of the coaxial cable dielectric suggesting this is not the case.

I decided to build working models of both to see for myself which Balun requires Velocity Factor correction.

First let’s examine the two Balun approaches.

1:1 Coaxial Cable Balun
Figure 1 shows the pieces of this Balun…

Fig 1 - 1:1 RF Balun using 1/4 and 3/4 wavelength coaxial cables.

This topology is deceivingly simple. A description can be found at I0QM’s web site PDF file.

Pawsey Stub
Figure 2 shows the idea behind the Pawsey stub which is well known in Electrical Engineering circles as a variant of the Split Coax Balun.

Fig 2 - Split Coax Balun (aka Pawsey Stub)

While the Gray conductor in Figure 2 only needs to be a wire of similar size to the coaxial cable feedline, it is often made from a scrap piece of the same cable. Each end of the outer shield of the stub is connected to the feed system. A common thought of many is since this is coaxial cable, we need velocity factor adjustments. Since the electric and magnetic fields (of the stub system) are in air, I think velocity factor does not apply.

Figure 3 highlights my reasoning…

Fig 3 - Electric and Magnetic fields in dielectric materials define when velocity factor applies.

Figure 3a shows the construction of coaxial cable we are all familiar with. In normal operation all electric and most of the magnetic fields are contained between the inner and outer conductors. Since the spacing between these conductors is maintained by an insulating material, the fields are completely dependent on the dielectric constant of this material.

Figure 3b shows the same coaxial cable, but this time there are two pieces side by side as used in the Split Coax Balun. This balun, essentially a parallel transmission line, develops all its fields between the outer skin of the cables’ shields, not within. The stub wire, as used in the Pawsey Stub method, could be a copper wire with the same effect.

The studious reader will notice the external fields are not entirely in free air. The cable jacket certainly has a dielectric constant greater than 1 and, as thin as it is, will retard the speed of light a bit. The effect is much less than the situation inside coax, however. So… the VF of free air is not quite 1, but almost is… about 0.90 to 0.98 or so.

I assert the typical 0.6-0.8 values of velocity factor of coaxial cable should not be used for stub length calculations for stubs with fields outside the cable’s interior.

Am I right?

Part 2 of this series highlights the actual test I performed to prove I am correct.

Despite being a popular and productive way of simulating amateur radio antennas, another method of electromagnetic simulation makes use of the Finite-Difference Time Domain (FDTD) method.

Without going into too many details, the method divides up the simulation space into little cubes of volume. Then the next magnetic field values are derived from the current electric fields. Then the next electric field values are derived from the current magnetic fields. Repeat.

FDTD makes use of Maxwell’s equations to calculate the above fields. Being a Time Domain method, what follows shows a movie like display of what is happening in the antennas in super slow motion.

The cool byproduct of this style of simulation is we get to see a movie of magnetic and electric fields as power is applied to an antenna. The fields build up around the antenna and eventually fill the volume with energy. For both styles of hex beam antennas you can see after a few cycles how the parasitic element becomes energized. Once both elements are energized the beaming action takes place and you can see energy propagating forward.

Both simulation movies reveal the magnetic fields in the first 50 seconds and the electric fields in the second 50 seconds. They, of course, happen at the same time to yield Electro-Magnetic fields, but I could not show both in a meaningful way.

Here is a 10 meter Traffie (Classic?) Hexbeam…

Here is a 10 meter G3TXQ Broadband Hexbeam…

Neat eh?

No simulation technique is perfect, but the FDTD method’s ability to show EM in time is very cool.

If you are interested in FDTD, Google has quite a bit of information. There are some free tools out there for the taking.

I already have a post concerning my selection for the hex beam’s center hub. After reviewing the several aluminum plate styles offered by Leo, Hexkit and many others, I chose the molded Hex Beam Aluminum Hub by DX Engineering.

