Ok, guys, as predicted it's the pits. Digital TV cutting in and out at random because of multipath and other disturbances. Analog never does that, it simply performs better. But it's almost gone :-(
Besides the fact that newer antennas should have their UHF section tuned to Ch51 instead of Ch69, what other caveats are there? I have seen some weird scenarios, like UHF-only yagis mounted vertically. AFAIK the transmitter antennas are supposed to be horizontal. Of course those simple FCC station lists say nothing about that, or much else for that matter.
I wish the situation improves when DTV partially migrates to VHF. At least then we could see the news.
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Regards, Joerg
http://www.analogconsultants.com/
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Bummer to hear about that. Not all DTV allocations replicate their analog coverages, but most do.
As for the broadcast end of things, the FCC's website does provide antenna detail. Manuf, model, height and pattern. If you're good, you can pretty easily decode the horiz & vertical, # of bays, and gain of the antennas just by deciphering the antenna model number...
For example, KFOX in El Paso, TX.
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Send me your coordinates (or nearby street intersection) and the channel number you are having trouble with. I'll be happy to take a look at it for you. -mpm
Yep. Of course, the FCC said it wasn't a problem with 8VSB. Right.
Ummm... what makes you think that UHF antennas work at the higher UHF frequencies? See some of the models below. The broadband performance is impressive, but far from ideal. I'm partial to single channel antennas. If I need bandwidth, then a bow tie inside a corner reflector. Also, a Hoverman:
Nope. Some of the energy is vertically polarized for "mobile" TV application yielding eliptical polarization. It's very common for FM and TV broadcast xmitters.
However, I haven't been paying attention to what is being installed for DTV antennas. I'll look or ask.
Try:
The bad news is $8 for 7 days or $70 for a year.
Wanna predict what TV channels the FCC will auction off next?
I think you'll find this useful: "Comparing some commercially available antennas"
Use 4NEC2 or EZNEC to view the corresponding models at:
Also see the Excel spreadsheet with the model notes at:
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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS
Well, a DIGITAL tv antenna is either THERE or NOT THERE; a simple one or zero. So no "fuzzy" signal is allowed. At least the US Gestapo has not banned TV completely...
Ok, yes, if you go into every filed record. That'll take forever. But not on a list.
Thanks, but it's actually most of the digital channels. In bad weather nearly all collapse. Yesterday I saw something weird. Outside TV didn't have 29-1 programmed, so I did an "add channel search" upon which it promptly lost all memory of any DTV station. Great. But it found a cable leak signal that happened to be the channel we wanted to watch, in analog. Then the cabnle company must have lost the feed just like we do, audio cut out, blocks show up, blocks get bigger, the whole thing freezes into a huge Picasso. Oh boy, I foresee a great unhappiness boiling up with the masses.
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Regards, Joerg
http://www.analogconsultants.com/
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People who do antenna design told me. Many are tuned at the highest channel because that'll be the one with the largest path loss. But not for CATV head stations, there the antennas are often custom.
A bow-tie would result in horrible DTV performance out here, too much multipath.
Aha! Thanks.
Nah. It has always puzzled me why the TV media in California are unable to provide a reliable and free directory like in other countries. After all, they should be after viewership. But they don't seem to get it.
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Regards, Joerg
http://www.analogconsultants.com/
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On a sunny day (Sat, 12 Jul 2008 06:47:22 -0700) it happened Joerg wrote in :
I am using bow-tie on the side (all terrestrial is vertical here) in the attic and it works great on long distances. Some multipath, no problems, but then again I am in Europe QAM 64. But the bow-tie is a nice antenna and at least has good screening for reflections from the back.
Wait until the Democrats get into power and execute the "fairness doctrine". Then you can only watch what big brother thinks is appropriate for you to watch :-(
...Jim Thompson
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| 1962 | Liberalism is a persistent vegetative state
As I recall, (back in the late 80's), this DTV thing was sponsored by the broadcasters, NOT the FCC. They had just seen channels 70-83 vanish to create cellular and you have to understand the mindset of TV networks: Their spectrum had been a sacred cow for years!!
Channel 37 was allocated for deep space telemetry, now cellular. What's next? Let's offer digital programming - that way we can justify the sacred cow.
Along the way, it morphed into an either-or situation. Somthing I'm still not too sure was ever in the mindset of the technology drivers at the time.....?
I was involved in the DTV test in Charlotte (WCNC-6) and the DTV trials in Washington. In the early days, there was no (or very, very little outisde the top-20 markets) financial justification for DTV. Consumer sets were extremely expensive, very limited availability, and it wasn't even clear consumers would upgrade to "better" over-the-air TV. DVD's, satellite and digital cable were eroding over-the-air, besides which, just hanging a new, separate DTV broadcast antenna on the tower was somthing that generally overloaded the tower structurally. Couple that with a new DTV transmitter, licensing, land permits, construction, etc..., and you're into some very serious capital expense.
But to answer Jeff's question - I strongly believe that TV-6 will be auctioned off next (most likely to the FM band). TV-6 is a terrible over-the-air TV/DTV channel anyway, especially given it's 10.7MHz mix with a mid-band FM channel. Propagation of DTV on 6, as well as 2, 3 and 4 is also pretty crappy. (Though I think a handful of broadcasters eneded up with these low VHF assignments during DTV optimization rounds.) Very, very few full-powers are currently on TV-6, and even fewer elected TV-6 for DTV.
Even TV-5 might see the day where its 6 MHz are converted to FM. The conversion of TV 5 & 6 to FM will mostly affect the low power TV stations (LPTV), with some notable exceptions, of course. There is an active, open preceeding at the FCC to reallocate these channels last time I checked. And it's not a new idea by any means, having been considered at least twice before. As they say: "Stay Tuned!"
