John Lemay wrote: >Good morning all > >I raised the issue of noise coming from my P3 several months ago. > >It is noticeable on 2m, using an EME array that is about 50ft from the >rig. There is a combination of azimuth and elevation in which the array >"looks" directly at my shack and under those circumstances the noise >level on 2m rises several dB. > >I was advised to put chokes on the cables at the P3 end, and to revisit >the cleaning of metal panels on the P3 where they meet. I've done this >till I'm blue in the face, but it doesn't help because the P3 radiates >a small amount of hash from the display screen. It's not practical to >screen this ! > >Regards > >John G4ZTR
It seems rather unlikely to be a radiating EM field launched directly out of the panel cut-out of the P3. The aperture is too small to act as an efficient radiator at a wavelength of 2 metres, and the internal noise source is unlikely to be driving it efficiently either. It seems more likely to be starting out as conducted interference - internal RF currents escaping perhaps through that hole or through other defects in the shielding (which unfortunately are endemic in this 'flat pack' style of construction). Those RF currents will then flow over the outer surfaces of the metalwork and the connecting cables, and that could be where the radiation is actually taking place. Have you checked which of the cables are actually carrying the noise currents? A clamp-on ferrite bead with a 10-turn secondary winding is a very good diagnostic tool, coupled into a spectrum analyser or a totally independent VHF receiver with an S-meter. Another option to use with the clamp-on transformer is W7ZOI's AD8307 microwattmeter, which is so sensitive it's scary. An interesting experiment would be to blank off the entire screen aperture with a metal plate, solidly grounded to the front panel, just to see what difference it really makes. It obviously isn't a solution, but it could be a useful as a diagnostic. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek ______________________________________________________________ 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
