Help identification of a military wavemeter poss from aircraft

[M0FYA Andy]

Before applying power you need to know what it is you are dealing with, so you need the circuit. I can tell you that it is in AP2545A, I don't have a copy but it is listed in TNA's online catalogue, so you could go to Kew and copy it.
Alternatively, it can't be a terribly complex unit, so draw the circuit out and post it on here for advice.

Andy

[Jon_G4MDC]

It's almost certain the detector diode will be dead having been killed by ESD from past events in it's long history.
That is all that is in it. There isn't anything else.

Applying power of any kind (except RF up the coax at the intended frequency) will ensure the diode is dead for sure.

[Luxman1050]

Okay guys cheers yeah not a complicated item in terms of a circuit. I'll test the diode to see if its knackered. Putting a new piece high grade screen cable in today and a clean up. Lots if silver plate in there I suspect they used it alot as it does not rust and acts as a good screen.

[Radio Wrangler]

The best thing you can do with it is to see if anyone wants it as an historic item. Changing the cable will reduce its authenticity.

Don't be too keen on trying to see if you can interfere with any radio signals to see what happens. Some signals are considered critical to the safety of life and limb and are monitored carefully for problems. Aircraft report any apparent problems they experience. Police, fire, ampulance etc use frequencies in this range. Ofcom actually do investigate these, fearing the consequences if they didn't. If the person creating the interference sees no immediate result, they are likely to keep doing it and moving the frequency around. When there is a response it involves policemen and handcuffs. The wireless telegraphy act got strengthened several years ago to include jail and unlimited fines. I'd steer clear of doing that. Most probably nothing will get noticed but is it a risk you'd choose to take? At least the thing you have is incapable of causing trouble. There's also one or two people reading this forum with involvement in the regulatory agencies.

David

[Luxman1050]

Bit extreme David you make it sound like I'm going to use it to deliberately wipe out emergency services signals. All I was saying be interesting to see if it works which I think for a brief period of minutes it would cause a major catastrophic event.

Diode not knackered in perfect condition 👌.
Pic attached.

[Radio Wrangler]

1N23 or predecessor, germanium point contact in low inductance package.

I understand that the risk of something getting noticed is very, very, low, but when they do get someone in court they always wheel out the full 'could have crashed an airliner into a cinema' thing.

Ofcom and before them RRDofDTI people had to investigate pirate broadcasters, and the stairs to rooftops on tower blocks were booby-trapped with contaminated needles and razor blades. The pirates were trying to infect the investigators with either AIDS or hepatitis C. As a consequence these things are taken more seriously. Some things are treated as attempts at acts of terrorism. What you do might not be extreme, but you should be aware that the response could be extreme.

David

[Luxman1050]

Well thats just ridiculous putting razor blades contaminated needles around as booby traps well they should be shot.

[geeoboeh2s]

This may be of interest.

Chris

[Luxman1050]

Wow that's fantastic thanks a lot I initially thought that bottom socket was for coils lol. Wrong on that one and DC output. I mean how you got that I've been looking around for about 2 weeks now. Nice one ��
Plus it does have the mica there still. Well it's complete according to the schematic. Thank you.
All best Chris

[Radio Wrangler]

That looks like the beastie... well found!

I'm trying to remember, was bagful used to listen for night-fighter radar as well?

David

[Luxman1050]

Oh well David don't think I'll end up in prison then lol no way of using that.

[Radio Wrangler]

Their capture rate seems to be rather low, except for people who happen to hit the well-protected frequencies. But I thought you'd better be aware of the extent of the risk.

David

[Jon_G4MDC]

It was said that using a multimeter to test IN23 and the like would probably kill them.
Maybe that only applies to the use of relatively low sensitivity Avos and such.

Can they be tested by modern DMMs without fear of damage? Of course they need protection from static but if they are Germanium then the forward Voltage can be tested so long as max forward current is not exceeded - or?

