I have been talking to another local ham about getting something simple and relatively inexpensive going for 10Ghz.
I came across this device: 10 ghz Dielectric-resonant Oscillator sold by SHF Microwave Parts Company in Indiana (http://www.shfmicro.com/gunn.htm)
I also have a Microwave Associates 10.280 GHz Gunplexer but have no idea how to get it working, and we would have to get another one the same.
Not looking for a contest station, just something that would get as across a car park would be OK for a start (yep, we are a couple of big kids and more than slightly ).
Would either of the above do the job, bearing in mind that the only experience we have with microwaves is the kitchen variety?
Using Gunn diode systems is certainly feasible. Our first 10 GHz system was Philips Gunn assemblies used for door openers etc. back in the mid 80s.
We easily achieved 100 km contacts with 60 cm dishes and 5 mW. IF was wideband FM broadcast receivers but in those days that band was nearly empty. Now it is very crowded so you will need another IF. They are not stable enough for narrowband. Some amateur transceivers can select wideband FM anywhere (FT100 and Icom 706Mk2g come to mind) so you could use 28 Mhz for example.
The only other issue is that you need to offset the each end oscillators by the IF frequency....so three way conversations are impractical!!
The FM BC band up here in Townsville is not as crowded as it is further south so an IF there is probably still possible. I am trying to source another Microwave Associates Gunplexer as that appears to be the simplest was to go. The one I have is 10.280 GHz Gunplexer, do they both have to be on the same frequency?
I just found hidden away in my pile of books "The Radio Amateurs Microwave Communications Handbook" by Dave Ingram K4TWJ that has some fairly simple circuits for the Gunnplexer I will chase up another one and see what we can get together before the next field day, but please keep the advice coming, we will need it.
VK4WDM wrote:The one I have is 10.280 GHz Gunplexer, do they both have to be on the same frequency?
No. They must be on different frequencies, with the difference being the I.F. you want to use.
For example, if you want a 100MHz I.F., then one Gunplexer could be on 10.28GHz and the other on 10.18GHz (or 10.38Ghz).
The Gunplexer will have a tuning screw you can use to adjust the frequency.
73
Iain Crawford - VK5ZD
Munno Para West, SA - PF95ih
As Iain said, the two Gunnplexers will need to be on two different frequencies. The difference between the two is the IF. Remember that the Gunn oscillator is your transmit frequency PLUS the local oscillator for the receiver. It mixes with the incoming RF to produce the IF in the mixer diode.
Some Gunnplexers have a varactor diode in close proximity to the Gunn diode. Applying a voltage to this is used to vary the frequency of the Gunn oscillator. Some do not, in which case you need to slightly vary the supply voltage to the Gunn itself. Gunns typically run on 7 volts. Modulation voltage applied is typically only a few millivolts! Circuitry required is pretty simple.
Take care with the mixer diodes. Static or exposure to high RF fields can kill them (trust me!)
Using FM broadcast band as an IF was convenient as the receivers are easy to get. We just set the Gunns 100 Mhz apart to give 100 Mhz as the IF, right in the middle of the FM broadcast band. Impossible now near a capital city as you will get massive broadcast breakthrough. 30 MHz was a common IF used in Gunn projects. It will be a full duplex link. No need for PTT operation. Be sure to add a tone oscillator to help you find each other.
Using the Gunn modules without antennas will easily get you across carparks and probably a few kms in the right terrain. Add an old sat TV dish and you will get over 100 kms. Once you get 10 GHz running, keep an eye out for some 24 GHz Gunnplexers....they are around and you can use exactly the same arrangement with them.
I still have a few old Gunn projects sitting on the shelf along with spare Gunns and mixer diodes......
Search the old 73 magazine archives, they had a lot of articles about modulating Gunn oscillators (FM). Back in the '60s and '70s. There was also a column called "Ask Kaboom", if I remember correctly.
Thank you guys, lot of good reading to do, but another question. Can you buy or build a field strength meter for this frequency? I am not too worried about it being calibrated, just want to know if the device is radiating. I suppose a "microwave oven leak detector" would be too low in frequency?
radar detectors are really good if you can find one in your shed etc.
china sells them on ebay for about $16 or so delivered and ,yes, they do get through customs.
not overly sensitive but workable and they run off 12 volts, so great for portable stations wanting to check tx signal
In car maybe yes, but at the shack as a receiver for 10 Ghz after a bit of work they are just another receiver. Remove the plastic case and underneath is some horns and diodes connected to a pcb. Its a radio receiver in a band we are licenced to transmit in.
Like this ebay item 151734164399
An older 'detector' i got going just needed the sweep ramp voltage removed and a pot put in place to make it tuneable. Excellent sensitive rx
). 
I will chase up another one and see what we can get together before the next field day, but please keep the advice coming, we will need it.
Maybe its only if you have them in your car? I will have a look on Ebay.