Expensive Jammers - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

dseymo1 · 13th Jul 2018, 4:04 pm

The Valve Museum link suggests that the 931A (a very common photomultiplier, used in all sorts of things) was introduced in 1950, so the equipment would, of course, be post-War.

ms660 · 13th Jul 2018, 4:25 pm

The 931A was introduced during the WW2 period, a book source says 1941 for the 931 and 1943 for the 931A.

Lawrence.

turretslug · 13th Jul 2018, 6:27 pm

Valve Museum is a very useful and wide-ranging resource- but some of its information can be contentious, particularly over dates of introduction. I suspect that "earliest use" is often anecdotal and difficult to corroborate, so they play safe and quote the dates found on data-sheets, which may have been subject to periodic revision or simply reflect the date that a particular manufacturer started offering a type of valve.

Were it detailing Kylie's or One Direction's timeline of single and album tracks, there would be zillions of people out there instantly in touch for correction and updating of its pages- but for our somewhat arcane minority interest, revision information is likely to be a bit more slow and sporadic....

m0cemdave · 13th Jul 2018, 7:43 pm

My loose leaf RCA master databook has the 931A specs from 1955, but one of the pages (Typical Circuits) is from an earlier version, dated 1943.

Nymrod121 · 13th Jul 2018, 7:52 pm

Quote:

Originally Posted by turretslug

Were it detailing Kylie's or One Direction's timeline of single and album tracks, there would be zillions of people out there instantly in touch for correction and updating of its pages- but for our somewhat arcane minority interest, revision information is likely to be a bit more slow and sporadic....

<chuckle!>

turretslug · 14th Jul 2018, 10:55 am

If the 931A was commonly used, it at least suggests an answer to a tangential question- an original use for the 11-pin IO-style base subsequently widely used for 3-pole changeover power relays.

KeithsTV · 14th Jul 2018, 11:43 am

About 35 years ago I acquired an item that looked a bit like a large electrolytic cap. Inside was a 931 and a light bulb. I'd assumed it was some form of opto-isolator but having read this it was probably a noise source. I sold it at a BATC rally to someone who wanted a 931 a few years later.

Keith

G6Tanuki · 14th Jul 2018, 12:15 pm

An interesting use of photon-effects as a noise source. I'm rather more familiar with the use of an emission-constrained diode [you vary the heater-voltage to vary the noise] in VHF/UHF test equipment.

[The original ERNIE used neon bulbs as a noise source to generate randomness: https://www.i-programmer.info/histor...enerator.html]

Radio Wrangler · 14th Jul 2018, 1:33 pm

Randomness is intriguing.

A message, carefully encrypted looks random.

There is a theorem which says that any channel carrying the maximum rate of information of which it is capable looks to be filled with white noise. Any recognisable characteristics mean there is a degree of predictability, and that means a reduction in information content.

If someone gives you a file, a recording, of seemingly random data, you could throw all the resources of a superpower at trying to decrypt it and fail. So is it really random, or is it just a better code than you can break? There is no way to tell. It could also not be secret, but just the content of a well-whitened comms link.

Turn this problem on its head: You build a noise source. How do you prove that it's really random? Try all sorts of analyses and if you find a feature, you've proven it's not random, but if you find no features you've either proven that your ability to find things is limited, or that there were none there to find. You can't tell which.

The only fallback is to trust the fundamental mechanism to be random. Something quantum-mechanical for choice. In electronics and telecomms it matters a bit, but in something with large amounts of money at stake the issue rises of proving it's not fixed and that all numbers have equal chances. How do you prove there is no tiny influence creeping in? You hit a floor needing trust.

Telecomms people are very interested in the statistical characteristics of noise. It is the noise peaks which are most likely to cause errors in their digital comms systems, yet measurements of noise level have to be statistical and averaged over a period to make sense, so average power is what you get. This relates to the RMS voltage, or the standard deviation of the instantaneous voltage. So these people are very pernickity over the peak to RMS ratio, usually called 'Crest Factor'... but those crests only have values if taken over a defined time... ideally they should be infinite... and here-we-go-again.

