Dallas LPTV stations getting weaker

[JHBrandt]

Let's start with KJJM. They've applied to move from channel 34 to 49 and lower their antenna 160 feet. Lowering their antenna will significantly reduce their coverage.

KSEX (don't get excited - it's just infomercials), currently a 100 kW analog station on channel 57, is out-of-core and needs to move. They've always intended to move to channel 20. In April they applied for a 10 kW digital license, which would've been about on par with their current analog signal. But last month they reapplied for a 5 kW license.

KNAV is currently a 150 kW analog station on channel 22. They want to go digital with a 15 kW signal on channel 29, which sounds reasonable - until you learn their antenna would be lowered from 348 meters (1160 feet) to 180 meters (600 feet).

KPFW is out-of-core and has applied to move to channel 33, reduce their power from 15 kW to 9 kW, and switch to a directional antenna that will reduce their coverage even further.

Finally, K31GL has also applied to move to channel 33 (obviously only one of KPFW and K31GL will get that channel) and increase their power from 8 kW to 15 kW. But they also want to lower their antenna from 330 meters (1100 feet) to 180 meters (in fact it'll share the antenna site with KNAV).

These changes will reduce signal strength and coverage for these stations. TVFool.com doesn't have the KPFW change in its database yet, but it's calculated the effects of the other changes at my home:

• KSEX would be reduced by 3.4 dB from their originally planned signal
• KJJM would be reduced by 6 dB
• K31GL would be reduced by a whopping 17.7 dB, despite increasing their power.
• KNAV is harder to compare directly, since it involves an A-to-D transition, but tvfool's noise margin estimates the effective signal strength would drop by 17.7 dB as well.

What's going on here? Are full-power stations having problems with adjacent channel interference and forcing the low-power stations to make these changes?

 

[JHBrandt]

Well, the FCC finally has their coverage maps for these new applications fixed. The coverage maps answer my question about KSEX.

KSEX has applied not only for less power, but also for a more directional signal with a partial null to the south. Clearly the concern is co-channel interference with KWBU, Waco's PBS affiliate.

Also, despite the much lower antenna, KNAV will have significantly broader coverage with their proposed digital signal than with their current analog signal. (The proposed digital signal will be weaker in my direction, but unlike their analog signal it'd cover Fort Worth.)

Still, why are KJJM and K31GL reducing their coverage? Why are KNAV and K31GL settling for the coverage provided by KODF's low antenna instead of going with K31GL's current high antenna? ???

 

[Bob E. Nelson]

[...details about low power stations elided for brevity...]

Are full-power stations having problems with adjacent channel interference and forcing the low-power stations to make these changes?

I'm not an engineer (and don't even play one on TV) so take this with an enormous grain of salt.

I was under the impression that all of the ``old rules'' concerning interference with adjacent channels were rendered moot with digital. For instance, in D/FW, we now have a lineup of KXAS(5/RF-41), KPXD(68/RF-41) and KDTN(2/RF-43). These are all full-power stations with transmission facilities located in close proximity. There's also KDFW(4/RF-35) and KDFI(27/RF-36).

So, those in the know -- under what conditions might a low power station cause interference to a full-fledged facility on an adjacent channel?

 

[Markxxx]

Digital channels can exist on co-channels, but only if they are at the same antenna farm or the transmitters within a certain distance of each other. Otherwise they can interfere with each other.

 

[dhett]

Digital channels can exist on co-channels, but only if they are at the same antenna farm or the transmitters within a certain distance of each other. Otherwise they can interfere with each other.

I think you mean adjacent channels. Co-channel rules are pretty much the same in the digital world ;-)

Adjacent channels are permissible for full-power stations as long as they're within 20 km of each other, or greater than 88 km, I believe. The 20 km permissible radius is because full-power stations will have sufficient relative signal strength to overcome interference issues. Full-power and low-power adjacents are always OK, because the LPTV station is never allowed to interfere with a full-service station anyway, and must accept any and all interference from all full-service stations.

 

[JHBrandt]

Thanks for the info, folks. I fear I've been mixing up two issues.

One is the requested frequency changes. Those don't really bother me; I'm just curious why, for instance, KJJM would rather be next to KSTR than KDFW (in frequency, if not geographically).

The other issue is the reduced antenna heights. This is the more serious issue, since it means some folks will lose these stations, but it may just be an economic issue. TexasTom has indicated that the folks who own the towers charge more rent for higher spots, which makes sense.

KJJM still puzzles me, though. Right now KJJM and KATA (both owned by Mako) share the same tower location, and KATA hasn't applied to move to a lower spot. Yet KJJM has! Wouldn't it cost more to rent two spots on the tower instead of sharing just one?

Clearly, there's still a lot I don't understand about this business.

 

[KERCAlum]

[...details about low power stations elided for brevity...]

