WW2 HF aerial distribution amplifiers

[John KC0G]

Jon_G4MDC commented on these in a recent thread https://www.vintage-radio.net/forum/...d.php?t=159082 and noted that Pat Hawker had written about them. I recall Pat's comments, but cannot find them. IIRC, Dud Charman, G6CJ, had his hand in them. I think that they were mainly used in the listening stations.

There is mention of these aerial distribution amplifiers in a paper "Multi-Channel Radio-Frequency Amplifiers", by R.F.J. Jarvis and R.A. Brockbank, Journal of the IEE, Vol. 94, part IIIA, No 12, 1947, pp 389-397. This was one of the supporting papers for the Radiocommunication Convention which was held at the IEE in 1947.

Section 4.3 on pp. 394-395 (see attachment) outlines three incarnations:
i) 3.3-6.6 MHz, step up transformer to an EL6 input valve to a 807 output valve. Voltage gain when terminated in a 50 ohm load was 20dB
ii) amplifier modified to cover 3-26 Mhz with three sets of input and output transformers. The bands overlapped, ie 3-7.5 MHz, 5.5-12.5MHz, and 11-26 MHz.
iii) 4-20 MHz in a single range with a four valve feedback amplifier.

There have been a couple of related threads
https://www.vintage-radio.net/forum/...d.php?t=158510
https://www.vintage-radio.net/forum/...d.php?t=108157
which were concerned with distribution amplifiers either side of WW2.

Please, can anybody shed further light on the WW2 amplifiers?

Thanks and 73

John

[Radio Wrangler]

Interesting!

I remember Pat Hawker mentioning the use of 807s. This may be the beginning of the technique of using medium power transmitting devices where high linearity amplification of groups of small signals are required. Power devices don't necessarily have bad noise figures, so this is a route to high dynamic range signal processing. Still true today with various types of transistors.

The Marconi distribution amp from the 50's in the cited threads shows push pull stages in grounded grid mode, which I think must have been found optimal for linearity. Broadband impedance conversion between stages was by transformers.

I think WWII pre-dates ferrite cores becoming common, so broadband transformers would have been very difficult. This appears in the first distribution amplifiers having to be split band, and were superceded by broadband units. The broadband units indicate that the banding was done not because it was wanted, but because it was then unavoidable.

Were distributed amplifiers used in this role? Percival's invention was in the 1920's so the idea was published, but the paper by Ginzton, Noe, et al, which popularised them and laid out design techniques was later.

Some manufacturers called distribution amplifiers 'Multicouplers' which as a search term might uncover more info.

David

[G3VKM_Roger]

I too can recall Pat Hawker mentioning in "Technical Topics" the distribution amplifier using 807s, I think it was in a rack in the receiver room at Hanslope Park during WW2 and was designed by an amateur on the staff there. It might be mentioned in "The Secret Wireless War", will have a look later today if no-one else nails it.

I have a similar post-war device, the US Navy CU656/U antenna coupler, one input and 8 or 12 outlets.

73

Roger

[G3VKM_Roger]

"Dud" Charman/G6CJ is given in The Secret Wireless War as the designer of the 807 distribution amp. Page 301.

[Jon_G4MDC]

The part I find interesting is the splitting network that follows the amplifier.

Of course that can be resistive but the lack of isolation between output ports means local oscillators of one RX can interfere with another working at the IF away. This drove the splitters to be done with hybrids having isolation between output ports.

As David notes if ferrite transformers could not be realised with the materials of the day how was that done? Wilkinsons can be made with lumped components. I wonder if these were made in multiple stages to broaden the response. That is done today for the cellular bands.

Another way might be to use a resistive splitter after a first stage of amplification and to let that be relatively lossy. A second stage of amplification could feed each output port. If the 2nd stage amplifiers have good reverse isolation then the problem of local oscillator crossover will be much reduced. Reading the Marconi marine system write up I think that is what they did.

[GW3OQK Andrew]

I can't speak for the wartime circuits but in my time at sea several 75 ohm cables were plugged into the amp going to different areas of the ship, from cabin to cabin. Output boxes were tapped on for each cabin. One cable would have, say, 6 boxes with the final one terminated by a 75 ohm resistor. The box had a high-ish resistance with capacitors to isolate and resistors to attenuate each outlet, which should help the local oscillator feedback mentioned.

If the line did not measure 75 ohms you knew there was a break, possibly by someone opening the box to try and get a better signal. I never did understand exactly how the wide band amplifiers worked.