Random emission of electrons due to illumination of a photoelectric surface, or just from a simple heated surface come to the same thing, but the photomultiplier has the attraction of a lot of gain built in after the tiny original randomness source. That's why they dd it that way, and it still needed a chainoaf amplifiers after it.

There are things that turn up as surplus that look like a length of waveguide with a fluorescent tube stuck through it. These are noise sources intended for measuring the noise figure of microwave stuff, but they age and drift. Solid state diodes can also create decent noise, and long term tests have verified the stability of carefully designed special noise diodes. You can also make RF noise using avalanche breakdown in the reverse-biassed B-E junction of an RF transistor (Don't plan on using it for anything else afterwards!) but they suffer from dopant migration.

Back in the late 90's I designed the N4000A family of noise sources at HP/Agilent, so I wound up fairly deep in the noise-metrology business. The noise figure analyser has reached the end of production, but the noise sources are still on the go.

David

jamesinnewcastl · 14th Jul 2018, 2:36 pm

Hi

Ask someone for a random number - in (my world of) theory you will die before that person finishes giving you their answer. Since there are an infinite number of numbers a random number is likely to contain so many digits that the chances of a truely random number having just a few digits e.g 135 is going to be nigh on impossible, although statistically just as likely of course.

The point here is that statistics doesn't care about the number of digits used - that is just our affectation. I've no point to make - it's just something no-one ever mentions when talking about 'random' numbers. Random discussions usually mean "random, but bounded".

Our company had a lone worker alarm that emitted a piddling 0.5mW signal using a small AA cell. The lone worker operating in a deep valley in Wales would eventually summonse help because our monitoring antenna spent many many hours looking for non-randomness in the background noise until it spotted a repeated simple number of bits - the number of the workers alarm. It didn't say where he was but you knew his schedule so a van would be sent out to fnd him,

Just some random thoughts really - which are obviously not random at all being associated with the current topic .......

Cheers
James

13th Jul 2018, 4:04 pm	#21
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Expensive Jammers The Valve Museum link suggests that the 931A (a very common photomultiplier, used in all sorts of things) was introduced in 1950, so the equipment would, of course, be post-War.

13th Jul 2018, 4:25 pm	#22
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Expensive Jammers The 931A was introduced during the WW2 period, a book source says 1941 for the 931 and 1943 for the 931A. Lawrence.

13th Jul 2018, 6:27 pm	#23
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Expensive Jammers Valve Museum is a very useful and wide-ranging resource- but some of its information can be contentious, particularly over dates of introduction. I suspect that "earliest use" is often anecdotal and difficult to corroborate, so they play safe and quote the dates found on data-sheets, which may have been subject to periodic revision or simply reflect the date that a particular manufacturer started offering a type of valve. Were it detailing Kylie's or One Direction's timeline of single and album tracks, there would be zillions of people out there instantly in touch for correction and updating of its pages- but for our somewhat arcane minority interest, revision information is likely to be a bit more slow and sporadic....

13th Jul 2018, 7:43 pm	#24
m0cemdave Octode Join Date: Feb 2009 Location: Bletchley, Buckinghamshire, UK. Posts: 1,219	Re: Expensive Jammers My loose leaf RCA master databook has the 931A specs from 1955, but one of the pages (Typical Circuits) is from an earlier version, dated 1943.

14th Jul 2018, 10:55 am	#26
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Expensive Jammers If the 931A was commonly used, it at least suggests an answer to a tangential question- an original use for the 11-pin IO-style base subsequently widely used for 3-pole changeover power relays.

