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Larkspur folded dipole antenna


Malteser

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Ian

 

It would be useful to get some idea as to the size of the antenna and where it came from - this will at least determine the range of possible sets based on the operating frequency. If it is around 2 metres long it will have been used with one of the combat net radios (A41/42, C42/45 or B47/48) in the Larkspur era and if it is short - less than a metre - it will have been used with a UHF air to ground set - either a mobile A43 or the ground based setups a Collins AN/ARC52 (aka PTR175 or Station Radio C48) that was used in landrover ground to air setups during the 1960s. It wasn't the original ASSU configuration with BE601 UHF, because that is specified as using a vertical rod antenna.

 

Regards

 

Iain

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Hi Iain, thank you for your reply. When its collapsed its about 4 1/2 ft long but I would think thats just for transporting as there are no markings when its extended which is about 10 ft. As its folded, looking at antenna length of approx 20 ft so possibly VHF, around 50mhz ???, regards, Ian.:nut:

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Hi Iain, thank you for your reply. When its collapsed its about 4 1/2 ft long but I would think thats just for transporting as there are no markings when its extended which is about 10 ft. As its folded, looking at antenna length of approx 20 ft so possibly VHF, around 50mhz ???, regards, Ian.:nut:

 

Anything over 8' puts it in the the military HF range, 1.5 - 30MHz at 1/4 wavelength. Hence eight feet of rod maximum for a C42, but up to 12 feet for a C13. (It is unrealistic to carry more than 12' of rod in an antenna base as it is unworkable: the antenna is tuned to the length by the ATU.

 

However, when using a mast (as an antenna if the wavelength is good or to support a dipole) as the frequency tends to zero, the antenna length tends to infinity: at really low HF frequencies, I have run out seriously long antennas.

 

I got myself on permanent nights in the MRG radio truck because I didn't trust them to change the frequencies and the codes correctly at midnight. (If you want it done properly, do it yourself. Eventually I had to let them learn as I was posted out, but there was to be no loss of comms on MY shift.) Many was the night I'd be dragged from my scratcher about 0030 with, "We've lost comms."

 

The downside of the night stag on the Logistic Guard Net (where the Main REME Group hung out) was that traffic tended to zero apart from the odd daily return. I used to spend the early hours of the stag calculating the antenna length for the next day's frequency so that at 2359 hours (there wasn't a midnight in the Armed Forces until July 1982 when a DCI defined it. Prior to that, the day finished at 2359 and the next day started at 0001: saved confusion at midnight) I'd retune the UK/VRC321, run outside, drop the mast, adjust the antenna length, erect the mast, run back inside and call Div for a radio check. I was usually left waiting (Logistic Guard Net was not their highest priority).

 

We did one day get a visit from GOC 1 Armd Div. He was next door in the Orderly Room having a quiet chat while next door I was bollicking a REEM because the bank was yet again complaining that he was overdrawn. The door between Orderly Room and Pay Office opened and the GOC's head popped round.

 

"I know that voice."

"I beg your pardon sir?"

"You're the man who's always on the Logistic Guard Net bollicking my operators for being slack and idle."

"Sorry sir."

"Don't be. None of my people ever bother to keep them in line. Keep up the good work."

 

Anyway where was I? Oh yes, permanent night stags. I quickly realised that calculating the antenna length from first principles every night was a waste of time, so one night I sat and plotted a graph of HF Frequency against 1/4 wavelength. Not rocket science, but long-winded. I Fabloned the graph to the inside wall of the truck next to where the lead passed out between set and mast. Trouble was it meant that in future there was even less to do before the frequency change and I was sat even longer waiting for Div to turn up on the new frequency. So I acquired spare sets of blank code boards (it was Batco and Slidex at that time) and filled the spares in readiness for the frequency change. Then at midnight I wiped yesterday's code boards.

 

Simple.

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Ian, Alien

 

A folded dipole is effectively two half wave dipoles connected at the ends in parallel (the join opposite the feedpoint is a low voltage/high current point being short circuit in many designs) so the wavelength in this case will be 9 to 20 feet = 3 to 6 metres - so VHF combat net radio of some kind rather than HF I think.

 

Regards

 

Iain

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Ian, Alien

 

A folded dipole is effectively two half wave dipoles connected at the ends in parallel (the join opposite the feedpoint is a low voltage/high current point being short circuit in many designs) so the wavelength in this case will be 9 to 20 feet = 3 to 6 metres - so VHF combat net radio of some kind rather than HF I think.

 

Regards

 

Iain

 

Your sums (and knowledge) look better than mine and I bow to your superior knowledge.

 

;o)

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It looks like the folded dipole from the Yagi Array No2, which formed part of SR C41/R222, a piece of VHF Radio-Relay equipment . So not Larkspur.

 

It came in three elements , the folded dipole, slightly longer reflector, and shorter director. Frquency range was 50 - 100 MHz. It had to be adjusted for the approximate frequency. The antenna connection was the same as Larkspur. Incidentally, the inside of the coaxial connector was filled with beeswax. It was a pretty messy job changing connectors on a cable.

 

Here are two arrays (without a full mast) on St Kilda 1969-71

AntennaFarm.jpg

 

and the beast it was attached to, SR C41/R222

 

RadioRelay.jpg

Edited by schliesser92
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Thank you for the information and photos Schliesser, amazing, never seen one before, that accounts for the two way supports, one for the main mast and the other to take the boom for the director and relector. Great info, and a serious piece of radio kit. Cheers very much, Ian.:thumbsup:

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Thank you for the information and photos Schliesser, amazing, never seen one before, that accounts for the two way supports, one for the main mast and the other to take the boom for the director and relector. Great info, and a serious piece of radio kit. Cheers very much, Ian.:thumbsup:

 

A surviving trailer-mounted station is in the Royal Signals Museum in Blandford. It must be the only surviving C41 station in the UK. They were also used by Rhodesia/Zimbabwe, and knowing their financial state, are probably still in service (or replaced by Chinese crud).

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