For wire I purchased 200 feet of 14 AWG Flexweave with Clear UV Resistant PVC Insulation. This wire is simply fantastic and has saved my bacon several times including at Field Day 2010 when I had to unravel the hex beam. My only concern is will it stretch over time and change the tuning. Time will tell.

So I had the hub and the wire. All I needed to finish the beam was spreaders and some rope.

I thought about the spreaders far too much. I read every post on the Hexbeam Yahoo forum. Many folks were using things like fishing poles, plumbing PVC and other locally available products for the spreaders. The consensus seemed to be fiberglass was the material of choice for long term enjoyment of the hex beam antenna.

Some folks said they found fiberglass poles locally. I could not. So I examined what Leo was using and saw Max-Gain Systems provides an appropriate kit of intersecting poles for both the Traffie style MW Hex Beam and Steve’s (G3TXQ) Broadband. I am not a cheap ham, but I did have a budget. After some thought, I realized I had already committed to Cadillac components starting with the amazing DX Engineering Hexx Hub. In about three seconds I decided to order the kit of poles from Max-Gain Systems and be done with the selection process.

Below are some photos of the arrival plus subsequent modifications and assembly of the Max-Gain Systems fiberglass kit. I needed some of the black rope also so simply added that to my Max-Gain order.

I cannot complain one bit about the Max-Gain Systems fiberglass poles. They just work.

Not discussed are the two 1 inch x 48 inch fiberglass poles also shipped by Max-Gain. One of these poles is for the vertical center pole of the antenna. The other is simply a spare pole that comes with the fiberglass kit. I wound up using PVC for the center pole and saved the other pole for future possibilities. However, I did make good use of the spare pole; I used some of it to reinforce the PVC from the bottom of the antenna to just above the hub. The 1 inch fiberglass tube fits perfectly inside 1-1/4 inch PVC. This allayed my concerns the PVC pipe would simply crush when clamped into the rotator and the PVC would buckle during rough handling. The fiberglass pole inside the PVC pipe provides a sturdy inner core.

I wish I could have run the fiberglass the whole length of my hexbeam’s center post, but the wire connection bolts prevent this. I am still satisfied as I think most of the stresses in the center post exist between the rotator and the center hub. PVC plus fiberglass core exist in this critical area.

I now have a portable (mostly) contest band broadband hex beam and it really does work pretty darn well.

This G3TXQ Broadband Hexbeam project exceeds my expectations wonderfully well.

Radios included an Icom IC-756 Pro, TenTec Omni VII, Icom IC-746 (for the GOTA) and a Icom 7000 for VHF plus HF spare. All these radios performed quite well despite the high temperatures.

The 100 Watt Elecraft K2 stood above the others not necessarily on performance, but the elegant way the radio’s owner configured his K2, 100 Watt Amplifier and 100 Watt Matcher.

For this Field Day, Tom brought his personally built Elecraft K2 QRP rig. Options include KNB2, KDSP2, KIO2 and KAT2.

Additionally, he brought his personally built Elecraft 100 Watt amplifier with the 100 Watt Antenna Tuner. Products include the KPA100 and KAT100-2.

No Case Change for 100 Watts
Elecraft has done a wonderful job with integration of all the above. The K2 and the KAT100-2 communicate with a serial cable. The usual approach for a 100 Watt K2 is to integrate the KPA100 into the K2’s case. However, Tom really wanted to keep the K2 a QRP rig. No problem. Elecraft supports the idea of placing the amp inside the KAT100-2 case. This leaves the K2 as is, but provides a power boost just by plugging in the KAT100-2 case. The K2 does not require a case change to get 100 Watts; Nice.

Look at this picture…

Clean, simple and effective Field Day Station with Elecraft K2

It just doesn’t get much simpler does it? Yes, I realize a typical radio with 100 Watts built in would yield one less box, but these are so small the extra box doesn’t get in the way. The two things missing from the above station layout is a good head set and CAT connection to the N3FJP logging software.

