GM4WLL
CURRENT PROJECTS
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10GHz Transverter
I have a "whitebox" commercial transverter, which I am slowly adapting for use as a 10GHz to 144MHz transverter, using information from the RSGB Microwav e Handbook and from the website of G3PHO (www.g3pho.free-online.co.uk).
The conversion involves several distinct activities:
1. Build a G4DDK 2.5GHz local oscillator - at the time of writing this is complete and I just need to find a suitable wavemeter to set it up. I suspect I may need to have a second go at the coils, but the wavemeter will show the way!
2. Build a G3WDG x4 multiplier to multiply the L.O. Signal to 10GHz. I've got all the parts for this, just waiting for a quiet child-free evening to start building it!
3. Build a power supply for the whitebox. It requires abouta dozen different accurate voltages, so this won't be too easy.
4. Build a microstrip divider to split the local oscillator signal between the transmit and receive sides of the whitebox.
5. Fabricate an OSM connector for the whitebox. I've never looked, but I'm told these are outrageously expensive and reasonably easy to replicate.
6. Create some sort of an antenna system. The likely options are a surplus satellite TV dish adapted for the purpose or perhaps a simple horn to start off with.
Incidentally, both the local oscillator and the multiplier contain a lot of components which are renowned as "hard to get" but I found pretty much everything from two sources. The pcbs and various other bits came from the RSGB Micorwave Components Service
(www.g3wdg.free-online.co.uk). All the really awkward bits came froma wonderful Dutch firm who seem to be able to lay their hands on anything without turning a hair: Barend Henriksen
Update 29 July 2001.
Simon GM4PLM has tracked down an original OSM connector, so that's one problem solved!
2.4GHz Receive Converter
This is based on the classic Drake 2880 TV downconverter. These are getting hard to get hold of. I was able to import one from Mark Fossum in the US, (www.markfossum.com) but I believe Mark is now out of stock.
The conversion is quite simple, basically the replacement of the crystal and then a simple inductor change to improve the noise figure.
There is an additional change which a lot of people have made, involving a change to the GaAsFET. Not sure if I'll do that or not! Full details of the conversion are on Mark's website, as well as G3PHO's and various other spots on the web.
For an antenna I'll probably use a dish of some sort. I already have the feed in the form of a tiny Log-periodic antenna printed on pcb material and fed with semi-rigid coax. The pcbs are available from the UK Microwave Group component service (www.microwavers.org).
Six Foot Diameter Dish
This is a plywood and mesh dish, based on a design in the RSGB Microwave Handbook. It was originally intended for 1.3GHz as I needed a high-gain antenna for that band, but I've since bought a WiMo 67 element yagi so this project has been set aside for the time being.
Clarke Pump-up Mast
This is a joint project with Jim Martin MM0BQI. The mast is an vehicle-mounted one which has now been adapted to sit on a stand. Fully extended with a rotator and stub mast it puts an antenna at over 35 feet above ground level.
The difficulties we've faced are:
1. Attaching a yagi antenna at the top. It was designed to be used with a simple vertical so there is no obvious way of bolting an antenna on withour risking the surface of the top hydraulic section. The solution we've arrived at is to use brass or tin shims around the mast section, to protect it from the antenna u-bolts.
2. Rotation - the mast is far too heavy to easily rotate in it's entirety, though we've considered using a base with a car wheel-bearing. Initially we used a cheap off-set rotator. Although the rotator was capable of handling the antennas, the fact that the weight of the rotator is set to one side caused problems with the top section of the mast angling over with the weight. I have now acquired an AR40 rotator, which should solve that issue.
Hopefully the mast will soon be in regular use for VHF and HF contests.
DEM 1296MHz Transverter
I've had this unit in use for some time now, but I'm working to fix a couple of niggles:
1. I cannot accurately fix the frequency of operation - it can up to 5kHz either side of where it should be.
2. There are large spurious signals 96MHz either side of the main 1296MHz signal. With an amplifier in use this is obviously unacceptabel.
The solution to both these problems is an upgrade kit from Down East Microwave (www.downeastmicrowave.com). This kit replaces the standard 96MHz local oscillator with a 192MHz one, placing the spurious signals outside the bandpass filters included in the design. Hopefully this, plus a Murata crystal heater will help me to fine-tune the local oscillator for greater accuracy. Time will tell!
Update 29 July 2001
I built the DEM upgrade kit and added a crystal heater. The effect is dramatic! There's a huge improvement in the harmonics. It does now take about 10 minutes for the operating frequency to stabilise, due to the crystal heater warming up. Once it's heated up crystal stability is rock-solid!
1296MHz 2c39 Amplifier
In the longer term I plan to build a 2c39 amplifier for 1296MHz. I have a suitable power supply, though as it was bought second-hand I need to check it over very carefully before hitting the "on" button - kV power supplies are not something to play with lightly! I also have a single 2c39 cavity, again bought second-hand but allegedly functional. I plan to use this to learn about the rules of engagement with 2c39 amplifiers before I start getting ambitious with a mult-valve QRO amp.