Unusual Interference Problem with RF Amps (please help)

Forums › Home Theatre (including HTPC and EPG Collector) › Unusual Interference Problem with RF Amps (please help)

pm

78 posts

Master Geek

#18496 12-Jan-2008 20:04

I've uploaded a schematic of how I've set up my home aerials & satellite to:
http://myfreefilehosting.com/f/8833d54b5b_0.02MB

(not sure how long it'll stay there...)

This setup was working very very well (for a year) until today. For some very weird reason the modulated signal (of my DVD player) suddenly decided to become very noisy. Naturally I tested the modulator which works very well with and without an amplifier.
It seems that the noise arrises from the output of the passive splitter (which is actually being used as a 'combiner/multiplexer').
I've swapped ports on the splitter and that didn't change a thing.

The rest of the satellite/tv channels work fine. Its just this one modulated channel that appears noisy. Why is it that noise builds up on this particular channel?? I have changed the channel on the modulator but I cannot tune into them because the signal was too noisy for the tv to realise there is something there...

cyril7

9058 posts

Uber Geek

ID Verified

Trusted

Subscriber

#104479 13-Jan-2008 09:17

You seem to have a lot of amplifiers, are they really needed.

Anyway, long shot, are you in a area where Kordia have shifted your local UHF channels to make way for the DTT service, they may have planted one on top of your modulator channel, try changing it.

Beyond that cannot help without closer inspection.

Cyril

pm

78 posts

Master Geek

#104480 13-Jan-2008 09:26

Yes I do have a lot of amps.
The masthead amp (power injector part) is necessary for UHF reception.
The distribution amp after helps because the signal is split and makes a noticeable difference to quality.
The second distribution amp is necessary because its sending the modulated signal around the house (which is a fair bit of coax cable...).

I'm in East Auckland (Bucklands Beach), but i'm not sure about that UHF channel using DTT. I can tune into this channel fine if I just combine it with the aerial and into my tv (without sending the signal to the rest of the house).
Changing the channel didn't make a difference too.

Is it possible that there is feedback going into one of the other amps? These are the standard old indoor amps.

cyril7

9058 posts

Uber Geek

ID Verified

Trusted

Subscriber

#104484 13-Jan-2008 10:13

Its quite possible that you have too much gain and its all gone into feedback. If you remove all the amps except the head amp does it come right (even though the levels would be low and noisy).

Cyril

pm

78 posts

Master Geek

#104529 13-Jan-2008 16:34

yes it does become right - but as expected all my channels are noisy. Maybe you might have some solution(s) to re-wiring my setup? It is all a bit dodgy, but I'm right on the border of receiving good reception, so having the amps is a must. I'm extremely picky with reception...

pm

78 posts

Master Geek

#104530 13-Jan-2008 16:37

On another note, does it matter if the splitter I use if full power pass even though I'm not sending any signal up to the satellite/amps?
If I'm just combining/splitting signals does it matter if I use the power pass port or not? I know they pass a DC voltage but is it possible that ordinary reception will pick up a dc component level that could harm the tv?

cyril7

9058 posts

Uber Geek

ID Verified

Trusted

Subscriber

#104533 13-Jan-2008 17:02

The tuner input on TV's is capacitivly coupled so DC will not upset it.

I would ditch the amp and attenuator after the decoder, and move the other amp to after the combiner before the main splitter.

Cyril