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Old 23-Aug-2012, 3:12 AM   #9
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,747
Hello RoyTV:

Hunting for channels that were missed during a tuner scan can be very frustrating. If a tuner is able to pick up a channel, then many TVs give a lot of useful information that can help with antenna aim, location, and comparisons. My SONY KDL22L5000 gives signal strength, errors, and SNR.

But, when the tuner is not able to pick up a channel, none of that information is available; you don't even know if the transmitter is active.

The terrain between you and your missing stations is very challenging; for example KING-DT:



On the other forum, member retiredengineer asked me how to hunt for and measure missing channels. I told him that it is possible to find and measure channels that were missed during a scan, but they might not be picked up by the tuner because of poor signal quality (high BER) from multipath reflections or low SNR. He said that for now it would be sufficient to find them and measure their strength with the emphasis on the pilot signal at the low end of the channel.

A spectrum analyzer would be an ideal tool, but they are expensive and hard to borrow. I developed a measurement technique that uses a signal level meter (SLM) and the details are in four posts on the other forum; the last post is here:
http://www.avsforum.com/t/381623/the...#post_22105317 #14972

The meters that I used were a Sadelco 719E that I bought when I retired in 1988, and a DisplayMax 800 that my wife gave to me when digital TV came along. The 719E was designed for analog signals, but it is useful for digital signals.



I used CH42 as an example of a missing channel:



The signal measures -14.5 dBmV, which is equivalent to -63.3 dBm. Most tuners can decode a signal stronger than -84 dBm, but this signal could not be decoded because of poor signal quality.

I tried another location for the antenna with this result that could be decoded by the tuner:



Notice that the top of the signal is flatter, and the pilot is shown at the low end of the channel.

A used DisplayMax 800 costs about as much as a 32-inch flat panel TV. Look for a meter in good condition that can be returned. Don't bid any more than you can afford to lose if it can't be returned. A used meter, like the 719D seen below, can be found for $50. Make sure that it can do VHF and UHF; a meter marked VS does VHF and superband, but not UHF. You don't need both meters as I used; either one would help you.



I am retired, so I understand your need to keep expenses down. I think you are going to need to hunt for your missing channels using a method like I have described. You will probably need a high gain VHF-high antenna for real channels 9 and 11 as suggested earlier.

A suggestion: When you use virtual channel numbers they should be in decimal form like 22.1 and 9.1 to keep them from being confused with real channel numbers. The TV displays virtual numbers, but when you are hunting for channels or selecting an antenna you should use the real channel numbers like 11 and 9.

Good luck with your hunting and let us know how you do.

Best regards,
rabbit
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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Last edited by rabbit73; 24-Aug-2012 at 12:54 AM.
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