Good points Jim, I would like to add a clarification and results that I use. 1. On point 2) I would rather power the accessories on the battery end of the rig power cord as the voltage regulation will not have the rig IR losses. 2. On point 4) I have used a 5 Farad cap with 3 inch leads to the rig. It does the best of trying to cancel out the IR losses on voice pikes and does a great job. This is the one used by the car monster audio amps. Cost is around $50 direct and less on eBay. Mel, K6KBE
--- On Mon, 10/8/12, Jim Brown <j...@audiosystemsgroup.com> wrote: From: Jim Brown <j...@audiosystemsgroup.com> Subject: Re: [Elecraft] Capicator Size for filtering across battery power To: elecraft@mailman.qth.net Date: Monday, October 8, 2012, 12:52 PM On 10/7/2012 7:06 PM, David Moes wrote: > That is interesting. I suspect that they are reacting to the > elecromagnetic field created by rapid current fluctuations in the DC > lines rather than picking up RF. NOT electromagnetic fields, just simple Ohm's Law. There's IR drop on the power cable between the battery (or power supply) and the rig, and if the rig is running full power, peaks of at least 20A, with an envelope that follows SSB modulation. If you are powering accessories from that same battery and have audio connections between those accessories and the rig, the IR drop (modulated SSB envelope) will appear between the chassis of the accessory and the chassis of the K3, and will be added to the audio. That will SOUND like RF feedback, but it is NOT. W8JI told me about this several years ago. There are at least four good fixes for this issue. I've set up and tested all of these, and all of them work. 1) Don't power accessories from the same supply that feeds your rig. Instead use a separate wall wart for them. 2) Power accessories from the same supply, but use a simple power splitter (Y-cord) at the RIG end of the power cable to get the accessory power. 3) Power the accessories from the battery or big power supply, but bond from chassis to chassis of all interconnected equipment with short, fat copper. 4) Power the accessories from the battery or big supply, but use a monster capacitor across the terminals right at the rig. When I say monster cap, I'm talking at least 10,000 uF. That's big, and it ain't cheap. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
