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Guest Message by DevFuse

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Signal Strength


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30 replies to this topic

#21 OFFLINE   RonPE

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Posted 27 December 2010 - 10:40 PM

Regarding Multipath -

For the last week or so my max signal strength has changed. Instead of having a high of about 92-93% and sometimes a dip to about 77-79%, the max is now about 84% with the same dip to about 77%.

If the 77% was due to multipath & I presume one signal canceling out the other, could the 93% have been from two signals in phase and therefore adding to other?

Mike,

The new snow on your roof is probably the cause of the reduced signal. Trees leafing out in Spring and higher winds can also cause this. WBBM-12 OTA signal strength at their present power of 8 kW is a popular topic at AVS Forum. It's unfortunate that WBBM's OTA signal is left in the dust by the IND/Religous/Spanish UHF stations. I'm 58 miles out West from Willis and my custom Yagi-12 antenna w/ pre-amp still struggles to get a stable signal.

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#22 OFFLINE   Mike109

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Posted 28 December 2010 - 12:16 AM

Mike,

The new snow on your roof is probably the cause of the reduced signal. Trees leafing out in Spring and higher winds can also cause this. WBBM-12 OTA signal strength at their present power of 8 kW is a popular topic at AVS Forum. It's unfortunate that WBBM's OTA signal is left in the dust by the IND/Religous/Spanish UHF stations. I'm 58 miles out West from Willis and my custom Yagi-12 antenna w/ pre-amp still struggles to get a stable signal.


I thought about the snow & am not disregarding it, however my antenna points out toward a vertical wall not the roof. Of course some signal may be coming in via the roof. I'm about 25 miles west/south-west of Willis Tower.

WBBM usually looks good from OTA, but every once in a great while there is a dropout or green pixels. I've been using OTA when possible in order to avoid loosing a signal due sat rain/snow fade. Other than one severe rain storm a couple months ago, WBBM via sat seems more reliable.

I'll have to try re-aligning the antenna again. It's just a real PITA to get to.

#23 OFFLINE   kenglish

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Posted 28 December 2010 - 06:36 AM

Multi-path is not just caused by reflections from buildings and such, but can also be caused by mismatches in the antenna and transmission line, which are often caused by materials in the antenna's near-environment. Snow on a roof (or, a wet roof), for example, can detune the antenna...even though it's not in the "path" of the signal.
A trick that can sometimes help, is to put an attenuator (-3 to -6 dB is typical) in the line, either at the TV or at the antenna (try both ways and see which helps). This attenuates the reflected signal twice as it "bounces off" the de-tuned antenna or mismatched TV tuner, while only attenuating the desired signal one time.

Don't sweat the readings on your set, as they mostly indicate how hard the equalizer circuits are working...i.e., how much they are trying to correct multi-path. You could have a very weak signal with no multi-path, for example, and show nearly 100%, or a super strong signal with bad multi-path could read very low.

If you have problems with just one channel, I have to wonder what is vastly different about it....is it a VHF (RF) channel? If so, it can be very susceptible to noise. Could be that a static discharge, or a "pop" from a thermostat opening in a furnace control or refrigerator (or, sump pump, etc, etc, etc) is occasionally disrupting the VHF signals...or, even a weaker UHF channel.

#24 OFFLINE   drjake

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Posted 14 January 2011 - 03:33 PM

CBS in Chicago is a VHF channel (I think at the old Channel 3 Frequency). It tends to have issues even fairly close. It is important to have a good antenna. I am only about 35 miles from the tower but I still use a preamplifier because of issues on CBS.
Drjake

#25 OFFLINE   RAD

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Posted 14 January 2011 - 03:44 PM

CBS in Chicago is a VHF channel (I think at the old Channel 3 Frequency). It tends to have issues even fairly close. It is important to have a good antenna. I am only about 35 miles from the tower but I still use a preamplifier because of issues on CBS.


AFAIK WBBM-DT hasn't been on ch 3 for almost a couple years now, they're on channel 12 now, VHF-hi band.

See post My Setup for configuration info.


#26 OFFLINE   drjake

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Posted 14 January 2011 - 05:33 PM

AFAIK WBBM-DT hasn't been on ch 3 for almost a couple years now, they're on channel 12 now, VHF-hi band.


Still VHF and less than stellar.
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#27 OFFLINE   RAD

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Posted 14 January 2011 - 06:17 PM

Still VHF and less than stellar.


Yea, but still a whole lot better then ch 3. When I lived in Mundelein it was a challenge to pull them in, especially when they were at reduced power for a while due to interferrance with the cable customers around the Hancock.

See post My Setup for configuration info.


#28 OFFLINE   Mike109

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Posted 30 October 2011 - 02:20 PM

I recently read somewhere that Dish DVRs might struggle somewhat when recording some OTA content because of their high bitrate signals. I can’t find the posting or article at the moment, but it did not go into any detail. My thought is perhaps the DVR might not be designed for these higher bitrates. If I understand correctly, Dish satellite signals are more compressed than OTA and they are only 1440x1080 instead of the full HD of 1920x1080.

OTA CBS/WBBM is 1080i and has no sub-channels. Typically this uses 80-90 minutes of HDD capacity when recording a 60 minute program, which is about double compared to recording CBS from satellite. Due to the high bitrate, does anyone think this may be the cause of the green pixels?

I'm not saying multi-path is not the problem. After reading the article it made me curious if other factors might also be involved.

#29 OFFLINE   Stewart Vernon

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Posted 30 October 2011 - 03:38 PM

I can't say it isn't a problem ever... but I can say that I record from OTA all the time, and have never seen an issue unless I had a signal drop due to weather or something else.

I've never seen the receiver struggling to keep up with the OTA bitrates.

Keep in mind that the oldest Dish HD receivers were slower than today's DVRs... and the oldest Dish HD receivers were in service before Dish started to reduce the bitrates.

Older customers remember some of those first Dish HD channels that were 1920x1080 and at full bitrate because they only had a few HD channels back then and no reason to starve them.

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#30 OFFLINE   CCarncross

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Posted 30 October 2011 - 09:02 PM

Transfer rates on USB 2.0 or eSATA is way higher than max stream rates from even the most aggressive OTA station.

#31 OFFLINE   Mike109

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Posted 05 June 2012 - 06:25 AM

The short version -

Dish did some re-wiring. Previously they diplexed the sat & OTA coax and it ran through several diplexers & splitters. They now separated the 2 feeds & eliminated a couple diplexers & replaced a 4-way splitter with a 2-way. CBS OTA signal strength increased from 79-81 up to 89-91. Gains were made on other channels also, but CBS was the main concern. If an antenna amp is needed at least it now can be powered via the coax, but I don't think it will come to that.




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