RDF'ing a Paraset

[NickG0HIK]

The construction of my Paraset is almost complete and it was suggested to me that more SOE agents were caught from the oscillation of the receiver than the actual transmitted signals.

So yesterday I connected the radio to a non-resonant "Long wire" and put an FT817 in the car with a mobile H.F. whip.

I feel these working conditions might simulate those in the field at the time, I could only detect the Regen oscillations around 200 mtrs away.

With this the case I'm surprised so many were detected this way. Has anyone tried this test and maybe suggest any historical reading of the accounts in the field.

Thanks

Nick

[Colinaps]

I think the procedure was to turn off the power one sub-station at a time to see when a transmission stopped, then send in the DF vans. It's not likely operators would have been able to change address every time there was a power cut.

Colin.

[m0cemdave]

I think the receiver radiation would be useful towards the end of the hunt, once the location had been narrowed down to a few hundred metres. A continuous signal of low strength would be easier to pinpoint in the final stages of tracing the station.

[ms660]

Originally Posted by NickG0HIK

With this the case I'm surprised so many were detected this way. Has anyone tried this test and maybe suggest any historical reading of the accounts in the field.

For the test was the regen set for max oscillation or just on the brink ie: just enough to resolve CW?

I've read all sorts about osc radiating all over the place trapping hundreds of operators, I suspect most of it is twaddle.

Lawrence.

[NickG0HIK]

Thanks for that, I was not aware of the technique to cut power to selective areas.

Yes receiver radiation would be useful to narrow it down to a property within a street etc.

[NickG0HIK]

Originally Posted by pwdrive

For the test was the regen set for max oscillation or just on the brink ie: just enough to resolve CW?

I had the regen control around half way between the points that you mention, When I get time, I'll get a scope on the radio and see how large a signal is produced between the max and min points

Nick

[M0SOE_Bruce]

I've heard the same story and agree it's twaddle. Most of the agents rounded up were through betrayal. M.R.D. Foot, who is the best historian on the SOE, wrote that the penetrated networks cost many lives. In Holland alone almost 50 people from one network were captured. Perhaps the "radiation" excuse was to cover the fact of infiltration.

[ms660]

Yes that could be well the case, I watched a program once on "flying saucers from outer space" the things that a lot of folks saw in the States, the military sort of supported that notion while at the same time doing things with their top secret flying gizzmo's....

I suppose field strength measurements would be a reasonable indicator for regen receiver osc radiation or comms set local osc radiation.

Lawrence.

[G3VKM_Roger]

Originally Posted by NickG0HIK

With this the case I'm surprised so many were detected this way. Has anyone tried this test and maybe suggest any historical reading of the accounts in the field.

Hi Nick,

Pierre Lorain's book "Secret Warfare, the arms and techniques of the Resistance", 1983 in the English version, has a detailed chapter of German D/F techniques and a sort of blow-by-blow account of an operation.

I believe it was (is?) common practice for French residential buildings to have a mains switch panel accessible from outside, possibly a fire precaution? If the Germans had access to such a panel it would be a simple way of narrowing down the origin of illegal transmissions by building, then by apartment, by turning off the power and seeing if the transmission or reaction radiation stopped.

73

Roger

[Radio Wrangler]

In wartime, most of the high power broadcast stations were shut down, and there wouldn't be all of the hash from the billions of switch-mode power supplies we endure today. There would have been a lot of military signals, but they would be terse transmissions with not much more power than strictly necessary. DFing HF signals might have been somewhat easier.

David

[Richard - F4VPR]

Originally Posted by G3VKM_Roger

I believe it was (is?) common practice for French residential buildings to have a mains switch panel accessible from outside, possibly a fire precaution?

Still do, it's a billing "precaution" as well. Usually the meter, sealed fuses (EDF) and a sealed, set EDF overload trip with a test button in a box. We have to "contract" for level of supply and outside town usually 12kW monophase is the top limit, 3ø is always provided to the box however and common in domestic use should you want more grunt.

Rural people being cheapskates with say 6kW supplies can often be plunged into darkness when over-exuberant with the amps and have a cold, dark and wet trip to the front gate to press the reset. There are no 12kW instant power showers in France.

