F Plugs

As do all F connectors which makes me wonder how John managed to get such a thin cable into a normal size connector!

No, because the size of that inner tube will be the same, whether the connector is a compression, screw on of crimp type for the same type of cable because the size of the inner dielectric is very carefully controlled (the characteristic impedance of coax is determined by the ratio of the outside diameter of the centre conductor to the inner diameter of the screen - the foil in the case of these cables).

Alter the size and the cable will no longer be correctly matched, leading to all sorts of problems.

The outer tube or crimp ring should be able to cater for slight differences in outer sheath diameter, provided the correct connector is used.

For example, the RG59 Headend cable I referred to would not fit a normal RG59 connector because it needed a connector with a crimp ring actually larger than a normal RG6/WF100 connector to allow for the bulk of the additional screening!

It was over 20 years ago, which makes it difficult to remember but it might have been folded back on itself - this could happen, I suppose, if it snagged on the internal tube when it was inserted.

The distribution point out to the network, actually, so yes, extremely critical.

However, I don't see that it would have made any difference if it was on an individual CATV, Freeview, Freesat or Sky feed

If this was a Sky install, why didn't the installer terminate the cable and, if it was pure DIY, what on earth was on the LNB end of the cable?

:)

Perhaps I am missing something here, but it seems to me that you won't be altering the spacing between inner and screen... at the point the short length of dielectric is exposed, it is protruding beyond the foil screen anyway - and 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.

Indeed.

Easy...

(although you do realise that you have just made me work with that horrid shotgun cable again!)

Take your thin co-ax and strip a length of outer as normal:

Now wind a few turns of insulating tape around the end of the cable outer such that the edge of the tape aligns with the cut edge of the outer.

It was a typical sky install - so no effort spared!

IIRC the owner decided he wanted the cable feed into his AV furniture more neatly than the installer had done it, and so cut the original connectors off the end of the cable so he could fit them through a hole. I can't recall now if they were originally crimped or had been discarded

- but they could not be reused for whatever reason.

I had intended to fit a wall mounted outlet for him and make up some flyleads for the sat box in normal CT100 style cable, before his parsimonious nature kicked back in, and asked if I could not just stick connectors back on the cable ends like before.

I did not look at the dish end of that particular installation.

I think you are! I was trying to emphasize that the allowable tolerance of the inner dielectric has to be much tighter than for the outer sheath

Is it? it isn't apparent in your pictures which appear to show the foil screen extending the full length of the dielectric, as it should do. Perhaps you meant to say the exposed length of the centre connector? In that case, the screening function is the responsibility of the F female which completely encloses it when the two are mated.

Which would be completely wrong. If you cut cleanly through the cable and view it end on you have the centre conductor surrounded by the dielectric with its foil covering. This is the coaxial cable. Additional screening is just that and the outer sheath protects the cable but they are not electronically part of the coaxial cable.

In which case, why did you find it neccesary to wind tape on the cable to increase the size - and would you have to do the same if you used the correct connector?

I'd love to know how you would get either of those connectors to fit over the sheath of RG11 (10.3mm nominal).

He could have saved a bob or two if he'd had the brains to drill out/ream the holes to take the connectors in the first place!

Or was this a freeby? :)

Whereas the crimp on ones have a flat, internal endstop, with a central cylinder sticking up from that endstop and forcing its way up, inside the cable itself, the screw-on type (or at least the ones that I have seen) don't. They simply have a flat, internal endstop, with a hole through.

SteveW

Of course - the outer does not have any significant effect on the cable impedance, where as, the radius of the dielectric, and the material it is made from does.

Indeed they do

(although I note that different plug manufacturers give subtly different examples of best termination practice - some show removing the foil at the point the outer is striped, and others continuing it a little further up to (or at least close to) the point where the inner wire is exposed - I favour the latter).

Right, and that is the same size regardless of the size of the rest of the plug.

In fact if you imagine preparing the cable as normal, and then connecting it to the socket *without* any plug at all, you would still have the same fundamental screening geometry. (ignoring the lack of electrical continuity of the braid for the mo).

Sorry, me being sloppy - provided by the threaded barrel of the socket not the plug. Either way the spacing/material of screen to inner in the socket will not exactly match those of the coax with either size cable, however they should both (in combination) approximate the same characteristic impedance.

Yup, I agree with that.

Because the rear section of the F plug's (i.e. the bit with the knurled outer and internal threads), only purpose is to facilitate attachment of the plug to the cable. Its entirely outside of the screen on a foil screened cable.

When sized for a normal CT 100 style cable, is too large to engage with the outer jacket of a shotgun cable.

So for example, on the left some Webro WF100, and on the right some Labgear R09W42, with the matching plugs:

No, because it would fit without. All the tape is doing on the smaller cable is making the outer jacket wide enough to allow the plug to grip.

You wouldn't - its insulating tape, not a TARDIS!

You can make a plug fit the "correct" size of cable or one a bit smaller, you can't as easily make it fit one that is too large to enter even enter to cable grip section at all.

What I am struggling with here, is what the actual thrust of your argument is... is it that the hole though the end stop in the plug is a different diameter? Vis:

Looking at the layers of the cable side on where it attaches to the F plug you have something like:

==== knurled barrel of plug ---- braid folded back pppp outer plastic jacket

---- braid ffff foil dddd dielectric iiii inner copper conductor dddd dielectric ffff foil

---- braid pppp outer plastic jacket ---- braid folded back ==== knurled barrel of plug

I am assuming that the characteristics of the coax are controlled by the spacing of iiii from the foil, and what material dddd is made from.

So altering the arrangement to:

==== knurled barrel of plug ---- braid folded back pppp outer plastic jacket - paddding pppp outer plastic jacket - paddding pppp outer plastic jacket

---- braid ffff foil dddd dielectric iiii inner copper conductor dddd dielectric ffff foil

---- braid pppp outer plastic jacket pppp outer plastic jacket - paddding pppp outer plastic jacket - paddding ---- braid folded back ==== knurled barrel of plug

Will not alter the critical defining characteristics of the coax at all.

---- ====

I don't think he had given it that much thought - it was just "I want to thread this through, but the plugs are too big". So I said (without having seen it!) cut em off, I will put a proper socket in anyway.

I was expecting him to pay for the materials...

When I told him what the wall mounted box, and a couple of modular F connectors in it would cost, he decided he did not need it *that* neat.

Yup, all the twist on ones I have seen have been like that - basically like a pipe connector, with an internal flange to stop you inserting the pipe too far.

The clearance hole just needs to be small enough to stop the outer jacket going through, while being large enough to allow the the foil, dielectric and inner to pass through.

That's pretty much how I've been doing it since f plugs came on the UK scene.

Bill

I must admit that I've never used a screw on F connector or even handled one - and I don't ever intend to!

I don't know how far back you are going, Bill, but the first time I saw them was when they were used for the internet connection on the early IBM PCs in the early 80s.

Nothing like that. It would be when the Sky Amstrad dishes came along.

Bill

I don't recall any networking standard that used F connectors?

Early thin ethernet with BNC connectors on 50 ohm coax certainly

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

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