View Full Version : Why is ATSC on VHF so damn finicky?


benman94
10-31-2017, 11:50 AM
Why is reception of ATSC on VHF, especially low-VHF, such an enormous pain in the ass compared to ATSC on UHF? In the analog days, my grandparents, who live in something of a fringe area, had a hell of a time picking up some of the NTSC UHF stations. Now with ASTC, the situation seems to be reversed, with any station on UHF coming in just fine and the handful of VHF stations in the Detroit and Flint/MBS markets being nearly impossible to receive.

More importantly, why the hell would the FCC approve a standard that doesn't work very well on VHF? In a place like Michigan, VHF stations were a must in getting adequate coverage of our geographically large markets.

Take for instance the upper lower peninsula and eastern upper peninsula of Michigan. Traverse City, Cadillac, Sault Ste. Marie, St. Ignace, Cheboygan, and Petoskey all rely on Traverse City stations (with full power translators between the Soo and the Straits filling in the gaps). Providing a quality signal to that vast area was feasible with VHF, it's near impossible to do with UHF. The local stations have resorted to sharing sub-channels to try and make up for the inadequate coverage. Still, if I lived in St. Ignace, I'd be pissed that FOX is only available in standard def on a subchannel of another station...

Jeffhs
10-31-2017, 01:11 PM
Why is reception of ATSC on VHF, especially low-VHF, such an enormous pain in the ass compared to ATSC on UHF? In the analog days, my grandparents, who live in something of a fringe area, had a hell of a time picking up some of the NTSC UHF stations. Now with ASTC, the situation seems to be reversed, with any station on UHF coming in just fine and the handful of VHF stations in the Detroit and Flint/MBS markets being nearly impossible to receive.

More importantly, why the hell would the FCC approve a standard that doesn't work very well on VHF? In a place like Michigan, VHF stations were a must in getting adequate coverage of our geographically large markets.

Take for instance the upper lower peninsula and eastern upper peninsula of Michigan. Traverse City, Cadillac, Sault Ste. Marie, St. Ignace, Cheboygan, and Petoskey all rely on Traverse City stations (with full power translators between the Soo and the Straits filling in the gaps). Providing a quality signal to that vast area was feasible with VHF, it's near impossible to do with UHF. The local stations have resorted to sharing sub-channels to try and make up for the inadequate coverage. Still, if I lived in St. Ignace, I'd be pissed that FOX is only available in standard def on a subchannel of another station...

Ben, I live in a semi-fringe area 30+ miles from all seven Cleveland television stations' towers, and do not receive two of them OTA. The problem is that the two stations I cannot get are on VHF DTV channels, while the others, every one of them, are on UHF DTV assignments. The only way anyone in this area can get channels 8 and 19 (FOX and CBS from Cleveland) is to have cable, satellite or a streaming video player such as Roku. I am using a Roku player and now get reception from every Cleveland TV station, including the two I do not receive OTA. I will probably use this system indefinitely, doing away with OTA television antennas altogether. I no longer use the cable connection, but I must still have a cable account so the Spectrum (formerly Time Warner Cable) TV application used with my Roku will receive local TV channels.

Low-power or full-power translators would solve, once and for all, the reception problems channels 8 and 19 (on VHF DTV channels 8 and ten, respectively) have in the area east of Cleveland along the south shore of Lake Erie, where I live, but the stations' owners flatly refuse to install such translators, probably for financial reasons. (Channel 8 did have a translator on channel 31 which it installed shortly after the start of the DTV transition, but it has since been deactivated.) The transmitter for one of Cleveland's UHF stations, along with its RF spectrum, were sold recently, the plan being to eventually put the station in question on a subchannel of CBS channel 19. I don't know if this has been done yet, as I no longer have cable (Spectrum cable in my area has been 100 percent digital since the third of this month) and the "MyTV" subchannel showing on the channel guide for my Roku player only receives a channel it refers to as "CLE 43".

BTW, if I could no longer receive FOX channel 8 in my area it would be no loss whatsoever to me, as I don't watch the OTA main channel. However, I do watch the Antenna TV subchannel on channel 8.2, although it irks me that the subchannel carries endless (or so it seems) strings of commercials promoting channel 8, as I do not care beans for that channel ever since FOX Broadcasting bought it out and switched it from CBS to FOX some time in the '90s. CBS was moved to a UHF station (channel 19) which, despite their 3.7-megawatt NTSC (now 9.5 kW ATSC) signal, does not reach much of the greater Cleveland area OTA, particularly the region east of the city along the lakeshore.

