My Orion TXCO Calibration Procedure
See the "Supplement: How to Zero Beat" below.
Here is my procedure for calibration of the master oscillator on the Orion and Orion II which is fairly simple and requires no special tools or equipment other than the Torx wrench that came with the Orion and a very small jeweler’s screwdriver. If you have the screwdrivers that come in a set of six, use the smallest flat-head. No need for an insulated tool since this is just a variable resistor, not a capacitor or inductor.
If you like the fan mod shown elsewhere on the site, do that first. In any case, let the rig warm up until there is no more drift, at least two hours, and note the difference with 15 MHz WWV at zero beat. Remember that things are mirror-imaged...if you read high, for instance 15.000.020, then the radio is calibrated low in frequency. By cranking the calibration 20 Hz higher, you will have to turn the dial 20 Hz lower to zero beat, and the reading will then be 15.000.000.
Open the radio from the bottom, and look on the A10 board for the master TXCO, which is marked with the brand name "Siward". Connect an antenna and power and tune for the zero beat on 15 MHz WWV. Remember this will show different than when the rig has the cover on, is upright and has warmed up for two hours. Zero beat WWV, then tune down 20 Hz if your reading was high when you checked it before when it was all warmed up. (tune up if it had been reading low). Using a very small jeweler's screwdriver, adjust the trim pot on the Siward TCXO for zero beat. That’s it. Put the radio back together. If you didn't do the fan mod, you will be very close to frequency after 2-3 hours following a drift up and down of about 20 Hz. If you did the fan mod, the drift should be about 8 Hz, most of that in the first 20 minutes, and within about 1 Hz after about 30 minutes.
Remember it will still drift as the shack temp changes, and there will be long-term drift as the crystal ages.
~~~~Supplement: How to Zero Beat.~~~~
It sounds simple, but the fact is that getting an exact zero beat is not easy. Here are some pointers:
1. Tune in WWV on 15 MHz and using UCW or LCW, with the Step set at 1 Hz, press the Spot button and tune until the "swishing" stops, or comes close to stopping. Make sure the Sidetone level and the audio level sound about the same. If there is no exact zero beat, choose the 1 Hz step that has the slowest swish. You can mentally interpolate between the two steps for fractional Hz accuracy. This is much like tuning a guitar string until the two tones the same.
2. A more accurate way is to download the free program Digipan and set it up to receive PSK31. Tune in WWV in USB or LSB and set the pointer to the audio beeps WWV makes each second that you can see in the window. The beeps will alternate each minute between 500 Hz and 600 Hz, and Digipan will read out the frequency within .1 Hz if your sound card is accurate. Set the Orion frequency to exactly 15 MHz, and look at the difference Digipan shows between either 500 Hz or 600 Hz, and you'll know your descrepancy within .1 Hz. If you switch to CW, you'll see the carrier, and it should be at the exact same frequency you have the sidetone set to in the Orion's CW menu screen.
Not sure your sound card is accurate? Switch to AM and do the same as above. The tones you hear are exactly either 500 or 600 Hz, and Digipan should show that. If not, you will now know how far off your sound card is!