[TenTec] transceiver test

Sun Jun 6 22:57:05 EDT 2004

Thanks for the various responses, ideas and such.  I'll expound on the issue
a bit further.

To determine the transmit frequency is easy.  I have a very good, highly
accurate frequency counter at my disposal so determining the TX frequency to
something less than 0.1 Hz is no problem.   The main issue is the receiver.
Oh I know what the read-out says and it displays to 10 Hz and thus the
apparent accuracy would be nearest 10 Hz +/- 1 count.  But what is the
actual RX frequency?  Using a very accurate external frequency reference is
the first though and suggestion from many.  But the question arises, how
does on know that they are actually zero beat with the external reference.
With no tuning change, switching from USB to LSB does not produce an audible
or measurable beat note.  The absence of beat output however is masked by
the fact that the audio response out of the receiver, or product detector
for that matter, is nil below 100 Hz.   So one could actually be 50 Hz or so
away from the reference and not actually know it as there is no difference
produced that is measurable.

In the old days, one could tune in a signal on AM, use an external
oscillator and zero beat the signal to the point the audio difference is
below the hearing range and then observe the S-meter swing as the two
signals added and subtracted to a point of less than 1 Hz difference.
Today, that method doesn't seem to work with a product detector.

The best solution I've come up with is to measure the frequency of the
various oscillators in RX and then calculate the frequency.  This was done
in receive and I arrived at a number which I believe to be the actual
receive frequency.  Then switching to transmit and measuring the frequency
of the nulled carrier (down some 60 dB) I can determine the transmit
frequency.  The measured TX frequency and calculated RX frequency are the
same.  However, from time to time in a SSB QSO I am told that I am "off
frequency".  If I adjust the tuning to a point when several stations agree
that "I sound right" then it is clear that on my end, they sound wrong.
Adding about 30 Hz of XIT corrects the concerns on both ends of the QSO,
mine and theirs.  This leads me to believe that the TX frequency is not the
same as the RX frequency.

Still puzzled.

73
Bob, K4TAX

----- Original Message ----- 
From: "Rob Atkinson K5UJ" <k5uj at hotmail.com>
To: <tentec at contesting.com>
Sent: Sunday, June 06, 2004 9:25 AM
Subject: [TenTec] transceiver test

> Bob, what i would do is get a separate rx and one of those frequency
> standards that used to be available (don't know if they still are or not)
> that consisted of a 1 mhz xtal oscillator in a small box with a 2 or 3 ft.
> whip coming out of the top.  put the rig and rx on cw and on harmonic
freq.
> and zero beat both to standard.  tx on rig under test into dummy load and
> observe frequency difference on separate rx, or zero beat 2nd rx to freq.
> standard, tx cw sig from rig under test and move it to zero beat in 2nd
rx,
> then unkey tx and observe where freq. standard is on transceiver's rx.
>
> Note that the standard doesn't have to be rock steady or accurate--just
not
> drifting a whole lot over time so that during the minute it takes to do
the
> test it hasn't drifted.   Since you are measuring relative to what you
zero
> beat on the separate rx, the exact freq. of the standard isn't extremely
> important--it's not what's being measured--it's just providing a reference
> to get everything set up on.  I think these things used to put out enough
> harmonics so they could be used a number of multiples off their
fundamental.
>
> Rob/K5UJ
>
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