19-Set Dummy Load

[David Dunlop]

When one uses this item with the standard Aerial base No. 8, the ground strap is long enough for the alligator clip to be attached to one of the bolt assemblies attaching the Aerial assembly to whatever vehicle, so essentially the Dummy Load is grounded to the vehicle.

What do you attach the ground strap to if the Dummy Load is being used with the Carriers No. 23 System?

Was a set of instructions ever issued for use of the 19-Set Dummy Load?

David

[Chris Suslowicz]

Originally Posted by David Dunlop

When one uses this item with the standard Aerial base No. 8, the ground strap is long enough for the alligator clip to be attached to one of the bolt assemblies attaching the Aerial assembly to whatever vehicle, so essentially the Dummy Load is grounded to the vehicle.

What do you attach the ground strap to if the Dummy Load is being used with the Carriers No. 23 System?

Was a set of instructions ever issued for use of the 19-Set Dummy Load?

David

It's not actually a dummy load, but a dummy aerial (it's a co-axial capacitor formed from the central rod, two insulating bushes, and the outer metal tube). This behaves like the standard rod aerial (30 picofarad capacitance) as far as the set is concerned and allows the operator(s) to tune up and (more importantly) net all the sets to the frequency selected by the net controller without radiating much signal. After that's been done, the standard aerial can be put back in the base and you're ready to go.

It was mainly used for "netting in harbour" with tanks, since if the rod aerial was used, the signal strength would be so great as to make it difficult to net accurately to it, which could be fatal once you were in action. (If the signal is strong enough you will get multiple possible "nulls" - the wanted signal, the receiver local oscillator (465 kc/s away from where you're supposed to be), or a multiple of the 465 kc/s BFO that is close enough to frequency to pass through the transmitter mixer tuned circuits and be broadcast.)

The dummy aerial wouldn't be used with the truck & ground station as they would not normally be netting in close proximity to control (and it won't fit anyway).

I don't recall seeing any instructions on its usage, but it's possibly in one of the sets of training notes somewhere. (Which have faded enough to be impossible to scan, and in some cases difficult to decipher with the Mk.1 eyeball.)

Chris.

[David Dunlop]

I am sure there were a number of manufacturers involved during the war in the making of the Dummy Aerials for the 19-Set. I have two NOS examples from the North American manufacturers, RCA and Zenith, and I thought I would post a photo of them for a comparison of the subtle differences. Most relate to the finish and can easily be lost over time, but a few are of a physical nature and are easily recognizable.

The item on the left was made by Zenith. The one on the right by RCA. My apologies for the glare on the RCA item.

The bodies of both were painted a near full flat Khaki Green, not including the two end insulators, which are their natural dark brown colour. On final assembly, however, RCA chose to coat the body of the dummy aerial, and the Mueller Clip, in a clear lacquer. The ends of the two insulators and the braided wire are uncoated.

The PC-Number is hand written in white paint on the Zenith product. RCA chose to use a 1/8-inch Gothic Print silk screen stencil and black paint for their PC-Number.

The central core of the Zenith unit extends 3/16-inch beyond the hex nut and lock washer assembly at the top of the Dummy Aerial. The RCA central core ends flush with the top of the hex nut.

The 5/16-inch wide connecting strap at the bottom of the body of each is identical. They both have a 1/8-inch hole bored through the centre of the end of the tab to fasten the braided wire. On the RCA, the wire is fed into the hole from the front lip and up the back of the strap for soldering. On the Zenith strap, the wire braid comes at right angles to the back of the strap, wraps around and into the hole at the front for soldering.

The same Mueller Electric Company Universal Clip No. 24A is used by both RCA and Zenith, but each company used a different fastening technique to the Mueller Clip. RCA chose to feed the wire braid over the end crimp tabs and under the retaining screw, secure the screw, solder everything in place, but did not bother closing the crimp tabs down on the braid. On the other hand, Zenith chose to drill a hole in the end of the braid, screw it in place and solder everything down, and then crimp the tabs over the braid.

I have another Dummy Aerial in my pile of bits that is still a mystery. The central core ends flush with the top of the hex nut assembly, but the two end insulators are black. Also, the end of the fastening strap at the bottom of the body ends in a 1/4-inch, 90 degree bend, with a 1/8-inch hole bored at the centre of the bend. The braid enters this tab and is fastened like the RCA Dummy Aerial here, but at the Mueller Clip end, the crimping tabs have been closed around the braid.

David

[things_green]

my contribution to this thread.

any thoughts as to if this would be set specific or, probably more likely, test kit for general servicing?

Brent.
NZ