Are full-power stations having problems with adjacent channel interference and forcing the low-power stations to make these changes?

I'm not an engineer (and don't even play one on TV) so take this with an enormous grain of salt.

I was under the impression that all of the ``old rules'' concerning interference with adjacent channels were rendered moot with digital. For instance, in D/FW, we now have a lineup of KXAS(5/RF-41), KPXD(68/RF-41) and KDTN(2/RF-43). These are all full-power stations with transmission facilities located in close proximity. There's also KDFW(4/RF-35) and KDFI(27/RF-36).

So, those in the know -- under what conditions might a low power station cause interference to a full-fledged facility on an adjacent channel?

I think KPXD is actually on RF channel 42.

 

[X-Man]

I'm having trouble picking up KATA Ch. 50 and their sub channels. I had no problem getting them before, has anyone had problems getting Ch. 50?

 

[JHBrandt]

I'm having trouble picking up KATA Ch. 50 and their sub channels. I had no problem getting them before, has anyone had problems getting Ch. 50?

I haven't had any trouble, but I wasn't up early this AM. They may have had some temporary problems that are now resolved.

 

[AlanB]

I am not able to pick them up in Plano currently (outdoor antenna on roof, home on Plano/Allen border).

I am not surprised by this because I am also not able to pick up any other digitial low power: 3, 31, 34, 50, or 61.

 

[JHBrandt]

I am not able to pick them up in Plano currently (outdoor antenna on roof, home on Plano/Allen border).

I am not surprised by this because I am also not able to pick up any other digitial low power: 3, 31, 34, 50, or 61.

Channel 3 gives almost everyone fits. Not sure what the problem might be on 50 and 61, but Tripinva mentioned something (on why KTXA-DT wants to move to channel 29 vs. back to 21) that may explain problems receiving 31 and 34:

Interference to one side is worse than the other. If I'm recalling correctly, a lower channel is interfered with more than an upper channel, so KWBU [channel 20 in Waco] causes interference to KTVT [moving back to channel 19] (which CBS can then choose to accept) but DT-21 would cause interference to KWBU (which would require an agreement with KWBU).

- Trip

So it would seem channels 31 and 34 are likely to have problems with interference from channels 32 (KDAF) and 35 (KDFW), respectively.

That could also explain why they want to move, respectively, to channels 33 and 49: They'd no longer have full-power stations immediately above their own frequencies. Given the weaker signals we'd be getting from their proposed new, lower antennas, anything they can do to mitigate reception problems makes sense.

 

[tripinva]

No, that is at a distance. If KWBU were co-located with KTXA and KTVT, 21 would be perfectly usable.

If they're at the same tower site, those interference issues should not be issues.

- Trip

 

[JHBrandt]

No, that is at a distance. If KWBU were co-located with KTXA and KTVT, 21 would be perfectly usable.

If they're at the same tower site, those interference issues should not be issues.

- Trip

That seems hard to believe. A 1000 kW station beats a colocated 15 kW station by about 18 dB. If adjacent-channel interference is impossible with 18 dB difference in signal strength, it seems unlikely there's anyplace within KWBU's service area where a hypothetical KTXA on channel 21 would cause a problem either.

Just as a sanity check, I pulled up tvfool.com and entered zip code 76645 (Hillsboro), which is near the northern extreme of KWBU's service area. If there's a place where a KTXA-21 would cause problems for KWBU, Hillsboro's gotta be it.

According to tvfool, KTXA (on channel 19) is indeed stronger, but only by 13 dB. (Add 1 more dB, for a total of 14, if KTXA were at a full 1000 kW.) But KDAF on 32 beats K31GL by about 20 dB at my own zip code.

True, I do receive K31GL, so even at a 20 dB difference, ACI apparently isn't a problem for me. But it must be a problem for some folks or the FCC wouldn't have rules to avoid it (e.g., in the KTXA vs. KWBU situation).

I could of course be completely wrong about all this (I frequently am), but I thought the reason the FCC doesn't have rules to cover the KDAF/K31GL situation wasn't that ACI was impossible, but simply that LPTV is a secondary service and has to live with any interference it gets from full-power stations. Doesn't the FCC require two colocated full-power stations on adjacent channels to be within a reasonable factor of each other's power level?

 

[tripinva]

There's no hard rule about power levels, the FCC just has a certain interference level that cannot be exceeded (0.5%). And you're correct--the low-powered stations simply have to accept any interference from full-powered signals.

Believe it or not, whatever you choose, but if a station is predicted by the FCC's software to cause more than 0.5% interfere, it's disallowed without an interference agreement with the other station, and a case like KWBU and DT-21 would cause predicted interference. I've tried to make the Fortran 77 (seriously) software operate on my system with a variety of operating systems and configurations without success. I would really like to be able to run interference analyses so I could give concrete answers.

- Trip