John, LF
it's crazy but we had probably the same thought...
I had a
similar idea few months ago wishing to leave the bulky although
satisfying Kenwood TS950 on HF instead of run as IF for my LF
transverter.
Just for fate (looking for a Drake VFO stabiliser) I went
to the site of Cumbria Designs: they offer a kit based on SI570
although with less features than the QRP2000... anyway I got it and I
find it suitable as candidate for the core of an LF exciter.
I suggest
you also a visit to theweb pages of Andy G4JNT http://www.g4jnt.
com/LFUpconv.pdf
and have a look on his way to interface the audio from
PC to the rf of generator.
At this time I have to make a new PCB
because I made an error ordering to digikey a couple of IC... with smt
components it happens! but waiting for the new pcb I'm amusing myself
with deadbug construction.
Just for fun find in attachment the
schematic at its 3rd release (sure not the last because I probably cut
the interstage transistors).
Have fun in construction!
73 Marco,
IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 25-
mag-2012 8.56 PM
A: <[email protected]>
Ogg: LF: 137 kHz
exciter
LF,
This is now working! I used the QRP 2000 synthesiser
(completed with assistance from G8DQX) and have added a divide-by-100
unit based on the design by G3KAU with some modifications:
- the
original design assumed 10 to 50 W sine wave input. I left out the
attenuator because the synthesiser delivers 2.6 V peak to peak square
wave, which is enough to drive the 4017,
- I was not intending to use
anything other than 137 kHz and the power amplifier requires square
wave drive, so I left out the post-divider filters,
- the output from
the second divide-by-10 stage is sufficient to drive my Class E Power
Amplifier so I didn't bother with a buffer,
- there are several
versions of the 4017 but with different capabilities and voltage
ratings. I used the CD74HC4017,
- and provided a 6 V rail rather than
13.
The unit is now in a die-cast box and I shall shortly be testing
it with the PA into a dummy load.
After that, I need to look at
software for driving the synthesiser. For test purposes I have been
using the SI570 programmes referred to in the documentation but they
clearly are not appropriate for transmission.
Many thanks for all your
help and encouragement.
73
John F5VLF
LFexciterrev3.pdf
Description: Adobe PDF document
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