Signal mystery

[pgitta]

Ok, this is a hard problem to describe, so I'll try to make it a simple example. Signals are same for all the channels to avoid confusion but they do obviously vary:

Say I get 10 OTA channels:

CH Signal Strength PRE lightning strike w/o preamp
1 65
2 65
3 65
4 65
5 65
6 65
7 65
8 65
9 65
10 65

CH Signal Strength PRE lightning strike with preamp
1 85
2 85
3 85
4 85
5 85
6 85
7 85
8 85
9 85
10 85

CH Signal Strength POST lightning strike w/o preamp
1 65
2 65
3 65
4 65
5 65
6 65
7 65
8 65
9 65
10 65

CH Signal Strength POST lightning strike with preamp
1 85
2 15
3 85
4 85
5 85
6 85
7 20
8 20
9 85
10 85

Note most channels at same level with preamp as before strike, but a few are almost non-existant now.

I have checked the cable as far as I can see and don'y notice any physical damage. Besides, non amplified signal is the same as it was before.

Replaced preamp...no change

Only balun has not been changed, but then again, no amp works pretty good.

Let's see someone figure this one out. I'm stumped. Signal TOO strong? Then why did it not happen before?

70 miles from Chicago
CM4228 UHF bowtie
CM7775 pre-amp
Cable run 60ft. w/ two 2-way splits

[GKusnick]

If you're asking for an explanation of the physics of it, I can't help you there. But it's not that implausible for something to be fried in such a way that it still works at low signal strength but clips or shorts at higher signal strength. (Think of blown-out boombox speakers that sound OK until you crank the volume.)

That would tend to point to something downstream of the preamp as the culprit -- like your receiver or capture device (probably not what you want to hear).

As to why it didn't happen before -- it hadn't been hit by lightning before. No mystery there.

[Kirby]

Just out of curiousity, which 3 channels are the bad ones? Physical channel numbers please, not virtual.

[garyellis]

what specifically did you use to measure signal strength?

I am trying to measure that to my tuner cards.

Gary

[pgitta]

Well, I think I've solved my mystery.

Thr first pre-amp I got must have been degraded or weak, because I've tried two others now with the exact same result. I believe the amp is over-driving my signal to the point where the tuner can't lock them in.

I had an 85 signal on FOX before the amp facing the tower
Then I had a 15 on FOX with the amp facing the tower
Then a 100 with the amp, but the antenna pointing 100 degrees away from the tower!

Sucks, because I can't boost the weaker stations I wanted to get without overloading the strongest ones and effectively making them go away.

For signal I'm using my Proscan HDTV receiver. VBox signal meter blows chunks.

What, did Chin Won write that on his lunch hour?