…and look at this…

The Elecraft K2 Field Day Station in Trailer with G3TXQ Hex Beam

Minimalist. Okay I agree anyone who brings a beam to Field Day is not quite minimalist, but really, even with the other dipole antenna, there isn’t all that much to this station.

Attaching the 100 Watt Tuner to a K2 with its own Tuner
Note the Elecraft K2 also has the QRP antenna tuner option KAT2. Both the KAT2 and KAT100-2 offer A/B antenna selection. Tom wondered if there would be a conflict or confusion with the K2 firmware if the KAT100-2 was added to the system already containing the KAT2. Specifically, when the KAT100-2 is attached, does the Antenna selector button know to move the antenna selection action from the KAT2 to the KAT100-2. The answer is yes it does. Simply connecting the KAT100-2 to the K2 causes the KAT2 to stay on one output, the one piped to the KAT100-2, and switches between 100 Watt antenna ports on the external box. Cool!

Elecraft to the Front Row
Tom has customized an ideal station for Field Day and I enjoy using it every year. As this year’s Field Day Chairman, I placed the K2 as the primary HF station, closest to our visitors are and showcased it to everyone I could. You hear that Elecraft? I showcase your products and don’t even own a K2 or K3 yet!

The K2 Station worked plenty of Phone and CW contacts with its wire dipole and hex beam on ports A and B of the KAT100-2. The K2 with Hex Beam worked the only Pacific contact, Phone, from our Virginia Field Day location; I was stoked.

Conclusion
With radios like the Elecraft K2, one can realize an effective Field Day station. By moving the 100 Watt amplifier from the K2 case to the KAT100-2 case, the K2 can switch to QRP with simple external cable changes instead of cabinet swaps.

Bravo Elecraft.

Even though building a new K2 kit costs more than the radio trades for on E-Bay, I plan on a purchase anyway just for the fun of assembling my own radio; I will seriously consider duplicating Tom’s configuration above. I can’t wait.

Bob Bruninga is organizing the second annual Golden Packet event up and down the Appalachian Trail along with some new West Coast trail activity. Last year the Virginia team was successful in placing an APRS packet repeater on White Rock Cliff. We desire to repeat the process again this year.

Details on the White Rock Cliff ARPS station are on Bob’s site…

Particularly needed is a backup APRS radio, like the Kenwood D700/D710 along with a 7 AH GelCell along with the Hiker to haul it up the mountain.

If you would like to join the hikers in this ham endeavor, please contact John, KX4O, at kx4o@hamradio.me.

One of the stations used an Elecraft K2 with an external power amp plus the 100 watt auto tuner. The Elecraft auto tuner provides two antenna ports. We connected a large dipole to channel 1 and left the other open for another antenna.

At some point during Field Day I decided things were going well enough for me to concentrate on my 20-15-10-06 meter hex beam of the G3TXQ variety.

As you can tell by the first photo below, the hex was hastily shoved into the trailer. However, I used good Flexweave wire for the elements and untangling the mess was straight forward. I decided the put the hex beam on the K2 station since it had the open antenna port and, for some reason, I think the K2 and the hex beam complement each other.

The hex beam was a bit loose in its rigging causing the elements to slump a bit. However, the thing tuned right up on 20, 15 and 10 meters similar to its debut during the Virginia QSO Party. Six meters was way off; I think the 10 meter wires were a bit too close to the six meter wires. No matter, the K2 had no 6 meters and 10 meters seemed to work well enough.

Results

Did it work? Boy it sure did. During my turn at the K2 Phone I found the hex beam provided two to four S units improvement against the dipole on 20 and 15 meters.

Late Saturday night I worked 4,800 mile contact with Hawaii (PAC) from Virginia with ease on 20 meters… on Phone! The Hex Beam and K2 bagged the only PAC contact of the four stations on site.

