interesting radio thing

Hi Ivan,
As you stated, mankind has wasted a lot of time and effort, and the most effort seems always to be military or espinage.

Most of the major scientific discoveries we have were developed and exploited by war, preparations for war and military supremacy. That, and money.
Did you know that there is more money spent on research on obesity in wealthy nations than serious ilnesses in under-developed countries.

But eavesdropping always has been a very popular subject for research. I remember reading that medieval catholic churches had a parabolic arch over the confession booth, which projected whispered sounds across the gallery to a similar arch. This created a "sweet spot" where confessions could be clearly overheard.

But then I am rambling on. It is a bit late - hafta get ready for bed. I have to deliver another training session tomorrow.

G'night all - Harry

Hi,
I expect microwaves (>1 GHz) were not used in this system. Both the microwave and laser technology were on a fairly low level in the 50s. I expect decimeter waves were used, some 200 - 400 MHz.
In a Czech film "Ucho" ("The Ear") eavesdropping plays an important role. A parabolic reflector (like one of  this type) with a rhomb in its focus appears in one scene - I believe a real, that time obsolete device was shown.
Mankind has wasted huge amount of time and material to get restricted information "from the other side"!

VBR from Ivan

hello,

well it was a hell of a job for both . Once for the poor man who stayed in a microwave oven for 7 years ,  and the other one who started the oven every day for seven years . What a useless way to spend life .... but they had an occupation.

I have read this post a few times and it never stopped amazing me.

As Ivan pointed out the RF power levels must be huge. perhaps an induction loop the other side of the wall would be practical, but then a drinking glass between your ear and the wall works just as well.

The power levels must have been so huge that people would surely have noticed?

A few years ago I made a "death ray" (photo's available if there is any interest) to project a beam of RF. I used it to burn grass (too lazy to do it manually on a steep slope). I also used it to melt snow on the driveway, and also to kill a giant anthill. At a distance of just 5 to 10 metres I needed an ERP of 8000-Watts. I used an 800-Watt 2.4GHz  magnetron with a satellite parabolic reflector, estimated gain 10dBd. A satellite dish is deliberately de-focused so you can find the satellite.

Ok, you would not need so much power, although you would need to transmit a much greater distance for it to be useful. It would still be like putting someone's head in a microwave oven  

I think I have some pictures of my laser pointer and rifle telescopic sight. I placed a photo-diode at the focus of the telescopic sights and adjusted it to view the later spot at a distance. With that I could eavesdrop something like 20m or 30m daytime (not with direct sunlight), but about 100m - 150m at night. That worked very well, but the laser spot shining on a painting was a "dead giveaway". It didn't work on curtains, but preparing the room with a bit of sticky paper on the window gave me fantastic results (the 150m test).

As regards the progress of moving houses - I only have two large metal chests and about 15 boxed left to unpack from the Spanish villa. Then there is installing everything in the house - window lamps, glass-showcase illumination, stained glass window, more cupboards etc. It is not much fun squeezing belongings from two homes into a small house  

But at least I have a gantry on the roof, and a couple of metal brackets will get me 27MHz and 29MHz mag-mount antennas on the roof.

Final comment, my 1962 DUX transistor radio is working fine. Lovely sound!! The Eveready D-size batteries (3D printed with AA cells inside) have original scans, including the text "For best performance install before Feb 1950".

Ok, goodnight all. BR Harry - SM0VPO

Hi Zsolt,
I suppose it required power not much less than a passive radar. Hundreds of watts might be in the ballroom. One drawback of these dewices was that long exposure of human bodies to the exciting RF energy was harmful.

BR from Ivan

hi,
best wishes for all, here is an interesting thing i found https://en.wikipedia.org/wiki/The_Thing_(listening_device)
I think it works like the key tags which open the doors. Who knows how much rf power they used to operate such passive transmitter