Are you out in the boonies or something?? In most cases DTV replicates the former analog coverages. Are you sure you don't have a bad cable, connectors, or set??
Sounds fishy to me. My two cents.
BTW: You only have to look up the stations of interest in your area. Just pick one that's not coming in, and review the 41dBu countour.
For instance, the KFOX-DT example provided previously. Here's its 41dBu contour:
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If you lived in El Paso, would your residence be contained within the blue line or not?
Actually, this is a really good example. KFOX (from memory) is on Ranger Peak. From there, at about 250 feet AGL or so, you could have skimming line-of-sight propagation into Las Cruces, NM - but I'll bet DTV coverage there isn't as great as advertised on the graph!! (?)
I believe these countours are calculated using Longley-Rice propagation models, which would consider terrain. But maybe KFOX is higher than I thought - though none of those towers on Ranger Peak are all that tall.. Hummm....
Anyway, I do think that poking around on a few channel contours would help you confirm whether you "should" be receiving signal or not. Or call the local station engineer. Most I know are very willing to help. It's actually part of their job description. Good luck.
This is only good for AM & FM. (From Doug over at VSoft) I do not know of a similar online resource for DTV, but there might be one out there. Navigate up a page to understand the dBu levels (signal intensity), if they are unfamiliar to you.
Yep, but you can't decode it from the FCC data. The typical Narda field strength meter:
yields the equivalent of a isotropic receive antenna by conglomerating the various polarizations into a single reading. That's what's plotted (and interpolated) on the FCC site.
One of the fun things to do is to use the antenna pattern from the FCC web pile to generate a field strength plot of the area using free software such as Radio-Mobile:
and the SRTM topo maps. The FCC does it crudely for "coverage area" such as this:
It would be rather bad if you were located in a protected null in the pattern. I can grind out a sample if you supply the station.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Joerg and I are in very similar circumstances regarding propagation. At our front door between us and the bay area there are these little hills called the Coast Range with the tallest being Mt. Diablo about two thousand feet higher than our elevation in the foothills of the Sierra and pretty much line of sight straight between us and the bay area transmitter sites. At our back door there is this little ridge of hills called the Sierra, most of which top out a little over 9 grand. And to our north and south we have little ridges and valleys of the Sierra foothills.
Boonies? Hey, we're so far out in the boonies they have to pipe sunshine in to us {;-)
Jim
Are you out in the boonies or something?? In most cases DTV replicates the former analog coverages. Are you sure you don't have a bad cable, connectors, or set??
Incidentally, the OMVC appears to be having problems submitting useful IDOV test results to the ATSC. It seems that ATSC will require considerable "enhancements" in order to function in a mobile environment. There were quite a few of these demontrated at the April NAB show, with varying degrees of success. Final standard is due in July 2009. It would have been a no brainer if the FCC had dumped 8VSB and gone with COFDM.
Not horrible, but better than a yagi, which has side lobes all over the place. The yagi also has a nasty F/B problem with a huge lobe in back. Reflector type antennas usually don't have that problem (if the reflector is large enough). I have both a yagi and a bow tie on my roof. The yagi has more gain, but really has bad analog ghost problems. It works with OTA DTV, but experiences dropouts, which I attribute to frequency selective fading caused by multipath. The bow tie has the same problem, but to a much lesser degree.
Broadcast TV station location:
This one is particularly nice because it includes antenna patterns.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
No clue who's behind it, but it seems very nicely done.
dBm is referenced to 1 milliwatt (into 50, 75, or 600 ohms). dBu is referenced to 1 microvolt/meter field strength.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
A Narda meter will read field strength in terms of E or H field, not power density. Though I supose if you know enough about the probe, you can do the conversions...
Also, be advised that for FM at least, the FCC uses a modified Bullington propagation model which will not consider obstructions (or water) closer than 3km, and no further away than 16km. So for FM stations along the front range in Colorado for example, the FCC patterns will deviate significantly from real world performance. (FCC plots have more to do with short-spacing and licensing issues, not coverage.)
The null you're seeing in the FCC pattern (KFOX) is terrain obstruction. Not an antenna pattern null. This pattern is typical of all stations on Ranger Peak.
Still, for the purpose of this thread (i.e. poor or no DTV reception), field is not the issue. Power density is. The numbers & plots provided on the FCC public website are completely adequate for determining whether or not you "should" be receiving a DTV signal at your location.
That same topography (all things being equal) should have been a problem for analog as well then. Though, with analog, you can still get a picture even with some multipath and/or knife-edge diffraction going on. Much less so with DTV, though the receivers are getting better....
As I vaguely recall, both Japan and Europe went to DTV first. The US equipment manufacturers beat up on congress to get the FCC to build them a market. The broadcasters were clueless and were desperately trying to do their usual by maintain the status quo and restricting progress. Amazingly, they received a great deal from the FCC just to stop complaining. They got a free digital channel for each of their analog channels, with almost no restrictions on content (i.e. data broadcasting).
Ever notice the draconian rules the FCC imposes on cable, while broadcast can do no wrong? Can you guess who's pulling the FCC's strings?
Yup. Good business for the equipment manufacturers. The broadcasters get a new "market". The antique equipment gets instantly obsoleted, which is good for a big tax writeoff (instead of the usual depreciation).
I beg to differ. The FCC has had all it can stomach from the broadcasters and will probably not do anything nice for them for a while. The current financial pressure and demand are in the telecom/datacomm markets, such as wireless IPTV, cellular, emergency services, LEO satellite phones, and wireless anything. My guess(tm) is that the higher channels that have not currently been cannibalized will be next to go. However, I also think the military is going to release more frequencies. Also, 14-20 are currently shared with land mobile in some areas, and will eventually go all land mobile.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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