Clandestine Crystal Sets - Channel Isles WW2

[colly0410]

This thread has got me thinking: Can the sensitivity of a crystal set be improved? I'm thinking along the lines of full wave rectification using two or more diodes &/or using more capacitors & coils in clever ways?

[Yorkie]

I think the more serious shortcoming of crystal sets these days is lack of selectivity, which wasn't an issue in the crystal set era when there were just a few stations within range. However, nowadays, with so many local radio stations - commercial and community broadcasters, the stations all come in on top of one another. 

That wouldn't have been an issue during the war years as all former regional BBC stations broadcast the same programs simultaneously albeit on different frequencies. That prevented enemy 'planes from using the individual transmitters for direction finding.

The more I think about clandestine crystal sets, the less convinced I am that they were a mainstay of radio news gathering on the Channel Isles during the occupation years.  As I said earlier, the late 30s was the high watermark for home constructed radios and hence, components to make small valve receivers would I think have been plentiful. Hence, why fiddle about with crystal sets?


 

[Alan Douglas]

Can the sensitivity of a crystal set be improved?

Not really, other than biasing the diode to the best point.  The largest improvement is a pair of sound-powered headphones (originally used for two-way communications on ships without using batteries).

[colly0410]

I'm trying to think what would have been the nearest British mainland TX to the Channel Islands during the war & how strong it would it have been there. Start point would have been the closest but closed down for normal service in 1939. However it started transmitting experimental horizontal polarised transmissions, I wonder if these would have been picked up well on horizontal long wire type aerials used with crystal sets?

[Yorkie]

I don't know where the nearest mainland UK BBC Broadcasting station would have been located during the war years, but the nearest large towns to Jersey would be Plymouth, which is about 120 miles from St Helier as the crow flies, and Southampton, which is about 160 miles - I'd have thought that distance would be well outside the range of a crystal set, even is there were BBC stations at either Plymouth or Southampton.  I think that it's fanciful romantic nonsense, which doesn't stand close examination,  for anyone to claim that a crystal set could have received news broadcasts from the BBC, and as I said in earlier posts,  I can't imagine why Channel Islanders, where - in the late 30s radio components to make small valve receivers would abound - would make life difficult by faffing round with homebrew crystal sets.

POWs using so called 'foxhole' receivers, yes, but even then, the claim is that such radios were used by GIs 'in Foxholes in Europe'. Really?  Surely GIs were well equipped with radios?

https://www.youtube.com/watch?v=skKmwT0EccE

Oh well, let's not let the truth get in the way of a good story!

[pwdrive]

Crystal sets are capable of DX, Australia, India etc, not sure what shortwave transmissions were done during WW2 by the BBC, but if any did take place then following the Grey Line would more or less take you to plonk on the Channel Islands.

GI's etc were equipped with radios......Well some were and many weren't and the ones that did have them had trouble getting them to work at all or if working then over any favourable distance let alone terrain restrictions, if you dig deep into WW2 communications you will find eff ups a plenty, Exercise Tiger comes to mind, again the destroyer my Dad served on (HMS Tanatside) is mentioned in that disasterous event, Some of the CNC's must have had a bad brain day, I would go so far as to say that some were not fit for purpose but that's my own opinion.

Lawrence.

[colly0410]

I can see what you mean about the insensitive nature of crystal sets, the only stations I could receive on mine were radio 3 from Daventry on medium wave from about 45 miles away, & radio 2 from Droitwich on long wave from about 65 miles away, both high power TX's. Nowadays I'd probably receive Gold Radio & Absolute from the Trowell Moor TX about 6/ 7 miles away. Mind you gold's on 999 khz & Absolute's on 1197 khz so a crystal set would have problems sepperating them I should think

[Alan Douglas]

Foxhole radios were used in Italy. For a while, the only reference was in a 1950s book by Jack Gould, and there was a suspicion the whole thing was made up, but somebody found a note in QST in (I think) 1945, so there is some historical basis. A google search would probably turn up the appropriate references.

I actually owned a copy of that book as a kid "All About Radio and Television" and it's still here somewhere.

GIs had radios but not for broadcast reception or entertainment.

[Herald1360]

Crystal sets are capable of long distance reception under favourable conditions. The standard single tuned circuit driving headphones via a diode is not much good but careful low loss design of multiple coupled tuned circuits matched both to the aerial and the headphone load results in a set with quite frankly amazing performance compared with the basic variety. A look at some of the professional "tuner" designs from the late teens/early twenties is an eye opener.

Even the two tuned circuit one I built from a Radio Constructor article was good for quite a few BBC stations in the day, with Luxembourg and other continental stuff heard after dark from behind the Malvern Hills in Herefordshire.

Whether the expertise for that was around in the Channel Islands during the war is less likely. It's clear that even many relatively clued up people here are unaware of the possibilities.

[colly0410]

I've been thinking. (took some effort) If you have 2 crystal sets connected to 2 aerials both fed in phase to a set of headphones would you get a approx 3db's increase in sound? Or have I missed something?