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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 11th Jan 2020, 4:30 pm   #1
nigelpritchard
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Default RF Dummy Load Identification

I'm hoping the RF Amateur Radio fraternity (probably only from the UK) might include someone who recognises an ancient RF dummy load that I've had for years and not used. I've posted some photos.

It is a "50-ohm" tapered slab-line device made with a 52 ohm carbon rod which has a tap at about 40% from which a germanium detector circuit and an Acorn glass thermocouple (Ormandy & Stollery style) power measurement circuit are connected. RF input is via N-socket. The slab-line is in very thick, and solid, silver-plated brass and there is also a RF sampling connector with capacitive proximity take-off at the top end of the carbon rod leading to what I believe is a Burndept Pattern-12 plug/socket.

It appears to have been made for the UK WD by EMI and has a Cat number of 6C/C33851 and manufacturing date of "ZD".

As you might see from the photos it is unlikely that the frequency response is very great because the feed to the thermocouple is somewhat lengthy. I'm hoping to get a bit more info about this assembly and in particular some idea of the bandwidth to be expected.

I could put the dummy load on my NanoVNA to look at it's parameters but that won't tell me what frequency the power-measurement circuit can work at.

Any ideas welcome. Regards G8AYM
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Old 12th Jan 2020, 2:08 pm   #2
G8BBZ
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Default Re: RF Dummy Load Identification

Hi.
Not much help but the date code equates to April 1968.
Good luck
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Old 12th Jan 2020, 2:21 pm   #3
nigelpritchard
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Default Re: RF Dummy Load Identification

Many thanks; how does this dating system work?
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Old 12th Jan 2020, 2:33 pm   #4
ex seismic
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Default Re: RF Dummy Load Identification

Cat number 6C.. implies Air Ministry.
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Old 12th Jan 2020, 4:17 pm   #5
nigelpritchard
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Default Re: RF Dummy Load Identification

Many thanks for the inputs so far.

Have now determined by use of my NanoVNA that it is quite respectable as a RF load up to at least 500MHz, with VSWR = ~1.05 over the range of 100-500MHz, and the minimum being at 432MHz (1.02). From about 550MHz VSWR is then rising to 1.08.

Now need to understand how it performs in the actual power measurement domain.
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