High Definition TV

It is common knowledge that the best way, probably the only way, to receive 1080pixels TV in North America is ODA. I just installed a TV Antenna and I am pleasantly surprised at the results. A signal that before would give a very noise picture, digitally, will give an excellent picture.

But I have a problem. How does one orient the antenna for the best signal. Before we would rotate the antenna for the strongest signal but with digital signals the signal is on or isn't there. Rotating the antenna and parking between the 2 "no signal" positions, is one way but I would prefer to adjust it to the maximum signal. There is probably an agc signal that can be tapped inside the rx but that I would like to do after the warranty expires

Another puzzle I have is that I installed an antenna that is no more than 40 x 50 cm with 6 elements and claims to have a minimum gain of

28 dB from 40 to 890 MHz. Four of the directors are inside of plastic that may have inductors to increase their electrical. The main dipole goes inside of a box that include the electronics to rotate the assembly and may have an rf amplifier.

Comments please.

John

Reply to
John
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In the uK, most digital Rxs have built in signal strength displays- AGC, SNR and BER. Tho these are mainly for satellite....

Reply to
TTman

Most TVs have a signal quality menu to help in programming the rotator.

There are plenty of fake TV antennas in stores and catalogs.

DTV frequencies vary by region so the type of antenna needed varies. If you're lucky, the lower frequencies aren't used and the longest rods of a yagi antenna aren't needed. If you're really lucky, it's all UHF so a small bowtie array can be used.

Channels 2-6 are for short range TV in the SF/SJ Bay Area. Nothing worthwhile has shown up there yet so I may change to a 7-69 channel antenna when my wideband antenna wears out.

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Reply to
Kevin McMurtrie

Panasonic kit in the UK also allows signal level and quality display for terrestrial DTV from the setup menu. The digital decode quality result is a bit abrupt, but the signal level indicator is useful.

In the US it seems most of these features are disabled or undocumented. Several vendors make aerial alignment aids that are little more than a fancy diode rectifier and a moving coil meter, possibly with an audio tone feedback that increases in pitch with higher signal levels. You need one extra F connector cable to put the breakout box in line. That's how I adjusted mine accurately onto the right satellite.

Regards, Martin Brown

Reply to
Martin Brown

Hello John,

Gain issue Probably there is an amplifier inside (that is fed directly from your receiver/set top box). So an overall gain figure is given (without any noise specification very likely). Making a 28 dBi antenna for these frequencies will be very large.

Wim PA3DJS

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without abc, PM will reach me

Reply to
Wimpie

Is there anything really worth watching on over-the-air TV, digital or otherwise? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Are you in the US? If so, visit the FCC (or other) web site. Get the coordinates for the TV's main tower (some stations in larger markets may have a 2nd transmitter as an emergency/spare/back-up at different coordinates). Get a map of the area. Then, go get out your boy scout compass...

The rest is rather self-explanatory.

Reply to
mpm

To my surprise I am getting Channel 3 and 5 that are about 50 miles from my location and as you know are below FM frequencies. To receive them with little noise it used to required an assembly of

2 five elements Yagies. Before they switched to digital and using the same antenna I wouldn't even get the sync signals.

Jim

The answer to that is that PBS (Public Broadcast Stations) have 2 channels on my area and each channel also transmits on 3 sub channels for a total of 8 channels that normally have different programs or have delayed broadcast. The main channels are 1080 but the sub channels are 720 or 410. The

410 is normally used for old and classic programs, unavailable to the staitions in HD. The CBC in Canada are also doing a good job with the news but they are schedule to go digital next year.

To my knowledge OTA is the only way we can get the sub channels. PBS has by far the best programming because it is subsidized by the government and the public. The commercials are limit to sponsors and the programs include a daily retransmission news from the BBC and believe me also from Algesiria. Of coarse they must satisfy a large number of the population with money and consequently include popular programming .

Just for this I think it is worth having an antenna

John

Reply to
John

The devices I have seen are for satellite adjustments that only receive one or two channels. Absolutely essential .

For OTA we need a unit with a band pass filter that rejects all minus one channel. Like a receiver. I have 2 sat receivers and they have the function you describe.

