2 Jul 2014

FT817 drift on 6m

G0LRD compared spots of his signal from G4IKZ and from me and noticed greater drift on my reports than from Nick G4IKZ. I think Nick uses a K3 with GPS disciplined reference.

Although I have a loaned 0.5ppm TCXO fitted (thanks to Bob G3WKW). the issue may be drift as the rig cools going from TX to RX. There is definitely Doppler shift (and multiple traces) on most of the GDX  signals I copy, much of the apparent drift may, in reality, be in my rig. 0.5ppm is still 25Hz at 50MHz .
at 16:47
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4 comments:

David (G0LRD) said...

Hi Roger,
I'm sorry if it seemed like I was harping on a bit about this subject, and I feel bad about giving you the bad news that your rig seems to drift around, but I was concerned that you were sometimes drawing conclusions about the nature of received signals without a reliable basis.

It struck me that your TCXO should be doing a better job, so I dug out the data sheet for it (NKD NT801B) which indicates that the 0.5ppm spec is actually only the initial frequency accuracy at 25C +/- 2C. There are various stability specs for that part, but the best one is +/- 1ppm over the range -20C - 70C. This equates to about 0.5Hz drift per degree change in temperature. This seems to stack-up with the likely PA-induced heating in a physically small rig.
David G0LRD

Wed Jul 02, 07:48:00 pm GMT+1
Roger G3XBM said...

Not harping at all David. It is worth me knowing.

Wed Jul 02, 08:49:00 pm GMT+1
Roger G3XBM said...

Only way to avoid the issue is to TX far less here, HI.

Wed Jul 02, 08:51:00 pm GMT+1
David (G0LRD) said...

It's perhaps a bit of an extreme measure, but when I was playing with 2m WSPR I had to wrap my old ICOM-260E in bubble-wrap! Helped to stabilise it pretty well! ;-)
David

Wed Jul 02, 09:06:00 pm GMT+1

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