14th Jul 2018, 11:43 am	#27
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,573	Re: Expensive Jammers About 35 years ago I acquired an item that looked a bit like a large electrolytic cap. Inside was a 931 and a light bulb. I'd assumed it was some form of opto-isolator but having read this it was probably a noise source. I sold it at a BATC rally to someone who wanted a 931 a few years later. Keith

14th Jul 2018, 12:15 pm	#28
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Expensive Jammers An interesting use of photon-effects as a noise source. I'm rather more familiar with the use of an emission-constrained diode [you vary the heater-voltage to vary the noise] in VHF/UHF test equipment. [The original ERNIE used neon bulbs as a noise source to generate randomness: https://www.i-programmer.info/histor...enerator.html]

14th Jul 2018, 1:33 pm	#29
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,872	Re: Expensive Jammers Randomness is intriguing. A message, carefully encrypted looks random. There is a theorem which says that any channel carrying the maximum rate of information of which it is capable looks to be filled with white noise. Any recognisable characteristics mean there is a degree of predictability, and that means a reduction in information content. If someone gives you a file, a recording, of seemingly random data, you could throw all the resources of a superpower at trying to decrypt it and fail. So is it really random, or is it just a better code than you can break? There is no way to tell. It could also not be secret, but just the content of a well-whitened comms link. Turn this problem on its head: You build a noise source. How do you prove that it's really random? Try all sorts of analyses and if you find a feature, you've proven it's not random, but if you find no features you've either proven that your ability to find things is limited, or that there were none there to find. You can't tell which. The only fallback is to trust the fundamental mechanism to be random. Something quantum-mechanical for choice. In electronics and telecomms it matters a bit, but in something with large amounts of money at stake the issue rises of proving it's not fixed and that all numbers have equal chances. How do you prove there is no tiny influence creeping in? You hit a floor needing trust. Telecomms people are very interested in the statistical characteristics of noise. It is the noise peaks which are most likely to cause errors in their digital comms systems, yet measurements of noise level have to be statistical and averaged over a period to make sense, so average power is what you get. This relates to the RMS voltage, or the standard deviation of the instantaneous voltage. So these people are very pernickity over the peak to RMS ratio, usually called 'Crest Factor'... but those crests only have values if taken over a defined time... ideally they should be infinite... and here-we-go-again. Random emission of electrons due to illumination of a photoelectric surface, or just from a simple heated surface come to the same thing, but the photomultiplier has the attraction of a lot of gain built in after the tiny original randomness source. That's why they dd it that way, and it still needed a chainoaf amplifiers after it. There are things that turn up as surplus that look like a length of waveguide with a fluorescent tube stuck through it. These are noise sources intended for measuring the noise figure of microwave stuff, but they age and drift. Solid state diodes can also create decent noise, and long term tests have verified the stability of carefully designed special noise diodes. You can also make RF noise using avalanche breakdown in the reverse-biassed B-E junction of an RF transistor (Don't plan on using it for anything else afterwards!) but they suffer from dopant migration. Back in the late 90's I designed the N4000A family of noise sources at HP/Agilent, so I wound up fairly deep in the noise-metrology business. The noise figure analyser has reached the end of production, but the noise sources are still on the go. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

14th Jul 2018, 2:36 pm	#30
jamesinnewcastl Heptode Join Date: Jul 2009 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 722	Re: Expensive Jammers Hi Ask someone for a random number - in (my world of) theory you will die before that person finishes giving you their answer. Since there are an infinite number of numbers a random number is likely to contain so many digits that the chances of a truely random number having just a few digits e.g 135 is going to be nigh on impossible, although statistically just as likely of course. The point here is that statistics doesn't care about the number of digits used - that is just our affectation. I've no point to make - it's just something no-one ever mentions when talking about 'random' numbers. Random discussions usually mean "random, but bounded". Our company had a lone worker alarm that emitted a piddling 0.5mW signal using a small AA cell. The lone worker operating in a deep valley in Wales would eventually summonse help because our monitoring antenna spent many many hours looking for non-randomness in the background noise until it spotted a repeated simple number of bits - the number of the workers alarm. It didn't say where he was but you knew his schedule so a van would be sent out to fnd him, Just some random thoughts really - which are obviously not random at all being associated with the current topic ....... Cheers James