Further info from my friend:
The basic up/downconverter will generate about 0.1mW, possibly a little more.
The noise figure will be around 12dB. The local oscillator will start with a
1ppm TCXO. A feed for an offset dish is designed and ready to prototype, and
I’ll also make a pre-drilled box available.
A primary aim of this project is to make the transverter very easily
upgradable. I plan to supply built and tested system components which can be
built into a system which can grow with the purchaser’s interest.
The next step will be a board with intermediate amplifiers to ~10mW on transmit
and a noise figure of about 5dB on receive. To go to this level will need a
bandpass filter between the up/downconverter and amplifiers to reduce the
transmit spurious products to an acceptable level and protect the receiver
from potential sources of out-of-band interference.
My plans beyond that are based around a 1.5W+ PA and a 1dBNF front-end.
A better, GPS-based LO reference is also on the cards.
–
Should anyone query the potential effectiveness of a 0.1mW transmitter, it’s
worth doing some sums!
Let’s use the longest line-of-sight (LOS) path in the UK (240km) as an
example:
The free-space path-loss over 240km at 10GHz is ~160dB.
If the gain of two 50cm diameter dishes (~33dB each at 10GHz) is subtracted
from the free-space loss is subtracted, the power arriving at the receiver
input is ~94dB below the transmitter power.
So with a -40dBW transmitter, we’d see -134dBW at the receiver input.
A 3kHz bandwidth receiver with a 12dB noise figure has a noise floor of about
-160dBW, therefore the received signal/noise ratio will be about 26dB. Of
course, if you use CW, the reduced effective bandwidth will result in even
greater effectiveness!
The basic up/downconverter with a suitable antenna should be capable of
working any LOS path with ease, and to be able to cope with many singly
obstructed paths, particularly on CW. It will also be capable of exploiting a
number of other propagation mechanisms such as tropo ducting, maritime super-
refraction, and even more intense rainscatter. Alternatively, a lower gain
antenna such as a 20dB horn would give good results over any usual LOS path.
Running a similar system back in the mid-1980s, my best DX was 250km during a
tropo opening.