My TV set is a 52" Sharp and I can't see any reference to help to adjust the Antenna. I may call Sharp and ask the question

Thanks

John

John

Reply to
John

Propaganda at its finest ?:-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

On the old days use to be easy, You just start by point the antenna on the same direction as all the others and then adjust for maximum. Today a TV antenna is a rarity.

I will follow your advise, thanks

John

Reply to
John

One more question:

I know that in order to maximize a power transfer the load impedance must be equal to the source impedance and the transmission line but, if I have un amplifier that uses a high impedance fet and is installed at the main dipole of an antenna and the line is located after the fet amplifier with unity gain, don't I gain 6 dB relative to a perfectly matched system ??? Assuming zero loss for the line attenuation .

Must the dipole see the right impedance in order to perform as in theory

I know that a fet exposed to that environment wouldn't last very long but that is another problem John

Reply to
John

I'd say it's worth the low cost of maintaining an antenna. There are a few good hours a week to watch.

An interesting effect of DTV is that what used to be a scattered bunch of low power analog signals with 1 to 10 mile transmitters is now 480i streams sharing channels on 15 to 60 mile transmitters.

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Reply to
Kevin McMurtrie

Two possibilities: look in your menus, lots of TVs or digital converters have signal strength meters builtin. And,

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has a utility for showing you the orientation to each local station; get some polar graph paper and draw in the orientations, it might be very clear how to aim your antenna after you do that.

There may be useful reflections from nearby buildings, though, that you just have to find by hunting. I had a distant station that was south of me, that I could only tune in with a high-gain antenna aimed west. My neighbor to the west had a ham antenna mast that was high enough to be in line-of-sight to that station.

Reply to
whit3rd

ZONE..

Reply to
Robert Baer

l
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Hello John,

For maximum gain, you are right, however for maximum S/N ratio, matching for maximum gain mostly doesn't coincide with maximum S/N ratio (minimum noise). This means you can have a FET (or other device) that has been optimized to be driven from a source close to

100 Ohms (as an example), but has input impedance far above this. If for some reason you want a matched input (for the amplifier), feedback is used to electronically generate the desired impedance.

For high impedance sources (like a wire antenna short with respect to wavelength), FETs are used frequently as these devices provide less current noise than BJT, of course depending on frequency range.

When the gain under best S/N ratio isn't sufficient to overcome cable loss, you need a second stage.

You are right, when the input impedance of the FET is far above the output impedance of the dipole, you will have about 6 dB gain. Note that 1/transconductance of the FET should be

Reply to
Wimpie

If you want to make your initial research on where all the broadcast towers are actually located (so you can more easily find them with a compass), some colleagues over at Cavell, Mertz & Associates have put together a wonderful tool that maps FCC data to Google Earth.

Download it here:

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-mpm

Reply to
mpm

Don't worry about it. If your picture quality is good and your not getting "loss of signal" type of errors(no picture at all) then your fine. You can be almost 100% sure that the quality is exactly the same as was sent. Digital is digital and there are great encoding schemes used that have great noise immunity and signal recovery. While I don't know much about DTV I imagine that it works much much better than analog.

With analog any noise on the signal in the appropriate band at the appropriate time would show up on the picture. This is not the case with digital as it is 1's and 0's(encoded in an analog signal but generally easily recoverable). It takes a lot of noise/low signal strenght to change a

1 into a 0 and vice versa. Of course if this happens one can generally tell if they use crc's, hashes, checksums, etc and even recover from such errors. This is virtually impossible to do with analog signals.

If you are getting good picture quality then be reasonably assure that it is the best picture quality excluding the TV itself. If you are getting blank screens intermittedly then your SNR is low. This could be do to antenna orientation or various other possibilities.

Reply to
Jeff Johnson

Early decoders were all-or-nothing because they couldn't re-synch the stream after an error. Modern decoders will show lagging or garbled blocks in moving images when the signal is weak.

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Reply to
Kevin McMurtrie

Excellent information from all of you.

My sincere thanks to all

John

Reply to
John

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