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| DL3PB's "all diode" transceiver |
Today I got this most interesting email from Peter
DL3PB. Peter must be congratulated on this excellent achievement.
Hi folks,
I'd like to share with you a long-cherished dream, that recently came
true, fourty years after I came to read about hams using tunneldiodes to
make QSOs when I was aged twelve or so:
Finally I managed a first skywave QSO with my
PARASAKI-transceiver, an 'all diode' rig: Christophe/F8DZY replied to my very first call on 20m band in
REF-contest last weekend. I was running 2mW into a
temporary vertical dipole on my balcony. Distance between us is
918km - obviously OM Christophe has excellent ears.
Those interested in the cruel details of my circuit, please find
attached a schematic and a photo of the pretty ugly setup. The circuit is
designed straight-forward with exception of the parametric VXO,
derived from Mike/AA1TJ's famous
Paraceiver design. (see
http://fhs-consulting.com/aa1tj/paraceiver.html)
The low impedance of the high peak-current tunneldiodes make it very
difficult to built a really crystal controlled oscillatorrather than an
LC-oscillator, synchronized by the crystal more or less, at least on
the higher SW-bands. The Parametric VXO provides a crystal-stable, chirp-free signal
on expense of an output power of two milliwatts only instead of ten, but with
an amazing spectral purity, no need for a low pass filter or such. Of
course it sounds pretty cool making a QSO with a 'bunch of diodes' and
a parametrically excited crystal, but believe me or not, I'd preferred
to bring that full ten milliwatt into the air - on the other hand that approach
allowed to tune the rig a bit ( ~ 5kHz/per xtal ), which
turned out to be much more valuable than a few milliwatts more while
being 'rock-bound'.
The receiver in its 'gain-less' version works fine for strong signals
- while listening to QRP(p) stations, the moderate gain of
the audio amplifier helps a lot. A comfortable frequency shift
between receive and transmit is realized by the 5µH inductor at
the LO-port of the mixer, with little effect on sensitivity.
Thanks for the bandwidth, OMs, won't bother again you with such mails,
unless I make a cross-pond QSO with that rig ( not that likely )
or any skywave QSO with homemade semiconductors ( probably impossible
)...
72!
Peter/DL3PB"