Several more 20 meter contacts were easily made to the West coast including LAX, SDG, SCV and WWA. I wish Field Day used Sections as multipliers, but I was glad to be able to add fresh contacts to the club’s totals. Tom, owner of the K2, quickly added many CW contacts using the beam.

The hex beam was up only about 15 feet and still worked quite well. Amazing.

We did have a rotator, but did not have it aligned with North. That was troubling, but I was just glad to be able to steer it at all at Field Day. We used a Channel Master TV type rotator. Yes, it works, but clearly is over stressed by the inertia of the hex beam despite its low mass. Anyone contemplating a rotator for their hex beam is well advised to “up” the rotator ratings quite a bit to ensure mechanical robustness.

Of all the compact compromise Yagi-Uda beam designs out there, I have to say the hex beam lives up to its own hype. There’s no magic in the hex beam (no matter what anyone tells you). It can’t outperform full size single band Yagi-Uda designs. However, for the investment, it is a superb value and deserves to be on anyone’s short list of antenna choices.

Choice Matters

The most important thing learned at this Field Day is having two antennas to select between makes a big difference in operating success. For some reason North Florida was alive with contacts and I sometimes used the hex beam and other times the wire dipole on 20 and 15 meters.

Yes, it’s Field Day and we tend to be minimalist. However, I designed this hex beam to be very portable and think it fits well with the Field Day theme with its simple tent peg tripod mount. It nicely complements a wire dipole.

The G3TXQ 20-15-10-06 meters Hex Beam antenna is a keeper for Field Days of the future.

Here is a picture.

Trailer Load for Field Day 2010

My finest hour this is not. It will do though.

Good luck with Field Day 2010 everyone.

John

Seafood, sand in everything you own, beach strolls, a time with family away from the usual distractions of life.

What better to do at the beach than visit the local lighthouse… especially a big coastal light station like Assateague Lighthouse on the Eastern Shore of Virginia.

Of course being a ham makes you notice things others miss with your “hammy eyes.”

Follow along in this picture tour of our visit to Assateague Lighthouse in 2007 and see the unusual thing we found within.

Welcome to the Lighthouse...

The Majesty...

Amazing Stairs...

There is just something cool about metal stairs forged from pig iron rather than crafted from sheet metal. Lots of people were climbing and descending and these things shook not.

Superb Views...

30 Mile Lights...

A Duplexer...

Stout Machinery...

WAIT

A Duplexer in a Lighthouse !?!?!

Yes that’s right. We walked right past a repeater system run by the Fish and Wildlife service. Here is a close up of the controller…

The repeater controller on its side.

…and here is a view of the duplexer…

The Repeater's Duplexer

Six cans… three each for receive and transmit. Each can has two connectors suggesting these are the band pass type. I didn’t see any external components like you find with Band Pass plus Notch types.

That looks like Heliax between the Tee connector and the antenna… Right On! Keep that IMD and PIM at bay. The whole system is just below the observation deck of the lighthouse. I sure hope those are N connectors and not PL-259s. Hmmm, I wonder where the antenna actually is? Let’s look at another ground view photo…

View looking up at repeater antenna.

Aha, I think I see it. Let’s zoom in…

Collinear Repeater Antenna

There it is… a four element Collinear array spread out a bit for coverage. I really have to wonder how the brick of the lighthouse, and its metal stairs within, mess with this repeater’s footprint. Of course it may be plenty good enough and we all know “Better is the enemy of Good Enough.”

I guess I was caught off guard seeing this equipment just laying on the floor for anyone to bump into. Notice the power cord is “right there” and not very secure. I’m not saying the Fish and Wildlife Service is an integral part of homeland security, but it probably makes sense to secure this equipment just a little better. These pictures were taken in 2007 so who knows what is there these days. I certainly can’t argue with the Fish and Wildlife folks about their choice for their antenna position. Assateague Lighthouse is the tallest structure along much of the shoreline.

