DTV frequency mapping

[Sceadwian]

I'm looking into DTV in my local area (Western NY, US) for some neighboors that don't want to get cable when the analog signals go dead. They're having trouble getting a signal because of the area we live in and I was going to try some home built antennas so they don't have to shell out too much and I'm curious as well. I can't for the life of me find the equivalent analog channel that a local station broadcasts at. It's DTV 21.4 (WXXI TV locally) But I believe all DTV stations are in the 52-67 range with some channels blacked out because they're being released to public services at some point. Is there any place to find the actual frequency mapping for a DTV Channel? My google searches don't seem to be netting any official information.

 

[mneary]

I found it at the **broken link removed**. It's 1998, and includes some VHF allocations, which I didn't think was the case.

 

[crutschow]

According to Wikipedia WXXI-TV - Wikipedia, the free encyclopedia WXXI's digital channel is on UHF 16.

It certainly looks like it will be more difficult to pick up the digital signal since it's being broadcast at a much lower power (1230 kW (analog) vs. 180 kW (digital)). You probably want to use a high gain UHF antenna with antenna amplifier mounted as high as feasible (or allowable).

 

[Nigel Goodwin]

OK, the UK has been doing digital terrestrial for many years now, and is currently in a gradual switch-off of the analogue transmitters.

The digital transmitters are all of considerably lower power than the old analogue ones, but coverage is supposed to be the same - they don't need as much power to give the same coverage.

As long as your analogue pictures were of good signal strength, and assuming it's using similar frequencies, then reception should be fine. All the UK transmitter details are freely available on the net, I can't see the USA ones aren't also available?.

An obvious (and simple) solution is to ask at a local TV shop, not a large multiple staffed by untrained kids, but a 'proper' small TV shop that knows what it's doing.

 

[Sceadwian]

Yeah, it's gonna be a problem I think, we live at the very base of a decent sized hill with a massive metal water tower directly between us and the transmitter it's a huge RF deadzone and unique to the area. A quarter mile away in any direction and you'll get signal again but not here. I'll see what I can figure out. Kicking myself though, I'm constantly posting people should check on google and wikipedia first, I forgot to check Wiki =) It's going to be a few weeks till I get my coupons for tuners but I guess I'll play around with regular analog reception on 21 see what I get.

 

[3v0]

One site has info on DTV DXing and shows stills from stations 300 miles away. I am guessing that they can not do that 24/7.

There is no TV reception where I live. The nearest transmitter is 60 miles away and a hill is blocking the signal.

Let us know what you come up with.

EDIT: Given that you can get by with less transmitter power I wonder if that will make repeaters less expensive.

 

[Sceadwian]

I slapped together a peeled back 1/2 wavelength dipole from a piece of coax and I can tune 21 without the greatest of pictures, but better than any antenna I have around the house. My first experiance tuning UHF locally. I'm getting diagonal striping pretty badly but I'm feeding the dipole via coax directly into the TV, so I'm guessing it may be a common mode pickup in the shield. There are antennas on the water tower which I'm guessing are public service repeaters. It is the highest 'bump' in the area for at least 15 miles so I'm guessing there may be some decent power going out of them. I have the same diagonal striping problem using my TV tuner card but that's using cable, I was assuming it was an internal frequency coupling issue with the PC to the tuner creating it but I'm not so sure now. I'm a little fuzzy on the local geology but we're supposed to be mostly bedrock in this area and the exact area we live in is known for flooding so I'm wondering (very wandering kind of wondering) if the local ground may be electrically floating a bit in relation to a more rooted ground outside of the immediate area. I have a generic 300 to 75ohm antenna transformer so I think I'll try a folded dipole next see how it compares. I can't do anything with the digital myself until I get some tuners (My coupons are in the mail) and the neighbors aren't home.

 

[Sceadwian]

Folded dipole sucked big time. First time I tried it it was into a splitter (as a cable sex changer) That introduced enough loss to kill the signal completely to static on even the highest power stations. Touching the center conductors without the splitter gave an image, but not nearly as good as the idiot dipole. I'm assuming the major reason for the bad signal was the loss in the impedance matching transformer itself. The stupid dipole was impedance matched to the cable in line by nature the only caveat being it was balanced to unbalanced along the cable. I've heard of simply placing a conductive tube around the base of the dipole 1/4 wavelenth long will act as a balun for a stripped coax dipole, but doesn't this introduce a 3db loss? Is there such thing as a 1:1 lossless balun for a 75~ohm half wave dipole?

 

[Boncuk]

DTV-Antenna

Hi Sceadwian,

you might try this antenna. It was developed by a german radio freak and reports say the reception quality is even better than that of commercially manufactured antennas.

It is called a "Dual hybrid quad antenna" and it is easy to build using aluminum or brass wire of reasonable strength. You won't need a balun for it. Just connect the coaxial cable directly to the antenna.

The main strut (drawn blue) has to be electrically isolated (PVC or similar)from the dipole and the reflectors.

The formulas are contained in the drawing.

Regards

Hans

 

[Uniballer]

Is the drawing for the Dual Hybrid Quad Antenna still available? Where can I get one?

 

[RadioRon]

Useful info here:

Local HDTV Info and Reception - AVS Forum

 

[k7elp60]

Here is another site that may be helpful.
**broken link removed**

 

[Dean Huster]

a 'proper' small TV shop that knows what it's doing.

Alas, Nigel, but that is something that is very, very rare here in the U.S. When I was a kid in the mid 1960s, that was all there were -- no big department or discount store TVs. The little TV shops have been run out of business by the likes of Wal-Mart and Best Buy, not to mention spending a lot of money for a repair when a new TV is about the same price. Our last shop in town here closed down just this year. He was only part-time anyway, spending most of his time as chief engineer for several radio stations in the area.

Dean