When TV was converted to ATSC from NTSC, the FCC should have, IMO, outlawed the use of VHF channels for DTV and reassigned the entire VHF TV band to some other service such as police, fire, etc. that really needs the spectrum space.

Sheeesh!

Ed in Tx
10-31-2017, 02:36 PM
If they transmitted near the same power on VHF as allowed on UHF there would probably be no problem other than co-channel interference from distant stations.

We have Ch 8 WFAA here on RF 8, and KFWD 52 on RF 9. WFAA is the ABC affiliate, been on the air here since 1950. They transmit an ERP of 37.9 kW. At a distance of about 27 miles I receive the VHFs just as strong, 95-100% signal quality as the UHFs. I am using a 30+ year old RadioShack (Antenna Craft) TV antenna that has good VHF gain, unlike a lot of the newer antennas that all but ignore VHF. The The local Fox affiliate, KDFW 4 transmits on RF 35 with an ERP of 153 kW. The differences in power allowed may well have something to do with the reception issues some people have. Then there are the so-called "digital" antennas that have no or very little reception of VHF.

Anyway they are supposed to move more stations down to VHF with the repacking. We have at least one here, KHPK-LD 28 that has moved to RF 10.

I do know that for some odd reason Dish network is suddenly promoting OTA TV by offering to remove the local channels from the Dish subscription with a $10 a mo savings, and will even send a technician out and install a new TV antenna, FREE! I have no idea why or what they are up to but they must think there's a good future for OTA TV, unlike in 2009 when there was a sudden "spectrum shortage" and some were talking about OTA just going away because the RF spectrum was too valuable to give away.

benman94
10-31-2017, 02:53 PM
My grandparents are using a Winegard 7698P which ought to have decent gain in the H-VHF region. We don't have any L-VHF stations in south-east Michigan anymore...

benman94
10-31-2017, 03:06 PM
Here's a TV fool report for their location:

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d00134b9f3ba862

Some of the Detroit stations seem to have gone missing from the TVFool database, but my point can still be made. WJRT blinks in and out all the time, WILX, WJBK, and CBET, which came in just fine in the analog era, haven't been picked up since the analog shutoff.

jr_tech
10-31-2017, 05:31 PM
A number of interesting articles here by Charles Rhodes, who I believe participated in the early ATSC standards work. A number of ATSC "pitfalls" are analyzed here:

http://www.tvtechnology.com/author/charles-w-rhodes/2/article

jr

centralradio
10-31-2017, 05:48 PM
Sorry to be negative. Dont get me started on DTV .LOL .Because. its a failed format.I said this before that I used too get all channels the analog way and some came in just with the antenna lugs.New I dont receive crap with this crappy new system.VHF or UHF.Its a pile of crap that was unloaded too sell off the TV channel bandwidth to the telecom people and other wireless companies. .Thanks to the MSM for the brainwashing the public saying its better then regular TV.Fake news BS..

End of my rant.

jr_tech
10-31-2017, 08:32 PM
Sorry to be negative. Dont get me started on DTV .LOL .Because. its a failed format.I said this before that I used too get all channels the analog way and some came in just with the antenna lugs.New I dont receive crap with this crappy new system.VHF or UHF.Its a pile of crap that was unloaded too sell off the TV channel bandwidth to the telecom people and other wireless companies. .Thanks to the MSM for the brainwashing the public saying its better then regular TV.Fake news BS..

End of my rant.

How far away are the local transmitters anyway? Have you run a "tv fool" analysis?

http://www.tvfool.com/?option=com_wrapper&Itemid=29

When the going gets tough, the tough get BIGGER ANTENNAS :D

jr

Ed in Tx
10-31-2017, 10:07 PM
Sorry to be negative. Dont get me started on DTV .LOL .Because. its a failed format...
That's too bad you have such bad results. It's 100% all good here. No airplane fading, no static noise slowly crawling up the picture from noisy power lines and other sources, no ghosting from multipath. Don't miss any of that. With a good antenna and tuner DTV works great. I even pull in a station from Oklahoma with the same picture quality as the locals and the OK station is about 100 miles away, on RF 12, KXII 12. Over 110 channels total. Much more efficient.

