Two radios on one power supply cause problem

A viewer has a problem powering two radios from one power supply.

This situation is quite likely very common among amateur radio operators who keep a simple shack set up with one large power supply feeding multiple loads.

Many operators use a DC power distribution system like the RIGrunner from West Mountain Radio to distribute the power.

In this case, the viewer simply has the power cords for both radios tied straight to the DC power output posts on the power supply.

Equipment involved includes:

  • Power Supply Astron RS35A
  • IC-746 (the non pro version)
  • Kenwood TS-180S

The problem:
Whenever the Kenwood TS-180S radio is powered on, the Icom IC-746 will not transmit and the display screen goes white with no visible characters.

If you turn the Kenwood TS-180S off, the Icom-746 returns to normal operation.

The Kenwood radio shows no problems when the Icom is on or off.

The viewer asks for thoughts on what may be causing this behavior.

4 thoughts on “Two radios on one power supply cause problem”

  1. You might try these steps:

    First, mess with the orientation and placement of the DC power cables just to see if there is any noticeable change in behavior. Try coiling the DC cable to make a simple RF choke.

    Second, try wrapping each power cord around a type 43 toroid one toroid per radio power cable; This will help keep any common mode energy contained and may help.

    Third, try putting one or both radios into dummy loads.


  2. Looking at the schematic of Astron RS35A power supply ( and after making some calculations for 60Hz mains, it seems there are no real design issues in the PSU. The only thing I would personally change is the low value capacitor C103 across the output connectors. It is stated to be 10 nF, but I would use a much higher value, like 0.1 or 0.47 uF (non-electrolytic!) to reduce the possibility for HF band RF problems. So the problem is probably not in the PSU itself. Note! I would NOT use this power supply in Europe with 50 Hz mains, because the main filter capacitors would be too small. Most likely the mains transformer is also designed for 60Hz and would overheat with 50 Hz mains.

    I hope you are not trying to transmit with both radios at the same time, because you WILL overload the power supply:
    – IC-746 = 100W power OUTPUT (*2.2 = 220W power input) = 15.94 A @ 13.8VDC
    – TS-180S = 200W power INPUT = 14.49 A @ 13.8VDC
    – Total DC current = 30.39A (approximately)
    The Astron RS35A is specified for 25 Amps max. continuous duty and 35 Amps max. peak. Astron doesn't say what duty cycle (pulse length) for the peak current. To avoid problems, I would absolutely NOT load the power supply with more than 25 Amps peak nor continuous.

    If your problem appears without transmitting with either radio, it may be very difficult to figure out without knowing what else you have connected to the radios, like a PC, digital mode interface etc. etc. It looks to me like some kind of "unauthorized data" is entering the IC-746 and the Icom radio doesn't understand it, so to prevent any possible damage turns itself to "sleep" mode. This data could be stray RF, as KX4O suggests (if you are transmitting with TS-180S OR some other radio) or it could come from some other equipment connected to IC-746.

    Jukka, SV9RMU and OH2AXE

  3. After my previous post another thing came to my mind: Measure the output voltage of the Astron RS35A, when the Icom IC-746 radio is on, but Kenwood TS-180S is off. Then turn the TS-180S on and look at the voltage meter, if the voltage drops. If the voltage drops down even for a very short period of time, that may cause the IC-746 to do strange things, like what you described.
    Jukka – SV9RMU and OH2AXE

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