Regarding the thread I started a couple of weeks ago... I found some strong intermod products from AM (medium wave) broadcast stations on and around 80m when using a large inverted L and low-pass L-network antenna tuner. The strongest was the combination of 2 x 1310 kHz + 580 kHz, two local 50 kW (I think) stations in Ottawa, which was about S9 on 3770 kHz using my K2/100 and not there at all on a Drake TR-7. The intermod was affected by the preamp and attenuator settings only to the same degree as normal signals.
After some investigation I have found that this intermodulation is occurring in the basic K2, apparently either in the T-R switch or the final (10 watt) amplifier transistors. The KPA100 80m pi-network actually was acting as an antenna tuner at 1310 kHz which made the intermod slightly worse when connected through the PA than when in QRP configuration. VE3TG's (QRP-only) K2 was also tested on the same antenna and gave nearly identical intermod levels compared to mine (going by S-meter readings). So it seems highly unlikely to be a build problem. The total input voltage at the K2/100 antenna input from the various local broadcasters was measured on an oscilloscope at about 1.5V peak-to-peak. I didn't find an obvious spot to add a high pass filter to the K2, so I will probably consider building a 100W-rated filter to add externally between the rig and the antenna. In most cases a high-pass antenna tuner is likely to be sufficient, I think. It would be interesting if someone with the right skills and equipment was able to make some 3rd order intercept point measurements on a K2 for out-of-band signals to see if the expected intermod levels agree with my observations. 73, Steve VE3SMA __________________________________________________________ Find your next car at http://autos.yahoo.ca _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com