Unknown Dummy Load

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vagrant

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I picked this dummy load up at an estate sale and it does not have any identifying marks. I presume it is oil filled. I can hear the liquid when I shake it, so I put a note on there for others if I loan it out.

What I do not know is how much power this can take at what frequency and for how long. I swept it and here are some numbers at 50 MHz and up. This is due to the N connector which has me wondering how high it can go and what it can handle. Any ideas on the model or exactly what it can handle? It may not be meant to handle above 30 MHz, but I am unsure what it could handle and for how long even below 30 MHz. One can guess, but it's worth asking, thanks.

927 MHz / 54.4 ohm / 1.162 VSWR
445 MHz / 51.5 ohm / 1.135 VSWR
145 MHz / 50.6 ohm / 1.057 VSWR
50 MHz / 49.6 ohm / 1.041 VSWR


It is not tapered toward the bottom, that's just the lens angle. It weighs around 7.2 pounds.

DL2.jpg DL1.jpg
 

digitalanalog

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Found this, just going by looks, the one in the front seems to look very similar, also the info for it.

"The dummy load (background) with the external RF sampler is the Bird Termaline RF Load-Coupler, model 6411 rated at 500 watts at 50 ohms. The Bird dummy load plus RF sampler weights 23.5 pounds. The dummy load (foreground), is a US Navy DA-75/U, rated at 1000 Watts average at 51.5 ohms nominal in the range of 1.3 to over 1000 mHz. The DA-75/U while looking similar in size to the Bird 6411 is actually 3 inches longer, has much thicker radiators and it weights 33 pounds (10 pounds more than the 500 watt Bird 6411). "

2005-0321-dummy-load.jpg
 

vagrant

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Thank you all for the feedback.

The Sierra / Philco 160B-150 or 160B-300 is what I was previously thinking due to the similar size and design, but made for Navy use due to the paint job it has. I just found a 1966 advertisement for Sierra dummy loads in some publication, via Google, that noted up to 5Gc (5 GHz). Still, I believe the dummy load I have is probably less than, or limited to, 1 GHz like the DA-75/U model, which is very similar in design to mine. What I have appears to be about 1/4 ~ 1/3 of the size of the DA-75/U. Also, the dummy load I have at 1 GHz is 60.8 ohms and 1.297 VSWR. At 1.3 GHz it changes to 64.75 ohms and 1.376 VSWR.

My "guess" is that it will handle:
A. 100W continuous 160m to 6m amateur bands.
B. 50W continuous from 6m to 70cm amateur bands.
C. At 33cm (900 MHz) the radios I have will only go up to 30W, which I "think" will be okay using this.

It may be able to handle more, but that is the maximum power I can put into it from the transceivers I have. I'll just label it 100W HF and 50W VHF/UHF. ( I reserve the right to be terribly wrong )
 

cmdrwill

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It may be able to handle more, but that is the maximum power I can put into it from the transceivers I have. I'll just label it 100W HF and 50W VHF/UHF. ( I reserve the right to be terribly wrong )

Sounds about right to me.
 

popnokick

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Many of the oil-cooled dummy loads of that era were filled with electrical transformer oil.... usually a Polychlorinated Biphenyl (PCB) oil, a known carcinogen. Handle it appropriately.
 

vagrant

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Yes, it is good to point out about PCB for anyone that stumbles into this thread and do not know better. Just a few years back, a fellow ham was telling us about an oil filled dummy load he had that was low on oil and how it looked and smelled bad. When asked what he did, he explained that he dumped it out near the side of his house. After a slight uproar on the radio, he was told why that was a foolish and dangerous thing to do.

Hmm..I may paint a biohazard symbol on the back, or put a sticker. Who knows where this thing will end up years from now and it may cause a person to ask after observing the symbol.
 
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