Re: [VHFcontesting] Bought a 24GHz gunnplexer...now what?

[Zack Widup <w9sz.zack@gmail.com>]

The Gunn oscillators are fun to play with but you will probably have
to build two complete systems and loan one out, or get someone else to
build one so you can work him. I should mention that most of the
contest activity on 24 GHz is weak-signal work using CW or SSB (CW
most often). This requires a full-blown transverter and an all-mode IF
rig, as accuracy is required at least down to a few kHz. I was lucky
to get one of the last few Endwave SDH units that was still available
a few years ago. It puts out 1 watt on 24 GHz and has a quite
acceptable receiver. It is best used with a 432 MHz IF, so I built a
W1GHZ  Miniverter-F for 432 and built that right into the system. The
weak-signal calling frequency in the USA is 24192.1 MHz. I believe
Europe uses 24048. I have made quite a few QSO's in the 50 to 70 mile
range with this, and one at about 110 miles (my best DX on that band
so far).

A Gunn oscillator can be phase-locked to a frequency but I tried this
with 10 GHz many years ago and it is actually a lot easier to build a
transverter with a phase-locked LO.

At any rate, a Gunn unit is a good way to "get your feet wet" on the
band but you'll probably eventually want to move on to something more
advanced.

73, Zack W9SZ


On Tue, Aug 8, 2017 at 6:44 AM, Steve Kavanagh via VHFcontesting
<vhfcontesting@contesting.com> wrote:
> There's a few (old!) articles on Gunn oscillator gear at 
> http://www.kwarc.org/10ghz/index.html which may help a bit. I still have a 
> couple of 24 GHz rigs based on the RF portions of Kustom speed radars, which 
> have been pressed into service regularly in various contests for many years.  
> But at least in this area there is zero regular activity on wideband FM now, 
> so two rigs are essential, one to keep and one to lend to a friend.
>
> There were a few peculiarities to these rigs.  One was that the warm-up drift 
> was greater than the electronic tuning range of the oscillator, which 
> necessitated using a tunable IF strip.  Second was that they came with 
> circularly polarized horn antennas with an odd circular waveguide interface 
> which was not amenable to replacement with dishes, making serious dx rather 
> difficult.
>
> I managed to find a surplus cavity frequency meter, so I was able to set my 
> two oscillators to frequencies about 30 MHz apart near 24.125 GHz  (I think 
> they were nominally 24.120 and 24.150 GHz but the rigs are lent out at the 
> moment so I don't have access to the frequency labels).
>
> 73,
> Steve VE3SMA
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