Conway,
If you have an oscilloscope, dragging it out is *not* overkill - it will
show you the peak to peak RF voltages as well as the waveform.
Lacking the 'scope, you can build up the RF Probe - the parts are
supplied with the K2 kit and the circuit board is part of the 'switch
spacing tool'. That RF Probe will indicate the RMS value of the RF
Voltage on your DMM.
I can't say what the response of your Fluke 77 may be on AC, but I made
a check with my Fluke 179 and at the 4915 MHz frequency, it does provide
a response comparable you your measurements.
Are you attempting to measure the Q24 response while either in transmit
or in the menu CAL FCTR state? If not, then your results are as
expected - Q24 does not pass the BFO signal on receive due to the
absence of voltage on the VALC signal line.
If you *are* in either CAL FCTR or transmit state when measuring at TP2,
then yes, Q24 may be the problem.
73,
Don W3FPR
Conway Yee wrote:
> On Wed, 3 Feb 2010, Don Wilhelm wrote:
>
>> So the problem is that the BFO is not oscillating.
>>
>
> Searching some more, I am no longer certain that this is the case, I have
> been using a Fluke 77 for AC voltage measurements. Checking the spec
> sheet, it appears thaat AC voltages are measured from 100mV to 750V with a
> frequency range from 45Hz to 1KHz. Certainly the BFO voltages are too low
> and the frequency too high to register.
>
> Testing this theory, I place my Fluke 77 to TP3 which is KNOWN to have
> 12099Hz, I read 0V. This MAY explain my zero measurements on TP2 and pin
> 6 of U11.
>
> Trying the frequency probe on pin 6, I see 4913.11Hz!!!! This is also seen
> on pin 7 (as expected). I also see the same on both sides of D37
> (although slightly higher frequency 4913.38Hz. Nothing is seen on TP2.
> and possibly on C168 (unstable number much smaller than 4913, mostly in
> the 2000 range). In summary, assuming that the signal is from the
> crystal, I see it up to the gate of J310 but not on the source.
>
> Does this mean that I have managed to fry Q24?
>
> I note that V_{alc} is zero. Could I have missed something that is
> supposed to be hooked up to the other side of R98? I still can't find a
> jumper in the instructions that is supposed to be soldered to the tracing
> extending from the other side of R98 toward the control board.
>
> Also, what test equipment am I supposed to purchase that is able to
> measure voltages in the MHz range? I can break out my oscilloscope but
> this seems overkill for the job. Is there a handheld multimeter that can
> handle HF frequency measurements?
>
> tnx.
> Conway Yee, N2JWQ
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