When I first installed the TXCO I could see that it was going work, as it did not produce the Hash (or fuzz) on the transmitted signal that was shown on previous blogs.
From turn-on the Frequency was very stable, after a few minutes no change could be detected. The output was NOT exactly on frequency, as I had not bothered to hook up the "frequency voltage control" line, I wanted to see the behavior without, and the single page manual does not provide much details of it's use.
The Frequency was low by about 1.4ppm as indicated on a previously calibrated Spectran. Within the Spin program I was able to correct the frequency and ran several more tests. All tests worked as expected (or hopped).
To complete the installation I hooked up a simple resister divider to drive the Frequency Control line; a 1K ohm fixed up to 3.3v, 2K ohm variable to Freq Control, and a 1K ohm fixed down to ground. Then I removed the previous Spin Freq Corrections and re-compiled the program.
The RF output frequency was within a few Hz of spot on, a quick twist of the variable Freq Control Pot put it on frequency. The pot is a little touchy for small adjustments; I will replace the two 1K ohm fixed resistors for maybe 2K ohms each.
|Beacon Stability with TCXO|
WSPR Above, QRSS Below
as Seen by my Local (overloaded) Receiver
More tests are needed, but I think this is a excellent fix for the RF Frequency Stability Problem for the Propeller Beacons.
I will add an installation photo here, later.