LNB Wobble | A tale of two LNB's

[G4IUG]

.
Off topic I know, but useful general, maybe ?

I have put this in 3 different user groups as it has many applications.

Many have noticed a frequency wobble on their 10GHhz downlink of Oscar 100.. It sounds OK but a minute later you are off frequency by a about 100Hz. Worse than that, if you listen to the CW Beacon you can detect by ear, the sliding and cyclic pitch instability.
So what to do ?

I assumed that as the frequency went forwards and backwards that it was not thermal or a crystal problem. Talk had been made about synthesiser chips ?

So I took two identical Triax single LNB's 304826. I chose these because their noise figure is good and the IF gain does not fall away until below 500Mhz unlike the Octagon that at 740Mhz has already decreased significantly. The synth chip is the 2566E and a 25Mhz crystal. Sure enough they both suffered the cyclic wavering of frequency.

I don't like the idea of GPS locking with all it's complication. So as I already had a Si Time 0.1ppm 25Mhz TCXO and grafted that in, with a 56ohm supply dropper and a 100n supply decoupler. The crystal was removed of course. The first thing to notice was the absolute frequency accuracy measured at 0.08ppm.. Was the tone of the CW better or was it "expectation bias" ? Whatever it's a perfect T9.

So what is it like ? Perfect, absolutely pitch perfect, no waver at all and SSB stations sound way more realistic. And they stay on frequency !

Worth the money? considering the cost of the whole station a resounding yes ! Here is the link to it https://www.digikey.co.uk/product-detai ... ND/8628633 or click here.

I suppose the question is why ? What makes it cyclic ? I really don't know, but with absolute frequency errors of up to a huge 400Khz and the awful pitch changes, it's not worth bothering with. There are other cheaper TCXO's available and YMMV.

Regards

Dave