Lighthouses offer something for the whole family and, in the case of Assateague in 2007, something for this ham too.

I needed some quick deploy Baluns for the 80 Meter Turnstile Antenna covered earlier on Ham Help Desk.

Also purchased were two DXE-UWA8X-KIT products which provide hoisting points and strain relief for RG-8 size coax.

Mechanically I could not ask for a better solution for a High Frequency Balun. At 31 oz. (878 g.) this unit is not a lightweight object, but has a good solid feel. The serpentine wire grip feature of the T-Insulator works absolutely fabulous for the #14 insulated wire I chose for my dipole elements.

The DX Engineering approach to their mast mountable HF Baluns works very well for my needs. I was concerned over reports about their Baluns not working correctly in the upper portion of the HF band; This is why I used these for the 80 meter antenna first. However, the VNA tests above indicate decent functionality up to 30 MHz as stated on their label.

The only issue I have with this product is there did not seem to be the right kind of fasteners to attach the strain relief bracket to the coax end of the housing. I wound up using one of the press fit bolts (bolts with a square shoulder that prevents the bolt from turning after installation into plastic) in the metal hole. There was enough hardware in total, but not quite the right assortment. This is obviously not correct, but my make shift rushed solution worked fine the day I put it up. If you are putting up an antenna with this Balun and its strain relief kit for your coax, be sure you don’t expect out of the packet perfection; If you want the correct hardware, allow yourself a day or two to make a trip to the hardware store (pick stainless hardware).

With good electrical response plus decent mechanical assembly, I am quite pleased with the money I spent on this Balun. DX Engineering has nicely solved the usual issues we have with our wire dipoles leaving only the task of how to hoist it up into the air.

http://www.nwaprs.info/

This site helped me shorten my APRS learning curve.

There is nothing new about small loop antennas. They have been discussed in the literature for decades. The ARRL has some very old articles about them in the 1968 March and July editions.

Constantine A. Balanis’ book on Antenna Theory discusses and defines large vs. small loops. This book is an essential reference if you seek the details on how loops work. The loop described below fits into the “small loop” category where the currents along the conductor are, for all practical purposes, constant. This is unlike full size antennas where current reaches a minimum where voltage approaches maximum. Since this loop is electrically short with respect to wavelength, current does not change “much.”

The bands of interest in this year’s experiments were 80 and 40 meters. We had to balance scientific research with a hard deadline of March 2010… in other words engineering.

Here are some highlights and details of our small loop…

• Loop dimensions 4 – 8 feet – Fits into the bed of a full size pickup truck,
• Feed point middle of bottom horizontal conductor,
• Capacitor middle of top horizontal conductor (Note the literature describes a way to avoid having the capacitor in the top, but we stuck with the simpler approach),
• Current of loop will be tens of Amps, perhaps up to 50 A – Fat pipe necessary,
• Voltage across Capacitor will be thousands of volts, perhaps up to 5 kV – Vacuum Variable is an good choice,
• We used shunt loop feed at bottom,
• We used 1 inch plumbing pipe and elbows,
• Silver solder a must to keep conductivity high,
• Vacuum variable capacitor selected to provide tuning capability – some use coaxial cable caps for fixed frequency use.

Here are various pictures…

Did it work?

It sure did. You might notice we never finished a method to tune the vacuum variable remotely so we were stuck with leaving the thing tuned for 7265 kHz. However, the mobile operator made frequent AB comparisons between the loop and his 40 meter ham stick. I was on the other end of the contact several times and could not tell any difference. This does not suggest the loop was better than the ham stick, but at least the loop didn’t stink.

We were pressed for time to get this thing on the air for VAQP 2010 so the mobile operator took the loop as is from our tree testing. During the contest he found the feed loop worked with a much smaller diameter than we originally anticipated. On the fly adjustments resulted in this final configuration here…

Finished HF Mobile Loop ready for contacts. Feedpoint shunt loop is much smaller than originally anticipated.

