Calibrate your Interface to be “dead nutz” on frequency.
TNX to Steve, N1SG and many others for their help with this page, Glenn W3GWW
I. RECEIVE CALIBRATION
1. Tune to the strongest WWV signal you can find on 2.5, 5, 10, or 15 MHz.
2. Switch your MixW software to the SSTV mode (you should be in USB now).
5. After some minutes, several (near) vertical lines will begin to appear in the SSTV
window. Wait for a full screen of lines to write. If your soundcard clock is perfectly
calibrated, the lines will be perfectly vertical. If not, they will slant either left or
6. Use the SSTV slant buttons to make the lines perfectly vertical. Use the arrow keys
to move the line closer to the screen edge. It’s much easier to correct the slant if you
can compare it to the vertical edge of your screen.
9. If you think you may have made an error or you wish to start over again, just click
“Configure”, and then “Sound Card Settings”. Change the number in the Clock
adjustment, ppm: “RX” window to ‘0’ and go to Receive Calibration step 1.
II. LOOPBACK TRANSMIT CALIBRATION
*Note 1. Transmit calibration should only be performed AFTER you have done a valid
WWV slant test and entered the resulting RX clock adjustment into the MixW
sound card settings. If you wish, you can also perform some on-the-air
receive testing of MFSK images to confirm your RX clock adjustment before
going to the next step.
1. Turn off your transceiver.
2. Connect the DB-25 loop-back connector to the rear of your Navigator.
3. In the sound card settings, select the “full duplex” box and insure the Sample Rate
is set to 11025.
4. On the sound card Input settings, change from LINE IN to WAVE.
5. Simultaneously press CNTL-SHIFT-T. A pop up window will appear.
6. You should see a strong “carrier” in the waterfall. Adjust the power slider in the
pop up window so that the signal sidebands are minimal and you have a nice red
“carrier” signal. This is your Navigator output “looping back” to the MixW input.
7. Let the waterfall write for a several minutes until you see that the TX/RX OFFSET
numbers at the top of the pop up window stabilize within a few ppm. This number
is the offset to be applied to your RX clock adjust setting to arrive at your TX clock
Note: This offset will be a positive or negative number. Example #1: If your TX/RX
offset reads “-200” and your WWV tested RX clock adjustment is “+85”, your
TX clock adjust would be set to “-115” (+85 – 200). Example #2: If your RX
offset was +50, the TX clock adjust would be set to “+135” (+85 + 50).
8. Hit ESC to stop the test.
9. Reset your Input back to LINE IN. (Leaving Full Duplex checked is OK)
10. Disconnect the DB-25 loop-back connector from the RigExpert.
11. Reboot MixW and you’re ready to operate.
Note: The clock adjustment in ppm (parts per million) is directly related to the Sample
rate using the following formula: (1 divided by Sample Rate) x 1,000,000 = ppm
per Hz Sample Rate. Using the Navigator default sample rate of 11025, one Hz
of sample rate equals 90.7 ppm of clock adjustment. Some hams change their
sample rate in Hz to correct their slant adjustment. However, it doesn’t take a
rocket scientist to see that using the ppm adjustment method allows for a far
more precise calibration.
There’s no reason to post a schematic diagram of the DB-25 loopback connector. It’s
easy. To make your own loopback connector, just connect pins #12 and #25 together
on the back of your Navigator DB-25 connector. Take a close look at the DB-25
connector on the Navigator. You will find that all the pins are numbered. You might
need a 10X loop to see the numbers if your eyes are as bad as mine. I used a small
paper clip to make the connection.