Steve, Since these are likely products of the K2 mixing scheme rather than 'real signals', comparison with another receiver that does not use the same mixing scheme as the K2 will not necessarily produce the same results - but your comparison with the Drake should confirm that they are indeed mixing products.
I would consider having several 50kW stations within 10 to 20 kilometers within the range of quite close!!! I wonder just how many volts of broadcast band energy you have on that antenna - an inverted L would likely pick up more of that energy than a horizontal antenna. In the area South of my current location we have an AM broadcast station on 680 kHz that is capable of putting a volt of 2 of RF energy onto telephone lines as far as 7 miles away from their antenna field (yes, I used to live there), so having a lot of RF on an antenna that is somewhere around a 3/4 wavelength long at the AM broadcast band center does not seem unusual to me at all. You may want to try adding a high pass filter on the front end of the K2 with a cutoff in the 1700 kHz range. The bandpass filter of the K2 is intentionally broad and just may not be filteing out enough of the energy, or as you have surmised, if the broadcast band energy is high enough, it could even be demodulated in the T-R switch and mixed with another signal. To my mind, adding a high pass filter on the antenna input would be the easiest solution since this may not be the only mixing product that you might encounter. A properly designed high pass filter could be left in-line all the time and have no adverse effects (conversely, a poorly designed one may cause significant attenuation) - I recall that either QEX or QST has had published some BC band filters designed by Zack Lau that I would consider good designs, but then you could design your own if you are so inclined - size the components for your transmit RF level. 73, Don W3FPR > -----Original Message----- > > I just had my first opportunity to use the K2/100 on a > fairly large antenna for 80m (inverted L with total > wire length around 150 ft., through a low-pass type of > antenna tuner). I noticed a few fairly strong > intermodulation products from AM (medium wave) > broadcast stations on and around 80m. There are > several 50 kW stations within 10 or 20 km, but none of > them are really close. For example, I found the > mixing product of 2 times 1310 kHz and 1150 kHz when > tuned to 3770 kHz (meter reads S9 with attenuator and > preamp off) and the mixing product of 2 times 1310 kHz > and 580 kHz at 3200 kHz. > > These signals were not present on a Drake TR-7 > connected to the same antenna/tuner. They also were > virtually unaffected by switching the KPA100 in or out > (either with power setting above or below 10 W or > using the PA ON/OFF menu settings). They appeared to > be affected by the attenuator/preamp settings in the > same way as "real" 80m signals, which seems to > indicate that they were generated in the T-R switch. > > Has anyone else experienced this (i.e. is it normal ?) > or should I be looking for problems in or near the K2 > T-R switching circuitry ? > > 73, > Steve VE3SMA > > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.371 / Virus Database: 267.14.7/214 - Release Date: 12/23/2005 > > _______________________________________________ Elecraft mailing list Post to: [email protected] 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
