Dieter Horst <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- I agree with the ferrite idea. Whenever I go to the club station DL0AO for a major contest, I have a few ferrites with me. And they did help a lot in the past.
Not only RF pickup in Mics and Headphones but also lots of computer problems like strangely behaving keyboards, mice etc. can be cured. At the last meeting of the Bavarian Contest Club a presentation was given on this subject by Hans DK3YD. The slides can be found here: http://www.bavarian-contest-club.de/storage/med/papers/linden2008/79_Linden2008_dk3yd.pdf (Sorry, all in German but you can see from the pictures how the ferrites are mounted. I may help with a translation if needed.) 73, Dieter DL5RDO > When and where to ground is not as simple as it sounds at first thought.? > Depending on circuit design, several grounding schemes for microphones > might have to be tried to ensure proper shielding while at the same time > not creating a ground loop.? Too, ferrite beads on each and every lead > going to/from the rig might help. > Just some random thoughts from a fellow Drake enthusiast... > -----Original Message----- > From: Jim Shorney <[EMAIL PROTECTED]> > To: [email protected] <[email protected]> > Sent: Wed, 2 Jul 2008 10:35 pm > Subject: [drakelist] Pondering RF Feedback (TR7/SP75) > "Jim Shorney" <[EMAIL PROTECTED]> made an utterance to the drakelist > gang > ---------------------------------------------------------------------- > Some readers may recall that last year I was plagued by RF feedback at > Field Day > with the TR7/SP75 > combination. Careful balancing of the mic gain and SP75 input and output > levels > could eliminate it most of > the time, but not always. > This year, I connected a ground strap from the SP75 to the TR7 chassis, as > was > suggested here. Well, that > helped quite a bit. However, I was still seeing some RF feedback this > year. It > was happening with the Yagi > (4-el 20 meter monoband) pointed generally southwesterly, which would have > been > pretty much over my > head. As usual, were stationed in an EMCOMM trailer on a concrete parking > lot, > with no station ground > available. The feedback could be mostly eliminated, depending on the > actual > position of the Yagi, by > reducing the TR7 mic gain. I couldn't nail down exactly where it was > getting in, > but it seemed to have > something to do with the microphone wiring - a Telex Echelon 150 aircraft > active > noise-cancelling headset > with a homebrew interface box. The box was solid aluminum, mic cable to > the SP75 > was RG-174/U coax, > and power for the ANC amplifier and mic bias was well bypassed. Sort of a > puzzler. > Then I found this surfing the web: > http://www.audiosystemsgroup.com/RFI-Ham.pdf > This may be old news to some of you, but what caught my eye was the > author's > description of what is called > "the Pin 1 problem". I recalled from having been inside these boxen that > the mic > ground connection inside > both the TR7 and the SP75 is not tied to the chassis at the point of > entry, but > rather, is wired to the circuit > board. According to the referenced article, this is bad. > I've made wiring changes to both the TR7 and SP75 to establish proper > grounding, > as described in the > article. There is also a tech note on Heil's web site regarding this > problem: > http://www.heilsound.com/amateur/tips/rfi_removal_mics.htm > Heil provides a method of grounding at the mic connector that is pretty > easy, > but I have a lot of microphones > and I like to try out different things. > It seems possible that this may be where my feedback was entering, but I > have no > way of duplicating the > Field Day conditions at home (and I doubt the radio club will want to drag > out > the trailer, Yagi, and tower just > to test my rig). I don't recall ever seeing this sort of RF feedback at > home, so > it will have to wait for next year > to test out the "Pin 1 problem" theory. I'm thinking I will take along > some > snap-on ferrite chokes next time as > well - or maybe I can get the club to add some to the Field Day kit. > Any thoughts from the gallery? > 73 > -Jim > NU0C > (BTW, the Echelon headset knocked the generator noise right out of the > headphones...) > ---------------------------------------------------------------------- > Submissions: [email protected] > Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > ---------------------------------------------------------------------- ---------------------------------------------------------------------- Submissions: [email protected] Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net ----------------------------------------------------------------------