centralradio
10-31-2017, 10:24 PM
How far away are the local transmitters anyway? Have you run a "tv fool" analysis?

http://www.tvfool.com/?option=com_wrapper&Itemid=29

When the going gets tough, the tough get BIGGER ANTENNAS :D

jr

Thanks Jr. . The closes is about 15 miles and the others very from 20 to 35 miles since I'm in the center of the state.The VHF station is the 15 miles away station.

centralradio
10-31-2017, 10:32 PM
That's too bad you have such bad results. It's 100% all good here. No airplane fading, no static noise slowly crawling up the picture from noisy power lines and other sources, no ghosting from multipath. Don't miss any of that. With a good antenna and tuner DTV works great. I even pull in a station from Oklahoma with the same picture quality as the locals and the OK station is about 100 miles away, on RF 12, KXII 12. Over 110 channels total. Much more efficient.


Thanks Ed.Wow you are lucky.It is a bad experience and thats why I'm probably so negative over DTV. I see the benefits of it but its useless if I cant get even one channel.I probably have put up a 50 foot mast antenna to get anything here.If it was the other way around .I would cut the cable and go OTA.For $36 bucks on cable and thats all its worth to me.

old_tv_nut
11-01-2017, 12:06 AM
This issue has come up on video karma multiple times, and I will now give the same answers I have before:

1) The FCC planning factors did not take into account the level of environmental noise present in the VHF bands
2) at low VHF antennas are less efficient than they could be due to size limitations
2a) at low VHF antennas are less directional and more susceptible to ghosts
2c) the ATSC 1.0 system depends on the capability of the receiver equalizer to handle ghosts, especially moving ones. ATSC 3.0, like DVB, will have a specific ghost immunity (guard band) depending on the particular choice of coding parameters for a subchannel; the broadcaster will determine at what delay range / level of ghosting the viewer will lose signal
3) During the transition from analog, the power could not be boosted due to interference with analog co-channel stations. Power could be boosted now, but in order for the more tightly packed digital co-channels not to interfere with each other, they would all have to boost simultaneously. Practically impossible both technically and economically.
4) Near the Canadian and Mexican borders (read, the complete tiers of northern and southern states), power cannot be changed without international agreement.
5) Because of antenna size problems, cell phones must use UHF. The cell phone providers have much more money and clout than the broadcasters these days, (there are many more cell phone customers producing much more revenue than the advertising that supports OTA TV customers, plus many people today are completely unaware that you can get OTA, but they all want mobile phones) so the spectrum negotiations go in favor of mobile.
6) Maybe ATSC 3 allocations and repacking will be a chance to raise VHF power, and maybe broadcasters will use more robust, more highly coded, (but lower bit rates) for at least some of their services; or some combination of the above. It remains to be seen.

old_tv_nut
11-01-2017, 12:23 AM
I would also note that VHF over the horizon is subject to smeared ghosting (energy spread over a range of delays), which analog viewers can look through, but is hard for digital systems to handle. In Europe, digital broadcasting typically repeats national feeds on multiple transmitters and different RF channels, so everyone lives within the horizon of one. This does not fit the American broadcasting model of big stick transmission to large local markets. ATSC 3.0 has specific signal features that facilitate use of single frequency networks (SFNs) where a market can be covered out to its legal limit by use of multiple transmitters spread over the coverage area but on the same RF channel; but in this case, DXing may become more difficult for those outside the designated area, since each transmitter has only enough power to cover its locality.

DavGoodlin
11-01-2017, 09:59 AM
WPVI (WFIL 1947-72) has remained on low band channel 6, having to increase power (more than one FCC construction permit) in order to overcome undersized antennas and higher noise levels that pixellate DTV by causing bit error rates. Prior to the transition to ATSC, WPVI 6 reached NYC, all of NJ, DE, northern MD and well into the Poconos and Appalachians.

:sigh:The VHF band is so loaded with noise from switch-mode power supplies, both radiated from fluorescent and LED lamps with electronic ballasts and drivers. The harmonic content of the non-sinusoidal current drawn is pretty harsh, just move a portable FM radio close to one and see.

But with DTV that shows a poor signal level, the only way you can tell WHY is to check you location with a spectrum analyzer(I don't own one0 or a SDR-Sharp application that turns your laptop into one. Signal to Noise is more relevant with ATSC.

