10GHz Transverter Project – Part 5: Finishing Touches

I’ve finally put the finishing touches to my homebrew 10GHz transverter (TVTR) and the lid of the die-cast box was secured for the first time with all six screws!

This project came about for the following reasons:

The desire to get out again /P on 10GHz without the need to use any of my existing 10GHz EME setup that I have spent hours and hours optimising.
Rather than simply buying another TVTR box “off the shelf”, to see if I could put together a solution using a modular approach based on the lessons learnt getting going on QO-100.

As things stand today the TVTR is working with a 432MHz TX/RX IF plus an optional 618MHz RX output for SDR, about 100mW RF output into WG16 waveguide feed, and all local oscillators are locked to a 10MHz OCXO.

The basic concept did evolve during the build process and end result is as follows:

The TVTR modules have been shoe-horned into a Hammond die-cast box. The internal layout can be seen in the fllowing photo:

The well known “German Tin Boxes” have been used for most of the main modules. To accomodate everything some modules have hade to be stacked two deep.

The main modules being (more details can be found by clicking on the links):

Tests undertaken so far suggest that the TVTR is working well on receive. Both GB3BED and GB3PKT beacons have been audible via RS using just a 20dB horn indoors pointing up through the patio doors.

The rather poor screen shot below shows GB3PKT being decoded at -14dB via RS.

Other than tests done listening to the TVTR on the EME setup and power measurements / spectrum analysis the TX side is still in need of a first QSO.

Lessons Learnt:

Based on results so far it would seem that a reasonably good setup can be put together using a mix of “off the shelf” and homebrew modules.
Having built two 10GHz LO boards now, it would seem that the board + “German Tin Box” combination works without any major issues.
An LNB plus down-converter can make quite a respectable 10GHz receive setup.
My original plan was to use a 144MHz IF but my initial tests showed that the LO leakage was only -37dBc. Changing to a 432MHz IF and with more careful tuning I was able to achieve better than -50dBc.
Whilst I’m fairly certain the overal cost (in £££ terms) of this new TVTR worked out less than any one of the few options available new “off the shelf”, it was costly in terms of time and the amount spent on decent internal interconnecting patch leads. Decent SMA connectors and semi-rigid cable do not come cheap.
Once the OCXO has stabilised the TVTR draws just over 1A on receive which is higher than I would like when out /P.
The commonly available “Chinese 10MHz OCXO” modules work surprisingly well. I did have to make a slight mod to get the pot to “fine tune” correctly but once that was done I was able to zero beat with my trusted G3RUH GPSDO 10MHz source.
It’s good to have a PLL Lock LED fitted to indicate things are all “good”. This was one of my finishing touches after I spent time monitoring beacons via RS and unbeknown to me the battery level dropped to a level where the OCXO was not running, the SynthShiel LO was off, and I was listening to white-noise on some obscure frequency!

What’s next:

Try to get the TVTR tested using better test gear to get an idea of phase noise, receive sensitivity etc.
To try and increase the RF output power from 100mW to around 2W.
Make the metalwork to mount the new TVTR, waveguide feed and 95cm offset dish on the new (to me) heavy duty pan and tilt head.
To get out more and use the gear /P.
Maybe add an SDR panadapter using a RPi and display. This would certainly help when searching for beacons / stations.
Find some better local /P sites for testing. Unfortunately Essex has very few high spots!