There are several things left to do including engineering some way to tune the vacuum variable remotely. This will be well worth the effort since our manual tuning revealed this should work on a variety of bands. The capacitor is a surplus 5-500 pF (5 to 3 kV) model form Surplus Sales.

According to the literature, small “magnetic” loops like this have an antenna aperture similar to a full size dipole. If this is true it should be an impressive benefit for otherwise compromised mobile operations.

If you are considering a small loop antenna be sure to understand this is a very small bandwidth antenna. A future post will provide details, but don’t expect the bandwidth to exceed a few kHz from center. You cannot use a traditional tuner with this antenna. The variable capacitor is the only way to move the frequency.

As a first foray into Magnetic Loop antennas, I think we achieved success. Work still needs to be done to see if this really is a practical antenna for mobile (or even fixed) use, but results show promise.

Thanks go out to W2BRI’s web site for lots of great ideas…

• http://www.standpipe.com/w2bri/

Money was really no object since the connector is often the weak link in the system and deserves quality. I just made an investment in 240 feet of LMR-400 cable and wasn’t about to shortchange the connector.

Friends suggested the classic twist-on then solder-the-braid type of PL-259. I recognized this type would fit my coax fine, but I ignored the advice since industry (especially Aerospace) shuns shield solder connectors for a variety of good reasons.

The attributes for my PL-259 connectors were…

• Low Ferromagnetic Content to reduce IMD – This is hard to find. “Pro” connectors are made of brass and plated with silver. Sometime in the 1970s nickel plated steel came on the scene. I certainly did not want Nickel Plating. I figured steel connectors were in my future, but silver plating was mandatory.
• Solder Center Conductor
• Crimp Shield Over Connector Barrel
• Adhesive Heat-Shrink Tubing to cover the crimp

Good connectors are brass with silver plating, solder center and crimp shield plus come with a pre-cut piece of appropriately sized heat-shrink.

Fleeman, Anderson & Bird Corporation offers a good compromise connector at a fantastic price.

It does NOT come with the heat-shrink, but they sell that too in four foot lengths.

A good crimp tool is necessary with a .429 hex crimp die.

Yes, these are not cheap, but I made the investment and put it in the tool bag. It has been used dozens of times spreading its cost. I have no regrets purchasing this tool.

So anyway this post is just to let amateurs know good quality crimp connections are available today with the supplies from Fleeman, Anderson & Bird.

Someone with a name like McVey, claims membership in REACT, is a Ham possibly, has Whacker lights on his mobile and carries a gun…

…is “held at the request of federal authorities.” Priceless.

You just can’t make this stuff up folks.

Article from Breitbart

It looks like the guy did nothing wrong, but being a whacker is not illegal, silly yes, but illegal no.

So…

I am finally getting around to using APRS. It seems to me APRS applications, such as UI-View, are older and lack recent releases. I realize UI-View’s author is no longer with us. Does anyone here have some thoughts on good software for use with the APRS system?

73
John

Fair enough.

I was glad to order this book to see how EmComm might be done from a well organized perspective. I sat down one evening and opened it up. Here is the first sentence…

?

There is nothing tragic about grammatical errors; I make quite a few myself. However, I would expect a published book to not have such a glaring error in the first sentence of the first paragraph of the first chapter! This is not a great way to initiate a knowledge transfer of EmComm techniques.

We need to keep one thing in mind; It is the liberal elite who are in charge at the moment and they do know their grammar… well most do anyway. They are the customer of what we are selling.

Thankfully, the content of the chapter contains some good common sense EmComm discussion, but the review of that is for another post.

I have been adding various gadgets to my Ford Taurus to bring battery power into my passenger area so I can get rid of my cigarette lighter plug for my 2m/440 radio.

Adding a wire to my original battery posts was a problem so I used replacement posts from the car audio market. This turned out to be a mistake.

