[Elecraft] Power Supplies

[Kevin - K4VD]

Hi Howard and thanks for your explanations and patience. I need to do some
more testing a little later on with the KX3 on the RS-50. If I remember
right, I could hear the hum and hiss from the RS-50 only when the antenna
was attached. I think that goes along with what you are saying and I just
need to wrap my mind around that. I am prepared to deal with RF issues
while transmitting but not so prepared to think the problem could show up
during receive also.

So far I've added the NI4L HF Choke/Line Isolator just under the BALUN at
the feedpoint and another just at the rig. I've also added a few snap-ons
to the DC cord between the RS-50 and the radio at the RS-50 side. I want to
add more as soon as I can find the rest of them or possibly replace them
with the 2.4" ferrites at your site.

After doing the above I've noticed my tuning points have shifted a bit. I
need to get the analyzer on it to see by how much. I also *maybe* noticed a
reduction in noise on the Flex but to tell you the truth, I never really
noticed it on the Flex, only the KX3 made it obvious being able to switch
from battery to external power supply.

I need to do a little more testing if I can find the time this weekend. I
see the 2.4" ferrite core on your website and will probably place an order
for a couple/few. Does something like this go on each end of a line or do I
pick an end?

Thanks again,
Kevin


On Sat, Jul 16, 2016 at 7:19 AM, Howard Hoyt <hhoyt at mebtel.net> wrote:

> Hi Kevin,
>
> As for common mode currents in the antenna... would that
>>> only be an issue during transmit?
>>>
>>
> Except for very special cases, antenna systems display reciprocity, and
> show very similar or identical current distributions at the frequency of
> interest in transmit and receive, although the magnitudes are obviously
> very different.  In a well-balanced antenna system the currents in the
> feedline are equal and of opposite phase, and in the case of a coax feedine
> the resulting fields are contained within the coax, i.e. there will be no
> current flowing on the outside of the coax shield.  Antenna system
> imbalances at the feedpoint will cause the imbalance current to flow on the
> outside of the coax shield and radiate in transmit and affect the antenna
> pattern.  In receive the exact same imbalance will exist and affect the
> pattern identically.
>
> In both transmit and receive, these common-mode currents will be conducted
> to the chassis of the rig and anything attached to it. They also
> capacitively couple through the power supply, you, and anything else
> touching or near the rig.  When these currents couple through the power
> supply to the AC line they effectively make the AC power system part of the
> antenna and couple any noise present in the AC mains to the receiver.  As
> the antenna currents pass through the supply they can also be modulated by
> the input-output impedance of the supply which varies at the rate of
> rectification, so the supply can add its own noise to these currents.
> Interestingly enough many people report stronger reception of the desired
> signals along with the increased noise, certainly proving the common-mode
> currents become part of the antenna system.  Breaking this current path
> with a common-mode choke will greatly reduce or effectively eliminate this
> current and noise.  For HF chokes we agree with Jim Brown's recommendations
> and we supply mix 31 cores for the purpose.  Proper grounding at the rig
> can also reduce the AC mains coupling.
>
> After selling thousands of these Kx33 supplies we have learned a lot about
> the nature of most "power supply" RFI.  We have found very few instances
> where any supply was causing RFI by transverse conduction (RF riding on the
> DC output) or radiation (proximity of the supply to the receive antenna).
> In the almost all cases, antenna system imbalances and the resulting
> common-mode currents were inducing RFI in the manner described above.  I'd
> be glad to send you a ferrite core to try, contact me off-line.
>
> I hope this helps,
>
> Howard Hoyt  - WA4PSC
> www,proaudioeng.com
>