Changes in DFW's LPTV market

[JHBrandt]

KPFW/18 and KJJM/34 have been off the air for a couple of days. This may be jumping the gun, but both programs on KPFW were on KWDA also, and KJJM was down to infomercials and color bars, so nobody's missing anything.

By the way I picked up KZFW's audio on 87.7 FM last Sunday. Are they broadcasting only an audio carrier now?

[fredcantu]

By the way I picked up KZFW's audio on 87.7 FM last Sunday. Are they broadcasting only an audio carrier now?

IIRC-- TV stations are required to transmit some kind of video, even if they're just interested in people tuning in the audio.

[tested]

KPFW/18 and KJJM/34 have been off the air for a couple of days. This may be jumping the gun, but both programs on KPFW were on KWDA also, and KJJM was down to infomercials and color bars, so nobody's missing anything.

By the way I picked up KZFW's audio on 87.7 FM last Sunday. Are they broadcasting only an audio carrier now?

All I know is I don't get a picture or audio on that channel with my TV, but I do get audio on 87.7. 

[JHBrandt]

KPFW/18 and KJJM/34 have been off the air for a couple of days. This may be jumping the gun, but both programs on KPFW were on KWDA also, and KJJM was down to infomercials and color bars, so nobody's missing anything.

Sure enough, I did jump the gun. Both are back on the air tonight.

KJJM has dropped the color bars on 34.4 but added a green screen on 34.1

[JHBrandt]

By the way I picked up KZFW's audio on 87.7 FM last Sunday. Are they broadcasting only an audio carrier now?

IIRC-- TV stations are required to transmit some kind of video, even if they're just interested in people tuning in the audio.

That's my understanding too - and I'm pretty sure the FCC doesn't license LPFM stations on 87.7 either. Methinks they're breaking the rules

[JHBrandt]

By the way I picked up KZFW's audio on 87.7 FM last Sunday. Are they broadcasting only an audio carrier now?

All I know is I don't get a picture or audio on that channel with my TV, but I do get audio on 87.7.

Interesting that the TV won't pick up the audio, since for RF channel 6 the audio carrier is 87.75 MHz.

It seems as TV tuners became digital and more complex, they became less able to deal with odd situations like this. Apparently your TV's tuner has to detect an analog video carrier - if not there, it won't tune the audio either. I bet if you tuned a vintage 1970's TV to channel 6, you'd hear the audio (but that's all).

[TexasTom]

Interesting that the TV won't pick up the audio, since for RF channel 6 the audio carrier is 87.75 MHz.

It seems as TV tuners became digital and more complex, they became less able to deal with odd situations like this. Apparently your TV's tuner has to detect an analog video carrier - if not there, it won't tune the audio either. I bet if you tuned a vintage 1970's TV to channel 6, you'd hear the audio (but that's all).

The vintage 1970s TV probably wouldn't pick up the audio, either.  In analog TVs, there were two ways to demodulate the audio.  One way would be to demodulate it directly from the downconverted audio carrier IF frequency of 41.25 MHz -- in this instance, you would be able to hear that 87.75 MHz audio in the absence of a video carrier.

However, it's cheaper to demodulate the video and audio together, which results in baseband video that includes a 4.5 MHz audio subcarrier, which is then demodulated to get the audio.  This is cheaper because it is easier to design and build the filters to separate the audio and video when working with an audio subcarrier at 4.5 MHz versus 41.25 MHz.  But if a video carrier is not present at the IF frequency of 45.75 MHz, then that baseband downconversion won't work and nothing will be present at 4.5 MHz for the audio circuitry to detect and demodulate.

[JHBrandt]

Now that you mention it, I do recall TV schematics back in the "olden" days having 4.5 MHz filters in the audio section. Logically when you demodulate the AM video it'll create an audio difference signal at 4.5 MHz, and that's what they must've used. But I'd forgotten all about that in the last decade or two

If you have one of those old radios that tuned TV-band audio, you can still use it on channel 6. And of course, most FM radios will tune to 87.7 MHz (which is close enough) even though it's outside the official FM band. But ironically, a real TV won't work!

Many modern TV tuners will show a "blue screen" instead of snow and mute the static if tuned to a vacant channel, and that's what I had in mind. BTW, I think this might explain KJJM's "green screen" on 34.1. Every so often, the green screen is interrupted briefly by snow. I think they may have something with an analog tuner in it (either an old DVD-R or an even older VCR) hooked up to the video inputs for 34.1, but with no disc or tape inserted, we see the "green screen" from the box's analog tuner. So whenever the tuner thinks it detects a signal in the noise, it sends a brief burst of snow to its video output. (I never hear any static, though.)

[JHBrandt]

KQFW has, for the second time, applied to displace to RF 24. They are actually licensed on RF 56 but AFAIK they're not broadcasting....

Their previous RF 24 application was rejected by the FCC, citing excessive interference with K25FW. But I didn't see any changes in this application. The interference report they filed looked exactly the same. It appears to meet FCC regulations, showing interference with only 0.4% of K25FW's potential viewers. But the FCC did their own analysis and came to a different conclusion last time.

BTW, a bit of trivia: D/FW now has 7 consecutive virtual channel numbers: 25 (K25FW), 26 (KODF), 27 (KDFI), 28 (KHPK), 29 (KMPX), 30 (KWDA), and 31 (K31GL). If this goes through, it will add 23 (KUVN) and presumably 24 (KQFW) for a total of 9 in a row. And then if KNAV goes online, that'd add 20 (KBOP), 21 (KTXA), and 22 (KNAV) for a total of 12 in a row! I wonder what the national record is?

Yesterday the FCC gave KQFW their CP for RF 24. (They never got on the air on RF 56 before out-of-core channels had to shut down.)

The first time the FCC claimed RF 24 would interfere too much with K25FW, as mentioned above, but they refiled essentially the same application and this time it went through

[tripinva]

The first time the FCC claimed RF 24 would interfere too much with K25FW, as mentioned above, but they refiled essentially the same application and this time it went through

First time they specified a stringent mask filter, this time a full service mask filter.

- Trip