different signal strengths on subchannels (1 Viewer)

Mr Tony

Thread Starter
SatelliteGuys Pro
Supporting Founder
Nov 17, 2003
289
35
Mankato, MN
need some help guys....and I havent heard this happen before

Can a subchannel have different signal strength than the main channel? Here is what I mean

Our local ABC (KSTP) is at channel 50 (mapped to 5)....main (5-1)and subchannel (5-2). On my Panasonic plasma it shows signal on
5-1 to be around 75-80
5-2 shows 40-45 and lots of pixeling

all the other stations in the market seem to have almost the same signal strength on the subchannels as the "main" (the -1) and that includes FOX, NBC, PBS, CW & My.

Using a Radio Shack U-120 antenna (as of right now all the stations are on UHF) and there is a split. One goes to the Panasonic and the other goes to the Dish 811 in the bedroom

Is this normal for that to happen???
 

jegrant

SatelliteGuys Pro
Aug 5, 2005
1,210
171
I don't know if this is the case, but is it possible that it's simply a very low bit rate subchannel, and therefore the slightest data loss affects it greatly?

Alternatively, is there possibly some kind of interference that could affect only the subchannel?

I agree - this sounds really strange, almost impossible. One would think signal strength would be identical among all subchannels of a digital signal.
 

texasbrit

SatelliteGuys Pro
Pub Member / Supporter
Apr 12, 2006
3,634
352
Actual signal strength will be the same on all subchannels, because it's the same signal. However, the signal "strength" shown on the signal meter isn't strength at all, it's a measure of the signal "quality" (including bit error rate). I suppose it is possible, if the signal meter is actually measuring each subchannel independently, for the signal "qualities" to be different (as jegrant says, for a low datarate subchannel an interference/noise problem might affect that more) but I must admit I have never worked that one through to see if it's possible.
 

Hall

SatelliteGuys Master
Feb 14, 2004
18,409
3,194
Germantown OH
Shouldn't happen.... As noted already, they're the same "signal". The pixellation you're seeing on the .2 channel suggests that they've starved the sub-channel to the point that they're not giving it enough (seen this myself with a couple sub-channels ... on the other hand, it means they're giving the main channel much more).
 

digiblur

SatelliteGuys Master
Jun 8, 2005
14,190
2
Louisiana
need some help guys....and I havent heard this happen before

Can a subchannel have different signal strength than the main channel? Here is what I mean

Our local ABC (KSTP) is at channel 50 (mapped to 5)....main (5-1)and subchannel (5-2). On my Panasonic plasma it shows signal on
5-1 to be around 75-80
5-2 shows 40-45 and lots of pixeling

all the other stations in the market seem to have almost the same signal strength on the subchannels as the "main" (the -1) and that includes FOX, NBC, PBS, CW & My.

Using a Radio Shack U-120 antenna (as of right now all the stations are on UHF) and there is a split. One goes to the Panasonic and the other goes to the Dish 811 in the bedroom

Is this normal for that to happen???

Not reallly...think of the stream as one transponder in the FTA world. Your TV just breaks out the video PIDS from the same stream. But it is very possible there's was an encoder problem causing the bit error rate to go bad on just one subchannel which caused your "strength" meter to go down. Most TV's just have one meter that is a combination of strength and quality. On my HDHomeRun tuner you actually have 3 meters, quality, strength, and symbol quality.
 

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