What RF connector is this? (TNC)

[dominicbeesley]

Hello all,

I bought a Texscan model RA-54 attenuator from ebay the other day which was advertised as 5V-TTL switched and having SMA connectors. It's turned up and it seems it is actually 24V and has connectors I've not got ends for - I bought some SMA ones but they are far too small!

Any ideas, they almost mate with BNC connectors except for being threaded but before I order parts do you lads know whether these are "N" or "TNC"..or something else? I don't want more expensive junk connectors!

I'd swap the ends but it is all nicely fitted together and would require major surgery to dismantle...

I've got all the parts to make this into a PIC controlled attenuator to replace my heath-robinson switched attenuator I made a few years ago which has been got at by damp.

Also, any information on the Texscan would be helpful I guessed at 24V as the relays seem to want at least 18V before they switch reliably...

D

[G6Tanuki]

That looks like a TNC to me. "N" connectors are much larger [nearly an inch diameter].

[Radio Wrangler]

TNC, 50 Ohm.

It's the threaded version of the BNC, designed at the same time by the same people.
Rated a bit higher in frequency because of the better fit, and it leaks less.

DAvid

[dominicbeesley]

Thanks everone, I'll order some now...it's a funny old world isn't it. I've just bought a NOS crimp tool for less than the price of two new BNC connectors. Crimp tools used to be very expensive when I were a lad and I made lots of Ethernet cables up with a special "die" in a vice that I'd knocked up with a file...or more often, on site, with wire cutters...

[Nicklyons2]

Originally Posted by Radio Wrangler

It's the threaded version of the BNC, designed at the same time by the same people.
Rated a bit higher in frequency because of the better fit, and it leaks less.

Paul Neill and Carl Concelman to be precise; two largely unsung great engineers who designed these two connectors amongst others, ('N' is for Neill type) around the time of WWII. Just look at how modern and still widely used these are and compare them with the sort of connectors which were used on British equipment of the same era - most looked like variants of 5Amp mains plugs with more or less pins and / or metal shield!

[dominicbeesley]

Yes, I've got a box full of old ones from WD and other equipment - I suspect a lot of it was to do with what parts were to hand and/or easy to turn up on a lathe without too much precision.

[Dave Moll]

So, presumably that means:
B = Bayonet
T = Threaded
N = Neil
C = Concelman

[Nymrod121]

Wikipedia supports that deduction:

http://en.wikipedia.org/wiki/BNC_connector
http://en.wikipedia.org/wiki/TNC_connector

Best wishes
Guy

[Biggles]

In fact I have this very day been wrestling with replacing a solder N-type on an outside aerial at the top of a set of ladders in the freezing cold at work. Gas irons aren't a favourite tool of mine. I had run out of crimp types or that would have definitely been an attractive alternative for a quick job. The equipment termination was a TNC, a connector that I don't see much of at all these days. They used to be very common on some types of PYE equipment in the eighties.
Alan.

[dominicbeesley]

Thanks all,

I've got the connectors from Farnell. I'm making a switched attenuator just two push buttons and a digital read out. It should in theory give up to 192dB of attenuation - whether that will be achieved in practice I don't know...

I've still not found any information on the attenuator module so I'm going to guess its a 24V one!

I've written the PIC software now I've just got to design and etch a circuit board for the microcontroller, driver transistors and DC-DC converter. The PIC software has a few "special" features...
- a delay before switching the relays so as to reduce wear when flicking through values
- attenuators are switched in individually starting with the strongest first then unwanted ones switched off strongest first - the idea being for the signal to always undershoot the signal to avoid overloads and to reduce current transients

This is all to replace my home-made attenuator which was a lot of small compartments of PCB material and toggle switches - it worked well but I didn't varnish it or clean enough of the flux off and a little bit of damp has destroyed it...

D

[FRANK.C]

Hi Dominic
That's an interesting instrument, keep us updated please.

Frank

[emeritus]

BNC connectors are prone to RF leakage at higher frequencies. When I was at Plessey, developing military radio in the 200-500MHz band, we had great trouble in replicating a test set-up that was used at Roke Manor, in which the transmitter was installed in a large Eddystone Die cast box, and the receiver connected via attenuators using ordinary single-screened 50 Ohm cable. They could wind down their attenuators to more than 120dB without signal leakage, whereas we had very variable results and could barely manage 70 to 80 dB.

The problem turned out to be the BNC connectors use by our attenuators ( HP 10dB-step and 1 dB-step switched attenuators connected in series). Roke used only screw connectors on their set-ups (Type N, SMA and the like). Our test gear stores dug out an old attenuator, also fitted with BNC connectors, and let us make up short adapter leads to Type N and solder up the BNC connectors solid. Our problems vanished and we could turn the wick right down with the receiver sitting on the Eddystone box that contained the transmitter with no signal breakthough. We didn't even use any RF gasket on the box lid, and the cable was ordinary 50 ohm coax, not double screened.

While Wiki is quite definite in the origin of the connector names, I recall that even in the 1970's there were conflicting versions. Another suggestion was BNC = Bayonet Nut Coupling, TNC =Threaded Nut Coupling. The N in "Type N" was said to stand for "Navy", it having been originally developed for the US Navy. I have no views either way!

[dominicbeesley]

I've started another thread that has some details of what I've been doing...https://www.vintage-radio.net/forum/...355#post741355

D

[Restoration73]

The BNC design was improved on by the TNC (Threaded) design

[chuckey]

Surely you should have used Plessey coaxial plugs and sockets?
Frank