Verticom Synthesiser
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Christopher Bartram <cbartram@...>
I'd just like to second Andy's comments on the performance of these
synthesisers. I've been using one on 24GHz for about 18months, (24048 - 438MHz)and the close-in phase noise is very good indeed. It's significantly better than my microwave spec. an. (HP70000 system). Unfortunately, I don't have a suitable mixer to use with my home-brew phase-noise test set which would then allow me to measure the parameter. The phase-noise and stability are probably better than most amateur LO sources and would be plenty good enough for 76GHz, and probably above. Writing some simple PIC code to programme it didn't present a problem. I've also used Dave 'FRE's code. The problems with the units are : * the physical difficulty of getting at the internal ovened reference to modify it for locking - I think even the aforementioned 'FRE baulked at trying to do that. * the odd - but by no means impossible - reference frequency * getting hold of the beasties: they can be found on Ebay, but they are rare. * the units available on Ebay seem mainly to be 'pulls' from link equipment. One of those which I have has a problem with the reference breaking-up when the case temperature goes above ~35C. YMMV... Vy 73 Chris GW4DGU
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Andy Talbot <andy.g4jnt@...>
I was wondering about converting it for a different reference input but have so far just had a cursory look inside at the non-RF side of the module (it has a lot of hex headed screws holding it together!). The 26.25MHz reference oscillator is followed by what appears to be the beginning of a multiplier chain - presumably driving a harmonic mixer. This is borne out by the fact that the offset frequency, 10500MHz in this case, is an exact multiple of the reference (400 times) so my plans to replace with a 10MHz input and change the R divide ratio look to be a definite non-starter.
Wonder if its possible to change the reference/step size to something nicer than the rather odd 416.666kHz? The BridgeWave (That's what the PCB is labelled, but it has been referred to as Broadcom) module I also got going recently http://www.g4jnt.com/Bridgewave_Synth.pdf is a lot nicer to do things with. It has a more conventional design, starting off with a 1400MHz Z-Com VCO and multiplying up to the final frequency. The 1400MHz is directly synthesized using an LMX2326 device so any reference and comparison frequency is possible within reason.
2009/7/31 Christopher Bartram <cbartram@...>
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Christopher Bartram <cbartram@...>
Hello Andy
I was wondering about converting it for a different reference input butThe simplest way to change the (effective) step size would be to replace the synthesiser chip with a Frac-N part, such as one of the AD415x series. With a few changes in loop filter constants, it's possible to obtain almost any step size, particularly with the AD5157... Modern Frac-N synths using sigma/delta interpolation can produce quite remarkable results, and I wish I had the time to complete some of the designs I have in mind for amateur radio projects. The AD 514x series are more-or-less pin-compatible with the LMX23xx parts, while the code needed isn't that different... Vy 73 Chris GW4DGU
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