John:
This looks like a simple procedure and it takes the guesswork out of
trying to zero beat WWV, but how accurate is the frequency readout
capability of Digipan or other PSK-31 software? Isn't it dependent on
the accuracy of the PC clock?
73,
Bob WB2VUF
John Clifford wrote:
>
> Hello Chris,
>
> It's really not that big of a deal.
>
> You need a calibrated frequency source, either a frequency counter, or you
> can use WWV on 10 Mhz. I find it helps considerably if I use a program with
> a frequency waterfall, such as Digipan or MixW, to help me visually align
> the unit. If you run PSK31 you are all set as far as the software goes.
>
> Unscrew the top of your rig, but leave the top on. Get your digital
> software program turned on. Turn your rig on and let it warm up for a
> half-hour. Then, tune the rig to 10 Mhz in CW mode. You should hear, and
> see (on the waterfall), a carrier at your CW offset (i.e., 700 Hz). You can
> use the 'CW Spot' function (pressing and holding the CW mode button) and it
> will put a signal on the waterfall at the exact offset frequency. Your goal
> is to get the WWV carrier _exactly_ aligned with your CW sidetone.
>
> The way I do this is to use the tuning knob to get the signals as closely
> aligned as I can. This will result in your frequency display being off by
> the amount that you need to align it by. Once the two signals are lined up
> on the waterfall, I then remove the top of the rig, and adjust either C31 on
> the Logic Board (if you are working with an original VI with the crystal
> oven... see the manual for location) or the trimmer cap in the TXCO (if you
> are working with an upgraded VI or VI+, and your manual will tell you which
> one you have) so that the frequency display reads 10 Mhz.
>
> You will need to go thru a few 'tune and align' iterations, where you tune
> using the knob to align the signals, then adjust the trimmer cap to bring
> the freq readout to the desired settings.
>
> Once you've got 10 Mhz exactly on the display and the carrier/sidetone are
> as close as you can get them, switch to USB mode. This should show you the
> regular WWV tones (at either 500 Hz or 600 Hz depending...). Note that as
> you switch between USB and LSB that the tones should move symmetrically
> around 10 Mhz, i.e., -500 Hz offset for LSB, +500 Hz offset for USB. Use
> your tuning knob to get the USB/LSB offsets to be as close to symmetrical as
> you can, and then use the crystal oven/TXCO trimmer caps to re-set the freq
> display to 10 Mhz.
>
> Using this method I'm able to get less than 10 Hz offset... on my rig within
> a couple of hertz.
>
> Hope this helps,
>
> - jgc
>
> John Clifford KD7KGX
>
> Heathkit HW-9 WARC/HFT-9/HM-9
> Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
> Ten-Tec Omni VI/Opt1
> Alinco DR-605TQ
> Icom T90A
>
> email: kd7kgx@arrl.net
>
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