TV antenna for scanning?

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jlochey

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I have a TV antenna that I have been hooking up to my base scanner and surprisingly, it works pretty good!

Is this just madness, or do others do something so daring! ; )




John
KC8JDI
 

maddogdecker

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My friend does that out at his house. It does really good for him. I think it is a really good idea. Use what you got. Very creative use of what you got.
 

gewecke

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You'll find that this trick works even better if you modify the tv ant. to work vertically
on it's boom! This is mainly because most vhf/uhf signals come from antennas which
transmit vertically.
Enjoy!
73's.
 

kb2vxa

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Hi John and all,

There are three troubles with using a TV antenna on a scanner.
1) It's horizontally polarized while the signals are vertical.
2) It only receives well from one direction.
3) It's made to feed twinlead and a 300 ohm receiver.

To fix these problems;
1) Find a way to mount it vertically.
2) Use a rotor but it still only receives well in the direction you point it.
3) Connect a TV balun and a short coax jumper with connector adapter between the twinlead and the scanner.

After all that rigamarole consider a real antenna.

Don, I have little doubt since that's exactly what I did to receive a weak ATV repeater. Since the 70cM Amateur band is a bit below it's 470-890MHz normal operational range things could have been better but it worked. That was just one repeater at another QTH, it wouldn't work here because I can't swing a dead cat out on the fire escape let alone a long nose corner reflector.
 

zonian149

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In Case no one saw this in the previous thread from Bill Cheek

Copyright (c) 1995-97 By Bill Cheek, COMMtronics Engineering
<All rights reserved>


TV Antennas for Scanners?


There is some controversy over the use of TV directional antennas for
scanners and scanning. This article lays out the facts and the
substance of the issue so folks can see, calculate, and decide for
themselves.


So why would you choose a TV antenna for your scanning post? To hear
all there is to hear, for one thing. The GAIN of the antenna alone
will enable you to hear far beyond your present range with an omni
antenna. But there's more! Big city environments are RF garbage
dumps, right? Noise and interference wreak havoc and consternation on
all but the best scanners, and sometimes even them, too.


Say there is a nearby repeater or pager transmitter that overloads
your scanner's front end. The expensive fix is to buy a notch filter
or a tunable filter and notch out the offending signal. Often it
doesn't work. A TV antenna will work! Sure! Just rotate the antenna
until one of its side or back nulls is pointed at the offender, and
the results can be startling! Oftentimes, the offender will disappear
into the noise, even if you're tuned to the sucker! When the offender
is nulled out, the antenna will still receive signals from the forward
and other directions.


A TV antenna has many peak and null lobes around its 360-degrees of
view. The deepest nulls will be on the back while the highest peaks
of gain will be off the front. Nevertheless, there are a whole slew
of minor peaks and nulls on each side of the antenna between front and
back, and these can be used to great advantage when selecting a
desired signal and rejecting one or more undesired ones. The list
goes on, but time and space force me to move on. You get the idea?


If you choose to use a directional TV antenna for scanning, it will
work wonderfully well between about 30 MHz and 1 GHz and better than a
discone down to 25 MHz and up to 1.3 GHz. The caveat here is HOW to
install it......NOT the same as for TV reception.


A TV directional antenna used for scanners and scanning should be
mounted in the VERTICAL plane....that is, with its elements pointing
into the ground and into the sky with the boom retained in the
horizontal plane as for TV reception. A short mast should be rigged
into the normal mount of the antenna....say 2-ft to 3-ft, max. This
side mast must mechanically join the real mast that rises vertically
from the rotator. Any number of methods of making this a rigid,
lasting mount can be employed and will not be presented here.


A TV matching transformer (300 ::75 ohm balun) should be fitted to the
antenna as is customary for coax feeds. Then use RG-6 satellite cable
from the other end of the matching transformer down to the scanner.
Use gold plated Type F connectors on each end of the coax. Down at
the scanner, use a gold plated Type F-to-BNC adapter to mate the coax
to the scanner. Voila! A low cost, high performance directional beam
antenna for your scanning post. Now here is why the sucker works:


Consider:


TV antennas for the USA are expressly designed as follows:


54 - 88 MHz Ch-2 - Ch-6 (34 MHz Passband)
88 - 108 MHz FM Broadcast (20 MHz Passband)
(Good for about 30 MHz to 158 MHz)
174 - 216 MHz Ch-7 - Ch-13 (42 MHz passband)
(Good for about 130 MHz to 324 MHz)
470 - 890 MHz Ch-14 - Ch-83 (420 MHz Passband)
(Good for about 352 to 1.3 GHz)


In order to get specified performance at the band edges, the
antenna has to be "overdesigned" by the mfgr, meaning that positive
gain and useful F/B ratio will be apparent well outside the bands of
design.....i.e., the TV bands.


Now let's look at the gaps in the above spectrum which include
desired scanner frequencies:

25 - 54 MHz (29 MHz gap)
108 - 174 MHz (66 MHz gap)
216 - 470 MHz (254 MHz gap)
890 - 1300 MHz (410 MHz gap)


Understanding that a wideband antenna will still perform with gain and
other specs within 1-octave of its design passband, it can be seen
that all of the above gaps are well within one octave of the
passbands. For instance....one-half an octave up from 216 MHz places
an edge at 324 MHz. One-half an octave down from 470 MHz places a
cutoff at 352 MHz. (I'm using half-octaves to be conservative even
though full octaves are valid).


