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 <[email protected]> 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 > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