Any CFL/fluoescent lighting system with a real iron-core transformer, like old T12 lamps is a radio-friendly system. Don't upgrade to "energy star"

I agree it was a bad idea to keep VHF for DT yet dead spots still exist for UHF and VHF does seem to work there. I sent a Winegard HD7697 and CM7777 preamp with my neighbor to the hunting camp in Sullivan County and all he could get was two VHF channels from Binghampton, NY. and not any of the Wilkes-Barre Scranton area transmitters now both on VHF and UHF.

Prior to Wilkes Barre getting local UHF in 1952, all TV in NE PA came at least 50 miles from channel 12, (pre-transition) of WBNG, if at all.

bgadow
11-02-2017, 11:21 PM
I hadn't done a TV Fool report in a while; some interesting data to mine. Generally, the farthest distance I'm seeing are the Baltimore stations at 65.1 miles. I see a number of stations which have popped up in the deeper fringes that I didn't know about. Hmmm...could cause me to try Dx'ing some night.

I'm torn on ASTC. It means a lot more to watch than we used to have, and a whole lot clearer than my stepmother gets with her dish. But the pixelation-I know I'm asking a lot for some of these stations. I have a decent Winegard on the chimney with a booster and rotor. I'd have to add height to see much more of a difference & I don't think that's happening anytime soon.

philcophan
11-03-2017, 11:16 AM
DTV has it's pluses and minuses for certain. Here in Allentown, we have channel 2, KJWP, on the same stick as all the other channels, yet it craps out exactly at sunset... it may or may not return as the evening continues... go figure. Their power is minimal in my estimation... like 7.6kw or something like that. Channel 6, WPVI, has been absent since the transition but ABC, for what it's worth (nothing), is available on 16 from Scranton. My BIGGEST gripe is move the antenna a degree or two and you lose it... must be aimed dead nuts on!!! My antenna is the biggest whopper Antennacraft ever made, the Discovery D9000, I think is the model. I have another and am considering stacking two.
My buddy lives 14 miles south of me on a higher area and receives NY, Philly, Baltimore and sometimes Washington reliably... I'm thinking the higher and bigger the better... YMMV...

Jim

benman94
11-04-2017, 06:40 PM
Well I have a bit of egg to wipe off of my face... My grandparents called me, irate that their TV set was on the fritz again. I went over to look at the situation and discovered that only channel 28 WCMZ was coming in. I dragged along a small table top flatscreen, hooked it directly up to the antenna, and discovered that all of the Detroit stations, all of the Flint/MBS stations, and all but one of the Lansing stations were coming in fine.

To make a long story short, I had a newer section of quad shield RG-6 (that I had replaced when changing the antenna out) that had more than likely been bad from day one and was only getting progressively worse. The moral of the story? Don't trust that anything has been manufactured correctly. I replaced a 25 foot section of wire inside the house and now they have more stations than they had in the analog era.

They still can't get WILX, which they could get before the analog shutoff, but the new stations more than make up for it. I owe Wayne and the others involved in the DTV standards development a qualified apology; VHF performance with DTV is less than ideal, but it's a hell of a lot better than I thought it was. This does bring up another point though, trouble shooting with analog was much easier than it is with the DTV standard.

Anyway, I'm sorry guys. :o

old_tv_nut
11-04-2017, 07:33 PM
...This does bring up another point though, trouble shooting with analog was much easier than it is with the DTV standard.
...

For sure. One of the inventors of digital VSB liked to say that "analog is the window on the RF world." The problem is that you don't see varying quality as you adjust an antenna or repair a RF feed - the picture is only there or not there, and you have no idea how much head room you have above the threshold. Some manufacturers have attempted tuning aids that give some sort of signal quality indication, perhaps combining both signal strength and ghost energy, but this has been only modestly successful as far as I know.

Colly0410
11-04-2017, 09:00 PM
Here in England it's all UHF & has been for 40 odd years. Digital is rock solid now they've upped the power after analog closedown. My local transmitter (Waltham) used to be 250 Kw's TX'ing 5 channels in the analog days; it's now 50 Kw's for HD & public service (BBC, ITV, ch4 ch5 etc) SD Multiplex's; 25 Kw's for other commercial SD mux's; (Quest, CBS, 5 USA. Food network, Tru TV etc) 5 Kw's for local Nottinghamshire TV station, (with a very directional TX ant) 10.2 Kw's for a mux carrying Viva, Russia today, Al Jazeera etc; & 13.4 Kw's for a mux carrying 5*, More 4+1 & some pay channels. I get all these mux's with no breakup or dropouts with a UHF ant resting on top of the central heating water feed tank in the loft..

