F Plugs

[Terry Casey]

I was responding to your earlier statement "the screen is now being provided by the threaded part of the plug - the size of which is the same for all sizes of connector." which is obviously untrue - you won't get WF100 into a shotgun type connector any more than you will get RG11 into any smaller connector. The size of the threaded part of the plug is NOT the same for all sizes of connector, as you have now stated.

But that is not what you previously stated!

Correct.

OK so long as the foil screen is not removed. However, after the problem I descrihed previously, I wouldn't take a chance.

[Terry Casey]

I've just been go I don't recall any networking standard that used F connectors?

Early th Yup. BNC was THE professional RF plug in the 70s.

F types I dont recall seeing before sattelite..but we had screw on coax - big ones - for radar and microwaves

*** My reply:

I only had knowledge of one network, albeit a fairly large one, so I wonder if it was vendor dependent?

Nobody, including me, had ever seen F connectors before, which caused a bit of a problem because equally, nobody had ever seen any instructions for using them!

The 'correct' method is to do up the connector finger tight then, with a spanner, tighten one flat - ie: one sixth of a turn. In practice, you can appply a lot more force than that without causing problems, but not when the female is a right angled printed circuit board mounting type!

The whole connector start to rotate, snapping of the PCB fixings and rendering the network card useless

I saw a anumber of these so there is no doubt in my mind whatsoever that they were F connectors!

[Terry Casey]

Another missing reply from John:

In light of that statement, this discussion seems to have taken on a rather ironic twist. Do I sense a little back tracking?

***

None at all. Assuming that, aside from the screwed thread, the plug's construction was otherwise normal, I couldn't see how it would be possible for the cable to straddle the central tube so that the screening braid and sheath were outside it!

Now that you've explained that there is no tube to obstruct the cable, I can see how you did it.

[charles]

When we first met them in the '60s, they were known as a "B***** Nasty Connector"

[The Natural Philosopher]

As a prentice in '68, one of our learning tasks was how to put them on seriously braided cable...

[tony sayer]

In article [e-mail]>, charles [e-mail]> scribeth thus

Bayonet Neill-Concelman is its correct name!..

Just use them for Two-way radio installs these days. "N" type for anything more powerful up to say 500 odd watts

and 7/16 DIN after that 500 watts and above and higher UHF frequencies

PL259 or UHF are s**te plugs

And TNC quite good for some instrumentation stuff and applications..

[charles]

There is/was a a large version of the BNC (simply C, ISTR) which is about the size of an N, but bayonet rather than screw.

[John Rumm]

I think you are confusing which thread - I am talking about the thread whose size is dictated by the barrel of the female F connector, and which matches the thread on the inside of the captive nut. These are the only threaded parts that *might* be acting as a screen - and then only when using "low loss" coax without a foil under the braided screen.

The thread designed to attach the plug to the cable is *always* outside of the screen - even on non foiled cables.

The bit I am talking about is the same for all F connectors. Its part of the standard. The other variable bit has no particular RF related function - its there to provide mechanical attachment only.

Its what I stated, but it might not be what you understood from what I stated! :-))

Even if the foil screen is removed on the stripped bit of the cable, the padding on top of the PVC sheath is still outside the *unstripped* part of the cable where is still has full screen integrity.

[John Rumm]

I did attempt in my very first post, make it clear I was talking about the twist on style of plug. To be fair I had assumed that you were familiar with this type of plug, which subsequently appears may have been an assumption too far. Hence why I was having difficulty seeing exactly what point you were getting at.

Hopefully now familiar with the twist on plug design, you understand that the bodge I described will not in any way impact the RF performance of the connection. Its just more time consuming and less convenient way of fitting a plug to a thin cable.

[Andy Burns]

Back in the 80's I used thinwire ethernet, arcnet (plus various twisted pair rather than coax cabling) none of them had F connectors all BNC, the PC cards that *did* have screw on rather than bayonet were IBM AS/400 and 5250 twinax connectors ...

[Terry Casey]

Actually, this is not correct - it is the ratio of the diameter of the centre conductor and the inside diameter of the foil screen which determines the impedance, as we have previously discussed. Different dielectic materials can vary the velocity of propagation of the cable but this is only important if you are using a TDR to trace the location of a fault.

Yes, but the hole in the connector is now determining the impedance of that section of the cable. Because the foil is very thin, this won't make much difference if the correct connector is used but if the wrong connextor is used there will quite a jump in the impedance over that section.

The padding, as you say, plays no part in this.

[Terry Casey]

Yes, I appreciate that..

But it is very important not to remove the foil screen from the exposed dielectric as I explained in my previous post.

[The Natural Philosopher]

TWINAX. NOW I remember what those screw things were.

Also token ring cards...remember those?

Type 1 connectors..

And 'bee sting' thick coax adapters that went to a huge D type connector on the card.

[Andy Burns]

Yes, but we used more Proteon cards (cheaper and 10Mb rather than 4Mb)

I think I know a server room where there's still one lonely type 1 connector on the wall ...

Only worked on a couple of sites that had thick wire ethernet still in place

[Jac Brown]

None of those used F connectors or anything like those.