str1der,
Hope Doc doesn't mind If I butt in here ... In a explanation of ATSC receiver design in the following document:
http://www.atscforum.org/doc/FieldTestReport.pdf
There is a mention of how "signal quality meters" can be implemented in receivers. This is an excerpt of what it says in 1st paragraph of page 3, and, from what I've seen, I highly suspect this is exactly how the "signal meters" on most models of DTV receivers are implemented - I've put the part we are interested here in all caps :
"The MPEG data sync is reinserted at the receiver output for subsequent processing in the receiver's MPEG transport decoder. The one-segment long binary frame sync not only provides pseudo-random number sequences(PN) for data frame synchronization, but can also be used as a training signal for the receiver's equalizer AND AS A MEANS TO MEASURE RECEIVED SIGNAL QUALITY."
In other words, even though it might say so right on the screen or in manual, it's not really a "signal strenth" meter. It doesn't measure signal strength. Except for rare exception such as the SNR and AGC readings on a Hauppage WINTV-D tuner card, which does measure signal over noise, right from the actual RF signal itself, it is a "Signal Quality" meter, and does not even look at the actual RF signal itself, instead, it looks at at the datastream, and at things such as bit rate errors that are occuring in the datastream, and basically, how "clean" the datastream looks to the decoder.
For this reason, a fairly weak signal, just a bit over the threshold of signal over noise needed for good DTV reception(Which is theoretically 15.3db of signal over noise) can produce a "100" reading, just as a much stronger signal might -- Although, that weaker signal is still actually more susceptable to dropouts(and fluctuating meter readings) from interference and Multipath issues than would be the case if an actual, strong signal was involved.
This is not to say, that you don't have a "strong signal" from WKRC-DT, you might. Unless your dealing with a quite weak signal that actually is just a bit under or over the threshold of signal over noise needed for good DTV reception, that meter is probably going to tell you pretty much nothing about signal strength. But it can tell you about "signal quality", and what is "good enough". It's also the case that an actual strong signal, with perfect reception still might not give you a "100 reading".
For the most part, getting good DTV reception is all about getting enough Signal over noise,(and that noise could be anything, normal "noise", noise from various interference issues/receiver desense/selectivity issues/etc), and in some occasions is about correcting for multipath. Normally, the more signal available, the easier it is for the equalizer in your receiver to correct for multipath problems, but there can be exceptions.
Of course too, there are situations when there is TOO much signal, more than the receiver can handle, which can also cause the meter to fluctuate and dropouts to occur. It might not even be the signal you are trying to receive that could cause the front end of your tuner to overload, it might even be a strong, nearby signal on a different frequency alltoghether -- This can cause your tuner to desensitize.
Receiver selectivity issues can also be an issue, for example, when a strong signal is on a channel right next to a weak signal you're trying to receive(which shouldn't be a problem for WKRC-DT), your receiver may not be selective enough to see the weak signal. I had also heard somewhere that a station 7 channels away can cause diffiuclties with this, although I've never seen it.
Generally speaking, it is probably most common that if the desired signal is fairly weak, then Multipath issues or almost any sort of interference issue or a little bit of "increased noise" can cause the meter to fluctuate, and dropouts to occur as you seem to be experiencing. Of course, however, given your results from the other stations, I wouldn't at all be surprised if a combination of issues which we've been discussing may be involved.
Clear as mud? I hope it makes some sense -- I do know that I wish our receiver's had better RF signal diagnostic tools to show us really what is going on, something that is going to even be more of a necessity when the analogs shut off.
