Wednesday, January 20, 2010

Ramsey QRP80C oscillator test

As promised, the results of the stability test of the Ramsey QRP80C oscillator. The oscillator is built using a new 3.579MHz crystal, no inductor and 1N4007 diodes in place of the varicap diodes. The following spectra show the carrier of the oscillator as received by the SR80lite. I did tests on upper and lower band edge, keying (by powering the oscillator) and some frequency sweeping.
Next to the stability of the oscillator, this test also shows how quiet the color burst frequency actually is. As soon as the TV qrm stops, it is clear that the signal carries some 50Hz hum, probably due to the power supply (rather old R&S regulated lab PSU).
Here is what the test looked like:

Power up, handling of the PCB, touching the xtal and some inital drift

Change from lowest to highest qrg

How stable is it when set anywhere else?

Keying test, since I shorted the keying, this was done by pulling the power cable from the PSU.

Some faster QRG changes and a final slow sweep, note the 50Hz when the next door TV gave me a break...

Some more stability in the midrange, note how clean the frequency range is...

HA! Finally something else (psk31) than just my carrier (draaggolf) and the TV set...

Some more lonely carrier...

And some final wiper play with the pot.