"F" Plugs (Very sad question....)

[j.m.]

Been looking @ pricing for "F" Plugs

I have bought 1 off Plug For £1, & I bought a bag of 10 for £1.80

The expensive one is a nicer looking job than the others, Deeper Knurling & a smooth rotation of the collar even under as much pulling force my lil fingers can muster......

Apart from that what is the diffrence between F plugs generally ?

I did say this question was sad, but would you listen "Noooooo"

 

[jimbo]

Not sure....what carat gold was the £1 one?

 

[rolfw]

Yes, 18 pence each seems more reasonable, after all, it either works or it doesn't.

 

[cpc]

Screwfix do 10 screw-on F plugs for 90p - they work too. They also do 100m "PH100" cable (air-spaced, copper braid, copper foil) for £23.49, so you only have to spend another £22 before you get free post and packing too.

 

[j.m.]

Wow just paid £46.00 for 2 X 50Mt Raydex CT100 :-0

Very pruddy cable tho

Dang CPC (thats www.cpc.co.uk)

 

[rolfw]

But they do 100m for £34.32 J.M.

CABLE SATELLITE CT100 100M BLK
Order Code: CBCT100-100BLK02 Unit Cost: £34.32

 

[j.m.]

But they do 100m for £34.32 J.M.

CABLE SATELLITE CT100 100M BLK
Order Code: CBCT100-100BLK02 Unit Cost: £34.32

Not my decision this...... It started off as adding Sky & 1 extra tv socket in the kitchen, & the job kind of grew ....... More bits arrived by the minuite, CPC trade counter 10 Mins round the corner O-no

Gonna start a complete alarm system rip out & replace...... My "Real Job" ;) www.thomsonsecurity.com (plug Plug) & then they are talking total re-wire too....... I'm gonna be there till I retire I think......... Ohh fones too...... They want a phone socket in every room too........... I'm gonna put one in the bog by mistake............ They have a sense of humour

 

[rolfw]

LOL, sounds good J.M.

 

[Old Fred]

F plugs come in various internal thread sizes. The smallest is about 4.7mm I think (for that double cable they use on SKY+ installations) and the biggest is about 7mm (for WF100). You can tell the size by the number of grooves in the knurling. Unfortunately, there don't seem to be any twist-on F connectors for the 8mm diameter H125. You have to buy a box of 100 crimp type, plus the tool!

 

[Channel Hopper]

Apart from that what is the diffrence between F plugs generally ?

The difference in price is in descending order
the manufacturing quality,
metal content and,
origin

I have had some truly awful ones from a large distributor in N London, manufactured in India, about 20% were machined with the thread (tuner) with very little metal , and the plugs would come unscrewed with vibration.
Some even had no thread as though the lathe operator had fallen asleep

Others can suffer from breakage where the tightening of the thread makes the two parts separate.

Normally the brass effect ones are of better quality and have a plastic seal between the two parts.

At certain frequencies (usually 2GHz and above) some of the signal can be lost through any squashing of the insulating dielectric when the F plug is tightened onto the cable.

 

[j.m.]

At certain frequencies (usually 2GHz and above) some of the signal can be lost through any squashing of the insulating dielectric when the F plug is tightened onto the cable.

Jebers a scientist

I gotta admiit I do prefer the easy spin around "Quality" ones........ So much easier on my lil pinkies

 

[rolfw]

On occasions when you are making 100 plus connections in an afternoon, crimp connectors can certainly make the day more bearable.

 

[Channel Hopper]

On occasions when you are making 100 plus connections in an afternoon....

Reminds me of a certain Manx cat, went on holiday near Wimbledon

I bow to the forum stud

 

[puffin]

F plugs come in various internal thread sizes. The smallest is about 4.7mm I think (for that double cable they use on SKY+ installations) and the biggest is about 7mm (for WF100). You can tell the size by the number of grooves in the knurling. Unfortunately, there don't seem to be any twist-on F connectors for the 8mm diameter H125. You have to buy a box of 100 crimp type, plus the tool!

I have also had big trouble fitting a CT 125 but there do exist a F-plug for that. Get the GV17T from Maplin.

 

[Channel Hopper]

CT125 can be made to fit into a standard F-Plug, it requires shaving off most of the outer sleeve using a razor blade, until a minute amount is left, remove the first 6mm of solid outer conductor and all but a few strands of the outer braid.

A good connection is achieved by careful use of a set of pliers to turn the f-plug on the cable, saves the pinkies

 

[PaulR]

CT125 can be made to fit into a standard F-Plug, it requires shaving off most of the outer sleeve using a razor blade, until a minute amount is left, remove the first 6mm of solid outer conductor and all but a few strands of the outer braid.

Surely this will alter the impedance ratio at this point as the plug will be the wrong internal diameter (the impedance being a function of the diameter of the centre conductor to the diameter of the outer conductor). This will set up a standing wave and cause a loss of signal.

Or do I just worry too much?

PaulR

 

[Channel Hopper]

The outer cover is the only thing that is sacrificed into getting all the cable into the f-plug.

By doing this the dielectric is unaffected in cross section.

Its good to worry sometimes, some people see the bus coming, yet miss the fact its not stopping.

 

[PaulR]

Actually I was thinking today that it was a load of bollocks that I posted anyway. The threaded part is always the same diameter regardless of what size the inner conductor is and hence would cause a discontinuity of some sort depending on what cable was being used.

Does anyone know what diameter conductor actually gives a 50 ohm impedance with the standard F socket?

This, of course, is the disadvantage of not having a proper machined centre pin like BNCs or N types.

I'm sorry, I'm worrying too much again aren't I? The losses are undoubtdedly marginal.

But I would like to know just so that I can file the knowledge away.

PaulR

 

[Channel Hopper]

I am sure theres a formula somewhere for working out the distances of inner to outer dielectric to determing the best impedence of a cable, but I dont have it here

50 Ohms is used whenever there is a need for high power to be passed through a cable (its lower impedance means delivery is better) and is characteristically used on systems that require a ground plane.

75 Ohms is used on predominantly receive only system (either on a dish/LNB, or in the standard TV system where there is a dipole aerial at one end). Its usually far cheaper per length, has cheaper conductors, and is usually more tolerant when a mismatch of equipment is connected at either end.

 

[PaulR]

Sorry, I meant 75 ohms. I am aware of the 50 ohm - 75 ohm but had a slip of the fingers. Yes, there is a formula for working it all out, dielectric constant and all, but all I wondered was: with the outer diameter effectively fixed then there is obviously an optimum diameter for the inner (dielectric being assumed to be the same) to get 50 ohms. Which size cable then is nearest to this optimum?

PaulR