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I have recently acquired a nice looking dummy load on military surplus sale. Being relatively new to the hobby, I assumed the connector on it was something common. Turns out it is not. So far nobody has been able to tell what it is. The most specific answer I got is that it is a 'large TNC', except I haven't been able to find anything like it. Looking for the model number on the manufacturer’s site also didn't bring up anything useful.

I thought also of replacing the connector entirely, but it turns out that the center pin and dielectric are integral parts of the resistor inside.

Here are a couple of pictures of the load and the connector up close.

The connector

The connector head on

The connector diameter

The load from the side

The load's model number

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    $\begingroup$ It might be useful to take a picture of the connector directly end-on, from as far away as still gives decent resolution (for minimum perspective distortion). This will allow people to get dimensions of the subcomponents of the connector from the photo. (On the other hand, if someone already knows it, that probably isn't necessary.) $\endgroup$ – Kevin Reid AG6YO♦ Jun 21 '17 at 17:20
  • $\begingroup$ @KevinReidAG6YO thank you for suggestion. I've just added such a picture. $\endgroup$ – Mchl SP5MKL Jun 21 '17 at 17:33
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The connector is called an "HN" type connector. It has a 3/4-20 thread and it is usable up to 4 GHz. The Amphenol data on it is available here.

enter image description here

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  • $\begingroup$ This might be it! The dimensions are pretty much spot on. Now I just need to find a place which wouldn't charge me $50 for a female connector (these are the prices I can see at local vendors). My best bet might be to drive back to place where I bought the load and dive into their bins of disassembled connectors. $\endgroup$ – Mchl SP5MKL Jun 22 '17 at 19:03
  • $\begingroup$ I can assure you that is the right connector. I looked up the specs on your Bendix 633.8 and then confirmed the dimensions just to be sure. $\endgroup$ – Glenn W9IQ Jun 22 '17 at 19:06
  • $\begingroup$ Glenn, where were you able to get the spec for the dummy load? I would be most interested in having a look at those too, to know exactly what I bought. $\endgroup$ – Mchl SP5MKL Jun 22 '17 at 19:08
  • $\begingroup$ Try this link: [link] (webflis.us/webflis.aspx?NSN=5985-01-034-8226) $\endgroup$ – Glenn W9IQ Jun 22 '17 at 19:22
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Looks like a male SC connector and the dimensions seem in the ballpark too.

I found this via a "Microwave Coaxial Connectors" PDF which describes it as:

SC (OSSC) - The SC coaxial connector is a medium size, older type constant 50 Ω impedance. It is larger than the BNC, but about the same as Type N. It has a frequency range of 0-11 GHz.

This matches what Amphenol says about their SC-Type Connector Series:

The SC-Type connector series is a medium size, 50 Ω series, with performance up to 11 GHz.

The SC-Type connectors are manufactured to meet MIL-C-39012 category D, specification sheets 35 through 43. The series meets all of the mechanical and electrical requirements of the Limited Co-ordination Specification (LC Spec.) as generated by the U.S. Air Force.

Connector mating is a .687-24 UNEF screw thread.

Tom Williams (WA1MBA) does not show this connector on his RF Connectors for Upper Frequencies page yet considers it "common":

There are many other common RF interconnects, but are not described in this treatment because their performance in the microwave region is very limited. Examples are C, HN, SC, LC, various EIA, UHF, mini-UHF, Motorola, HV, SHV, and RCA Phono. [emphasis mine]

(Clearly that's a bit at odds with the "up to 11 GHz" frequency range I see cited everywhere else.)

Maury's "Microwave Coaxial Connector Technology: A Continuing Evolution" PDF also lists it amongst "General purpose coaxial connectors in wide use for systems application" and summarizes it as a

Threaded version of type C for aircraft and EW applications.

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  • $\begingroup$ This looks promising! $\endgroup$ – Mchl SP5MKL Jun 21 '17 at 18:00
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    $\begingroup$ Your Amphenol link shows a conical mating surface (I assume of the dielectric), but the connector in the question photos looks straight-sided in that aspect. $\endgroup$ – Kevin Reid AG6YO♦ Jun 21 '17 at 18:10
  • $\begingroup$ Indeed, this section is cylindrical in my connector. Also, some of the dimmensions are close, but others differ by as much as 2mm $\endgroup$ – Mchl SP5MKL Jun 21 '17 at 18:38

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