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Yes Stefan
You go to bed and leave a machine churning out Beacon
callsign es Locator. That is not amateur radio but Appliance Operator black box
syndrome.
You do not need to be a Radio Amateur for such operations
just a plug and play Robot
I suppose this approach avoids perfecting a Receiver that
works, just rely on the Internet for some sort of response.
de G3KEV
----- Original Message -----
Sent: Friday, October 12, 2012 4:03
PM
Subject: LF: WSPR on the 630m band
MF!
Last night i built a transmit converter which allows
me to transmit WSPR on 630m now.
Yes yes yes yes yes Mal, CW is
preferred! But many OMs go to bed quite early i find. Not so their PCs, they
run over night, and so my transmitter will do this weekend if all goes right.
:-) I'm not present in the shack anyway, so no chance for CW...
I'm
using normal WSPR, not the slow versions.
Right now the
first tests are running and i check if the system becomes to warm.
The
design of this mixer is quite chaotic but i like it :-) It is a modular
system...: First, a tone of 14700 Hz is generated by the WSPR program. Is is
decoupled from anything by an audio isolating transformer. This signal is
applied to a SA612 mixer. The LO (461 kHz) in this test setup comes fom my DDS
VFO which is used in the first VLF experiments. The output looks very well as
expected on the scope. Filtering of mixing products is done in my MF
meachanical filter which is use in front of the receiver normally! I've
published the nearly perfect filter curve some weeks ago. Of course the sine
wave coming out from the filter looks very well! This sine wave is applied to
an OP AMP which is switched as a comparator. I've added a small hysteresis (10
MOhm / 47k) to prevent an oscillating output when there is no input signal.
Works well! The output of the OP AMP is fed to a ICL7667 (FET driver) which
makes a low impedant output. In series with 1 Ohm and 1 uF this rectanfgular
waveform is applied to a small ferrite toroid with a trifilar winding. So this
output is again galvanically decoupled from the circuit and provides an
opposite phase rectangular signal at 475.7 kHz.
Since my PA was/is
designed to have a 4f input (1900 kHz -> 475 kHz out) i had to make a tap
behind the divider, so i have to take care to maintain the 50 % duty cycle in
the new circuit. The new external drive signal from the converter is applied
by a simple headphone jack/plug! I actually found a 3.5mm stereo-jack with
dimensions 10mm x 5mm and also found a few holes to add this on the board. So
the PA is now able to run as before and additionally with this new
converter......
The AF signal levels and the LO signal level is
critical. Choosing wrong values will change the 50% duty cycle which will
quickly kill the FETs in this PA design. So i'm using an old modified PC power
supply that will shut down quickly if the current exceeds a certain
limit...
After writing this email the PA became hand warm so it looks
all fine. I will go down to 50% TX duty cycle now and even receive during the
breaks in WSPR. However the MF filter is now used for the TX so the RX
performance may be slightly lowered...
Reports about my
transmissions on 475.700 kHz are very welcomed. I'm also receiving and
uploading to the WSPR database...
Maybe i will run the test until monday
:-)
Best 73, Stefan/DK7FC
PS: https://dl.dropbox.com/u/19882028/MF/stuff.JPG
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