Dude, You are indeed the King. Let me press forward with your suggestions. I'll let you know what I find. Joe N9JR
Don Wilhelm <[EMAIL PROTECTED]> wrote: Joe, Not the counter probe - use an RF Probe or a 'scope - the significant factor is the RF voltage, the counter probe will only provide the frequency and I expect that will be correct. What you may be encountering is low injection to the mixer - the level should be +7dBm for the TUF-1 mixer - if that level is reduced, the mixer IF output will also be less than it should be - and decreased receiver sensitivity will be the obvious result. This is separate from a VCO lock condition, but the VCO lock condition becomes more unstable at lower (R30) voltages. The other possibility that I can think of is a leaky coupling capacitor - particularly those associated with the D6/D7 switch - in combination with the RF Chokes, there could be some strange condition that only occurs on 30 meters - A short burst of transmit would change the DC conditions on the capacitor and restore things to 'normal' until it charged up again - as far as I know, the only real way to check for that is to substitute capacitors in hopes that it will be found - not the best way to de-bug, but sometimes that is the only way to go. Remember that Murphy rules in instances like this - if it can't happen, it WILL!! 73, Don W3FPR > -----Original Message----- > > Thanks Don, > > I'll move the probe to TP1 and see if it changes when receiver > sensitivity falls off. > > I thought that if VCO voltage was low PLL lock would be lost. > When this happens, the PLL stays locked, as verified by listening > to stronger stations. Also the VCO/PLL chain is before any RF > amplification of a transmit signal. Hence my perplexing > question. A single transmitted dash brings it back. (As I was > typing it went quiet, and a single dash made things right.) > > To pose another hypothesis, when it goes insensitive (I can > still copy very strong signals) it is almost as if the 20m > components were being switched back in. There is no relay > chatter, and I set sidetone level to zero, and AF to zero after > it happens, and when I transmit no relay noise. Could the I/O > controller be the problem? Sending a small voltage to the relay, > but not enough to latch it back causing a high resistance > connection at the wipers to partially enable the 20m components > in the BPF. And transmitting a signal forces it closed? > > After I added the KX60V I went through and did the VCO voltage > measurements and 30 was fine. > > You are correct that there are very few portions of the radio > that are band specific, namely the VCO circuit which switches > the diodes, the LPF and BPF, and the I/O controller which affects > the first three. > > I'm feeling pretty stupid as I can't find the problem. I knew > once I posted you would be kind enough to give me your > experienced opinion. I am just suprised that as the Dean of > Support you have not seen this before. > > Again thanks for taking time to consider my plight. > > Regards, > Joe N9JR > > Don Wilhelm wrote: > Joe, > > Try checking the RF voltage out of the VCO (at TP1) - compare 30 meters to > 40 and 20. If the 30 meter output is low, that could be the major cause of > your problem. If this is the situation, look first at the voltage at R30 > for clues. Normally the 30 meter VCO alignment falls quite within range, > but if the capacitors in the VFO selection area are not quite the right > value, it could make any one band go out of range. > > Other than the BPF and the VFO range, there is not much that is band > specific in the receiver - all it takes is things tuned to the correct > frequencies. > > 73, > Don W3FPR > > > -----Original Message----- > > > > I have been pulling my hair out for about a month with this > > problem, and perhaps someone has seen it before and can point me > > on the right path. > > > > I have an issue on 30m receive only. When I transmit on 30m I > > get full power, and it receives normal, but after a while it > > loses most of its sensitivity. Transmit again and it will hear > > the other side of the earth. I have noticed that once it goes > > partially deaf I can get a High Curr indication on the first dash > > I send, but after that it puts out full power with no complaints > > and of course after every transmission it is that beautiful K2 receive. > > > _______________________________________________ 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