Fortunately my disjoncteur is in the house although the rest of the gubbins are a short walk outside.
Things like cookers and immersion heaters are always link-able for mono or 3ø here.

Way off the topic and I apologise.

However my club has a member with an original Paraset MkVII and uses it regularly. (F5RUJ)

R.

[kenneth]

Not quite on topic but a good account of the Dutch SOE agents infiltration is given in Leo Marks book 'Between Silk and Cyanide'. A Dutch agent was caught and 'turned' and many subsequent agents were later parachuted into Holland to the waiting arms of the Germans. The sorry part of this saga was that Leo Marks, whose job with the SOE was devising new codes and training training agents in their use, had figured out that the Dutch network had been rumbled but the Dutch SOE couldn't be convinced. Leo knew the agents of all the networks, and their capabilities, and kept statistics of their transmitted message mistakes which could arise from transmitting covertly in often uncomfortable, temporary and hurried situations etc. The Dutch network became so efficient, in contrast to other networks, that he knew there was something fishy there but his difficulty was in persuading others. An interesting and very readable book. The author was responsible for having the agents code keys written on silk - hence the title.

[Ted Kendall]

Could have been some self-deception or propaganda going on at some level, since the Germans themselves were spoofed that their Metox sets were being tracked by radiation and spent huge amounts of time and effort screening them. The POW who sold them this line has never been identified, but he should have got a medal - think of all that effort he tied up to no purpose!

I don't think the Gemans used Lissajous displays for DF in the war - they of course can be very quick to get a bearing, as in Huff Duff.

[GMB]

I believe there was also a spoof about detecting superhet mixers of U-boats radios, to cover the real reason for success in locating them using centimetric radar.

[Ted Kendall]

Yes, that was the Metox set. Incidentally, the Tonschreiber tape machines, which could compress time without affecting pitch, were introduced to make DF of U-boats more difficult by reducing transmission time.

[Station X]

I've heard that merchant ships sailing in convoys had their RECEIVERS sealed so they couldn't be used except in an emergency. The idea was to prevent U Boats homing in on the Local Oscillators.

[ms660]

I'm not saying it didn't happen but it might have been a risky strategy for the U boat cap'n.

Lawrence.

[G3VKM_Roger]

Using local oscillator signals to locate clandestine and other military receivers became a well-used technique on both sides in WW2 and afterwards. The US Navy in particular used a lot of very well-made and screened TRF receivers.

See also "Operation Rafter", a post-war operation which is covered in some detail in Peter Wright's "Spycatcher" book.


https://en.wikipedia.org/wiki/Operation_RAFTER


73


Roger

[m0cemdave]

A friend of mine worked for a certain government department (that Roger will be familiar with).

During the Falklands conflict, one of his jobs was to modify a batch of Eddystone receivers to proof them against L.O. radiation. You can recognise these, when they occasionally come up for sale, by the metal grille behind the transparent tuning scale. They were for use in, er, let's just say, South America.

[turretslug]

I've read and heard a great deal about the possibilities of LO radiation being a liability, but it seems to be difficult to find corroborated tales (as opposed to passed-along received wisdom) of it actually proving to be so in practice- possibly, there was an element of being thoroughly cautious on the grounds of "even if we haven't been able to do it so far, <they> might have invested more effort/discovered some new techniques that could (in some cases literally) sink us". Certainly, receivers with powerful and "leaky" local oscillators, infamously the HRO and TCS, could probably have proved to be locatable over some distance in an ad-hoc experimental sort of way and this was sufficiently attention-getting to sufficiently many people that it became highlighted common knowledge and cause for concern. The Scott Laboratories SLR receivers, which were otherwise unexceptional rack-mounting "quality" broadcast receivers rather than full-blown communications receivers, took some care to suppress local oscillator radiation from the aerial terminal but this might simply have reflected the fact that, as the war progressed, more and more radio communications devices were present as standard shipboard fitment that were required not to interfere with each other, rather than the headline/PR wisdom of preventing LO DF'ing.