Posted by
Joseph Reed-2 on
Apr 23, 2006; 1:41am
URL: http://elecraft.85.s1.nabble.com/Strange-receive-problem-tp389057p389060.html
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 <
[hidden email]> 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.
>
> Here is the kicker - 20m is great. The only difference in the
> LPF is K3 switches out some capacitors. I have resoldered all
> the connections, and replaced K3 (bought a Hakko 808 just to do it).
>
> I think we can eliminate the BPF as nothing changes in it for
> either 30 or 20. And since I replaced K3, I am beginning to give
> up hope that it is something in the LPF.
>
>
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