The AM Forum

 Have obtained a spool of RG22 Twinaxial cable for antenna to my R390a. The cable is too large dia. for the plugs normally available. Can anyone help with a connector type/number for the male plug?  Thanks. Lane

Not sure how big RG-22 is, but, they did make a connector that is the same size as a PL-259 that had two center pins.  Used for twinaxial cable.

Fred

 Hi Fred ; Yeah, this stuff is about the dia of RG/8..Normal Twinax plugs are smaller, but they do make them in the larger size. I need a retail source.. Numbers I've found are HiRose #313-0193-7 40 and TWT2-P-22/U(40) I'm not sure if that last number isn't like a generic type such as what PL239 is....

 It is an Amphenol #32225...Can't seem to find on-line..Unknown military equiv. May need to take my small ones to a machine shop and opened up, have the dimensional specs now.

Lane,
        Why even worry about it? ?  Everyone that I know just uses the type "C" "whip antenna" coax input. Also someone used to make an adapto connector for them that screwed onto the large twinax connector and ended with a single SO-239. I dont remember who made them, but I have 1 or 2 laying around the shack somewhere. Someone else here might know the nomenclature for them.

sounds like a good interface to a low noise RX ant.

The C connector doesn't use part of the front end and was intended for use with a short whip antenna on a mobile communications shelter.  That being said, most of us probably won't notice any difference.

There was a "twin" connector the same size as a PL-259 which is obscure and never really survived WWII.  It was used on some DF and radar type gear and Hammarlund seems to have fallen in love with it for the Super Pro 600's.  Other than that, I have never seen the need for one.

The 390 and A do not use that style connector. They use a larger connector, for Twinax balanced line, and that connector is common (was common) in mainframe computer systems for networking.  I made adapters with a chassis mount male on a mini-box and the other end having SO-239's, banana socket posts, BNC's, and so on.  I got the connectors from Mendelson's Surplus in Dayton for under a Dollar.

Pasternak or equivalent probably have the connectors to mate with the appropriate cable, although I am not sure what the RF loss specs are as that cable today sees service for data.  I am cheap so I just went with the minibox method.

I bought some of those twin PL-259's as recently as 20-25 years ago.  Probably not even made today.  I'll have to hunt around the shop and see if I can find them.

I located some of the females chassis connectors.  The numbers on it are SO-264,  UG-103/U, 02660, Amphenol

Not sure if this is the connector you have on the R-390A.

Fred

OK, here's the line of Amphenol Twinax connectors, find one that works for you.

http://drawings.amphenolrf.com/pdf/169.pdf

Most available from Digi-Key.

Yes, it's not the best idea to use the BNC antenna connector on the 390A. It's for a short whip antenna and you lose a stage of RF selectivity by using it. Best to use the Twinax antenna fitting, ground one pin and connect antenna to the other pin.

Thanks Guys ; I made a three band fan dipole fed with the thin twinax that's made for indoors use. There is a good noticeable s/n ratio improvement.That being said, the indoors computer cable would be short lived, I needed an outdoors type twinax and found this spool of new RG22 on line. Larger diameter than expected. So now to adapt it for use..The plugs are listed by Amphenol but are not in anyone's stock that I have found.Also they are very pricey. So I will open up the smaller ones and use them..Thanks for all the positive feed back..

That is an old computer connector and should be available on the Bay!!
I really did not notice more sensitivity as others claim. It is VERY slight, if any.
I had to do a little modifying. Removes some series resistors, if I remember.

Fred

I found an adapter once and mounted a BB transformer in it to go from single ended coax to balanced input. It went when I sold the RX.

I'm told (but I have never seen it) that the SP600 has an antenna jack on the back that's like a coaxial UHF jack, but with two parallel sockets instead of just one in the center.

The SP-600 twinax jack and the R-390(a) twinax jack are completely different.  The SP-600 is a PL-259 size whereas the R-390 jack is larger.

How do I know this?  I bought a box of what I thought were the R-390 twinax connectors.  Nope, too small, but they fit the SX-73 and SP-600 fine.

I found something really interesting here for the R390A............
Comes with built-in balun for the 125 ohm requirement.

http://www.ebay.com/itm/Collins-R-390A-R-390-Twinax-antenna-adapter-BALUN-/330590619004