First:? I think the QDX is a brilliant piece of engineering and a great little transceiver.? I have one, and have just ordered two more for use in "network base station" operation.? My interest in the frequency-setting issue is mostly because it's a topic I find interesting, and there are some modes I am exploring where this issue (soon to be corrected, I hope) will be a problem.? Most people using the QDX will neither notice, or care about this issue -- the rig will just work for them.
So I finally set up an audio frequency ramp feeding the QDX USB input channel.? Output frequency measurements were made with my home-brew counter.? The displayed frequencies are after down-conversion in my counter, the absolute values are arbitrary and what matters is are the frequency differences.? I was using a Windows program called "NCH Tone Generator" to create the frequency sweeps.
First, to check the sweep itself, I sent the audio to my IC-7200 transceiver, set for 20 meters.? This is a slow sweep, 1000 Hz - 1010 Hz, taking 60 seconds:
There is measurement noise, but the frequency ramp appears to be smooth.
Then I sent the same audio sweep to the QDX, on 20 meters:
You can see that there are nine frequency steps over the 10 Hz range, each step roughly 1.25 Hz.? It is obvious that this will not work with the 1.46 Hz steps used in FST4W-120, and will cause some frequency error with the?1.4648 Hz steps used in WSPR.
Things got slightly better on the 30 and 40 meter bands, on 40m there were eleven steps (per 10Hz), but while I had expected better frequency resolution here, strangely the steps were less even than the 20m band:? The 30m band also showed eleven steps, although the spacing distribution was somewhat different.
40 meters:
Fractions are funny things, and perhaps if I had tried other audio frequencies the results would have been a bit different.
Finally, I set the audio sweep for 1000 - 1100 Hz, this time on the 10-meter band:
While the steps were uneven, there were no major discontinuities over this 100Hz range
So there you have it.
--
Paul Elliott - WB6CXC