[Luxman1050]

Test with proper diode tester. How would you test it with a DMM? Can't say I've tried.

[turretslug]

Analogue moving-coil meters like AVOs can be a bit brutish on the low ohms ranges as far as test currents go, checking delicate semiconductors with them is a bit like using a chain-saw to top your boiled egg. Most DMMs will be a deal more subtle, the instructions may well mention test currents, and they often have a "diode test" function giving the forward voltage at a low test current, giving you an idea of the type of semiconductor involved. 578mV as shown on the component tester is suggestive of a silicon diode just turning over at a very low forward current- the silicon crystal microwave mixer/detector was an early device used at SHF in devices like radar and was less susceptible than germanium to being smoked with less than instantaneous transmit/receive switching, though they eventually got cooked by the edge of the transmit pulse and suffered performance deterioration ("burnout").

Correction- 576mV, comments as above!

[Luxman1050]

seems more interested in the diode odd it's about a wavemeter and historical background. But if you want to buy one there £50 NOS.
So historically the wavemeter was used in the Lancaster Bombers. It was used with Boozer MK2
AR1 5557
Receiver R1626
Rx unit type 165/170
Indicator 181,186,338
Modulator type 27
Aerial 315/323
But still not a lot of info on most of this kit. There is obviously a reason why. So bit more digging required.

[Radio Wrangler]

Most WWII radio kit got sold to radio amateurs and shortwave listeners. Stuff that couldn't be turned into receivers, transmitters and accessories for such use simply didn't sell other than for scrap metal weight.

So the things available now were filtered by this process. Sets got butchered, dynamotors, navigational and intercom sections got torn out to make space for mains power supplies and audio amps with enough beef to drive a speaker.

Nowadays such items have become wanted not for use as affordable receivers, but as museum pieces for collections and authenticity and completeness are now wanted.

David

[Luxman1050]

Ah that explains why then. So in essence not much of this gear left? I found a receiver up for sale well sold but that was the only one. Still seems to be quite a few military wavemeters around for sale though just not one of these. Suspect there end up stripped? Still after one I can use though but look into those military ones up for sale see if I can make use of one. Was looking at the Marconi ones but you need all the coils but was hoping not the case with the military ones.

[Radio Wrangler]

There are some people after R1155s and T1154s plus all the much rarer cables and accessories with such diligence I swear they won't stop until they've built an entire Lancaster.... which leaves me wondering just who they plan to bomb?

David

[Graham G3ZVT]

Originally Posted by cdm1christopher

Ah that explains why then. So in essence not much of this gear left? I found a receiver up for sale well sold but that was the only one. Still seems to be quite a few military wavemeters around for sale though just not one of these. Suspect there end up stripped? Still after one I can use though but look into those military ones up for sale see if I can make use of one. Was looking at the Marconi ones but you need all the coils but was hoping not the case with the military ones.

"Wavemeter" describes more than one type of instrument, we would call them "Frequency meters" today.

First there are the passive ones, "absorption wavemeters". Your instrument would fit into this category it has a tuned circuit, or in this case a precision cavity, and you direct some of the energy from your transmitter or RADAR set into it then bring it into tune by watching for a peak on a meter then read off the frequency.

The other main type or active, WWII types include the Class D wavemeter and the American BC221 these are variable frequency RF signal generators with one or more reference crystal oscillators that you would use to check the calibration, you could use this instrument to compare the frequency of a transmitter or a receiver by listening for a hetrodyne and adjusting for "zero beat"


Another kind of instrument is the GDO or grid-dip oscillator, more likely to be a FET-dip oscillator with modern semiconductors.

This is like the absorption wavemeter, but it is active, and generates an RF signal. Its meter shows a sharp change when a tuned circuit resonant at the same frequency as the GDO is bought near to its coil. It's the principle that supermarket security tags work on.

I'm sure others could give a better lesson but I hope that helps.