Hi Cor
0.08ppm is quite good enough for me ! Also it needs no extra cables or complication. Why would you need anything better ?
Dave
Hi Cor
0.08ppm is quite good enough for me ! Also it needs no extra cables or complication. Why would you need anything better ?
Dave
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/prod…X/1473-30922-1-ND/8628633.
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
Hi Michelle
All done and an email sent
Thanks Dave
Hi Michelle
You probably don't know me, but I supplied John Beanland with a lot of the equipment he sold. I warned against Phase 3D on the basis of its over ambition.
The latest AMSAT-NA magazine has nothing about Oscar 100 in it, nothing at all ! Why ?
Could you add me to your engineering list please.
Regards Dave
Several chips have wobble and I have a partial cure that I'll publish in the next few days.
73's Dave
P4B will only locate the USA ridesharing an US GEO-sat.
So at what position will it be ? And what up/down frequencies ? Is this a real satellite and not "fake news" ? I would love it to be real.
That looks good, what are the up/down frequencies and desired location ?
Well, why dosen't AMSAT USA put one up over the Atlantic ? I would help fund it in a modest way.
Quote from DH5DAX Michael
He said "Because we are radio amateurs, not internet amateurs" did you miss that ?
If this were to happen I'm off !
Hi Peter, OK thanks. It is a great satellite, truly great and makes me wonder why it didn't happen before. As we say here in the UK "gilding the lily" would be better dynamic range SSB for better audio quality. Presumably the AGC only kicks in with an overpowered signal ? Hi Fi and audio archiving is partly what I do for a living, but I'm also a qualified and experienced RF engineer. Is it possible to know how the NB "through gain" and AGC works ? No hurry and I know I have no right to ask. Thanks Dave
Presumably you are going to reduce the through gain to give more dynamic range ? That would be a good move. It would be interesting to know, as you go, by how much ?
If you can't find a good reference to 24Mhz, try what I suggested above ?
Dave
I have downloaded that document and there is no mention other than 25Mhz. I would look at the base-band noise on an analiser and inject 25Mhz into the chip after removing the crystal, then go downwards until the device/noise stops. However I think others would have done this if it were possible ?
Dave
Can you link me to that application note please ?
Is it a mod known to work ? Did you look at before and after on an analyser?
Dave
there are two models available the BPC2425M9X250 for e.g. 269.95 at digikey and the BPC2425M9X2S250-1 which is mentioned in the article you posted. This is the more expensive one e.g. 400.69 at avnet.
What is the difference between the two modules ? I'm up for trying it, I have the test gear, but I'm short of time.
Dave