LRDG Wireless set up

[Charlie Down]

Hi Ron,
So the No11 set would use 12 volts from two 6 Volt batteries in series to power the set. On the LRDG trucks this would be achieved by using the truck 6 volt battery connected to the battery on the side step in series through the Charging Switch Panel.
Would there be any possibilty/need for a third battery to boost the signal for long range transmissions? And would sending the signal flatten the batteries sufficiently to require a alternative source of electricity to start the truck? Would the truck engine be switched off during signalling to prevent interference?

[David Dunlop]

Morning. Charlie.

Unfortunately, the idea of a third battery in the Wireless System to provide 18 volts to the wireless set will destroy said set. You would instantly burn out the heater/filaments in the sets valves which were designed with a very narrow +/- 12 volt operating range. The wireless set will have a theoretical operating range limit factored into its design that no amount of extra voltage will increase. A whole host of environmental factors may, however, increase/decrease range from time to time.

Wireless vehicles would definitely have had wireless suppression kits fitted to them to eliminate vehicle electrical interference with the wireless set. This was not necessarily done to other, none wireless fitted vehicles early in the war, but became much more common as the war progressed for several reasons, from both production considerations and bad experiences from vehicle operations in theatre. My thought would be that given the nature of the work the LRDG was doing, they would have wanted all vehicles wireless suppressed, either from the factory, or mods done upon receipt in the field. So the two vehicles being so close in your photo would not surprise me.

Keeping a pair of wireless batteries charged in the field by the LRDG would be an interesting challenge. The standard norm is a set of four 6 volt batteries. Two charged and running the wireless set while the second pair are being recharged through a charging system via some form of charging set. The charging set for the LRDG would likely be one of three things available to them: a small gasoline powered chorehorse, the vehicle generator from one of their vehicles, or perhaps a secondary mechanical generator driven either directly, or indirectly from the PTO of one of their vehicles. This latter option was often found in jeeps, during the war, mounted over the PTO assembly, between the two front seats.

Hope this helps a bit.

David

[Lynn Eades]

Some ramblings:
I would tender the idea that most early war radio equipped vehicles were 6 volt and carried a petrol gen set (300 watt chorehorse or Brit equivalent?) The U.S. would have been the first of the allies to go over to a 12 volt vehicle electical system to cater for "in house" radio support. The belt driven (pto) generator in the Jeep was the same Autolite (different end plates) generator that was fitted in the Dodge Radio Car from circa 1943 (as well as late carriers)
These comments with respect to 12 volt Jeeps, from a thread in G503:

The W7 modification is in the February 15, 1945 SNL parts book.

I know the 12v PTO units were in production and Navy contract radio jeeps delivered by Willys-Overland in May of 1943.

The following TM for radio installations implies the conversion was in use at least by January 1944.

I think the 12 volt conversion in a WWII jeep was not so common until quite late in the war? (my comment)

Obviously, the problem with having a 6 volt vehicle and a 12 volt radio is that you need a second 6 volt battery. Keeping two separately used batteries evenly charged is not so simple. To manage this for soldiers that were in majority, farm types, required some extra care and skills.
To this day there are somewhat complicated systems in motor homes.
The radio op. would have used an hydrometer to check the state of charge of his batteries. This can be a bit vague, without familiarity.
For an LRDG radio op., with vibration, heat and evaporation, he would have been constantly mothering his batteries.

All the above stated from a position of "not much knowledge"

[Ron Pier]

Lynn, like you without the benefit of huge knowledge, but from my own experience. My 1940 FFW Morris and Austin Tilly are both 12v which was supplied by twin 6v batteries wired in series.

The wireless batteries were kept charged by means of a PTO driven generator through a switchboard charging unit.

I would need to research other makes and models to confirm if this was the norm. Ron

[Charlie Down]

Yesterday I got Brendan O'Carroll's new LRDG book, 'Fighting with the Long Range Desert Group' (which is excellent) and found a photo of a Wireless Chevrolet WA with panel on the side that could be a charging switch panel. I have now found 2 other WA photos with the same panel fitted. I have grouped a close up of the panel with the panel partially seen on a 1533X truck for comparison.
The panel has at least one knife switch and I assume based on other charging panels it would need 3-4 to make it work (see attached MKV Panel).
Hanno has suggested that the panel could be a main on off switch and posted the image attached. It doesn't match the original photo but has opened up more questions about the set up.
I've been working on the assumption, based on feedback from various wireless forums that the trucks would need a charging switch panel to manage the power and charging of the batteries. There are so far no known charging panels that fit the photo of the 1533X2 panel, so it has been presumed that it would be relatively easy to make one in a base workshop with a few suitable components that would fit onto a truck. I don't know why they didn't use a standard panel, they weren't the only wireless trucks in service in the Desert at that time. And I imagine they would have access to any if they were available. The early British Wireless trucks normally operated with 4 6 Volt batteries, and a separate battery for the vehicle. 2 batteries would provide the necessary 12 volts and the other 2 would be charged, usually by a chore horse or later on, a PTO driven generator. There is no evidence that the LRDG had that many batteries, although the spares could have been stored in a locker or in a box, ( I need to check the battery inventory) which would make sense as the Patrol was really about escorting the Wireless truck to a position to transmit intelligence back to base, and not having back up batteries would seem like a stupid idea, and the LRDG weren't stupid. It was suggested that the 1533X2 panel used knife switches on the charging panel based on the photos, and that they could be commercial not military. The LRDG did have some Chore horses on their inventory, but not it seems enough to equip all the Patrols and they seem to have been retained by HQ. Sorry for the random ramblings and thoughts. Its a serious test of my limited Wireless knowledge. I also need to stop calling the battery on the side step a spare battery, when it was clearly a Wireless battery in series!

[David Dunlop]

My guess on the knife switch, Charlie, is that it is the selector switch between two distinct aerial setups for the wireless set so the operator can change quickly from one operating frequency to another.

Another factor to consider. Vehicle starting batteries are a very different design from wireless batteries. They are meant to provide a huge starting current quickly and then have very little to do other than sit and get recharged.

Wireless batteries, on the other hand, are designed for deep discharge where a few amps are needed over as long a time as possible. In fact, you will often find operating ratio data provided in wireless manuals advising operators of the best possible combinations of receiver time (low amp draw) and transmitter time (high amp draw) to enable the wireless batteries to last on a full charge as long as possible. Wireless batteries are quite happy under a float charge, most vehicle batteries do not like it. Vehicle batteries will experience increased failure under high deep discharge conditions as well.

The LRDG would have been aware of all the limitations of the two sets of batteries on patrol. Just another set of supply considerations each time they set out.

One other thought. What is known of the fuel supplies for the LRDG? Did they have access to fuel depots placed in the desert while on patrols, or did they have to carry all they needed from start to return? If fuel was not an issue, having a chorehorse as part of your kit would make sense. If fuel was critical, maybe they deleted a chorehorse from patrols and used PTO driven generators for charging the wireless batteries. Either way, you would still need the switchboard seen tucked behind the drivers arm.

David

[Bruce MacMillan]

In the photo from Charlie it shows a 4pdt switch on the side of the vehicle. It's in a convenient place on the side where batteries would be kept. My thoughts are this is for charging batteries. Here are some diagrams of the battery system from my M152 sigs van. You can see there is a 4pdt switch to select battery banks and each bank has a pair of wires connecting to the switch. This allows one set to be used and the other to be charged. The knife switch is not rated for radio frequencies so you wouldn't want to attenuate the already low power output.