73, Andrew

[G6Tanuki]

Originally Posted by Jon_G4MDC

The part I find interesting is the splitting network that follows the amplifier.

Of course that can be resistive but the lack of isolation between output ports means local oscillators of one RX can interfere with another working at the IF away. This drove the splitters to be done with hybrids having isolation between output ports.

That would always have been my big concern when running multiple receivers from the output of a single antenna through an amplifier: it's well-known that the HRO-series of receivers were really rather 'leaky' as far as the LO and its harmonics were concerned - letting these leak back up into the back-end of a distribution-amplifier could have resulted in a whole slew of unexpected mixing-products.

I can't but avoid thinking that this 'back-feed' of LO signals must have also been an issue with the early cable-TV networks? Seems that the immediately post-WWII Abingdon "cable-TV" network used 'distributed amplifiers' using twelve EF95 valves and a sort-of travelling-wave-line to couple them together in order to drive the coax that fed the downstream dwellings...

http://www.aeolian-hall.myzen.co.uk/circuit.gif

I also remember something reported from the WWII days of 'intercept stations' where bored listening-operators - most of them onetime radio-hams - worked out how to 'key' the local-oscillators of their receivers and, using the coupling of the common antenna-distribution system, managed "QSOs" between the different huts.

[Jon_G4MDC]

One of the earlier references above went to a '50s Wireless World article that described the daisy chain of tap off attenuators approach. That was followed by a band splitter for Radio, Band 2 FM and Band 3 TV.

My parents house was equipped with exactly that (external TV/Radio aerials not allowed) and at the end of each block a large grey box containing the valved distribution amp was screwed high on the wall. The cable daisy chained house to house under the eaves. The tap boxes were up there and each fed a down lead to the front room.

Inside the room a little square white fronted box contained the lumped element filters. At about age 12, I took the front off said box. I didn't know what I was looking at. Little coils of wire and brown oblong lumps.

That WW article explains it all!! Only ~45years later. Apart from any effect of the LP/BP/HP filters between different bands the resistive taps have no attenuation against LO leakage. It will go upstream and downstream.

Interesting that one of the other articles referenced (RCA I think) mentioned transformers on "magnetite" was it? I forget. They looked like the forerunner of ferrite and bifilar winding of today.

(G6T Just taken a look at your circuit and I reckon that may well be what was on the end of the block! The date is hard to make out 1962?
The stuff I mention was being used for 625 Colour in late 60's early 70's. It needed an upconverter box to suit UHF colour TVs. I suppose they downconverted UHF to Band 3 needing to upconvert again back at the telly? We had a box for that mounted under one of the back cover screws. Labgear I think but could be wrong. )

[Jon_G4MDC]

After a little more thinking on the subject...it doesn't help much with the WW2 question but what came later must have sprung from it.

Pye Telecom did their RDA = Receiver Distribution Amplifier. It was basically their FET Cascode VHF front end of the 1970s (R7, R8, R18 etc) followed by a splitting network. Was that hybrid based or just resistive I don't know. I had one once - long gone. Does anyone know about it? Any gen to be had out there?

My main memory is the Aerial Facilities RSA (Receiver Splitter Amplifier). Attached the block diagram. This was typically set for 2-5MHz BW at VHF or UHF but there were other versions.

[G6Tanuki]

Originally Posted by Jon_G4MDC

(G6T Just taken a look at your circuit and I reckon that may well be what was on the end of the block!

The full details of the Abingdon cable-TV distribution setup are here: http://www.aeolian-hall.myzen.co.uk/mva.htm

There were loads of these small-scale setups around in the 50s and 60s; I'm halfeheartedly researching such a system in Marlborough. Only the occasional bit of coax and junction-boxes remains.

[Jon_G4MDC]

Thanks - There is lots of that to read and I hope to do so soon.
It looks similar to what I recollect. Since it's off topic in this thread shall we continue somewhere else?

[Radio Wrangler]

Don't put too much weight on talk of hybrids. Hybrids are balancing acts and produce their isolation by cancellation in a circuit that is equivalent to a bridge with a transformer replacing two of the arms. If you don't feed it and load it with the planned impedances, you may not get much isolation. The input impedances of receivers are notorious for being away from nice exact 50 or 75 Ohms.

A better-behaved system which tolerates the foibles of receivers is to have a buffer amp for each output to a receiver, and to do the splitting before these buffers. Well desifned buffers will give some isolation from reverse LO signals and whatnot.