Therefore, even in the widest gap of 216-470 MHz, there is ample
overlap coverage from the passbands of 174-216 and 470-890 MHz.
The worst coverage in the spectrum will be between 324-343 MHz,
but even there, it will be superior to that of a discone or any other
omni scanner antenna!


The simple conclusion, which can be empirically demonstrated with
minimal effort, is that a TV antenna will perform well above a discone
at 343 MHz, a point halfway in the gap of 216-470 MHz. It doesn't
matter that performance will be slightly down from the TV band specs,
because GAIN, F/B ratio, and side-lobes will still make the antenna a
superior performer to discones, dipoles, and even narrow band yagis,
and for that matter, log periodics which have low gain for their wide
bandwidth....typically 6-8 dB.


A TV antenna will be competitive with the log periodics even in the
gaps of its performance........and as a PLUS, will cost a LOT LESS.
More of a PLUS is that TV antennas are easier to install and maintain
than the larger, high profile log periodics. Finally, neighbors are
less likely to *****, whine, complain, and turn you in to some nasty
authority when all you have on the roof is an innocuous TV antenna,
even if it is mounted "all wrong". Neighbors will just think you are
stupid and leave you the hell alone.......which is what you want,
right?


(c) 1997 <All rights reserved> Bill Cheek
 

timmer

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I can verify that having a directional antenna cuts down on intermod/interference. I have a Grove scanner beam pointing north that not only pulls in more signal than my discone ever would, it cuts intermod from nearby strong transmitters and pagers by about 75%. It works great! I'm going to get a second scanner beam and point it south/southwest to get more coverage for my other scanner. That way I don't have to worry about or mess with a rotor.
 

kc9neq

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timmer:
if you use two antennas. one north and one south, how would you connect these to one radio?
 

timmer

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I will have them connected to two different radios. I usually have two and sometimes three scanners going at any one time. I usually have one locked on a single channel, usually the local fire dept. pager freq. One for State Police and one for local city police.
 

ActionJackson

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I use a Radio Shack UHF TV antenna turned sideways to pick up a 800MHz system that is a bit far away. It works pretty well on UHF as well.
Turned sideways as in still horizontal but elements pointing ground to sky ? Or back of antenna pointing to the ground and the tip pointing to the sky with elements pointing side to side (which I believe would be vertical ?)...Can someone help a brutha out ??
 

danieldad

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Turned sideways as in still horizontal but elements pointing ground to sky ? Or back of antenna pointing to the ground and the tip pointing to the sky with elements pointing side to side (which I believe would be vertical ?)...Can someone help a brutha out ??
What you need to do, is to take the antenna, & turn the antenna so that the elements are pointing up to the sky, & the other side of elements are pointing down towards the ground.
Then follow the eminent (late) Bill Cheeks directions regarding running the coax to your radio. I didn't use the gold connector, but the gain I get far outweighs any signal loss I have, in just using the common coax connectors. I can null out noise to the west, & listen to my old buddies working up in NYC, - from Southern NJ.
Hope this helps.
 

n5ims

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Turned sideways as in still horizontal but elements pointing ground to sky ?
Elements pointing ground to sky would be vertical polarization. This is what you need for scanner use. Note that the antenna would be directional so the shorter elements should point towards the signal's transmitter and the long elements pointed away from it.

Or back of antenna pointing to the ground and the tip pointing to the sky with elements pointing side to side (which I believe would be vertical ?)...Can someone help a brutha out ??
This would be horizontal polarization with the antenna pointing out into space, where nearly nothing will be sending signals (unless you're trying to do something like radio telescope, but this antenna wouldn't have nearly the gain necessary for that).
 

wtp

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no rules

there are no rules for receiving so try it out. even using a splitter forwards or backward. two radios one antenna, two antennas one radio. bnc connector with a paper clip for 800. i sis say no rules. what might be bad for some works for others.
experiment and have fun.
 

Voyager

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I haven't read this entire thread, but there are TV bands adjacent to most scanning bands, so it should work well. I've been looking for a cheap TV antenna to use for just this purpose. Mount it vertically rather than horizontally for optimal performance.
 

bigcam406

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i have an Antenna Direct DB2e mounted on my wall that i use from time to time.picks up 7/800 bands that are being broadcasted in my surrounding area (35miles).
 

nbdyspclk

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I use a HDTV antenna from Walmart ($12.00) on a pic post 6' mounted on the roof and run 25' tv coax with adapter cable to bnc into the scanner (536hp).pull in colorado springs public safety and no static or signal loss.70 miles south of me.

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nbdyspclk

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I use a HDTV antenna from Walmart ($12.00) on a pic post 6' mounted on the roof and run 25' tv coax with adapter cable to bnc into the scanner (536hp).pull in colorado springs public safety and no static or signal loss.70 miles south of me.

Sent from my SM-N910T using Tapatalk


Sent from my SM-N910T using Tapatalk
 

ActionJackson

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there are no rules for receiving so try it out. even using a splitter forwards or backward. two radios one antenna, two antennas one radio. bnc connector with a paper clip for 800. i sis say no rules. what might be bad for some works for others. experiment and have fun.
Laughin' my tail off cause I've done all those and then some !! You're right, whatever works just run with it. I have a coat hanger shoved into a Radio Shack mag mount base to pick up low band (CHP) and 800 MHz. Best tri-band antenna for my Pro-163. Oh, and it's in the trunk so it's the ultimate in stealth !

Thanx all for clarifying the orientation of the TV antenna.
 
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