Wireless of the Week - week 15

[Bruce Parker (RIP)]

Er, quite enough for people who want the basics (my target here) without being electronic whizzes....though your description is more accurate and will no doubt assist those wanting to fully understand the inner workings of a Fullerphone!! Thanks again Chris for your input.

Originally Posted by Chris Suslowicz

Er, not quite...

Most signalling was done using buzzer morse, and the interception was simply a sensitive valve amplifier with the input connected to a couple of earth pins suitably spaced apart. This picked up the AC buzzer signal for a considerable distance and standard telephony was not safe either. The "danger zone" was somewhere between 3000 and 5000 yards deep.

The Fullerphone is a DC telegraph working on a very low voltage (1.5 volts from a single 'S' or 'X' cell) and it has filtering (inductors and capacitors) between the key and the output terminals. This smooths the transitions so there is no AC component for the enemy to detect. At the receiving end, the incoming (tiny) signal is converted to AC by the chopper and fed to the headphones. It really does work on tiny voltages and currents and is pretty much undetectable. The potentiometer is fitted so you can cancel out any stray voltage due to soil conditions (electrolysis of metals in the ground) and reduce any background interference. Only really a problem with earth return circuits, and they were switching to copper pairs wherever possible - again to defeat the interceptors (who could still get pickup due to leaky insulation on cables in shell holes, etc.).

Louis Meulstee has a nice page (well, lots of excellent pages really) on the Fullerphone as well as the usual radio topics. http://www.wftw.nl/ful.html



Chris.

[Bruce MacMillan]

Originally Posted by Bruce Parker

Er, quite enough for people who want the basics (my target here) without being electronic whizzes....

Especially with an audience of pongos, zipperheads & dropshorts...

The Fullerphone was not without faults. Here's an extract from a 1919 report by Lieut. W Arthur Steel, 4th Canadian Div. Sigs.

"In February 1918 another interesting fact was brought to light through a listening post. It was discovered that under certain conditions fullerphone messages could be picked up by amplifier sets. This was fully investigated and it was found that if one of the instruments in a circuit was faulty then all instruments, whether good or bad, could be picked up by the amplifier. All the instruments from an affected circuit were returned for testing. One type F and one type D were found to be defective when on the send-receive position.

On the type F set it was found the lead from the common side of the condenser to the right contact point of the send-receive switch was broken, leaving the circuit open. The type D set also had a similar issue with this part of the circuit. The solution was to check and test all sets before deployment."

The monitoring of communications by our own security people wasn't popular but necessary.

[Joe C]

Capt Steel's full report is available on RCSigs.ca. The first part is already transcribed, the rest is being worked on. For now, the entire report is also available in pdf format. Enjoy!

http://www.rcsigs.ca/index.php/Wirel...Canadian_Corps

I have also posted an interesting report on the type of conversations being picked up by the IT sets. The above report has the following incident:

Some 5.9’s were dropping near a heavy Trench Mortar Battery and the operator on the IT set, overheard the F.O.O. call up the Bombardier in charge and ask whether damage was being done. The Bombardier replied “No, they are falling about 150 towards to our left, Sir”. Although the Hun had been pounding away for over an hour, it only took him fifteen minutes to switch and put the Mortar out of action, incidentally killing the Bombardier and all but one of the crew. This statement is vouched for, as the battery was not more than 200 yards from the IT Post.

Other conversations are in a report from 1917. http://www.rcsigs.ca/index.php/Repor..._6_August_1917

[Bruce Parker (RIP)]

Updating with Fullerphone manual.

[Joe C]

Finally acquired my own example. This one is a near mint (the unit and case interior, unfortunately not the outside of the case) Northern Electric Mk IV* serial number C-1739 manufactured in 1943. More photos at: RCSigs.ca - Fullerphone Mk IV (Canadian)

Now for my questions.....

The plug on my headset has a 'fat' connector while others seem to have a slim connector. Any significance to that?

Meulstee says there were 14,000 Canadian Mk IV and Mk IV* units made in 1942/43 but I've never seen a serial number that high. Bruce's example (original post) is a nice early example from 1941, serial C-329 and appears to be a Mk IV. Mine is a Mk IV*, 1943, serial C-1739. When did they switch from Mk IV to Mk IV*? Did they restart the serial numbers with the Mk IV*s?

Meulstee also says that early models had a Canadian Key W.T. 8 Amp No. C2 but that later units were fitted with Canadian Key W.T. 8 Amp No. C3. Based on my example having a C2, it looks like the change over was with the Mk IV*. Does anyone know at (or about) what serial number the change over happened? Are there known examples of Mk IV with a Canadian W.T. 8 Amp No. C3?