Sunday, 15 September 2013

More 4m

DUBUS turned up two days ago. Interesting that it contains a nice 4m transverter design by DF4UE. What is surprising is how similar some of it is to my Nacton design. Maybe I shouldn't be surprised at the similarities. Anyone starting out to design a transverter today would probably choose to use modern MMICs for the RF stages. Indeed DF4UE has chosen to use the same MMIC for the RF stage. Even the mixer(s) are the same as used in the Nacton, although I use just one whilst Johann uses two.

I have added more interface switching options since the original design. When interfacing the original transverter module to the PA, external linear etc it became obvious that it needed a few more options. I'll talk about this at the Convention.

As I mentioned in my last blog I have spent a lot of time during the week drawing the schematic circuit diagram using my PCB CAD package and then modifying the PCB mask to correspond. Or maybe it was the schematic modified to agree with the PCB?........
Anyway, both are now ready to be used in my Convention talk next month.

I've etched another couple of PCBs, using the latest mask, drilled them and am now ready to assemble another transverter using some alternative and easier to obtain parts to those in the early transverters. In particular I have had to order a set of tuneable coils from Coilcraft. Coilcraft are usually happy to supply free samples as long as you are not too greedy. The chosen tuneable inductors are similar to the now-obsolete TOKO parts used in the original design. I am keen to check that these ones do fit the hole pattern in the PCB and have an adequate adjustment range to cover the required 4m frequency range. I've been informed that the samples have been dispatched and hopefully will arrive this week.
Dave, G4HUP, is currently stocking what appear to be suitable 42MHz third overtone crystals in HC49U package, so I will be obtaining one of those tomorrow in order to try it in the oscillator stage. The transverter has facilities for an external LO input where the requirement for greater stability warrants it.

If all goes well I plan on getting a small batch of PCBs made in the next few weeks.
I might have these back from production before my talk in mid October.

The other thing I have been doing is working out how to assemble my 3cm band EME RF feed unit. After weighing the successful 6cm EME unit I have found that the 3cm power amplifier, waveguide switch, and adapter weighs in some 1kg less, leaving just enough margin to add the mounting plate, transverter and feed without exceeding the target weight of 4kg I have arbitrarily set.
As my TVRO dish has a quadrapod feed support, meant to support a lightweight Chaparal horn and LNB, it has limited ability to support a heavy RF head. It will probably need further supports to prevent sag when the dish is elevated.
As we approach the autumn equinox the sun is getting lower in the sky so that sun noise testing time is reducing rapidly.
Sam
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