[Elecraft] Power Supplies

[Don Wilhelm]

Kev,

Yes, common mode current can be a problem on receive as well as transmit.
Transmit will cause RF-in-the-shack which is more obvious because you 
can be 'bitten' by RF.  On receive, the common mode current will result 
in added receive noise due to pickup of noise on the transmission line.

OCF antennas are notorious for common mode currents as are end feds.  A 
balanced antenna is usually easier to tame, but are not immune.

For effective common mode chokes (some call them baluns or in-line 
isolators), review the papers of K9YC Jim Brown on the subject. He has 
posted many times on this reflector - bottom line is that many baluns 
and in-line isolators are not very effective, how much so depends on the 
frequency and the core material used.

In addition, if your antenna feedline does not run perpendicular to the 
antenna for at least 1/4 wavelength, it can pick up currents from the 
radiator.  Yes, transmit is more extreme, but it happens in receive as 
well.  Antennas and transmission lines are bi-lateral devices, so what 
happens in transmit happens in reverse on receive.  The transmit effects 
are easier to measure because the signals are larger.

As for the power supply itself, heed the information provided by Howie 
Hoyt in this thread - he has done extensive testing in his development 
of the PAE Kx33 power supply.

73,
Don W3FPR



On 7/15/2016 5:01 PM, Kevin - K4VD wrote:
> Thanks Dick and Howard...
>
> The RS-50 is pretty new - maybe 6 months old and is in daily use. It wasn't
> until I had a rig I could easily run on batteries did I notice the noise.
> The RS-12 is quite old, maybe 15 years? It had been in storage about 10
> years until trying it out today. I think I need to dig into the RS-50 and
> just make sure everything is soldered and connected well.
>
> As for common mode currents in the antenna... would that only be an issue
> during transmit? I have an OCF so I know it can be an issue on transmit.
> The OCF has a 1:1 current BALUN in the center. Is that enough or do I need
> to add some additional choking just below the BALUN? I have a couple of the
> NI4L line isolators (http://www.ni4l.com/hf-choke-line-isolator-1-8-300-mhz/).
> I could put one up there and see what it does. I also have plenty of
> clip-ons laying around. I'll try them on the power lead from the supply to
> the radio.
>