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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 7th Sep 2019, 6:38 pm   #21
budkor22
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Default Re: MFJ Dummyload faulty?

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Spec VSWR on that model is 1.3:1 so they are inside that.
Yes, it is 1.1:1 at 100W. I couldn't decipher that too. At 60 ohms, I would have thought SWR would be higher.

But then my meters, are they accurate? I am not sure

They are vintage meters but sturdy well made heavy ones.

OSKER SWR-200

I have two of them, and they were reading the same SWR and same power output.
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Old 7th Sep 2019, 6:54 pm   #22
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Default Re: MFJ Dummyload faulty?

And there lies another story - you are looking at one frequency with some other factors thrown in - some the meter in use, some your connecting leads and then the TX is not a 50 Ohms source anyway.

MFJ and all the rest are fulfilling a need in the market. I just wish they would use larger boxes for their ATUs compared to the inductor diameters.
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Old 7th Sep 2019, 7:00 pm   #23
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Default Re: MFJ Dummyload faulty?

MFJ was at one time said to stand for "Mighty Fine Junk".

I suspect your dummy-load may have been overcooked at some time.

At junk-sales/hamfests/rallies you come across Heath "Cantenna" dummy-loads - oil-cooled beasties built into what looks like a paint-can. These were designed for the US market where Kilowatt-capable ham radio stations were commonplace - so Cantennas can take quite a thrashing.

https://www.eham.net/reviews/detail/13123

My dummy-load-of-choice when I was designing juicy RF-stuff was a big grey-finned beastie about the size of a large load-of-bread, by "Aspen Electronics" - you occasionally see these at rallies etc and they still sell for 3-figure sums.
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Old 7th Sep 2019, 7:07 pm   #24
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Default Re: MFJ Dummyload faulty?

The grey one that looked like a radiator for your house?
I think Bird made that...but Aspen were their agents.

Just spotted you said loaf of bread... too small.
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Old 7th Sep 2019, 7:13 pm   #25
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Default Re: MFJ Dummyload faulty?

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It is square pillar shaped ones, I used them to restore 1940s all valve radiogram once, and leftovers from the work. Like this one in the link.

https://www.digikey.co.uk/product-de...kaApcREALw_wcB
Wirewound... pretty much useless at RF, I'm afraid.

Also, shunting the bad dummy load relies on the value of that dummy load being stable. If it's been overcooked, then that might be a problem. A changing load could cause a lot of confusion sometime in the future.

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Old 7th Sep 2019, 7:34 pm   #26
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Default Re: MFJ Dummyload faulty?

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Just spotted you said loaf of bread... too small.
Mine wasn't the "heater radiator" type, it was more like the Bird 8135. It would take two-tone SSB to 1Kw for 30 seconds or so. I remember having two fan-heaters-set-to-cold-blow to cool it when doing intermodulation tests.
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Old 7th Sep 2019, 8:31 pm   #27
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Default Re: MFJ Dummyload faulty?

Yes OK - I think the 8135 could have a meter head fitted at the front which was my most common encounter of it.
Most Bird stuff was no good for IM testing below the -30dBc or so of SSB specs. I used to hold them off by long reels of RG214 until they would not generate.

Intermodulation testing can have a thread of its own. Or a book.

Last edited by Jon_G4MDC; 7th Sep 2019 at 8:43 pm.
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Old 9th Sep 2019, 10:00 am   #28
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Default Re: MFJ Dummyload faulty?

I ordered another dummyload MFJ 264. It is 1.5Kw rated, but I will never have occasion to use that power ever. Maximum 100W would be my usage for the dummyloads.

Hopefully it will have good spec not too far way from 50 ohms unlike the cursed MFJ 265B.

No, I am not a dummyload collector.
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Old 10th Sep 2019, 11:06 am   #29
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Default Re: MFJ Dummyload faulty?

Not yet
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Old 11th Sep 2019, 7:55 am   #30
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Default Re: MFJ Dummyload faulty?

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Not yet
My encounters with dummyloads had been always, buy cheap, buy three times case
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Old 11th Sep 2019, 4:34 pm   #31
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Default Re: MFJ Dummyload faulty?

MFJ 264 arrived, and it is measuring 50.1 ohms.

Metal casing is substantially larger than the 260B, and well within spec. and 1.5 Kw rated. It seems more trusty and dependable dummy load, although more expensive.
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