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Old 3-Mar-2016, 2:04 PM   #1
ZippyTheChicken
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Posts: 59
Co-Channel and Signal Power how much db difference is necessary

I have a few co-channels in my area and a couple of the stations are ones I want to get.

The problem is that the station I would like to get only gives me 10db to my area but its co-channel station is much weaker at -7db...

is there any rule of thumb to know when trying to get a station if its worth trying a bit more or if a co-channel is just going to knock it off the air.

17db is not that great a difference its not like one is 60db and the other -20db

I have a few of these type stations and normally one is above and one is below zero but many of the stations i get here are weak and under 20db so i am fighting things..

I want to get abc from one direction and the rest of my lineup from another but some of the cochannels are in the direction of that abc station....

then again i just looked through the zap2it guide for ABC and that station is mostly garbage now heh maybe i can do without it.. but they do play some sports on the weekend and maybe one or two shows in prime time.

anyway is there any rule of thumb?
or is this pretty much factored into the results page and anytime there is a C you are going to get knocked off
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Old 3-Mar-2016, 3:42 PM   #2
Tim
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The directions the stations are located and the type of antenna you have play a key role in this. It would be helpful if you could post your TV Fool report, the make and model of your antenna/preamp and the particular stations you are referring to.
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Old 3-Mar-2016, 4:49 PM   #3
ADTech
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Quote:
is there any rule of thumb to know when trying to get a station if its worth trying a bit more or if a co-channel is just going to knock it off the air.
Off the top of my head, it's around 35 dB at the input to the tuner. for adjacent channels [emphasis added, the factors Tim mentioned come into play for this] This also presumes you are not generating either IMD or harmonics in the receiving system before the tuner that fall into the weaker channel's bandwidth lowering its SNR. For co-channels, I'd have to look it up.

Quote:
or is this pretty much factored into the results page
It is not factored in at all.

Quote:
anytime there is a C you are going to get knocked off
No, you have to manage the co-and adjacent signal forecasts separately and manually.
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Last edited by ADTech; 3-Mar-2016 at 5:02 PM.
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Old 3-Mar-2016, 7:30 PM   #4
rabbit73
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The general rule for co-channel interference is that your desired signal must be at least 15.5 dB stronger than any other signal on the same channel.

ATSC Recommended Practice:
Receiver Performance Guidelines

Document A/74:2010, 7 April 2010
RECEIVER PERFORMANCE GUIDELINES

5.4.1 Co-Channel Rejection

Quote:
The receiver should meet or exceed the following thresholds for rejection of co-channel interference at the following desired signal levels (Table 5.1).


The general rule for adjacent channel interference is that your desired signal must not be any weaker than 33 dB as compared to the signals on either side of it.

5.4.2 Adjacent Channel Rejection

Quote:
The receiver should meet or exceed the thresholds given in Table 5.2 for rejection of first adjacent-channel interference at the desired signal levels shown above the columns therein.


These rules assume that the signals are in the same direction, they don't take antenna pattern into consideration, and there aren't any spurious signals created by IMD (Intermodulation Distortion) from strong signal overload (as ADTech said).
Quote:
or is this pretty much factored into the results page and anytime there is a C you are going to get knocked off
It is only factored in to the extent that you get an A or C warning to the left of a callsign in the report. You must make the calculation.
Attached Images
File Type: jpg Co-Channel Rejection Thresholds2.JPG (42.3 KB, 586 views)
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Last edited by rabbit73; 3-Mar-2016 at 8:29 PM.
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Old 5-Mar-2016, 9:34 PM   #5
ZippyTheChicken
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excellent and thank you especially rabbit for digging that up i know it takes a bit of time to do that...

on a couple channels I would like i am very close to that 15.5 but hopefully enough that i can at least try to get signals from 2 directions and it won't knock off my philly fox station.. if not i might actually pickup another fox from baltimore and that one comes with a 24/7 weather station and Sports Network..

did a little testing today .. i might end up getting one of those 8bay uhf antennas that you can point each side in different directions.. one side would be at 31magnetic for philly and the other side at 275 magnetic for baltimore.

Right now i have a ClearStream 4v and get channel 12 from philly about 55miles away.. i get 3bars when i pair it with a ChannelMaster 7777 (yeah i can hear ya)

a db8e would be wonderful i guess

but maybe my budget can only afford a
Xtreme Signal HDB8X-NI
http://www.amazon.com/Xtreme-Signal-.../dp/B00CXQO00K
or a
Steller labs Dual Quad Bay Outdoor
http://www.amazon.com/Dual-Outdoor-B.../dp/B00DHHMOUW

I really like Stellar labs db rating on that thing hahahaha
hey who knows though heh

but if i can find a deal and they come around once in a while for $50 i might give it a go with one of those three.. and my 7777

since you guys have been very nice with the info
here is my report
http://www.tvfool.com/?option=com_wr...f1f0bef57dd8d9

today I verified that I get

Pointed at about 31degMag
fox29philly at 5bars
WHYY12 at 3bars
WBOC marginal lock but ok once locked

Pointed at about 275degMag
WMAR i get 5 bars
WUTB at one bar - grit tv
WBFF 3 bars with weather station & ASN


I have a snow storm coming in from the west about 3-5hrs out
during testing sun was shining and nice
might be getting a slight bounce off that snow storm.

thanks again guys
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