TV ANTENNA INSTALLING

 

We have a 60 miles BIG antenna ( 6-7 ft long) on the roof that gets 5-6 stations at the city 50 miles away.. We have the round DISHTV dish to get most channels... then DSL on local telephone line to get internet.

Most people who aren't 'radio guys' treat antennas as VooDoo magic. 

Most consumer antenna and related equipment manufacturers tout their products like they're VooDoo magic.  They rate it by 'miles'.  Totally inaccurate... but that's the figure they use, because that's something that an ordinary person might accept as a relative indicator of performance.

The concepts, by stark contrast, are VERY simple.

Imagine you're standing atop a really high roof, and you're looking for the lights of a really tall tower... and you can SEE them.

What's happening... is that your EYES are actually RADIO RECIEVERS... they are fantastic little receptors of electromagnetic radiation in the 430-770 TeraHertz range... that's 380 to 790 to 405 NANOmeters... that means they can recieve a fairly wide-banded range... The low frequency end starts at 740nM (405THz) (we call it "infrared", up to   380nm (790THz) (ultraviolet).  You see a red flashing light from the tower, you're seeing what we call a 'continuous wave' at 680 nanometers.  If it's a green light, you're seeing 530 or so.

Now... imagine if you will, that instead of looking with bare eyes, you use a telescope... a 4x telescope... that telescope doesn't 'amplify' the intensity of the source, but it takes a larger surface, and 'focuses' it on a smaller point, so that more of your visible surface is concentrated in the direction of that light.  Easier to see, right?

That's called GAIN...  you've DIRECTED the incoming light approching at a large surface to a smaller, such that it's intensity at the receptor (your eye) is much higher, thus, 'easier to see', right?

Signal strength and sensitivity is generally expressed in terms of GAIN... and the unit of measure is a 'ratio'.  We use the ratio unit 'DeciBels' to describe differences in signal strength.  A doubling of the signal strength is referred to as 3 DeciBels (db). Each time you double the signal strength at your eye, you're seeing a relative gain of 3db.  Doing basic math, that means your 4x telescope is exhibiting 12db of gain.

Simple enough so far?  Good, because you need to know what a Decibel IS.

Now... you're not gonna mount some big darned antenna in your livingroom... first of all, it's inside, it's too big to turn, it's lookin' at walls and draperies.  Instead, you mount it outside, and if you're smart, you mount it up as high as you can get it... look over the tops of trees and lower buildings.  By doing that, not only are you getting rid of stuff that'd block your view, it gets rid of surfaces that could be 'reflecting' noise from BEHIND you (f/b ratio, remember?).  Best of all, you're higher up off ground level, which means you can see further.  If you're standing at the Bonneville Salt Flats, and there's a flashlight on the ground, you'll loose sight of it before you make it to 3 miles distant.  You know that your line of sight of another PERSON maxes out around 12 miles or so... but get 50 feet in the air, and your line-of-sight goes to about 9 miles.

Imagine that flashlight is 750 feet off the ground, and your antenna is 50 feet off the ground... you can now get a reach of about 49 miles with a 'clear view'.

BTW... my name is Dave, I'm a Ham Radio Operator, and it's not uncommon for me to be able to watch TV shows from Ann Arbor, Michigan from my home here in Iowa...

...and yes, it's using really special stuff, and just-the-right weather conditions.  There's days when my fancy stuff can't get good reception from stations 100 miles away, and even more that won't make it well at 25 miles away, but the cheezy little patch pointed south from my attic window will get me 34 local feeds from 7 broadcast locations...

Yes, Louis... that's absolutely, positively correct... when using an amplifier, it belongs AT , or as CLOSE TO the antenna FEEDPOINT as possible...

The amplifier doesn't magically 'suck' a signal out of the air... it merely takes what the antenna gathers, and gives it a boost.  This boost helps overcome feedline losses to your receiver(s).

A couple other things to know about amplifiers:

They're neither same, nor equal, and they're not magic.  as already noted above, broadchast television channels appear over a REALLY WIDE range of frequencies.  An amplifier that works well at 60MHz won't do the same at 100, or 350, or 700MHz.

The proper name for an amplifier that you mount near the antenna, is called a PREAMPLIFIER.  It's a wide-band, low noise gadget specifically tailored for driving a long feedline from your antenna feedpoint.

IF your house has several TVs and they're all tied into one distribution block, you'll need what's called a DISTRIBUTION AMPLIFIER.  it's not the same thing as a PREAMP... the DA's job is to take the antenna signal, and FOLLOW it with individual amplification to each TV set.  They're wide-banded also, but have totally different characteristics associated with keeping video quality when a signal's been split ten different ways.

NEVER use an amplifier on an non-directional antenna... you'll find that it does an excellent job amplifying all the stations you do NOT want.  You have a fairly strong signal coming in on one channel, your ability to recieve the station on the adjacent channel 60 miles away will get swamped because the amplifier will be blasting the stronger signal.  It's like trying to hear someone whisper to you when you're standing in the 12th row at a KISS concert.