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.
***********************************************
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.
*********************************************
