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Stefan
I build during daytime and work DX night time. Worked the
Antartic (South Shetland Is ) earlier on today on HF CW.
There was NIL acty on LF or MF
de Mal/g3kev
----- Original Message -----
Sent: Friday, October 12, 2012 6:11
PM
Subject: Re: LF: Re: WSPR on the 630m
band
No, i did not go to bed, i built (with happiness) a converter
for 475 kHz until 4 AM local time! This is not an appliance operator syndrome
:-)
Now we're all playing our role again, isn't that fine?! :-) Like in
the good old days ;-)
73, Stefan
Am 12.10.2012 20:03,
schrieb mal hamilton:
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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