Electronic M
11-04-2017, 11:44 PM
The Zenith DTV converter boxes (IIRC 900/901) have a great signal strength indicator. I always like to use them for setting up an antennas and or DXing.

Jeffhs
11-06-2017, 10:28 PM
DTV may have issues as far as reception range, etc. is concerned, but the picture quality from DTV stations rivals NTSC many times over. I remember watching TV in 4:3 aspect ratio from the '60s until the DTV switch in 2009, and am nothing short of amazed at the improvement in picture quality (over NTSC) afforded by the ATSC standard. I have a 19" flat-screen HDTV that produces a picture sharper and clearer than I ever saw on NTSC analog. I watch my area's local channels via streaming video (Roku), and, again, am very impressed by the much sharper/clearer picture afforded by DTV; needless to say, I would never go back to NTSC analog, even if I could.

DTV's reception problems are here to stay in most areas, due to the lower ERP power (compared to NTSC) of local stations. The use of an outdoor TV antenna, cable, or satellite is almost mandatory to receive consistently good pictures from DTV stations. Of course, if you want to sidestep these issues, you can--by using devices such as Roku, Google TV, Apple TV and other streaming-video boxes. "Cord cutting" has become very popular in the US, much to the dismay of the cable companies. The number of cable subscriptions, in fact, has dropped dramatically since the introduction of streaming-video players such as the ever-popular Roku, et al., which is no doubt making the nation's cable operators very nervous as to their future survival in the 21st century. As cable TV subscription prices continue to rise (and the quality of said service declines at the same time in many cases), I see many cable operators scaling back their services or, at worst, going out of business entirely. Many people, myself included, do not like the idea of using a cable box ahead of their TV (to say nothing of paying outrageously high cable-TV bills), so I think the sales of OTA TV antennas and streaming-video devices will continue, as strong as or stronger than ever, as they have for some time.

Will streaming video eventually kill cable and satellite TV? :scratch2: Only time will tell, although, as I said, the increasing popularity of the Roku and other SV boxes means fewer subscribers, which is not good news by any means for pay-TV providers. Then again, perhaps cable and satellite TV may have seen better days, and it could be time to move on to better technologies.

Robert Grant
11-29-2017, 11:32 PM
When discussion of HDTV started getting serious in the early nineties, the plan was for all over-the-air television to migrate to UHF on channels 14-69, with VHF television to be discontinued.

Then. Congress got greedy. They added high-VHF (7-13) to the plan, in order to sell channels 63-69 to cellular interests. Quite quickly, they added low-VHF (2-6) as well, leaving channel 58 as the top channel. Later, channels 52-58 were cut out of the plan.

Well, when the VHF channels were added to the plan, the FCC worried that the DTV stations on VHF would have an "unfair advantage" of greater coverage compared to UHF stations (as lower frequencies do carry further over the cuvature of the Earth). Thus, lower power levels were prescribed for VHF high stations and much lower power levels were prescribed for low-VHF stations.

This had the drawback that high-VHF stations would have weaker signals in areas that were NOT on the fringe, and low-VHF stations would have MUCH weaker signals.

Go to rabbitears.info, and look at the longley-rice coverage maps of any lowband DTV, and you'll see a lot of red and orange shades!

To make matters worse, the early years of the DTV transition coincided with an electronics revolution that filled the spectrum with an unbelievable surge in the amount of RFI in the VHF bands.

How bad VHF is for DTV depends on where you live. While the power levels for UHF are the same throughout the US, VHF power levels are divided into zones. In areas where many cities are packed close together, low-VHF stations are limited to a paltry 10kW and high VHF are allowed a maximum 30kW (and many of these are limited further). In the rest of the country, lowband stations are allowed up to 45kW if their towers are not very tall, and highband stations with short towers may be as powerful as 160kW!

Finally, antenna manufacturers had heard that all TV was going to UHF and didn't get the memo when Congress shifted the TV bands (to this day, I hear from people who insist that all TV is UHF now), so a lot of people buy cute little antennas, and wonder why they're not getting all of the local stations.