Previously we discussed SO2R gear arrangements which have two antennas connected to two radios, one antenna for each radio.

If all you have are two antennas for your two radios then there really is no point in putting in a matrix to allow either antenna to route to either radio.

However, let’s assume you do have a pressing need to multiplex the antennas and use this as an evolutionary step in our series of posts.

If we take our previous Simple SO2R station setup and add a routing matrix, we will have something like this…

The less simple SO2R setup adding an antenna multiplexer

The only difference from the previous design is the “Antenna Routing Matrix” box. This box allows the vertical antenna to connect to either radio and allows the dipole to connect to either radio. In this system you would basically have a straight-through or cross-over connection. Pretty simple and pretty pointless for only two antennas with two radios.

So let’s evolve the design to include an advanced, not so simple, contest station with many choices of antennas…

Advanced Antenna Multiplex with six antennas and two radios.

O yeah… that’s more like it. A 160 meter inverted-L, 80 meter dipole, 40 meter vertical, 20-10 meter dipoles round out the six HF contest bands. How I wish this was my station.

So what does the Antenna Routing Matrix do with the coaxial connections of our six antennas and two radios? Let’s stipulate some requirements…

• The Matrix shall allow Radio #1 to connect to any antenna.
• The Matrix shall allow Radio #2 to connect to any antenna.
• The Matrix shall prevent both radios from accessing the same antenna at the same time.
• The Matrix shall maintain RF electrical isolation between the radios.
• The Matrix shall never, ever allow one radio to transmit directly into the other no matter the excuse.

Here is one way to achieve these requirements…

A simpler version of a 6 x 2 antenna matrix switch

The radio RF ports connect to jacks J1 and J2. The antennas connect to jacks J3 through J8. Switches S1 through S6 allow any antenna to connect to either radio. Note how the topology prevents the radios from ever connecting to each other so long as the antenna ports are never connected to each other.

One problem with this design is the need for center off switches. Otherwise all antennas will be connected to the radios in some combination. If you want to use relays, one way around the center off requirement is to put another switch between each switch and the antenna port. Since most relays do not come with a center off option, this additional antenna isolation switch is a necessity.

Another common method adds two 1 x 6 switches like so…

A more sophisticated 2 x 6 antenna multiplexer

Switches S7 and S8 assign each radio to a particular antenna. The antenna switches S1 through S6 select which radio to connect to the antenna. Again neither radio can transmit into the other by accident; Even if both 1 x 6 radio switches select the same antenna, the antenna 1 x 2 switch selects one or the other, never both.

This is the method used in a few commercial products. Some products contain the whole 2 x 6 matrix. One product is a whopping 2 x 10 matrix. Still other products are piecemeal 1 x 2 and 1 x 6 switches leaving you to connect them with coax; As you can see this design requires a lot of coaxial connections, but many people do it this way.

The added bonus of the “more sophisticated” approach is the increased isolation between the two radios. Instead of one switch contact, there can by up to two open switches and one contact gap between the radios. This adds up to an incredible amount of separation between the radios made even better by the band-pass filters.

Available products include:

• Array Solutions Sixpak – Nice 2 x 6 coax switch with separate control head – $450
• Microham Double Six Switch – Indoor/Outdoor 2 x 6 coax switch – No manual control box option, expects connection to other products – $649
• Microham Double Ten Switch – Indoor/Outdoor 2 x 10 coax switch! – No manual control box option, expects connection to other products – $969
• Top Ten Devices Six Way Antenna Relay Box – Indoor/Outdoor(with drip enclosure) 1 x 6 coax switch usable as part of your 2 x 6 system per second schematic above – No manual control box option, uses control signals (from their band decoder for example) – $125
• Top Ten Devices A/B Station Selector – Indoor 1 x 2 coax switch usable as part of your 2 x 6 system per second schematic above – product designed to maximize isolation between ports, > 80dB – $77 or $390 for six

The above products have been available for some time. The contester crowd seems to use them often for their SO2R and multi-multi setups.

Conclusion
When you are ready to make a big leap forward in your contest station with ever more band-dedicated antennas, the above switching gear is what you will need to help implement SO2R.

In the next SO2R post, we will talk about the operator interfaces: microphone, morse keys, and computers.

Having one transmitter spewing energy at full power while trying to listen on the other radio’s receiver is daunting. Unless you have an Elecraft K3, your radio’s ability to perform adequate band pass filtering is probably not sufficient for the 2nd and 3rd harmonics from the transmitter resulting in severe de-sense of the receiver signal chain.

Orienting the antennas to minimize their interaction will help. If you are lucky you may well achieve good isolation between at least some of the cross band combinations.

To help radios avoid this interaction, a few manufacturers have products which provide excellent band pass filtering.

Enter the tunable (or selectable) band pass filter.

