Jon, How far out of the ham bands you can go with the K2 depends on 3 factors. First is the range of the VFO tuning. If you measure the PLL/VFO range at the left end of R30, but extend the voltage range to 1.0 volts to 7.0 volts. and you will have an indication of how far out of band the VFO will tune. Beyond those points, the VFO indication on the display will not be reliable. The second is the falloff of the bandpass filter. That can sometimes be modified slightly by tuning at a different frequency than is indicated in the K2 manual. For instance, if you need to tune up to 4300 kHz, you may be able to shift the bandpass filter tuning by setting the frequency to 3900 instead of 3750 when tuning the 80 meter bandpass filter. The response falloff at the edges of the new "BAND" limits should be checked. The 3rd thing is the Low Pass Filters. Remember there are 2 sets in the K2/100 - one in the base K2 and another in the KPA100. The bands that they cover are not necessarily the same. For instance, the base K2 LPF combines 30 and 20 meters, so if you want to transmit at 12 MHz, that one will give you no problem, but the 40/30 meter LPF in the KPA100 is designed to cut off the 2nd harmonic of 60 meters, so it has a rather steep cutoff after 11 MHz, so attempting to run a 12 MHz signal through that filter will likely result in low output and high current drawn by the KPA100 and there is a liklyhood of damage.
Bottom line - unless the MARs frequencies are quite close to the ham bands, the K2 will not do the job. It could be modified for the MARs frequencies, but it may not cover the entire span of the ham bands afterward. I would discourage such modification, and any mod to the VFO Range Select is quite tricky (a change of a few pF makes a big change in the range) and not all K2s will respond the same to any given capacitor due to component tolerances. So, yes, the K2 can be modified with a LOT of work, some of it requiring redesign of the VFO, Bandpass Filter, and the Low Pass Filters. When you are done, it may or may not be usable on the ham bands. I believe the K3 (with the KBPF3 option) and the KX3 are better candidates for MARS operation. 73, Don W3FPR On 9/24/2012 11:34 AM, Jon Perelstein wrote: > Is the K2 a viable radio for MARS work? I found some references in > the archives from back in 2005 suggesting that it won't transmit on > some of the MARS frequencies even though it appears to be transmitting > on them -- the VFO display shows the desired frequency, but that far > out of band it's not transmitting on the frequency it's displaying. > The issue appeared to be one of how far out of band the PLL will go, > as opposed to there being a restriction programmed into the > microprocessor. > > I confirmed last night that mine (#6550) will not -- on some of the > bands -- transmit as far out of band as needed, even though it is > transmitting. > > There was no mention in that exchange of any mods that might be done > to make the K2 capable of transmitting on the MARS bands, and I > haven't found any other useful posts on the subject. > > Has anyone successfully modified a K2 for MARS operations, and if so > what did you do. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
