What causes this type of TV interference?

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Sample analogue pics here:
http://members.iinet.net.au/~mbuckler/interference/Doc1.htm
All the analogue channels are affected.

The digital channels are unwatchable as the picture just breaks up a third of
the way down the screen.

I'm in a low lying area and the signal has always been weak, but good enough for
analogue and normal definition digital. Things have suddenly become much worse.

Is this symptomatic of a masthead amp with problems?
Also there's house building activity about 200 meters away and roughly in line
of sight with the transmitter. Can metal roofs produce this kind of
interference?

Mike

Re: What causes this type of TV interference?



"Mike B"
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 **  Yep - a bad PSU.

 Do your neighbours have the same pic problems ??

 You  MUST  find this out to see if it is interference or not.




......   Phil



Re: What causes this type of TV interference?


Seem to be fault with TV. What TV is that? (CRT, plasma, LCD, etc?)

Do you have same problem when watching from AV inputs, DVD for example?

If DVD is OK, then bad signal is likely to blame.

Rudolf

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Re: What causes this type of TV interference?


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I see the same problem with two different receivers. One is a combined
analogue/digital TV capture card, the other is an 8 year old analogue TV.

If I unplug the power supply to the masthead amp the distortion disappears, but
the signal becomes very noisy (as you would expect) as the receiver its using
whatever signal manages to leak through the unpowered masthead amp circuitry and
antenna cable.

Mike

Re: What causes this type of TV interference?



"Mike B"

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** That is near perfect proof the PSU is dud.

 Bad filter electro causing lotsa ripple voltage most likely.

 Try another one ASAP.



......  Phil



Re: What causes this type of TV interference?



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Looks like you are right.

I replaced the original 22v AC phantom power supply  with a 12v DC regulated
power supply and the interference has disappeared.

Thanks!

Mike

Re: What causes this type of TV interference?



"Mike B"

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 **  Whoooooooahhhh  -  wait on half a mo.

 AC feed means the PSU is really  INSIDE the masthead amp.

 If you keep using the DC supply in lieu , expect to get serious corrosion
problems.

 Looks like it is time to get out the long ladder  ......





.......   Phil





Re: What causes this type of TV interference?




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Replaced the rectifier diode and electrolytic cap inside the masthead amp and
restored the AC power supply.

Picture looks OK, so it appears to be fixed.


Mike

Re: What causes this type of TV interference?



"Mike B"
"Phil Allison"

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 **  Was this operation  carried out at high altitude ?

      Or the sane way ?



........  Phil





Re: What causes this type of TV interference?



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Desktop height.
http://members.iinet.net.au/~mbuckler/interference/Doc2.htm

It looks like it was flow soldered then a few components were hand soldered. The
rectifier diode was one, so I'm guessing that it got cooked.

Mike

Re: What causes this type of TV interference?



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If you happen to have (access to) a CRO, check the waveform of the supply to the
MHA.  If it shows material distortion, try a replacement PSU.  If not, there are
two lines to follow:

1.  The MHA is rooted.
2.  The extra gain from the MHA is causing a problem in the receiver.  But two
receivers?  Nah!

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