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What causes this type of TV interference?

Sample analogue pics here:

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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

Reply to
Mike B
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"Mike B"

** 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

Reply to
Phil Allison

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

Reply to
Rudolf

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

Reply to
Mike B

"Mike B"

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

Bad filter electro causing lotsa ripple voltage most likely.

Try another one ASAP.

...... Phil

Reply to
Phil Allison

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!
Reply to
quandong nut

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

Reply to
Mike B

"Mike B"

** 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

Reply to
Phil Allison

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

Reply to
Mike B

"Mike B" "Phil Allison"

** Was this operation carried out at high altitude ?

Or the sane way ?

........ Phil

Reply to
Phil Allison

Desktop height.

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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

Reply to
Mike B

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