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This is the second night in a row that KCRW (RF33) has been off the air.
As per usual with coverage problems, facts blow up fanciful theories and leave the situation as muddled as ever.
The high VHF signals (channels 8, 10 and 12) were the same which destroys any overload from FM theory.
Then, channel 2 got worse while channel 6 was essentially unchanged. Channel 2 is actually transmitted on channel 24 while channel 6 is on channel 25. The two are literally transmitted from the same antenna with (it is said) the same power. But, at my house in Aloha, channel 2 is consistently 3dB or 4dB louder than channel 6 on an outside antenna and a dB or two smaller on an inside antenna. Go figure.
If it weren’t for the dratted Covid, I would loan you a ChannelMaster 600 MHz LTE filter to see if you are getting whacked that way. Since you say that your other (preamplified) antenna works well, that’s probably not the problem either. So it’s not worth the ~$35 cost for you to make the experiment.
If you want to experiment and it’s easy, you might trade the locations of the two antennas just to see if the problem travels with the antenna or whether the location is pretty much the issue.
Which stations got better?
Which one got worse?
Just pondering if the preamp is overloaded. Does it have an FM trap? Overloading because of FM signals can clobber channels 8, 10, 11 and 12. Overloading on DTV or LTE signals can get others.
Sorry about that.
On all the sets I’ve looked at, the signal level function is more of a S/N* meter rather than a signal amplitude meter. KNMT may be just the signal with the lowest multipath.
A preamp may help just a bit. ATSC threshold with a clean signal is when the signal exceeds kTB noise (-106dBm) plus ATSC’s required S/N (15.5 dB) plus the set’s noise figure. Most sets have a noise figure of about 5dB or 6dB. This means that, with that clean signal, they will come above threshold with a -85dBm or so signal. Sets have enough gain to overcome low signal amplitude but not when the signal crashes into the noise floor of the world. S/N is all that matters, not signal amplitude alone.
In situations where there is a long coax between the antenna and the set, the coax’s loss will move that threshold up 1dB for every dB of its loss. Preamps are mostly useful then to put at the antenna end of that coax to raise the signal’s amplitude enough that the coax’s loss doesn’t matter and the preamp’s noise figure dominates the situation. A preamp is also useful when the antenna’s signal is split to two or more sets, but is does the most good when it’s at the antenna.
Preamps typically have quite low noise figures. That’s why it may be helpful in your situation. If the set’s noise figure is, say 6dB, and the preamp’s is, say 1dB or 2dB, you will gain perhaps 4dB or 5dB S/N. You will, in effect improve a weak signal’s S/N enough to bring it above threshold or give it more margin above threshold.
All these numbers assume a clean signal. In real life, multipath tears up the signal and the receiver’s threshold increases as its equalizer works to fix the problems. There isn’t much known about how much the threshold is increased for a given amount of multipath.
Remember that once one has enough S/N that the signal has lots of margin (say 10dB to 15dB above threshold), more signal doesn’t help. In fact it sometimes causes problems.
* Signal to Noise ratio. Needs to be added to the Jargon File. Noise Figure could be added also.
What a difference a day makes! Today KOXI-CD is apparently up to full power (about 6 dB lower in amplitude than KPXG-LD) and the signal readily decodes. I see six subchannels 20.1 to 20.6.. 20.1 is a 720P, 16/9 format signal in Spanish. I did not watch long enough to get an ID. 20.2 to 20.6 are 480i, 4/3 format signals. I caught the ID of 20.4 as TimelessTV and from its logo 20.6 is apparently PeacockLX.
I decided that yesterday’s receiving problem was probably just an ordinary poor S/N. That is, the signal wasn’t 15 dB above the noise in the channel.
In principle, at least, KOXI-CD (RF20, Vir20) has returned to the air. From the RabbitEars’ Portland tuner data, it was on last night (11-27) but at such a low amplitude I missed it. I can barely see it on my spectrum analyzer using my low gain un-amplified outdoor antenna. Using my high gain antenna plus a preamplifier I make it to be 29 dB lower in amplitude than KPXG-LG on RF21. KPXG is co-sited with KOXI and rated at 15kW ERP. Over the air measurements are always of iffy accuracy, but 29 db below 15 kW is only about 20 Watts.
Even then, the signal from my high gain antenna measures as 15dB or more dB above receiver threshold. But, my receivers won’t decode KOXI’s signal. One of them says there’s an ATSC1 signal present but that it’s below threshold. This could be caused by either poor signal quality or the receivers objecting to such a large adjacent channel signal.
After almost two months of transmitting an ATSC1 carrier with no modulation, KPXG-LD RF21, Vir42 has finally added modulation to its signal. I see two virtual channels, 42-1 and 42-2. Both are religiously oriented.
KPXG-LD first appeared on RF21 on 12-20-19 at a low power level. It continued at that power until it left the air on 8-10-20. It returned to the air at a higher power but without modulated (i.e.beyond the transmitter’s spectrum spreading code) on 9-17-20. Yesterday it added modulation to its signal.
There apparently will be a noticeable delay before the real availability of ATSC3 receivers. The consumer electronics industry just this week adopted what features an ATSC3 receiver must have. This is intended for the 2021 model year sets. No one is in much of a hurry.
I can find KGW’s application for rule making but I’m unable to find any action the FCC has taken. RabbitEars.info shows the application as Pending. Is it there and I didn’t find it?
DTV transmitters inherently dump a fair amount of splatter (interference) into their adjacent channels. If the difference in amplitude gets too large the splatter from the bigger signal will cause interference problems to the lower power station by driving the S/N below threshold.
DTV stations are allowed by the FCC to operate on adjacent channels as long as the lower adjacent channel is 28dB or less greater in amplitude and/or the upper adjacent channel is 26dB or less greater. (CFR 47 73.623(c)2) I have never heard an explanation for the two dB difference
I receive the KJYY (RF 26) signal well above threshold at my house. I hate to be picky, but three of the four virtual channels on that carrier produce a black picture. The fourth, ACE TV, just makes a lumpy blue bar across the bottom. I get the same results on three different sets.
Have I some oddball problem or is this what everyone else is seeing?
Two new ATSC 1.0 DTV transmitters turned on yesterday.
The first is on RF ch. 21. This is probably KPXG-LD, but it has no modulation yet.
The second is on RF ch. 23. This is apparently KGWZ-LD but my TV IDs it as KGW ch. 8.10.
As a follow-up, KOXO (RF ch. 15), after being on the air with an ATSC 3.0 signal for 41 days went dark seven days ago on 9/8/20. I delayed reporting, thinking it might be just one of life’s little bumps.
I observed KRCW’s power fall an average of 1.2 dB as it changed over to ATSC3 and wondered if it was real or my SA’s reaction to the new signal. On the other hand, KPDX’s power also declined an average of 1.3 dB as it changed over so I am still left unsure.
KPDX’s transmitter is just meeting the FCC’s emissions mask close to the channel edge. KRCW’s signal is buried between to adjacent channel signals so I can’t measure how it’s doing off air.
Don’t forget what is probably KOXO’s ATSC3 signal on RF channel 15. It turned on a day after KPDX and KRCW. At turn on, it was rolled off 20 dB at the edge of what should have been a flat spectrum. That’s been fixed but it’s still emitting adjacent channel emissions well above the FCC’s mask.
One can determine some of the parameters of a given ATSC3 signal from spectrum measurements. Unfortunately I have no means to actually decode the signal to see what is being transmitted.
A third ATSC3.0 DTV signal has appeared on RF ch.15. Sometime in the last 24 hours.