Radione RS 20M transmitter and R 3 receiver restoration Survey.
Briefly modifying
our Radione portable transmitter and receiver sets
as to prepare them for future applications.
From the historical point of view, should we do it?
These devices have been built in at least several thousand numbers; hence, we aren't destroying a unique historical device.
Our major motivation:
The weak point of all Radione products, is, that genuinely these were actually civilian-like products,
fit mainly with non-military standard components.
Fore example: they used broadcast type electrolytic capacitors and/or so-called
block-capacitors, based upon 'wax dielectrics'; which material is highly hygroscopic and
therefore useless nowadays, when applied within high-voltage circuits.
It has to be noticed, that all belligerents suffered from this downside equally.
Albeit, that up to, say, late 1942, German military gear was generally equipped with
hermetically sealed types. Which even after > 75 years still function fully reliable at full rate.
Page initiated 24 April 2020
Current status: 7 May 2020
Our transmitter type RS 20M and receiver type R3 were once owned by late PA 0 MM
According to the accompanied papers, he obtained the two suitcases in February 1946.
We obtained it in 1979; I suppose - by then PA 0 MM had passed away already.
When I opened it in 1979, it proved that the HT block capacitors for smoothing of the 460 V HT had already been removed and some substitute capacitors had been 'amateur-like' built-in.
Schematic of the RS 20M transmitter
Please click at it as to open it in PDF.
Upper-left-hand side, some PA 0 MM explanations.
Recording some of what Hans Goulooze has accomplished after some weeks during our Corona forced isolation
The two glowing yellow like neon-gas voltage stabilisers.
Hans has done a great job, but encountered: that albeit a quartz crystal had been inserted and measurements showed current consumption, he could not detect any RF output power.
Therefore, I had to break our obligatory mutual insulation, and it was found that the quartz crystal was defect; replacing it, directly resulted in a sufficient RF output signal.
I used the opportunity to take some photos as to show these on the web soon.
Maybe you might recognise that on the left-hand side, the "Soffitten" bulbs (two) are glowing
But at the same time the neon voltage stabilisers, stopped glowing. Why?
What might go wrong?
Click at it to open it in PDF!
Please look at the schematic and trace the two neon stabilisers in series; look also for the two 1 MΩ resistors each connected onto the extra ignition anodes (up of the EZ 12 rectifier valve)
Please consider it carefully, and you might recognise that it solely is stabilising the LV 1quartz-oscillator stage.
This stage is being switched on-and-off by means of the morse-key in the cathode circuit. This would, without extra provision, causing that 460 V HT would be fed onto the LV 1 stage; as well as putting quite a high voltage across the open more-key contacts.
I consider, therefore, that the neon-stabilisers only act voltage limiters.
More-key not touched we measure across say 305 V, but with morse-key down we measure ca 235 V, far too low for igniting the two 150 V stabilisers in series.
The 10 kΩ (10 TΩ) in series we measured about 8 kΩ; thus sufficient.
This photo allows a better vision upon the now glowing Soffitten bulbs
These bulb-types were for a long time used for car-interior lights, but also for other purposes.
Please notice below in the set the epoxy plate where upon Hans mounted, soundly, the electrolytic replacements.
Viewing the RS 20M front-panel
By the way, the M stood once for Marine (Navy); this correlates also with the application of three pin KM "Stecker" (connectors)
Apparently PA 0 MM must have had access to some stocks of British type quartz crystals
Maybe, he might have grind them, as to get these operating exactly at HAM frequencies. We possess also two genuine suitcases and in the R 3 receiver suitcase a full range-sets of crystals for the 80 and 40 metre amateur-bands is incorporated.
Please notice the pointer of the moving-coil meter and the glowing "Soffitten" bulbs showing that the transmitter is generating sufficient RF energy
The meter actually is indicating the antenna current; by this means an operator can tune the PA antenna tuning controls optimally. Which is particularly of significance when operating a random wire-antenna for various frequencies.
Please notice the meter draw about up of the LS 50 PA valve
The switch allows: in one position to measure the antenna current and in the other position to control the appropriate tuning of the driving circuit.
Down we get an idea as to how the R3 receiver on the left being interconnected with the RS 20M transmitter on the right-hand side.
For the technicians among you: please notice the lowest winding of the antenna-tuning circuit.
Its purpose is to provide the "neutrodyne" signal, which is in counter-phase supplied onto g1 of the LS 50 power amplifier. By this means, the anode - g1 signal-feedback can be countered - by injecting a counter-phase signal of the same amplitude.
Please notice the trimmer capacitor in series, by with means the correct injection voltage is to be adjusted.
How, can this be accomplished correctly?
For this means the HT voltage has to be disconnected from the LS 560 PA stage. Tune now the trimmer such that you reach the lowest signal level passing through onto the antenna connection. Sometimes it is necessary to use an additional receiver as to accomplish this sufficiently.
I suppose that the meter deflection is sufficiently explained
The switch to change-over from antenna current measurement to driver-circuit tuning, is the small (blue) circular push bottom down on the right-hand side of the moving coil meter-housing.
