Posted by
Don Wilhelm-3 on
Sep 30, 2004; 1:21pm
URL: http://elecraft.85.s1.nabble.com/K2-Frequency-Counter-Sensitivity-tp370633p370635.html
Don,
I did not see an answer to your question on the reflector, so I pulled the
left side panel from my K2 and took some readings.
The peak to peak voltage at my TP3 is about 2 1/2 volts with the probe
attached and the K2 in CAL FCTR mode, so yours is within reason. This level
signal is amplified and shaped by Control Board Q9 and Q10 to a clipped and
shaped 4 volts p-p at the collector of Q10 (you can read the voltages at RP4
pins 1 thru 4). Q9 and Q10 are amplifiers rather than flip/flops - with
this front-end amplifier on the counter, it is quite sensitive and should
read input levels as low as 0.1 volts or so.
Check out the soldering on the Q9/Q10, RP4/RP5 area and you should find th
problem.
Also, check to see that the frequency probe is connected to the Control
Board properly (the shield should be nearest the left side panel).
73,
Don W3FPR
----- Original Message -----
>I am having trouble reading out the frequency of the signal at TP3,
> the first step of checkout after part 2 of wiring up the RF board.
> The Frequency Counter probe is fine and all components of the
> frequency counter from the input through the flip-flop Q9/Q10 check
> out perfectly with capacitance and ohmmeters. Supply voltage to the
> flip-flop at U6-10 is 4.75 volts.
>
> The frequency readout from the K2 varies from nothing to almost normal
> (12+ MHz) depending on whether or not I have scope or frequency
> counter probes attached ( The additional capacitance from the probes
> increases the signal level slightly and the counter counts, but
> unsteadily.
>
> My external frequency counter reads the signal at TP3 just fine and
> frequencies are within specification.
>
> The signal at TP3 is about 2 volts peak-to-peak. Is this a normal
> value? It looks marginal to me for triggering the Q9/Q10 flip-flop.
> If so then the PLL Ref Oscillator has a problem.
>
_______________________________________________
Elecraft mailing list
Post to:
[hidden email]
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.htmElecraft web page:
http://www.elecraft.com