Bt am60-550
 

I have a Blonder Tongue AM60-550 setup and am getting pretty good results all around the house with it. The problem I am having is that when using the signal from the BT I get a 1" darker bar that drifts up the screen from bottom to top and at times there are two bars. Has any one seen this issue and is there a fix. Its really not that bad but if there is an easy for it that would be great.
Thanks

Gregb

Ground Loop hum bars?

https://www.google.com/search?q=grou...Ch3osgEB&dpr=1

Thanks Jim, makes sense to me. I will check how everything is connected when I get home.

Gregb

My TV transmitter rack is plugged into an isolation transformer to kill a ground loop problem. One of my agile modulators despite that seems to like to swamp it's inputs out with hum at random though. :sigh:

Another possibility is bad filter caps in the BT power supply.

In CATV service, these units operated 24/7, for years at a stretch, while packed into hot, crowded equipment racks. Perfect conditions for degrading the electrolytics in the PSU.

That's what I thought so I have recapped it. The picture quality improved a bunch but the bar is still there. I have a few ideas to try tonight and will report on any positive results.

Gregb

OK, here are my findings with the bars on my TV's. Like I said I have recapped the BT modulator, that greatly improved the picture quality but also made the bars that much more visible. I have tried an isolation transformer, I have tried reversing plugs to try and get the commons all in the same place. I went into my panel where the cable feed comes in and tried without the ground connection and with the ground connection, no difference.
I found the problem by accident, I was working on trying different things and I moved the antenna and when I tried the set out I noticed the bars were not as noticeable. So I moved the antenna about 10 feet away from the BT, no more bars, perfect picture. Must be some kind of signal feedback with the antenna to close.
Hope this works for anyone else having the same issue.

Gregb

Interesting! there has been some speculation on earlier threads that strong rf from the modulater is getting back into the modulator power supply and causing the bars. Most of the time it appears that new filter caps solve the problem, but not always. I suspect that your solution supports the rf interference theory.

http://www.videokarma.org/showthread...ight=modulator

jr

Greg-

Did you move your transmitting antenna ten feet away, or the antenna connected to the TV set?

I moved the transmitting antenna away from the modulator.

Gregb

In my case I found that what mattered was getting the antenna in a good clear place, away from switching supplies, and well matched. I think noise from switching supplies was backing up into the output amplifier feedback loop.

OK, thank you for this tip! I have seen the hum bars with a modulator here, too, so I will try this trick.

I don't know what the technical reasons for the improvement are but moving the antenna gave me a good picture without the bars. It was easy to do and cost nothing. If there is a switching supply in my cable box moving the antenna got it away from that as well so there could be merit there as well.

Gregb