CH-113 Labrador helicopter HF set question

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yahya

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I'd like to ask for help in identification of the High Frequency (HF) radio set from ca. 1963 used on the Canadian CH-113 Labrador helicopter (a version of the CH-46 Sea Knight). The control unit of the HF set is visible on the image below under #8. Notably it has separate controls for the transmitter and receiver frequency channels. Could it be the Canadian ARC-508?

RCAF CH-113 Labrador heli avionics panel.jpg
 
I managed to ascertain that the said HF set was made by the Canadian Marconi Company (CMC) in the 1960s. Its type and specs however still remain unknown.

The CH-113 used peculiar HF antennas in a shape of a blade just aft the cockpit in conjunction with the above mentioned set. A photo of such a HF-equipped helicopter can be found at:
https://cdnsarlab.blogspot.com/sear...00-06:00&max-results=7&start=13&by-date=false
See the last three images on that website.
 
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I'm not sure what the illustrated control unit is. But, that CMC connections is intriguing.

CH-113s never carried the AN/ARC-508 HF set. They were fitted with Collins 618T SSB radios. Closest (in designation) to your AN/ARC-508 would be the CH-113s' AN/ARC-505(V) - aka commercial Collins 618T-3. But, back in 1963, the Labradors would have had Collins 618T-1 model Airborne SSBs. Those sets had no DND '500' number - the DOD designation AN/ARC-94 being used in Canada.

In the timeframe that you're interested in, the 714E-1 control used would have been designated C-3940/ARC-94 ... but it looks identical to other 714E units. And the problem is, the Collins 714E series looked nothing like your drawing. So, the mystery remains.
 

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Avialogs has a CH-113 manual, which is actually silent on the equipage nomenclature, but shows a small CMC logo on the face of the HF radio control unit (pages hotlinked below).

My understanding is that the CH-113 Labrador, when introduced in ca. 1963, was first fitted with the CMC HF set with a wire antenna. Some experts whom I consulted with suggested that the CMC radio products were not too good.

Then, came the Collins 618T with the Collins 437R-1 vertical "blade" antenna aft the cockpit, and eventually there came an update with the towel hanger antenna and more contemporary HF set also from Collins.

698e17666a594803e3cab6f927e5a089.jpg



3a8258d3423df23991f2bcfeefbb3b1c.jpg
 
The blade antenna is for UHF radio
yahya said:
I managed to ascertain that the said HF set was made by the Canadian Marconi Company (CMC) in the 1960s. Its type and specs however still remain unknown.

The CH-113 used peculiar HF antennas in a shape of a blade just aft the cockpit in conjunction with the above mentioned set. A photo of such a HF-equipped helicopter can be found at:
https://cdnsarlab.blogspot.com/sear...00-06:00&max-results=7&start=13&by-date=false
See the last three images on that website.
Click to expand...
Referring to the picture the blade antenna is an uhf antenna while the double whisker antenna that follows is for the COM Vhf range; The antenna generally used even today on helicopters for the HF range is that tube at the bottom that still follows that looks like a handhold and is a loop antenna that needs its own special tuner and given the particular selectivity of the system I don't think it was very practical to use channels too far apart between receiving and transmitting without re_tuning the short loop antenna
 
Right. I should have called the Collins 437R-1 HF antenna visible on the three last pictures from the link above a vertical tube or cigar.

Now, I presume that the HF setup of the CH-113 varied:

(1) The earliest one was the CMC HF radio of unknown nomenclature with a long wire antenna. I do not know if it used any kind of antenna tuner.

(2) Since the CMC set was probably not too reliable, it was replaced with the Collins 618T HF set and the Collins 437R-1 tunable vertical tube (or cigar) antenna.

(3) Then, solid state HF set was used, perhaps also with a long wire antenna as it had a dedicated automatic antenna tuner.
 
Thinking back to the low efficiency of the old radiant system and the remote control with 10 independent diversity rx-tx channels it is most likely that the antenna tuning system was static with preset channels adjusted to the ground; a system that could not adapt to weather conditions and designed for low susceptibility therefore low radiation efficiency, in fact it was replaced with an automatic adaptive one with continuous and flexible tuning losing however the possibility of independent rx-tx channels.
 
I agree with you. I think that the Canadians quickly realized that the mysterious CMC-made radio was not too efficient, and then they adapted the Collins 618T HF set with the Collins 437R-1 "vertical tube" antenna. The Collins catalog that you mentioned claims the 490T-1 Antenna Coupler was to be used in conjunction with the Collins 437R-1.
 
I already wrote them and they replied that they were unable to recognize the type of the set from the CH-113.
 

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