Please pardon my repeating myself, but this thing has really got me buffaloed, and I've found that this is the place where the most knowledgeable people about this sort of thing hang out
I am feeding DC down my feedline to the ARR preamp in the RX antenna hub, and also to the relays and the logic inside it (my cheapo Chinese relay board). I now have the hub sitting out there with no antenna connected, so it is effectively just the preamp and the relays on the end of the coax, plus common mode pickup on the coax. On 1550 KHz (my local 70-over-9 broadcast station), this combination is > 70 dB down as compared to my 160M shunt fed tower. However, if I go up to 20 meters and find a strong station, then the feedline-cum-hub combination receives about as well as the tower, and is only ~20 dB down from a single small tribander. Now here's the mysterious part. If I remove the DC power from the preamp, the 20-meter signals drop from S9 to barely audible. This is also noticeable, but just barely, on the 1550 KHz signal. Is it possible that the preamp, which is between the feedline and the primary of the binocular matching transformer, is somehow amplifying the common mode signals? The shield of the coax connects to the shell of the preamp, and from there to the secondary of the matching transformer (the 75-ohm side). Is it possible that common mode signals are getting back into the preamp input through the matching transformer primary? If so, any ideas on how to clean it up? Or should I just get rid of the preamp out there and do my amplifying in the shack? -- 73, Pete N4ZR The World Contest Station Database, updated daily at www.conteststations.com The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com, spots at telnet.reversebeacon.net, port 7000 and arcluster.reversebeacon.net, port 7000 _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
