Coax to phono connector wanted

[ef37a]

No, it's not that fussy, just that there are about 4 or 5 parts to a BNC connector and you have to get the wire right or it won't go together or it will short.

Well now I'm confused! I though you had live and earth (or ground)

Ha! Ha! viz...https://uk.rs-online.com/web/p/coaxial- ... rs/5464875

Dave.

[Hugh Robjohns]

Well now I'm confused! I though you had live and earth (or ground)

It's signal and screen, but yes, two connections.

However, video (and digital audio and RF) are all high frequency signals that require the cable to have specific characteristics if the signal is to get to the other end intact.

One of those characteristics is called 'characteristic impedance' and its why the cable is identified as 75 Ohms or whatever. The connectors must have the same characteristic impedance too.

The characteristic impedance is determined by the dimensions of the cable and plug/socket – the spacing between the signal core and screen – and the insulating materials between and around them.

That's why BNC connectors have a specific insulation sleeve and screen terminating ferrule, and why the cut cable dimensions are critical. They are fiddly to assemble with the proper tools, and a nightmare without.

Crudely joining two dissimilar cables will create an impedance mismatch, degrading the cable's ability to convey the signal.

RCA-phono plugs/sockets aren't actually 75 Ohm connectors, but they're close and cheap enough for non-professional applications. That's why they're used on consumer video and digital audio equipment in place of the standard professional 75 Ohm BNCs.

And that's why the best solution for interconnecting video gear using BNCs with RCA-phonos us to use standard BNC cables with phono adapters as I linked above. That way the characteristic impedance is maintained and everything works.

[Guest]

However, video (and digital audio and RF) are all high frequency signals that require the cable to have specific characteristics if the signal is to get to the other end intact.

Are, the higher the frequency the shorter the wave band, they don't tend to travel very far or travel well though buildings and hills unlike long wave radio or base notes do they

[James Perrett]

I used an old phono cable and a coax cable soldered together

As Hugh says, just any old phono cable won't work. It needs to have low loss at high frequencies and a characteristic impedance of 75 ohms. That's why the CPC cables I linked to use RG59 cable which is likely to be similar to the cable used by the BNC cables.

A random join in a video cable is likely to have a very different impedance which will result in much of the signal being reflected back to the source and very little actually getting through. There are ways of joining video cables to preserve the impedance but it requires very careful trimming of the cable and very neat soldering.

Oh - and just to confuse things further - BNC connectors and cables are available in both 50 ohm and 75 ohm versions. You need to make sure that you have the 75 ohm version for video and digital audio.

[Guest]

As Hugh says, just any old phono cable won't work. It needs to have low loss at high frequencies and a characteristic impedance of 75 ohms. That's why the CPC cables I linked to use RG59 cable which is likely to be similar to the cable used by the BNC cables.

Oh - and just to confuse things further - BNC connectors and cables are available in both 50 ohm and 75 ohm versions. You need to make sure that you have the 75 ohm version for video and digital audio.

But what about when the connector arrives and if I use one of my cheep phono cables to connect to the fitting. I mean I bought them from the pound shop and not Dawsons. But they are OK for sound, but will there be any different for video?

[James Perrett]

But they are OK for sound, but will there be any different for video?

They're no good for video.

[Guest]

So I need to get a 75 Ohm one. Dam! I wish I ordered it at the same time when I ordered my plug as part of the fiver handling charge

[ef37a]

So I need to get a 75 Ohm one. Dam! I wish I ordered it at the same time when I ordered my plug as part of the fiver handling charge

Hang on a minute there OG and other chaps. I have an external camera which has a very thin, ~3mm cable with it. Some 5mtrs long and BNC to BNC. Yes it is just your bog standard composite colour signal but it is pin sharp on a 40" FSTV. There is no trace of reflection bands. The camera was only 50 quid from Maplins years ago so I doubt the cable is anything special. In fact I know it isn't because I had to chop one of the plugs off to get it through a window frame. I then used a pair of RCAs and a coupler.

In fact the video and sound go into an RCA to CAT5e extender box, round the roof space, 30mtrs easy and into a recorder in the living room. Yes, that does degrade the video somewhat but again, no reflections.

I very much doubt you will have any bother friend. 4k maybe.

Dave.

[Mike Stranks]

Couple of points...

You can get - and I have used a few times - solderless BNC connectors. They're more expensive, but if used properly and carefully can save a lot of hassle.

Hugh has already mentioned, and Dave has endorsed, that for short runs then 'bog-standard' phono-phono leads should be fine. When I first came across this (in composite video days of yore) I raised an eyebrow, but was assured that for our application it would be fine. It was. As Dave says, whether I'd want to attempt it with 4K and large screen is another matter...

