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Old 21-May-2016, 8:07 PM   #8
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,518
Quote:
Originally Posted by bobsgarage
Thanks for posting that for me. It's a shame there is no one managing the forums.

Yes, Stellar Labs 30-2476 Hi VHF. To be honest, I stumbled upon it after searching for a VHF only antenna. Some reviews said it was well made and I have to agree. Just a foot note, I ran across some tech article, some guy was buying them and experimenting with making one antenna out of two.

Just an update, the signal increased to 88% to Chicago and 84% when rotated to Milwaukee after lifting the antenna mast 5 more feet. VHF was good also.

Truthfully though, I thought the signals would be higher, but it seems to be good enough for now.

Also, I see a lot said about signal strength, but others mention signal quality. My TV doesn't have a quality meter, how can I check that?

I wanted to set up the rotator with a compass, which I tried but I don't know how accurate I was. Although it had some sights on it, I couldn't be too sure, but it appears 355 degrees gets me Milwaukee and 166 degrees gets Chicago well. A few degrees either way seems to be just as good. Pretty happy about that.

Thanks, Bob
Quote:
Originally Posted by bobsgarage
Thanks for posting that for me. It's a shame there is no one managing the forums.
Yes, the forum is a valuable resource, and is getting harder to use; new members are not being approved.

I am also worried about the site. We really need tvfool reports to be able to help people with reception problems; there is no good substitute.

I wonder if anyone knows why new members are not being accepted?

What happened to GroundUrMast; is he still alive?

What happened to Andy Lee; is he still alive?


I find it hard to believe that Andy would let his "baby" die a slow death from neglect.

Quote:
Just an update, the signal increased to 88% to Chicago and 84% when rotated to Milwaukee after lifting the antenna mast 5 more feet. VHF was good also.

Truthfully though, I thought the signals would be higher, but it seems to be good enough for now.
As long as the reception doesn't have any problems, don't worry about it. It's pretty much either you get it or you don't because of the "Digital Cliff." OTA signals are constantly changing in strength; you need a Fade Margin of about 10 dB to allow for drops in signal strength. You can test to see how much margin to dropout you have by inserting a variable attenuator in the coax line to the tuner and increasing attenuation. The technique is described in the link in my signature.

If you don't have a variable attenuator, you can use a few splitters as attenuators. A 2-way for 3.5 dB, and a 4-way for 7 dB.



Quote:
Also, I see a lot said about signal strength, but others mention signal quality. My TV doesn't have a quality meter, how can I check that?
That's a good question.

Signal quality, as defined by SNR and uncorrected errors, is at least as important as signal strength, if not more so. It is possible to have a strong signal that is difficult to receive if it has poor quality. One example is when a strong VHF signal has a high noise level from electrical interference that reduces the SNR to below the 15 dB minimum required. This was so bad in Chicago that WBBM CBS had to move from real channel 2 to channel 12. The noise level on VHF-Low is worse than on VHF-High. If the current auction forces broadcasters to use VHF-Low, it will be necessary for them to increase their power for satisfactory reception.

When aiming an antenna, I first adjust for max signal strength. Then I monitor signal quality for final adjustment. Max signal quality isn't always at the same azimuth as max signal strength, usually because of multipath reflections that create a non-uniform field.

My Sony KDL22L5000 has a Diagnostics Screen that gives signal strength, SNR, and uncorrected errors.

Bad signal with picture freeze, SNR below 15 dB, and errors:



Good signal:



It is also possible to check signal quality with converter boxes or external tuners that have two signal bars, one for signal quality (the inverse of uncorrected errors), and one for signal strength, like the Apex DT502 or Centronics ZAT502HD:



You can also use the Diagnostics Screen of the TiVo Roamio that gives signal strength, SNR, and the inverse of uncorrected errors; see attachment 1.

or the SiliconDust HDHR that shows signal strength, signal quality (SNR), and symbol quality (inverse of uncorrected errors):



That image is from a thread by GroundUrMast:

An Alternative to Rotators and Antenna Combiners
http://forum.tvfool.com/showthread.php?t=820

You said you had a Zenith converter box. I connected a Zenith and an Apex to a splitter and used both to aim an antenna. My tests seem to indicate that the Zenith signal bar is a combination of signal strength AND signal quality. The Apex, with a separate signal quality bar gives better resolution of changes in signal quality. See attachment 2.
Attached Images
File Type: jpg TivoDiagScr (2).jpg (186.8 KB, 412 views)
File Type: jpg Zenith SigMon_2.jpg (95.4 KB, 421 views)
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Last edited by rabbit73; 22-May-2016 at 3:02 AM.
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