Question about repeating tv antennas. 1

[Yort1]

I've recently "cut the cord" as they say and ditched our cable tv for OTA. I'm now searching for the best digital antenna money can buy. After all since OTA is free I might as well invest in a good (outdoor) antenna that will get the best reception - the more channels the better.

After doing some research on antenna's I became curious about the antenna repeater - that is an antenna that receives and then transmits the digital signals it receives. My question is, is it theoretically possible to repeat a signal that is broadcasted from say LA all the way to New York? Put more simply, if everyone owned a repeating TV antenna would it be possible to receive hundreds if not thousands of television channels?

 

[VEBill]

For many reasons, no.

 

[MikeHalloran]

An indoor folded dipole works pretty well for me.

It comprises about 6-1/2 feet of 1/2" CPVC tubing with 18 gage insulated wire taped along it. The wire folds back at the ends of the tube, about 12" or so.
At the center of the tube, the wire is cut and extends radially to a 300ohm/75ohm balun. The balun connects to coax, to the TV's antenna/cable input.

I used to have it taped to a window, but it fell down, and still works just fine on the floor behind the sofa.



Mike Halloran
Pembroke Pines, FL, USA

 

[zappedagain]

In the simplest model, every amplifier adds noise. Put in enough amplifiers and the noise will overwhelm the signal.

 

[Yort1]

Okay, thanks for the simple explaination.

 

[Comcokid]

I "cut the cord" too. You don't need a "digital" antenna. I'm using a TV antenna made in the good-old analog CRT TV era just fine. Frequency bands are the same. Digital TV signals are more suceptable to strong reflections (i.e. path delay or phase distortion), and picture freeze or break-up with weaker signals. The old analog signals would just overlay multiple images with path delay, and just increase the level of 'snow' (noise) as the signal got weaker.

 

[IRstuff]

While a chain of "antenna repeaters" might not work, one could easily imagine a bunch of people streaming their reception through a website on the internet for others to see.

TTFN
faq731-376

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[VEBill]

The frequency bands are the same (the UHF TV band has been trimmed), but Over-The-Air digital TV channels (ATSC in North America) are sometimes not what they appear. They use virtual or logical channel numbering.

In my city, local TV channel "8.1" actually is on VHF channel 8 as one might expect. But the other local TV channels "3.1" and "5.1" are not actually transmitting on the VHF band; they're assigned to UHF channels 39 and 48.

This type of information can help in selecting or building a TV antenna that performs better, if required, by covering the correct VHF and/or UHF frequency range. If it's not required, don't worry about it.

 

[DanEE]

Ditto VE1BLL comments..

My local area "channel 2" which had an analog video carrier frequency of 55.25mhz is now broadcasting digital with a pilot carrier frequency of 692.310mhz.

"Channel 4" analog was a 67.25mhz video carrier frequency, now is a 536.310mhz digital pilot carrier frequency..

This type of frequency mapping is typical, and if the original poster has similar conditions in his area, an old low band TV antenna and possibly marginal feedline, may not work very well at these much higher frequencies..

"Digital" antennas (to use a generalist, consumer term) are designed to have much better gain at the commonly used "digital frequencies" and in many cases ARE needed for this reason along with better quality feed line. Only testing in original poster's specific area will tell if an upgrade is needed for certain.

There are a number of issues why the old lowest analog frequencies are not used for digital transmission, including encoding rate/frequency ratio, vulnerability to commonly occurring impulse noise in low band, and so on.

The 8VSB modulation scheme adopted in the US for HDTV is very unforgiving of multipath signals and easily looses sync.. Unfortunate that the standards committee involved did not wait just a bit longer and adopt the COFDM scheme used for cellular, DSL over copper, wifi and; HDTV in most of the rest of the world.

 

[Comcokid]

Sometime back I read an article by a technical expert who was involved in the standards committee. He implied that the cable companies pushed hard for the 8VSB modulation in order to deliberately cripple over-the-air reception as much as possible. The object of this was to push more people into paying for cable.

 

[DanEE]

Never heard the story of cable companies pushing 8VSB, would not be surprising; but competition between chipset manufacturers based on the architecture they chose to develop for a new emerging market would have been a major force.

I met and got to know Harvey Arnold decades ago when he was Director of Transmission Technology for our state public TV network.. He was on the technical standards committee and fought hard for COFDM to be chosen, but lost the battle. Initial chipset development schedules for COFDM receivers (I vaguely remember being done largely in Europe, I don't know who at the time, Phillips?) was slightly behind that of the 8VSB chipsets. The decision was made (by the FCC for the U.S.) and then it ended up taking 5 iterations of the 8VSB chipset design to come up with anything reliable enough to be marketed... You can find many of the original papers by googling his Harveys name and 8VSB

http://www.broadcastingcable.com/article/492730-Harvey_Arnold.php

4K UHDTV (native video at a minimum resolution of 3,840 × 2,160 pixels) is bringing this discussion back to the table again... in that it would be impossible to do 4K UHDTV OTA using the current 8VSB HDTV standard, given the data rates required.

http://en.wikipedia.org/wiki/Ultra_high_definition_television

4K UHDTV sets are in the market place now, but no OTA capability as there is no standard for it.. I have been told that way Harris and many others implemented their HDTV transmitters that simulcast of old HDTV 8VSB and a newer COFDM on the same pilot carrier is technically feasible...

Another thing that was lobbied for (and lost) was upgradable codec technology in the TV receivers (just as codecs are upgradeable in your computer and BluRay player, given the base platform has enough processing power to support it). There now are far better compression technologies (H.264) compared to the mpeg2 in today's current HDTV.

But some of this has to be tempered with decisions had to be made based on technology available at the time..

 

[VEBill]

...upgradable codec technology in the TV receivers (just as codecs are upgradeable in your computer and BluRay player, given the base platform has enough processing power to support it).

I'm glad that you mentioned the proviso about having the necessary processing horsepower. Because, over any significant amount of time (e.g. ten years), it's the unfortunate reality that that particular requirement comes to dominate. It's typically more than enough to single-handedly derail the dreams and promises of software upgrades to future waveforms.

My general rule is that software defined radios can go sideways (similar but distinct waveforms) much easier than they can move forward over the longer term.

Newer waveforms almost always require more computational horsepower.

 

[Higgler]

I had OTA reception for a while. Frustrating that the signal will disappear at any time (due to wind mostly), with no hint when it will come back. Only use this if you are reasonably close to TV transmitters (i.e. living in a city).

I suggest you order cable internet, buy a Radio Shack 3 dB splitter, connect one output to your cable modem, the other to the antenna input of a modern TV having a QAM Receiver (I think they all have QAM nowadays), you get alot of channels for free (100+) when you tell the TV to "search for channels", then you delete the ones you don't like (which can take many minutes.

Hence fast internet plus Cable for $50ish per month.

 

[Yort1]

Yes, I was looking into QAM. I'm using a Tivo Series 3 and I believe it is a QAM receiver. I have read that some cable companies(Comcast)are eliminating thier QAM channels though. I will give it a try!