Dear Geri,
your rallye report reminds me of my my time being a wireless operator on german
ships in 1956-58. But I had simpler types of transmitters, one big valve in the
VFO, two of the same type in parallel in the PA, both stages tuned by
variometers on ceramic forms, ganged by a chain like those from a bicycle . . .
'Geri' Kinzel, DK8KW schrieb:
Hello Lowfers,
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.
I suppose this variometer will be too small for LF but may be used as the
variable part of an LF variometer if a fixed coil is added.
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.
For conversion to LF the inductance of the output transformers may be too low
due to the frequency difference! You have to find out.
The following variometer is simply 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!).
I have losses in the same order.
When with SIEMENS I have met an old engineer who had designed marine
transmitters with TELEFUNKEN before the second world war. He said that the
output match for these transmitters were ok under the assumption that all
transmitter power is dissipated in the loss resistance of the antenna
variometer. That means: Practically no ground resistance of the ship herself!
Therefore there is a need to get amateur stations on museum ships etc qrv on LF!
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 has been done much simpler in the old transmitters. Most ships had DC mains
on board, and therefore a motor-generator converted DC to 220 Volts AC 500 Hz
(!!). The mains transformer of the transmitters converted this 500 Hz into a
suitable voltage for the tube heaters and for the plate voltage, and the energy
to modulate the transmitter for A2 had also been taken from this source.
We have been told that those 500 Hz generators were first used in the spark
transmitter age, to provide a voltage peak every 1/1000 second for the spark
gap. When the spark age came to an end in the early twenties the
motor-generators were still in good shape, and therefore TELEFUNKEN (and
I suppose other manufactureres too) decided to design the new tube transmitters
for a 500 Hz supply.
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 ;-).
YES, I DID, when measuring the ground loss of my LF aerial and calculating its
radiation resistance! All this would be much more favourable on MF! But on MF I
would suggest to use a frequency band around 410 kHz, the former direction
finding frequency, and slightly higher. Because we would get into trouble when
using the range 454 kHz to 480 kHz where the (final) I.F.s of many receivers are
situated.
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.
There will be many applications, also on HF and even higher, but you have to
find out. But - How long it will take to QSY? This is often a problem with this
kind of equipment.
73 Ha-Jo, DJ1ZB
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