BTW; for the longer runs to and from the control room, we always used 'proper' 75-ohm coax into a Distribution Amp at the 'downstream' end.

[MarkOne]

The thing I love about this forum, is it's probably the only place on the internet where a simple question about a BNC connector can get to be 3 pages long!

[Guest]

BTW; for the longer runs to and from the control room, we always used 'proper' 75-ohm coax into a Distribution Amp at the 'downstream' end.

So the longer the cable the longer the signal and the more resistance therefore the better quality cable needed, fortunately for me this is just to test my cameras so a short distance of say a meter cable from the camera to the TV should be enough

[ef37a]

BTW; for the longer runs to and from the control room, we always used 'proper' 75-ohm coax into a Distribution Amp at the 'downstream' end.

So the longer the cable the longer the signal and the more resistance therefore the better quality cable needed, fortunately for me this is just to test my cameras so a short distance of say a meter cable from the camera to the TV should be enough

The cable resistance matters not a jot because it will be far less than the 75 Ohm source. I dare say there is a limit but CCTV is piped around buildings,100s of mtrs.

I have not got clear picture of what you intend to do. If you intend to 'splice' a BNC cable to an RCA cable a twisted join offends us but up to a few mtrs would probably work fine. Better to solder the join and 'lay' the inners in line, tape up then lay the outers on top, more tape.

We have all had to do 'Terrible Things' to get out of shtuck in the PA and TV game!

Dave.

[Guest]

The thing I love about this forum, is it's probably the only place on the internet where a simple question about a BNC connector can get to be 3 pages long!

Er, if you think this is bad you should check out the electrical forums on Screw Fix and DIY Not, there they really know how to make a song and dance out of a mountain out of a mole hill

https://www.diynot.com/diy/threads/cctv ... 588/page-6

FFS Its 12v power supply they come in all shapes and configurations …why on the electrical forum is everything a big song and dance ….?

... perhaps because the OP is having a big problem in understanding how to connect his 12V PSU to the two (polarity marked) power input terminals on his camera?

It seems quite apparent you haven't read the thread, I don't believe there is a song and dance here, hasn't even been spoilt by our resident joker.

The thread is running just as designed, to assist someone asking for advise

True. My only reservation about that, which I have also mentioned previously, is that if he cuts the plug off, the OP could well then find himself with some very iffy (perhaps 'tiny') conductors that he could well struggle to connect to the terminals of his cameras. Even an 'adapter' would require him to be able to somehow interface it with his cameras.

Making the wires twice as long (or even 3 times) and then folding them over and twisting them and maybe even soldering them should work hear

Youi have to play it by ear. There's always going to be some solution but, as I've said, one often finds oneself faced with (sometimes 'tiny') 'wires' that are quite difficult to deal with when one cuts a lead such as that one.


We are up to 10 pages now and I have not even got my first camera to work yet. BTW I have about 20 of them different makes and models, this could be a very long thread

[ef37a]

Are you telling us you need assistance getting power to the cameras AS WELL!

Dave.

[James Perrett]

We are up to 10 pages now and I have not even got my first camera to work yet. BTW I have about 20 of them different makes and models, this could be a very long thread

However, if you had followed my advice in the first reply to your question you'd be all set and working now. If you are taking the same approach and ignoring good advice on the other thread then I'm not surprised.

I'm starting to wonder if you are trolling us?

[ef37a]

I wonder too now James.
Just for the record? Tried to find the core resistance of 75R video cable. No joy but it seems to use around 23AWG core wire and that runs out at 20.36 Ohms per 1000 feet. I.e. not to be concerned about.

Dave.

[Guest]

Although electricians do install CCTV systems for companies as part of there job, I came hear because I though the Knowledge would be more pacific and specialised to my subject

But they do still seam to be of the opinion that the cable I have made up should get a signal for its short distance. But as you stated it would not work so I have taken your good experienced advice (again why I came hear in the first place) and this is why I ordered the fitting the other day and I look forward to it arriving and pressing on with the project

[Mike Stranks]

Organ Grinder:

This: https://cpc.farnell.com/pro-signal/psg0 ... no%20leads will also provide what you want. This is a complete lead with 75-ohm cable.

Nothing more we can say really...

Good luck in testing the gear!

[Guest]

This: https://cpc.farnell.com/pro-signal/psg0 ... no%20leads

[Hugh Robjohns]

Excellent. I like a happy customer supplied with a range of practical solutions. Case closer.