Converting Twisted Pair To Bnc

[rickl242]

Hi,

I recently installed a DVR system for a customer who had previously been on an ADE Opticam system.. He wanted to keep his cameras so I made a test lead, everything worked ok(i.e. I saw a picture).

Now I have come to fit the Geovision DVR system which uses BNC connectors and I can't get it to work at all, I tested the Geovision is working ok by connecting a lead from the back of his DVD player.

The Opticam cameras use 5-core shielded cable with a 6-pin Mini DIN(same as PS/2 mouse) connector.

1-PIR

2-Video - 1V pk-pk PAL Video in from camera

3-Ground

4-N/C

5-Audio

6-12v 250mA Max per camera

The first lead I made used the power from the original recorder, but I took the Video and Ground to a phono connector... and from there to a modulater.

The 2nd lead used some screw terminal junction blocks to connect the power to all 6 cameras, all the grounds together and a short length of CCTV coax going to each BNC.

The 2 things that are different between the two leads is power and video.... AFAICT the power is ok.

So my question is, can I connect a coax cable direct to multicore?

Do I need some resistors?

I have seen baluns for sale, am not sure how they work.

Thanks for any help

Regards,

Rick

[arfur mo]

Hi,

I recently installed a DVR system for a customer who had previously been on an ADE Opticam system.. He wanted to keep his cameras so I made a test lead, everything worked ok(i.e. I saw a picture).

Now I have come to fit the Geovision DVR system which uses BNC connectors and I can't get it to work at all, I tested the Geovision is working ok by connecting a lead from the back of his DVD player.

The Opticam cameras use 5-core shielded cable with a 6-pin Mini DIN(same as PS/2 mouse) connector.

1-PIR

2-Video - 1V pk-pk PAL Video in from camera

3-Ground

4-N/C

5-Audio

6-12v 250mA Max per camera

The first lead I made used the power from the original recorder, but I took the Video and Ground to a phono connector... and from there to a modulater.

The 2nd lead used some screw terminal junction blocks to connect the power to all 6 cameras, all the grounds together and a short length of CCTV coax going to each BNC.

The 2 things that are different between the two leads is power and video.... AFAICT the power is ok.

So my question is, can I connect a coax cable direct to multicore?

Do I need some resistors?

I have seen baluns for sale, am not sure how they work.

Thanks for any help

Regards,

Rick

Hi Rick,

camera's can work on a standard alarm cable over a short distance, but picture degrad's rapidly as that cable is extended more than 5 yards or so.

you can run camera's over CAT5e cable but you need the baluns at each end. these act to lower the line imdepance between points (camera and DVR) then convert it back to a normal signal, but with some signal lose. maximum for colour is 100mtrs and less if screened (STP) cable was used

you can by baluns with screw terminals for ease of connection

regs

alan

[Guest anguscanplay]

screened alarm cables fine upto about 100m ( systemq made their name on it ) but you can only send one camera per cable - no muticoring ie cam1 on blue and yellow cam3 on green and white

screen and black = power -

red = power +

blue = earth video

yellow = video

connect screen,black and blue to video ground at cam then yellow to video, red to 12v in and at the mx end use screen and blue to the outside of the bnc with yellow to the centre pin of the bnc with your power

to sum up earth at the camera not the mx

[ian.cant]

So my question is, can I connect a coax cable direct to multicore?

Do I need some resistors?

I have seen baluns for sale, am not sure how they work.

Yes

No

You dont need baluns! Visit NVT.com if you want to learn about baluns and twisted pair CCTV.

[breff]

i've converted a few opticam systems to dvr's no problem, no need for baluns just solder some coax to the end of the leads so you can fit bncs or fit phono plugs and use phono to bnc convertors.

As Angus says, the video ground and the negative are commoned.

So pin 2 coax centre core, pin 3 coax screen and 12v negative, pin 6 12v positive.

[rickl242]

Hi,

thanks for your help, have ordered a BNC-to-phono to test with

good to know that other ppl have done it

Regards,

Rick

[rickl242]

Hi,

I've been back to have another go with this system... the results I got confuse me /sigh

Using a lead I originally made to test (6pin miniDIN plug to take power from the original base unit.. phono socket for the video out and 6pin miniDIN socket to plug in a camera) I can take the output directly into the modulator and see that the camera is working... but when I plug in a phono-BNC connector and attach to the geovision cable I get nothing

I also tried taking the video output from his DVD player into the geovision.. also nothing. I also cut the end off an RCA lead and touched the wires directly on the GV BNC socket.. not a sausage.

So at least i've proved the output is getting to the end of the RCA. I also tested the GV multi-BNC to VGA lead with a multimeter and there doesn't seem to be a short or open where there shouldn't be...

Could I have some problem with PAL/NTSC or perhaps a setting I need to change in the GV software?

Also when I built this system I tested that I could receive a video signal ok by connecting the video card RCA output to the GV BNC and got a nice view of my screen cascading into infinity

Thanks for reading