I found the following manufacturers with band pass offerings:

• W3NQN FilterMax multi-band BPF – 200 Watts – 160, 80, 40, 20, 15, 10 meters – Front Panel Controls plus remote control and an Ethernet option – ~$900
• ICE 419 B – Combination multi-band BPF – 200 Watts – 160, 80, 40, 20, 15, 10 meters – Front Panel Controls plus remote control – ~$288
• Dunestar Model 600: Multi-Band Remote Switched BPF – at least 100 Watts – 160, 80, 40, 20, 15, 10 meters – Remote control only – ~$379

There may be others so look around. Note some of the above manufacturers also have single band band-pass filters available. These might be appropriate inline near mono-band antennas. However, it is likely you are using one antenna for a few bands if you are just getting started in SO2R.

If we modify our station system diagram (shown in the previous post) by adding the multi-band band pass filters we get…

A simple SO2R setup including two band pass filters

I personally own an ICE 419B. I like it fine. It offers front panel controls as well as remote operation via signal inputs.

In the “Basic SO2R” you are unlikely to have automatic band switching capability (we’ll cover that in a future post). So having front panel controls makes sense. Not all models have front panel controls so you need to be sure you understand what you are purchasing if you decide to drop the coin on BPFs.

Contest Bands Only
There’s one thing you need to understand very clearly about these Amateur Radio Band-Pass Filters; They are for contest bands only. They only allow 160, 80, 40, 20, 15 and 10 meters through. WARC bands won’t work.

The ICE 419B has a “no filtering” mode. I don’t think this means the filters are removed. I am pretty sure it just allows all filters channels through in parallel. This suggests only the contest bands get through this device either one at a time or all at once.

The point is this. If you design these filters into your shack, you may well have to do something extra to operate in the WARC bands. Contest stations and regular stations have competing requirements. Keep that in mind.

Mixed Blessing
Adding filters to your ham shack is a great way to ensure your two SO2R radios have as much isolation as possible. As you continue to evolve your shack you will most certainly want to automate these filters so they track the selected band on the radio. Until that happens understand you will now have one additional thing to twiddle when you change bands.

Is filtering really need with modern rigs?
There are reports the Elecraft K3 provides sufficient filtering to prevent interference from the second harmonic of a lower band. True? I have no idea. If I had a K3 I would still have filtering until I know for certain I won’t damage the front end with the energy.

Conclusion
The market has provided band-pass options for contest stations for quite some time. The models appear to be mature and ready for your application.

Next we will examine how to take advantage of more than two antennas.

The ability to add a bit more excitement to those late contest constant CQs with an additional radio looking for other contacts, especially new multipliers, is inviting.

There are many resources on the Internet about why to do SO2R. I invite the reader to explore these resources. We will review a couple key concepts on why to do SO2R and then dig in deep to some technical approaches.

Reasons for SO2R

• Use an extra radio to search and pounce extra contacts while calling CQ with the “main” radio
• Turn late contest dead time into productive search and pounce on another band while still maintaining CQ on another channel
• Operated two bands at once – only one carrier at a time of course
• Multipliers can be significantly enhanced for your score
• Make better use of your antenna farm resources – two in use at a time rather than just one – again only one transmitting at a time

Basic SO2R
In theory SO2R can be accomplished with minimal resources. The figure below reveals just such a configuration…

Barebones SO2R

Key points include:

• Two transceivers each with mic and keys
• Two antennas suitably arranged to minimize mutual coupling – in this example Radio #1 uses a vertical antenna while Radio #2 uses a horizontal
• One computer to record contacts (yes, I know… I know this is not a practical contesting setup, but is possible)
• One savvy operator who can manage two radios at once and move between the two

Two Transceivers
Having two sets of inputs (mic and key) for the radios is not an ideal SO2R approach, but will work. One advantage of this arrangement is you always know exactly which radio you are transmitting with unlike more complicated approaches discussed in future posts.

Antennas
Since you are contesting, you are probably working on most or all of the usual 160, 80, 40, 20, 15 and 10 contesting bands. If you have only two antennas, each will need to be some kind of multi-band type. Another approach is to have one antenna on the lower bands and the other on the high bands. A tuned feed all bander for the low and a 20-15-10 beam for the high bands is one possibility.

Dual Microphone and Morse Paddles
While ultra redundant, having two mics and two Morse code keys is a mixed blessing. You probably have a favorite key which cost you good coin; Duplicating that can be expensive.

Logging Computer
No contest is really possible without the advantage of computerized contact logging. Dupe checking is the obvious benefit. Most folks connect their logging computers to their radio’s CAT port. However, if your logging software can’t handle multiple rigs you may as well leave it disconnected so your band settings can be set to whatever band “either” radio is on.

Summary of Barebones SO2R
Can Barebones SO2R work? If you have an extra rig and two antennas suitably arranged, sure. However, there has to be a better way. Read the next post for the next step up in SO2R complexity.

There is nothing like combining aspects of Field Day with a QSO Party style contest. Or is there?

Visit QSOParty.com for discussion about the creation of a new QSO Party.

See the post on QSOPARTY.COM for more details.

Thanks.