The mains cable is for all Radione products a nice feature
When appropriately fixes and mounted the correct ac powerline voltage is guaranteed.
A better view on the power connector
OM Metselaar, PA 0 MM was a meticulous man, please notice the framed tuning settings.
The set can also, at will, be driven from a 24 V external battery, a vibrator pack (Zerhacker) is implemented in the set.
I suppose this drawing is self explaining
We can clearly notice: that the receiver antenna connection is connected onto a special connector at the transmitter. Reason: the antenna is only connected onto the receiver when applied. When the transmitter mode-switch is set at receiving, the receiver antenna is now connected onto the existing antenna.
Yesterday 23 April 2020, Rudolf Staritz noticed "B-K Betrieb".
B-K stands for: Break-in operation.
This special mode of operation was quite often used by the German Abwehr communications.
Often for practical reasons, as agents in the field got often only three quartz crystals. Thus could only transmit on three different frequencies. These were selected considering the to be expected propagations, during seasons and day or night times.
It is understandable that also in these cases B-K mode was possible:
the transmitter sends at a different frequency (QRG) than the receiver on the other end is listening at.
From the point of security it is to be favoured, as interception is becoming more difficult; and operation can also be speed up.
Rudolf Staritz (DL3CS) told me, that on fixed lines of communication (say: Stahnsdorf in Berlin and Sabine in Madrid) and you knew who was operating on the counter side, that when one was receiving and, for whatever reason lost some of the coded message, he only touched the morse-key and did sent a single dot instantly.
His colleague on the other side directly stopped and went back some coded-blocks and repeated his message and continued thereafter.
But, when B-K mode is concerned they needed an additional separate antenna. The transmitter wasn't switched off; the operator simply did not touch his morse-key.
Very convenient, with on both sides well acquainted operators.
Staritz also told me another story: that for instance at Stahnsdorf, when the shift changed that some of his colleagues, often already amateurs, opened their bag and took out their own "Bug" morse-key. These devices generate themselves series of dots, the dashes the operator had to give manually.
Bug keys, allowed rather high-speed morse-code transmissions. Whether it was officially allowed? Who dares, as long as communication traffic runs smooth and fast?
(2)
On Thursday 7 May 2020
Today Hans Goulooze will demonstrate our just restored Radion RS 20 M transmitter, operating in full order.
Shown the RS 20M modulated by means of a loudspeaker fed from a Siemens Summer tone-generator
I guess 30 à 40 % modulation depth.
The loudspeaker is directly fed from the tone generator output and the audio tone originating from the loudspeaker being picked-up by a genuine Wehrmacht carbon-microphone.
Viewing the Summer-Ton-Generator, this version was supplied into the radio-service
It used two RF generators (I guess) at 100 kHz and these two signals being mixed by means of a ring-modulator.
Providing 0 - 20 kHz continuously tuning. The loudspeaker being connected onto its 15 ohm output.
In the background we notice the A 3 modulation which currently seems to be I suppose ca. 70 % depth.
I guess 70 à 80 % modulation depth
Viewing the test set-up
On the left-hand side the loudspeaker, the black bakelite device is our genuine Wehrmacht carbon microphone.
The RS 20M is apparently operating in mode A3. The meter pointer is indicating sufficient RF which is also indicated by the glowing dummy-load Soffitten bulbs. on the right-hand side of the transmitter.
You easily notice that the transmitter being switched off
Why?
The dummy-load on our left-hand side isn't glowing and the two neon voltage stabilizers do not glow.
I have to apologise for the apparent over-exposure
My aim was, to show more in detail Hans Goulooze's board carrying the replaced electrolytic capacitors.
A more detailed photo of the oscillator stage
YouTube Films
Film 00052: Viewing the just restored RS 20M transmitter. On the right-hand side the dummy-load indicating, say, 50% modulation. The audio tone in the background originates from the green loudspeaker on the far left-hand side. The audio tone being picked-up by the black bakelite device in front, being a genuine German Wehrmacht carbon microphone. This one, fit with a new microphone insert, proves to be very sensitive. later Hans switches over from A3 to A 1 mode (Morse mode). Hans is giving some dot signals and the dummy load should that RF power is really supplied onto it.
Film 00053: Now view the screen of our oscilloscope where we first see a modulation depth of, I suppose, ca 20 %. Thereafter has hold the microphone nearer to the loudspeaker and more than 100 % modulation is visible. You might recognise my voice picked up from the microphone in the background.
Film 00054: Viewing now the way Hans is manipulating the microphone on the table and also what the impact is between keeping it near to the loudspeaker and further away of the latter. The dummy bulbs are indicating my voice spoken from more than one meter distance of the microphone at the table.
Film 00055: Viewing the interaction between the ignition of the two stabilizer devices and operating the transmitter, causing the switching off the two neon stabilizer, during transmission. Hans is demonstrating what the interaction is between A 1 transmission and the glowing neon stabilisers. The neon stabilisers aren't stabilizing the operation HT voltage, but are limiting the HT fed onto the LV 1 oscillator stage.
By Arthur O. Bauer
