Again, my message was chopped off. I try it again ...
Hello Lowfers,
many of you post their weekend activity report here, which
I appreciate very much.
After a very succesful weekend looking around for longwave
stuff on a fleemarket (some of you say "rally") in Hamburg, I would
like to post some interesting equipment news over here today.
I got hold of a complete mediumwave ship transmitter named
DEBEG 7121, including full documentation. This "boatanchor"
has got a beautiful large variometer inside.
Looking at the schematics, it might be possible to convert it to
longwave. Besides the oscillator (chrystals in the range of
5 MHz, divided by ten, resulting in seven channels between
410 and 500 kHz), most of the following modules look like
the broadband stuff we use for LF. Following the oscillator
there is a driver stage using BD231/BD230 transistors to
achieve an output of about ten watts. This stage is followed by
two parallel PA modules using two BDY58 each in push/pull
configuration. Those modules look very similar to the design
G0MRF uses. The output transformer has got three taps to be
able to configure the system for antenna length between 12m
and more than 50m, as stated in the documentation.
The following variometer is simly in series with the longwire
antenna, a system that we on LF also typically use. An antenna
current meter between the PA modules and the variometer
allows to match the system for best output.
Interesting is the handwritten antenna current for various
frequencies that were noted by the ship's radio operator
when the unit was still in operation. With the
main antenna, they achieved antenna currents between
6.25 and 7.25 Amperes! Considering the 130 Watts this
transmitter delivers, this results in a loss resistance of about
2.5 Ohms, a value most of us only can dream about
(I have got losses in the range of 100 Ohms!).
Besides this straighforward transmitter design, the unit
also contains an AF module to allow to modulate the
PA with a 730 Hz AF tone to achieve A2 instead of
A1. The unit runs on 28 Volt at 18 Amperes max. in A2.
This transmitter was relatively cheap (80.- DM) and
more of them might show up, now, after most of the European
authorities have decided to stop operation on 500 kHz. It might
be worth looking for those units. I will keep
you posted on successes or failures in getting this unit
into operation on 136 kHz (btw: has anyone thought about asking
for an allocation for the amateur service between
410 and 500 kHz? This might save me from converting
this transmitter ;-).
The second device I got hold of looks like a giant (60 lbs)
synthesized SSB Exiter named "Schlumberger SSB 30".
No documentation, but this thing produces an output
frequency that can be adjusted between 300 Hz and
32 MHz (!) in 1 Hz (!) steps. No documentation, so I have
to find out what it does. Maybe an easy way to get an SSB
(respectively AFSK, PSK31, Hell) signal produced
on 136 kHz? I will keep you posted.
Best 73
Geri, DK8KW (W1KW)
P.S.: I will put some photos of those units onto my homepage
(http://www.dk8kw.home.pages.de) later this week.
|
