C-42 Set Aerials

[David Dunlop]

The standard aerial for this set is the two section 8-foot whip, but the manual makes reference that if the set is to be operated as a stationary location, a special elevated aerial can be issued. End of information.

Do these special elevated aerials have a formal name, stock number, etc.? Was there a series of them as per the 19-Set? Anyone ever found a detailed description of them?


David

[Chris Suslowicz]

Hi David,

Yup! "Elevated Aerial 30 - 60 Mc/s"

Full kit is "Elevated Aerial 36-60MCS Kit No1 Z1-ZA53380".

It fits on top of the 27-ft telescopic mast and consists of an elevated aerial base with co-ax connector and downlead, a length-adjustable vertical element (frequency marked), and three replacement top guy assemblies that include a wire section that acts as a ground-plane for the vertical radiator.

If you need to shift frequency dramatically you also have to lower the mast and adjust the vertical element to the new frequency, then raise the mast again.

The 27-ft telescopic mast is an unfriendly beast: very heavy, the rigging kit weighs more than the mast, and it has a nasty habit of lowering itself very rapidly if you don't tighten the collars, or let the mast slip when adjusting it.

Mind Your Fingers!

Mast kit comes with an extremely heavy base spike, a flat plate for vehicle roofs, and there were special "bumperette" mounting kits for Land Rovers - a mast socket and a clamp that fitted the hoops.

(The Clansman-era equivalent used a "pineapple" adapter that had a resistor network inside; this had the effect of reducing the reflected power where the aerial length did not suit the frequency in use, protecting the set - it also got hot in those circumstances and was visible in infra-red! (High power sets could also burn it out, so it's advisable to test before buying a used one.)

The gain in effective range was worth the reduction in transmitted power, and the removal of the need to adjust the aerial length in use was a great improvement.)

Chris.
(There was a lower frequency version available for other sets, covering 23-38Mc/s.)

[things_green]

what he said ;-)

looking through the user handbook. "... can be used with SR A40, SR A41, SR B47, SR C42, and CPRC-26"

I have one (not much use since I swapped my C42 for a C13)....I've never tried to elevate it because as Chris said its enough of a mission erecting the mast. clunk clunk clunk cluck....bugger, try again.

Presumably the Lower freq unit is for the C45/B48 ?

Chris.....are the same 3x radials (top guys) utilised on both antenna or have they got specific lengths of the steel wire for the slightly different ranges?

more great looking larx kit.

Brent.

[Chris Suslowicz]

Originally Posted by things_green

what he said ;-)

Presumably the Lower freq unit is for the C45/B48 ?

Chris.....are the same 3x radials (top guys) utilised on both antenna or have they got specific lengths of the steel wire for the slightly different ranges?

Brent.

Yes, the C45 and B48 used the lower frequency aerial kit.

The radials are specific to the antenna, and the setup is apparently quite critical - you can get a mismatch and potentially damage the set if not erected correctly.

<Fetches "book of words">

Elevated Antenna (LARKSPUR)

Characteristics

Essentially a vertical splayed dipole, elevated above ground to minimise
ground effects.
The top part of the dipole is a telescopic rod, adjustable for frequency.
The bottom part of the dipole is formed by 3 splayed wires, incorporated
into the mast stays.

Construction

Issued as a kit in two versions, 23-38 MHz and 36-60 MHz.

The telescopic rod is adjusted exactly to the working frequency and is mounted on the top of a mast.

The top of the mast is supported by three stays containing the splay wires (length 2.9 m (9 ft 6 in) for 23-38 MHz, and 1.5 m (5 ft) for 36 - 60 MHz). They must be equally spaced around the mast 120 degrees apart, and make an angle of 30 degrees to the mast in the vertical plane. (The stay pegs must be 4.5 m (15 ft) from the foot of a fully extended Mast, Telescopic 8 m (27 ft).)

Any variation from the correct lengths and angles of the splay wires would cause:

Mismatch, possibly with damaging amounts of powerreflected back into the radio set.

Change in the direction of radiation away from the horizontal.

The base insulator of the mast must NOT be fitted.
The ATU is not used
Masts higher than 8 m (27 ft) can be used and will give increased ranges, but the orientation of the splay wires MUST be maintained at 120 degrees apart and 30 degrees to the vertical.

Radiation.

Mainly space wave. The range will be about twice that obtained from a 2.4 m (8 ft) whip
Vertically polarized.
Omnidirectional.

===================================

Elevated antenna (CLANSMAN)

Characteristics

A broadband (30-76 MHz) omni-directional antenna intended for use at permanent stations where speed of erection/dismantling is less important.
The design is a sleeve dipole.

Construction

The antenna is constructed from 3 basic component parts, an upper radiating element comprised of 2 x 2 m rods, a lower radiating element consisting of a coaxial sleeve, and a base unit. The latter item contains a number of resistors designed to absorb reflected currents, thus matching the antenna to the set over its working frequency range.

====================================

(Note: the base unit contains beryllium oxide in the resistor pack, so messing with it is inadvisable. Also, the unit heats up when in use to the point of being detectable by night vision equipment, potentially giving your position away if the enemy can get suitable bearings on it. (My informant said they used to set up with a hill between themselves and the opposition, which reduced both the direction finding risk and the infra-red signature.)

Chris.

[David Dunlop]

I think this is the 'pineapple' unit Chris mentioned earlier. Looks like it could be cast aluminium, but I am not at all sure how it would all go together with the 27 foot mast system.


David

[Chris Suslowicz]

Originally Posted by David Dunlop

I think this is the 'pineapple' unit Chris mentioned earlier. Looks like it could be cast aluminium, but I am not at all sure how it would all go together with the 27 foot mast system.


David

It is indeed the Clansman EVHF adapter or "pineapple", but I don't think it fits the Larkspur 27-ft mast, and is intended for the 8-metre Pull-Up mast.

See http://www.g0ozs.org/clansman/EVHF/

There is an error in the manual that I posted the description from, the top whip aerial is made from two 1-metre rods (2 metres total length) and that fits to the lower "sleeve dipole element" whic goes on top of the pineapple.

Chris.