David

[G3VKM_Roger]

Here's the cct diagram of the US Navy multi-coupler I mentioned in an earlier post, might be of interest:-

I have the manual as well, about 3 Mb in size.

73

Roger

[Radio Wrangler]

Originally Posted by G3VKM_Roger

Here's the cct diagram of the US Navy multi-coupler

Ooooo-Eeeeee! They really threw everything at that one.

It's a pair of distributed amplifiers in push-pull
Each stage of those amplifiers is a pair of triodes in cascode configuration.
There is a tree of hybrid transformers at top right, splitting the signal to multiple receivers.

Not shown, the receivers will probably present resistive terminations to those hybrids.

Warship HF systems are RF hostile. Multiple receivers need to be in use, even while the ship it transmitting on other frequencies, and you can't even site the antennae very far apart.

Aircraft VHF systems pose a similar problem. For some reason they don't want their instrument landing receivers to go barmy whenever a pilot talks to the ground, only a few MHz away.

David

[Richard - F4VPR]

Originally Posted by Radio Wrangler

Interesting!

I remember Pat Hawker mentioning the use of 807s. This may be the beginning of the technique of using medium power transmitting devices where high linearity amplification of groups of small signals are required. Power devices don't necessarily have bad noise figures, so this is a route to high dynamic range signal processing.

Certainly did use 807's, when I was at GCHQ around 1965/6 we were required to work for some time at the various CSOS receiving out-stations, I recall being shown the RX distribution amps feeding rack upon rack of RA17's and being surprised to see handfuls of 807's in there.

Regrettably that part of ship wasn't in our brief so apart from a look at them we were not given any more detail.

HNY!

R.

[m0cemdave]

The following information is from David White, who worked for the Diplomatic Wireless Service at Hanslope:

The HF receiving station at Hanslope Park had a set of wideband multicouplers; these are the ones referred to by Pat Hawker and designed by Dud Charman. They were built in 1942 and mounted in racks at one end of the radio room.
The multicouplers used a small red-coated valve (octal, so not an EF50 - I wonder if it was an EF39) feeding an 807 cathode follower, with 8 outputs per amplifier.

When they were eventually replaced with solid state, they couldn't find the key to the cupboard / rack room and had to chisel the lock off. The original amplifiers (covered with dust but still working) were then skipped, and no details of the circuit have been found.

Originally the multicouplers fed 66 HRO receivers, most of which were installed in pairs in 32 bays, 16 on each side of the radio room. Most of the aerials were rhombics.

--------

The story about operators running a mock Field Day and having CW QSO's with each other is true. It happened when conditions were flat and there wasn't much to do.

Each operator had a pair of HRO's and they keyed the aerial lead of one set as a transmitter (using the infamous oscillator leakage) and received on the other, after indicating the frequency to use by hand signals across the room.

Each receiver had a left-right switch to select either the multicoupler or a local vertical aerial, so it could be used like a sideswiper Morse key connecting the "Tx" receiver to the vertical to radiate a carrier.

David White has a box of QSL cards, exchanged at the time, given to him by one of the operators many years later.

[G3VKM_Roger]

Is there a reference to the hams at Hanslope holding a mock-NFD somewhere in this thread? If so, I can't spot it. In 1967-69 I worked at Creslow, the transmitter site paired with Hanslope. An operator friend, now SK, told me he used Eddystone 730 receivers at Hanslope but he kept quiet about other equipment he used there.

73

Roger/G3VKM

[Jon_G4MDC]

I think it was G6Tanuki in post 7 who triggered that.
It used to go on in the Pye Telecom factory too beating against the headphone distributed Radio 1. Anyway enough of that it is very OT.

This from m0cemdave "The multicouplers used a small red-coated valve (octal, so not an EF50 - I wonder if it was an EF39) feeding an 807 cathode follower, with 8 outputs per amplifier." is interesting.

It tends to point away from a first RF amplifier before splitting and a high reverse isolation buffer amp per output so I am still interested to know what the splitter looked like. Maybe purely resistive?

[Radio Wrangler]

The game at HP was lots of radios loudly playing radio forth or radio clyde up the production line in a large open plan building. The radios had to keep changing frequency to try to keep one step ahead of the signal generators in R&D just over the divider.

David

[Herald1360]

How many Cs in the ongoing EC......CM battle?



Production at Racal weren't keen on Radio 4 nor Classic FM rather than Radio 1 at teatime.