The original equipment battery posts on my car were the molded type which left no room to add any terminal or lug to the tightening hardware. So I turned to the Hi-Fi car audio market to see how the massive power needs of the “booming” stereos are met. All I found were fine looking chrome products. I really did not care about the chrome, but the terminal did have multiple holes for four wires: two large and two small. It looks like this…

Scosche battery terminal

Nice features include a way to attach your large gauge starter cable, the car’s power cable and your additional power cable for your extra equipment. Unfortunately, my Taurus’ starter cable is small and won’t fill even the smaller socket. I stuffed the car’s negative starter cable and power system ground into one of the smaller holes. Since I was not quite ready to install the rest of my power system, I left the positive terminal stock.

Then the big 2010 snow in Northern Virginia occurred. The house power went out so I retrieved the battery from my Taurus to run my 12 Vdc backup sump pump. This worked great. However, when I put the battery back into the Taurus and tightened the Allen screw to snug up to the negative post, the mechanism inside the Scosche terminal broke. Off to the auto parts store I went.

The only battery terminals available at this particular auto parts store were the simple lead clamp style. I purchased two installing one on the negative lead. This terminal has only one place to clamp wires. I decided to put not only the starter wire and the electrical system wire, but also my negative transceiver power wire into this clamp. I was worried about just shoving all three wires into this clamp, but, in the end, I got it in. After tightening, all three wires feel very secure. The car started with no issues suggesting this method is working for now. Here is a picture of the new terminal with all three wires…

Lead Terminal - Simple

No this isn’t much to look at, but makes the point this simple $1.25 post works just as well or, in my case, even better than the fancy chrome terminal. Don’t get me wrong, if you are pimping your ride, these chrome terminals look great, but I am trying to pimp my power.

This figure reveals the old and new posts along with the broken piece.

Fancy and traditional battery post terminals.

That extra sleeve sitting on the battery handle near the broken piece came with the chrome post adapter and was needed to make it work on the negative terminal. Yes, the negative terminal is the larger of the two posts on batteries so I don’t know why I needed the sleeve, but I did.

Conclusion

I was confident the Automotive HiFi accessories would provide benefits to the ham community with their similar peak current electrical environment. A post with multiple output ports seemed like just the thing for grabbing additional power straight from the battery terminals. In practice, it turns out to be not a good fit… at least for my Ford Taurus. The Ford’s wires were too small to take advantage of the large wire holes. The chrome post adapter easily broke with routine use. In the end, a good old lead terminal worked just fine even with three wires stuffed into it. I will check this terminal’s wire clamp often to be sure of its longevity.

I think I can now replace the positive terminal with confidence the $1.25 terminal works better than the chrome model.

Mine sure does, but I found a simple solution that keeps things cool without a lot of whoosh noise.

I have a CSi/SPECO 13.8 Volt 18 Amp model which serves my puny little 100 Watt station very well.

This power supply is a linear regulated type with plenty of pass transistors in the back embedded in a nice large heatsink. There are two problems: the heatsink fins are oriented horizontally and the heatsink gets far too hot to touch after being on for a while.

I know… I know many of you are thinking my 18 amp power supply is a little underrated for a 100 Watt station and that is the reason for the excessive heat. You may have a point, but the situation here is this power supply gets way too hot to touch with no load on it. It takes quite a while, but the heat eventually builds up and reaches an equilibrium point where you simply cannot touch it for more than a few seconds. I never measured the temperature so cannot be sure how hot it really got. It was just… hot.

As a circuit designer I am well aware of how much punishment good final transistors can take (some have max junction temperatures of 275 C!!!). However, cooler running is always going to increase reliability of all electrical components.

It’s a shame the heatsink is oriented horizontally as the system would probably be measurably cooler with chimney effect air flow. I was not willing to put the power supply on its side.

