question for signals members or amature radio buffs

[David Ives]

i have a old larkspur 27ft mast and wish to connect a clansman320 to it

do i need anything between the mast and the radio to tune it in or do i just set the radio to a mast hight of 27ft or is it easier just to run up a external wire

as the mast just has a wing nut at the bottom would a bit of d10 probably do or do i need some proper coax to connect it up

can you give me some ideas please;)

[g0ozs]

David

 

I think when used as a radiating element rather than to support an elevated antenna, there was a (ceramic?) base insulator for the 27 foot Larkspur mast - I'm sure that you could make one from rubber or plastic now . In that case you attach the 320 antenna terminal by a short wire to the bottom of the mast and the 320 earth terminal to a counterpoise wire laid out on the ground. In its original Larkspur role the 27 foot mast was used with a remote antenna tuner at the bottom of the mast (with a counterpoise or ground spike) and there was a coaxial lead from the tuner to the transmitter. Using the Larkspur tuners with Clansman radios is not ideal because the Larkspur sets used 75 ohm coaxial cables and "Burndept" connectors whereas Clansman uses 50 ohm and BNC. You could use a Clansman RT321 tuner (TURF 25W) in a similar way with the 320. The downside is that you need two operators (one to key the radio and one to tune) or a lot of running back and forwards once they are separated, since the 321 tuner is manually operated.

 

It is notable that the slightly later RT319 special forces manpack reverted to the Larkspur design of having a separate (automatic) tuner that could be separated from the radio so as to be at the bottom of the mast so I think it is a better idea than the sloping wire from mast head to radio. The modern commercial SGC automatic tuners work in a similar way to the RT319 auto tuner and are ideal for this kind of set up.

 

I have an insulating base (a metal plate with a rubber lined cup for the bottom of the mast) for the 11M Racal telescopic mast which allows it to be used in the same way.

 

The 5.4 metre fibreglass mast contemporary with the 320 could not be used as a radiating element itself so came with a wire antenna that stretched from the top of the mast down to the 320 for the same purpose, so a sloping wire tied off (but insulated from) the top of the 27 foot mast might well be a simpler alternative, again used with a counterpoise wire.

 

Note that the 320 tuner is designed for use with short wires up to 1/4 wave or long wires around 3/4 wave at the frequency in use (based on the antenna cutting and tuning data plate on the back of the set) so some optimisation is possible by adjusting the length of the mast or sloping wire.

 

D10 is OK for short connections but is steel cored for strength (so stiff) and has relatively few strands - I would usually use electrician's earth wire which is copper and so more flexible and less lossy.

 

Regards

 

Iain

73 de G0OZS

[David Ives]

yes i have the insulating basr for it but as you say probably easier to run a lead down from the top in a sloping lead design

[Chris Suslowicz]

yes i have the insulating basr for it but as you say probably easier to run a lead down from the top in a sloping lead design

 

Well, if you're going to do that, you might as well use the halyard and one of the proper PRC-320 braid aerials. That would allow you to change the length with ease when switching frequencies.

 

(On the other paw, the 27-ft mast is going to weigh several times as much as the set, and using the "proper" 5.4 metre lightweight mast would make it possible to carry the entire setup without too much difficulty.)

 

Another thing with the 27-ft mast: they don't always "play nice" as a vertical aerial, and standard practice is to connect a length of copper wire (Wire, Electric, R4 is traditional) between the top knurled nut (for the whip sections) and the wing nut at the bottom to ensure you've got the electrical length that matches the physical length.

 

Insulated wire can be used, but not D10 (which has a high resistance: 4 steel and 3 copper strands, I seem to remember).

 

Adjust your mast height to match the table on the 320 for the frequency in use and it should tune up OK.

 

Best,

Chris.

[airportable]

I can second how heavy the larkspur 27ft mast is! Bought one in error last year for the display, did not even try to put up, hate to think what would happen if a peg came out.

The Clansman elevation kit is very easy to set up on your own after a couple of times, and at the mo. realy very affordable. Think mine was £25 last year, pegs etc. still new bagged.

[Chris Suslowicz]

I can second how heavy the larkspur 27ft mast is! Bought one in error last year for the display, did not even try to put up, hate to think what would happen if a peg came out.

The Clansman elevation kit is very easy to set up on your own after a couple of times, and at the mo. realy very affordable. Think mine was £25 last year, pegs etc. still new bagged.

 

The Larkspur mast is based on the WW2 Canadian telescopic mast, I think. It's a big improvement over the British 34-ft steel vertical (all those 3-ft sections in the golf bag) at the expense of being less versatile (you can't make 2 x 12-ft masts out of it) and a lot heavier. The rigging kit is considerably heavier than the actual mast!

 

The Clansman 5.4 metre mast weighs less than the base spike for the 27-ft mast.

 

Chris.

[AlienFTM]

Insulated wire can be used, but not D10 (which has a high resistance: 4 steel and 3 copper strands, I seem to remember).

 

D10. Was it not two cables of D5, each comprising 2 steel (for strength) and 3 copper (for conductivity), making 4 steel and 6 copper in total?

 

I didn't tend to investigate too closely: I only really cared because because the prickers for cleaning the jets on petrol cookers were like rocking-horse droppings and we used to cut a couple of inches of D10 off, strip back half an inch of insulation, remove the bared copper wires and leave just the one steel wire which could then be used to clear the soot out of the cooker jets (but it was under-calibre and wasn't as effective as using a proper pricker.

 

It was a long time ago so I stand to be corrected.

[Chris Suslowicz]

D10. Was it not two cables of D5, each comprising 2 steel (for strength) and 3 copper (for conductivity), making 4 steel and 6 copper in total?

...

It was a long time ago so I stand to be corrected.

 

Um, no. It's actually part of the stores designation: Cable, Electric, (type) and goes back to the first world war!

 

Somewhere I have a table of the various types, but WW2 started out with D3, D3 twisted, and D8. D9 was a PVC insulated telephone cable that may never have been issued, and D10 is the one still in use today.

 

There were also two varieties of "assault cable", No.1 which was effectively painted steel wire on wooden spools, and No.2 which was 7 strands steel, 1 copper, PVC insulation, and arrived in a hessian dropped "ring donut" that could be airdropped without a parachute!

That was used with a 2-part drum and a "J hook" layer that went over your arm for paying out or reeling in. (The No.1 type was not intended to be recoverable/reusable.)

Other Signals wire (and cables): Cable, Electric, P11 - used for aerial feeder, and P13 with thicker insulation for high power (like the WS53 and C13).

 

Wire, Electric, R4 is the 7-strand bare copper aerial wire used to make most of the WS19 (etc) wire aerials, with P11 for the insulated feeder section.

 

Chris.