Having successfully bench & on-air tested a x2 harmonic amplifier
method of driving my G0MRF Class D LF transmitter, I ran a beacon last
night (Saturday 19th) on 137.500 kHz.
An extract from my previous e-mail description is shown at the
end.
Using the equipment & method described below, the ERP from my 12
metre vertical antenna was around 150mW. The mode was ROS MF-1, 100 Hz
bandwidth.
I received the following report from Michel, F5WK in JN18HP, a
distance of 410 miles (661 kilometres) in daylight.
>> Not even a faint trace on a QRSS3 spectrum
but:
>> RX1: 19:23 @ 5.9 Hz: 9 <STOP> -37
dB
>> RX1: 19:28 @ 5.4 Hz: O4WGT <STOP> -34 dB
>>
RX1: 19:33 @ 5.4 Hz: G4WGT <STOP> -31 dB
The x2 harmonic low level amplifier is a simple way of driving a
Class D type of transmitter which employs a divide by 2 drive chain. My
limitation with multi tone drive is that my DDS VFO will only produce 2
frequencies ie. the main frequency & a CW/Rx offset which has
previously limited me to 2 tones as with RTTY & DFCW modes.
Please bear in mind that it will not be suitable for modes like PSK
were tones are transmitted simultaneously.
At the moment the 2 small PCB's are precariously lying on the desk,
when I have cased them I will publish the circuit & pictures.
73
Gary - G4WGT.
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After a few days experimenting & bench testing a method of
driving my
G0MRF Class D Tx on the 137.000 kHz band from my linear
transverter I finally
constructed a harmonic amplifier producing a
274.000 kHz signal from 137.000
kHz input. An "on-air" trial was
conducted resulting in a QSO with
Graham G0NBD on 137.000 kHz using
ROS data mode software.
My thanks to Graham for his ideas
& tests.
The mode used was ROS MF-7. The equipment used
for the QSO was as
follows. Kenwood TS-440 to my LF-MF linear
transverter producing the
137.000 kHz signal, followed by a tuned
harmonic circuit & buffer
amplifier whose output was 274.000 kHz
therefore at x2 drive for the Class
D Tx. The x2 signal is then
divided by the Tx driver chain in the
normal way to provide 137.000
kHz to the PA.
This method should also work well using WSPR
& other similar modes.
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