I have had 2 problems with my P3 Panadapter, both were the subject of comment on the Reflector.
The first was spurii radiated from the P3 DC cord and picked by my nearby antenna on 144 MHz. This problem was largely solved by fitting a commercial RFI filter in the DC cord and ensuring that all panels were clear of paint in the corners where the connections are made. The second problem was the occurrence of wideband noise humps which drift across the display from time to time obliterating the genuine signals. I dubbed the characteristic doubled-humped noise signature as my noise monster. Experiment showed that these spurii and noise products were being generated in the P3 itself. It was not possible to precisely pin-point the source of these signals inside the P3 using a small pick-up loop. The signals were strong everywhere inside the P3 box, but, perhaps, were strongest near the processor chips. This would seem to make sense, but not everyone has these problems, so clearly the mechanism for producing this hash, varies from chip to chip. Thanks to everyone who responded. I am now able to report I have found a complete cure for these problems which works in my case, but, of course, I can not guarantee it will work in every similar case. The cure involves the use of conductive foam. This is the black foam that ICs are normally pushed into when they are delivered. It is carbon impregnated. You can tell the difference between this conductive foam and ordinary foam using an ohmmeter. Pressing the probes against the conductive foam will give a reading of a few Kohms. Ordinary foam will be open circuit. This foam is available from many electronic suppliers. I bought my foam from Farnell Electronics (Now called Element 14 in Australia), order code 168-7846. The cost is 89 cents for a sheet about the size of the P3 side panel. I cut the foam to form compartments to completely isolate the front panel, IF input board, and IO board. I even put foam between the folds of the ribbon cable. In doing this I was carefully not to allow the foam to actually touch any components or bare wires, otherwise a circuit would be formed. I cut the foam panels deliberately oversize vertically, so that when the lid was screwed down, ther e was pressure to make sure the foam had a conduction path to ground. The result of this work was that all spurii have disappeared and my noise monster has never shown its face again. My theory is that the foam is effective because it actually absorbs the RF signals and turns them harmlessly into minute amounts of heat. The problem with metal screening and chokes/capacitors is that these devices simply reflex the RF back. But back to where? The whole P3 box is already abuzz with these signals and they will try to get out anyway they can. The foam kills them dead. That's my theory anyway. If you have these or similar problems, give it a go. 73 Roger, VK4YB ______________________________________________________________ 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
