I decided to build this 80M ARDF transmitter as described by
DL4CU. in 2008.
A previous President of the SARL expressed a wish to one day
witness the participating of South Africa in the Region 1 International
ARDF championships. I decided to set the ball rolling by building
a 80M ARDF Transmitter thereby enabling radio amateurs to organize
"fox hunts" in this country if they so wish. Rather than trying to
re-invent the wheel I searched for a 80M transmitter that would
be easy to setup and that conforms to International ARDF Rules and Standards.
I wanted an automated fox transmitter with a micro-controller that will operate unattended.
Having
found a design on the Internet I decided to build the transmitter.
It is very neat and compact design and is currently being used
very successfully in Germany on 80 meters for ARDF. I
completed the transmitter and tested it successfully the last few
days with the help of Johan ZS2I, Francois ZS1Q and Nico ZS4N.
The "fox" was even heard in Bloemfontein all the way from Mossel
Bay. The "prototype" transmitter is still under construction
as I would like to make certain changes to the PIC Software before
finally releasing the transmitter for "fox hunting" in South Africa.
In the meantime I will reveal the outcome of the provisional
tests
carried out on 3579Mhz last week.
The transmitter was build on
PCB and all components were soldered to the board. A mishap
occurred when I switched the transmitter on while on the test bench.
No RF output on the power meter, but the final transmitter would
got very hot. Somewhere was a component that
"blocked" the RF from getting to the watt meter and antenna. What
happened next is not unfamiliar with many homebrewers.
Smoke! Smoke! Smoke! At least I could send some smoke
signals with the transmitter. I determined that the 6 uH inductor
decided to send a smoke signal. Back to the schematic diagram to
look at the inductor specifications. I used a 6uH inductor rated
at 380mA max. When you look at the transistor specs it is clear
that this inductor will not be able to withstand the load. I
replaced the 6uH inductor with a 3A rated inductor but still no RF
power reflection on the watt meter. At least there was not smoke! I did
some further tests and it revealed that I had a short on L3.
Fixed L3 and the watt meter reflect an output of one and a half
watts of clear RF power. Enough RF to be heard around the world.
With the help of the above radio amateurs it was possible to test
the transmitter on the air. Nico ZS4N gave me a signal report of
S4 from Bloemfontein. (+-1000km) He also confirmed that the
transmitter was "narrow minded" with a good CW "output". After
the "smoke signals" I decided to run the transmitter into a dummy load
for 6 hours continuously. Well needless to say it operated
smoothly with very little heat coming from the final transistor.
Absolutely a little "GEM" of an ARDF Transmitter.
