Tuesday, 7 June 2016

Couple of mods that I have done to DATV-Express

External reference added

C91 change
The first was to modify one of my boards to accept an external frequency reference
in this case 10 MHz. The reference must be greater than 0.3V pk-pk and less
than 4v pk-pk.

The second change I made was to change C91 in the PLL filter from 4n7 to 47n.
As you can see from the phase noise plot this reduces the noise at 100 KHz by
around 17 dB. I very much doubt this makes much difference to the DVB-S
performance but as I intend using the Express board for SSB as well, the
2 changes I have made should make a difference.

I am currently waiting for my SRP (Special Research Permit) for 71 MHz to
arrive, more on that when it turns up.

I am also waiting on some eBay 'bargains' to arrive as well. These include some
tunable 50 - 80 Mhz BPFs from Poland that I will put on the VNA as soon as
they turn up.

Finally I have added an E4437B 4 GHz signal generator to my rack of test gear.
It is the unit at the top of the pile. I offered the dealer around half what he was
asking and I was surprised when he accepted the offer. The guy on the
Signal Path Blog recently torn down and repaired one of these units, so I had
an idea of the risk before I bought.

I was getting a bit frustrated with my old Marconi 1 GHz signal generator as
most of my activities are above 1 GHz now.The generator has lots of neat
features including the ability to do multi tone testing of amplifiers and of
playing back test waveforms downloaded over GPIB.

Other projects in the pipeline include 70 Mhz PA re-vamp and a universal
receive converter for DATV (it uses eBay surplus so isn't reproduceable at
low cost).

That is all for now.

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