OLD TV Transmitters

[flintstone mop]

Are we ready to jump on any deals for old retired TV transmitters? After FEB 18, they're off the air!!!!!!!!
No mods needed for audio.......the visual transmitter.

And why was A.M. used for TV transmissions anyway? My reading at one time was that an A.M. transmitter responded faster to the complex video waveforms than an F.M. system.

Food for thought

fred

[Bill, KD0HG]

Because they could do AM with one suppressed sideband, cutting the channel bandwidth in half. Analog TV isn't DSB AM, it's SSB AM.

FWIW, the stereo composite signal FM broadcasters send out is AM as well!

[W3LSN]

Analog TV actually uses "vestigial sideband AM" or VSB which includes a carrier, one whole sideband, and part of the other sideband. This is not the same as SSB or one sideband with carrier.

For that matter, the digital modulation scheme for the ATSC standard DTV system is also using the VSB technique, and it's called 8VSB developed by Zenith.

73, Jim
WA2AJM/3

[Ed/KB1HYS]

The radio add said that certain low power or local (don't remember which) stations would NOT be making the transition.  So do those fancy boxes allow analog sigs to pass through??

Interesting Idea though,  aren't those transmitters in the multi-kilowatt range too?
Liquid cooled BIG tubes...  Hmmm...   

STRAP

Hang on OM while I kick in the coolant pumps for the Rig over!!!   

[Opcom]

channel 2 TX = possibly 6 meter AM. like never before. The problem is the size of those things. I'd like to see who is first to get one. The 480V or what have you is another fun thing.

[k4kyv]

I am wondering how the TV channels will be numbered.  Some of the LPTV stations will not be required to make the change.  Some that do make the  change will stay on VHF while others will migrate to UHF.  Will channel 4 still be channel 4 after the change?  Will the FCC issue a new frequency table for the TV channels that will be the same nationwide? It all seems very confusing to me. But with 85% of the public using satellite or cable, it's becoming kind of a non-issue.  I suspect that free, over-the-air TV is going the way of medium wave AM broadcasting.

Regarding the retired transmitters, John, WA5BXO and I shared a channel 11 transmitter that was taken out of service in Houston back in the late 70's.  It stood about 6 feet high and must have been 12 feet wide.  We took out a lot of goodies, but much of the stuff was of limited use to us.  I think John got stuck with the cabinet and sold it as scrap metal.  The thing had enough heavy gauge sheet metal to make all the transmitter cabinets you would need over a lifetime.  But it would have been too expensive for me to ship up here merely to use as raw material, and John didn't have any place to store it.

Unfortunately, the big strapping power supplies in those transmitters are nearly all three-phase.

[flintstone mop]

I thought that channel numbers were for station use and they would keep them so there won't be mass confusion for the non-technical TV viewers. The digital stations will be in the UHF spectrum and have the option of multicasting. In the end WE get screwed, as we will not see the full HDTV (1080i) signal. I think it's one 720i or p, Hi-def channel, and 3 digital NTSC equivalent "channels". Chan 33-1, chan 33-2, etc.

As for the Vestigial sideband, it is not done in the transmitter. This is what makes TV stations expensive. It's done with filters on the output of the visual transmitter and expensive copper plumbing and a dummy load to dump the unwanted sideband power into.
If I'm in left field, would a TV engineer, please step up and educate me/us. It's an other intersting facet of RF, even though the entertainment industry is mind numbing at best.

Fred

[K3ZS]

With digital TV there is no correlation between channels and frequency.     Around here, the digital channels are all on UHF but are keeping their old channel numbers.   Although the field strength functions on some converters tell you what the actual UHF channels are.    Seems like most stations are multicasting one HD and 2-480i channels on their channel.    The HD channels look good, but probably would be better if all the channel's bandwidth was used for HD.  The HD channels for CBS, NBC and PBS are using 1080i, ABC and FOX using 720p.

[k4kyv]

So channel 8 on my digital TV here won't necessarily be the same as channel 8 in some other part of the country?  How can that be if I move across the country and use the same TV set or converter box?  So they are going to use whatever UHF spectrum they can find to broadcast the the digital signal and name it whatever the old channel was?

[flintstone mop]

hi Don
The converter box will decode what station you are watching and display its call and real channel. On my digital tuner I see the name of the TV show and description. I'm sure the FECES will be assigning the freqs as usual.
I see stations I.D. channel 4 'digital', and then the UHF channel and dash if they're multicasting...............cheating us out of a Hi Def pic.
Fred

[K3ZS]

That's right Don.    Your old analog channel 8 will probably be 8-1, possibly 8-2 and 8-3 on digital.    It could still be on VHF channel 8, but more than likely some UHF channel.    Around my area,  PBS VHF channel  3 on digital is 3-1, 3-2 and 3-3, and it is on a UHF channel.    The neat thing about the digital TV is that they can have repeaters on the same channel.     The transmitter for the VHF channel 3 is 60 miles away, the digital transmitter is at the same location, but it is repeated 3 miles from here on the local mountain top.   The same with channel 6, its digital signal on UHF is also being repeated locally, even though channel 6 analog is about 60 miles away.   I have stopped using the cable for network programming and TIVO recording.    Using a single UHF antenna now.    The PBS digital is great, now with three stations on one channel, all with separate or time-shifted programming.   I am a night owl and watch the PBS Newshour at 3 AM on 3-3 (when I am up) , the first showing is on HD at 7 PM on 3-1.   Some old PBS programs our shown on the alternative channels.     There are some travel programs that are shown only on the HD PBS channel, not shown at all on the analog channel.   It is a whole new world of broadcast TV and I like it a lot.    I could dump the cable but my wife likes the Food Network and some of the woman oriented channels.

[k4kyv]

I'll probably keep the cable for the high speed internet service.  I just have the minimum bare bones basic TV service.  Don't watch enough TV to make it worthwhile to pay extra for premium cable TV.

My wife is interested dumping the land line telephone and opting for the cable company's "bundle", which includes telephone, high speed internet and cable TV.  It would save us a few bucks each month and give us access to many more TV channels, but I'm not sure I'm sold on the idea. Her boss at work got the service, and so far she says she is satisfied with it.

[flintstone mop]

The BUNDLE is great ONLY for the first year and then ........hold on to your wallet.
I keep the basic TV so the high-speed internet won't hurt and I use Vonage. That is very reliable and stays at $24.95/mo. Nation-wide calling and all of the bells and whistles of the wired telephone.
Fred

[Ed/KB1HYS]

not to mention the "Bundle" deals usually have a high penalty if you decide that you don't like it and want to change providers before your contract is up.  You endup paying almost what you would if you had just kept the service in the first place. 
CAVIAT EMPTOR

[John K5PRO]

Just to confuse things more, not all VHF television stations are relocating into the UHF spectrum. We have several in Albuquerque that are staying right where they are, just switching off the analog transmitter and popping on the digital rig.

Many VHF transmitters in major markets have already been solid stated, since those rigs have been available for over 10 years now. The days of finding a 4CX5000A in a television socket are gone. Some tetrode rigs still can be found, but many were sold off into third world markets already. RCA/Burle tubes in Lancaster does a lot of biz with these markets for replacement tubes and cavity amplifier parts. Best bet for finding a big tetrode amplifier are in the smaller market stations that haven't been bought out by the big conglomerates.

The tube amplifiers were all in cavities, so they won't be reusable at HF, but the screen supplies, bias, and fans might be reusable. Most of the big iron was 3 phase, and very heavy.