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