So what to do…

Adding a fan to move air across the heatsink was an obvious necessity. I considered AC fans and 12 Volt fans, but found them to be quite loud. They work fine, but made far too much whoosh noise. They work so well they blow a great deal of air across the heatsink, but I wondered if I really needed so much air flow to get my high temperature under control.

As it turns out I had a similar issue back in the 1990s when faced with defending the movement of a heatsinked 7905 regulator connected to -12 Vdc from just above some cooling fans to a few inches away. The original designers were concerned my moving the regulator away from the direct blast of the fans would be too costly in cooling performance.

The regulator was dissipating several watts of power so this was a reasonable question. I devised a test to determine the cooling performance of air flowing past a heat sink vs. the fan-heatsink distance.

I moved the regulator circuit with its heatsink out of the cooling cage and into still air. I placed a thermocouple on the heatsink. I obtained a muffin fan and wired it up to a power source. While holding the fan various distances from the regulator, I made the following observations.

Fan Off:

The temperature of the heatsink climbed steadily past 50 degrees C above ambient reaching dangerous levels in a short time terminating this test.

Fan On and held 1 inch from the heatsink:

The temperature of the heatsink remained at room temperature.

Fan On and held 6 inches from the heatsink:

The temperature of the heatsink was, maybe, about 1/2 degree above ambient.

Fan On and held 12 inches from the heatsink:

The temperature was about 2 degrees above ambient.

Fan On and held 18 inches from the heatsink:

The temperature was about 4 degrees above ambient.

Fan On and held 24 inches from the heatsink:

The temperature was about 7 degrees above ambient… O come on how can this be still cooling the regulator at two feet?

Fan On and held 32 inches from the heatsink:

Temperature about 20 degrees above ambient.

Fan On and held about 36 inches form the heatsink:

Temperature about 40 degrees above ambient and varying quite a bit.

This data is better shown in the graph below…

Heat Rise vs. Fan Distance (Airflow)

This revealing test shows fin heatsinks are actually very good at coupling heat to the air with remarkably little airflow. However, there has to be at least some airflow to prevent heat saturation at the heatsink air boundary and that is, apparently, where you realize most of the cooling benefit.

All I needed was some airflow, not a hurricane.

All the fans I found all worked great, but made a lot of noise. I thought about creating a simple little regulator circuit to knock down the 13.8 Vdc to something lower and slower. With the goal of operating a fan lower than its voltage rating I remembered some DC busses run at 24 volts or so and have plenty of compatible products including fans.

So I decided to purchase a 24 Vdc fan and run it off the 13.8 Vdc power supply voltage to slow it down to a slight breeze. Avoiding the step down regulator by simple component choice kept things straightforward.

Here is the simple install of my 24 volt fan running “slow.”

Slow running fan provides adequate air flow.

The use of banana plugs keeps fan power connections tidy.

I found some twisted pair cable and used that to connect the 24 Vdc fan to the power supply’s output via a couple of banana plugs. The green banana plug is not related to the fan, but illustrates the ease of adding more connections by stacking the banana plugs. No RigRunners or Anderson Power Poles needed for this low current load.

Results?

With the 24 volt fan running on 13.8 Vdc, it quietly and gently provides airflow across the horizontal fins of the power supply’s heatsink. This airflow works so well you can barely feel any rise in temperature when touching the heatsink. Success!

The final issue I had with this arrangement was the fan vibrating my desktop thereby generating audible noise. This was easily solved by putting a loosely folded piece of paper underneath the fan to serve as a vibration isolator. It works FB. No its not earthquake proof, but functional.

Conclusion

Power supplies, especially economy models like mine, often omit fans and rely on the very high temperature rated components to just take the abuse. This can work, but the addition of a simple 24 Vdc fan running slow on the supply’s 13.8 Vdc output provides more than enough cooling capacity to keep the output transistors at a far lower temperature than without. Cheaper insurance is hard to find.

Cool your power supply today… It will love you for it.