Modulator Problem

Joined
28 Nov 2004
Messages
74
Reaction score
2
Country
United Kingdom
Hello all.
I've installed a diy cctv system to my house and wired it so that all the TVs can view it. The signal coming from the camera is pretty sharp, until I feed it through the modulator (which I need to in order to convert the scart). After that, the image becomes very grainy and has lines running up and down it. This is the modulator: http://www.maplin.co.uk/module.aspx?TabID=1&criteria=modulator&ModuleNo=33050&doy=3m10 (i hope that link works - if not, it's a Maplin modulator VH89W, which I think is probably pretty bog-standard.

It seems to me that the picture gets grainy when I introduce the main aerial to the modulator - the picture is clear until then. So perhaps that's causing interference?? Does anyone have any ideas as to what I might be able to do to stop the interference from the main aerial t other modulator.

Or should I go for a better (more expensive) modulator. I've seen this one on another post
http://www.satcure.co.uk/accs/page4.htm#rfmod. Although not sure if that'll make any difference.

Thanks in advance. Apologies if this is a no-brainer to some of you.
JS

++++
I'm very pleased, I though this was going to be a gripe at me!

Mod Rupert
+++++
 
Sponsored Links
I use those exact same modulators for my CCTV and video distribution.

I've got four of them daisy chained and they all work in harmony with no problems.

Using the DIP switches you can change the channel they output on, I suspect you have a clash at present with a terrestrial channel you are recieving through the aerial.

You'll normally find that stuff either end of the band is clear, so maybe try channels 21-28 or 58-63 (you set this channel/freq via the switches on the front)

Good luck.
-Dan
 
Thanks Dan - I already tried doing that (I should have said - sorry) but it made no difference.

Any other ideas? Maybe I need to put some type of filter bteween the aerial jack and the 'aerial in' socket on the modulator??? or a different modulator??? No idea where to turn to now.
 
What I did with mine was auto tune my tv with the modulator out of the circuit and see what parts of the freq spectrum seemed to have nothing in them, I then set the modulator(s) to have a freq in the middle of these empty regions.

By this I mean that when tuning a TV you often see welsh, london and various other channels that you can't get a clear picture of, but they are just about there, you need to avoid all these channel numbers as well as the more obvious BBC1,2 ITV C4 and C5 etc....

There must be a gap in there somewhere, if not then maybe you have an aerial amplifier infront of the modulator that is swamping the modulators (smaller) output. If so then an attenuator is what you need.
 
Sponsored Links
AHA! :D yes, there is an amplifier before the aerial comes into the modulator (something called a loftbox in the....loft). Please tell me more about the attenuator that I might need - I've never heard of one of those before and perhaps that'll do the trick!

Thanks for all this by the way - really helpful.
 
Have you tried connecting the modulator to a TV with the camera feed into it but without anything connected to the 'ant in' socket?

If so what is that picture like?
 
Right, you say you have a loft box, so this makes the situation a whole lot easier, assuming that the loft box distributes all your tv round the house

If you look at the loft box you will see that there is an input socket specifically designed for a modulated CCTV system.

You need to connect the video signal to the modulator, and then take a co-ax or better still a satellite grade co-ax cable from the modulator 'to tv' socket to the CCTV in socket on the loftbox, leaving nothing connected to the 'ant in' socket on the modulator.

Then all you need to do is tune your TVs in to find the CCTV signal.

This is the exact setup I have at home and it works a treat. Any more problems, feel free to ask
 
Hi thanks for the advice - yes the loftbox does have a cctv input. The only problem is that my loftbox is in the loft but the cctv unit and modulator is on the ground floor - so that's why I'm using the aerial cable to send it around the house. I can't really run a fresh cable to the loftbox input as the cables run under the floorboards throughout the house and that be a whole separate problem.
Is there anything else that you think might do the trick?
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top