Hi Earl:
In reference to adjusting TCXO oscillators, within 20 Hz to 30Hz is
not
really too bad. Most of us in the field do not have equipment accurate
enough
to adjust TCXO oscillators. The environments of temperature, altitude, and
age of the oscillator has a lot of things to do with accuracy.
Most TCXO oscillators are designed with known aging parameters, in that
as the crystal ages it will move up in frequency. This change in frequency
may
be rapid the first year, then it will settle down and not move much after
that.
The crystal will have a known aging parameter and in about a year you
will
find that the oscillator will be closer to being right on. The oscillator
will not
move much after it ages in as they say.
I would recommend that not too many adjustments be made to this
oscillator
until it has some time on it. As long as it moves closer to being right on,
if it goes
the other way you will want to adjust on the side that moves closer to being
on
frequency. If the oscillator moves up as it ages and goes past the
frequency, you
would adjust a bit below the desired frequency. After the crystal has aged,
perhaps two years, you will not have to adjust it much at all.
So a good thought with new equipment is to let the TCXO age some and then
look at it. Thirty Hz is real close any way.
I grind FT 243 crystals, and I have messed up some TCXO oscillators
playing
with them, so be gentle, the TCXO is an expensive oscillator.
Great procedure to setting the oscillator, I have an old Kenwood TS440S
and it
has a reference oscillator, however it is not a TCXO, and I have to check it
each
year, it does move with age some and is not real stable. I wish I had a
TCXO for
the radio but they only have that option for the TS450S.
Ed 73 K7DXV ewell2@cvc.net
----- Original Message -----
From: <k6se@juno.com>
To: <tentec@contesting.com>
Sent: Thursday, May 22, 2003 6:41 PM
Subject: [TenTec] Orion Frequency Accuracy
> When I checked the frequency accuracy of my new Orion, the LCD readout
> when 10 MHz WWV was zero beat was about 20 Hz low (after a long warmup).
> On 15 MHz WWV it was 30 Hz low. That's not too shabby, but when the
> receiver displays down to 1 Hz you tend to want to make it more accurate.
>
> Studying the manual, I determined that the TCXO (Temperature Compensated
> Crystal Oscillator) was located on the Synthesizer board, located at A10
> (page 4-4 of the manual). Here's the procedure I used:
>
> 1) Remove the Orion's bottom cover. Use the provided spline wrench (the
> manual calls it a "T10 Torx Wrench") to remove the 9 small-headed screws
> around the back edge of the bottom cover, then use a Phillips screwdriver
> to remove the 4 large-headed screws on the sides of the radio (2 0n each
> side). Pull the bottom cover rearward and lift it off of the radio.
>
> 2) Find the small module located near the rear edge of the synthesizer
> board. It should have "45.55 MHz" written on it. The small hole in the
> module is where the oscillator adjustment trimmer is.
>
> 3) Connect an antenna and power to the radio and sit the radio on its
> side where you can view the LCD display and have access to the oscillator
> trimmer at the same time.
>
> 4) Power up the radio and tune in WWV on the sub receiver (use the
> highest-frequency WWV you can receive for greatest accuracy - WWV
> transmits on 2.5, 5, 10, 15, 20 and 25 MHz). Set the MODE to either USB
> or LSB. Let the radio warm up for at least 30 minutes.
>
> 5) Tune the sub VFO so that the displayed frequency is exactly WWV's
> frequency. For example, adjust the VFO so that the readout says
> "10.000.000" if you are using 10 MHz WWV.
>
> 6) During most minutes, WWV modulates the carrier with an audio tone for
> 45 seconds. While the audio tone is being transmitted, change the MODE
> to the other sideband. If the pitch of the tone is not the same when
> switching between USB and LSB, the oscillator trimmer needs adjustment.
>
> Note: The pitch of the audio tone alternates between 500 and 600 Hz each
> minute. A 440-Hz tone is transmitted during the 2nd minute after each
> hour. Don't let this throw you off during the adjustment of the
> oscillator. The object is to adjust the oscillator so that the tone is
> at the same pitch when switching between USB and LSB. During minutes
> when voice announcements or silent periods are scheduled, no audio tone
> is transmitted.
>
> 7) Set the MODE to the sideband that the pitch of the tone is highest on.
> Using a suitable alignment tool, adjust the trimmer so that the pitch of
> the audio tone is slightly lower (the trimmer is not too tight and
> adjusts easily).
>
> 8) Listen for any change in the pitch of the tone while switching between
> USB and LSB. If necessary, adjust the trimmer again. When the trimmer
> is adjusted so that there is no discernible difference in the pitch of
> the audio tone while switching between USB and LSB, the oscillator is
> calibrated. When you get this close, you may also hear a slowly
> pulsating "whoosh". The slower the "whoosh" pulsates, the more accurate
> the calibration is.
>
> 9) Ensure that the frequency display is still "10.000.000" (i.e., you
> didn't accidentally bump the VFO knob during the procedure).
>
> 10) Replace the bottom cover.
>
> The accuracy of the frequency readout on my Orion drifts about 20 Hz at
> 10 Mhz (2 PPM) during the first 30 minutes of warmup. The direction of
> apparent drift of WWV is downward which would explain why the factory
> adjustment of the oscillator was that amount -- perhaps their lab is a
> cooler environment than my hot shack or they don't allow enough warmup
> time before making the adjustment.
>
> 73, de Earl, K6SE
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