I recommend to try a relatively inexpensive fix. This works for only resonant (in band), single band antennas. I used this method for contest stations that I built back in the 80's where we had multi op stations operating side by side. We had burned out front ends on receivers from adjacent stations with huge harmonic energy. This is also a good field day trick for club stations with multi transmitters/receivers. Use a 75 ohm coax stub with an in line T-Connector on the antenna. Cut the length of 75 ohm cable with velocity factor figured in so that it is resonant in the center of the desired operating band. This produces a band pass filter so out of band signals are rejected. Also works on transmit to reduce harmonics. It will take LOTS of power, so do not worry about burning it out! Also gives you some lightening protection as it grounds the antenna and eliminates any static that builds up on the antenna. You can add multiple stubs to increase the Q of the bandpass filter, but in most cases, one will do it!! Harry W9BR In a message dated 7/8/2008 11:01:31 A.M. Central Daylight Time, [EMAIL PROTECTED] writes:
Hello to all, I have an issue here with a 50KW AM BC station about 6 miles away. I have IMD/spurs/carriers all the way up from 160M to past 20M. The signal strength of the AM 640kc station is -3dbm on the flex meter and I have crud all over hell's half acre up thru the bands...most are just above the QRN, but sometimes not ;-)This AM powerhouse always mixes with another station beating together on frequencies that show up across the bands. I purchased a KIWA BCB reject filter and put it in the RX1/2 in/out loop and use the antenna selection option to put this inline and it definitely knocks down the 640kc AM >70db when the flex is in GEN mode tuned to 640kc. The problem is that when the BCB filter is inline with RX1 loop, I have major intermod all over the bands...on 20M I heard CHU this afternoon at 14.030, +/- propagation and AM carriers all over the spectrum, some are S9+10 in DSB mode on 20M. If I take the KIWA BCB reject filter and put it inline with the antenna in any ANT1/2/3 port life is good...all the crud is gone, but I can't TX with the KIWA BCB filter. Anyone care to figure this one out? I know W9NQN TX/RX filters are an option, but a $60 RX only should have worked IMHO. Enjoy what's left of our holiday weekend! Mike, K4EAR **************Gas prices getting you down? Search AOL Autos for fuel-efficient used cars. (http://autos.aol.com/used?ncid=aolaut00050000000007) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
