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NOARD INC ( formerly Northern Ohio Amateur Radio Depot ) no longer |
Getting Better Performance with VHF/UHF Antennas
A Guide to understanding "how to" get the
most from your Antenna Installation.
Hints provided by Rick Wells, K8SCI of
Northern Ohio Amateur Radio Development
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**** GAIN ****
How Does DB Gain effect your ability to Receive/Communicate ?
What's more important, Antenna GAIN or Antenna PATTERN ?
What's a DB ?? THREE DB is equivalent to DOUBLING your
POWER (when your talking about GAIN), but is also equivalent
to CUTTING your POWER IN HALF (when your talking about
LOSS). If you double your power, do you double your distance ?
The Answer is NO. Only SOME of the hiss noise will be reduced
on weaker signals. Most human beings cannot detect any differ-
ence in how a signal sounds with a 1 DB change. How can an
Antenna have GAIN ?? If a antenna has 3 DB gain, it doubled
your power, right ? WRONG ! It gets this gain (only in certain
directions) by taking away its ability to receive (or transmit) in
other directions. That could be good (if you didn't want to receive/
transmit in that other direction) or it could be bad (if it caused you
to lose the performance you wanted in that particular direction).
The Antenna Pattern tries to illustrate what you may experience
when using a particular antenna for a particular application.
*** H.A.A.T. *** - Height Above Average Terrain.
Your Elevation Above Sea Level should be compared to the
Elevations Above Sea Level in a 360 degree circle around your
location. Take a measurement
at every 1 or 2 mile point
extending out 10 to 20 miles from your location at every 22.5
or 45 degree direction. Add to your Elevation Above Sea Level,
the Height above ground your antenna is. If you compare that
total (Your E.A.S.L. + Antenna Height) to the E.A.S.L. 's in
each direction, as soon as the directional E.A.S.L. equals your
Antenna E.A.S.L., your reception in that direction will start
being Shadowed by that ground. The higher the directional
E.A.S.L. is above your antenna E.A.S.L., the greater the shadow
effect will be in causing attenuation of VHFUHF radio signals.
For Good VHF/UHF results in a desired direction, your antenna
should be located (following Common Sense Safety Guidelines)
as high as possible above the E.A.S.L. in that desired direction
with the proper amount of Gain, and, more importantly, the
right Antenna Pattern (see GAIN above).
*** COAX *** - Types to Use, Losses.
The LONGER your Coaxial Cable length is from the Antenna to
your Radio, the more attention you must give to the type of Coax
your using. You could be losing most of the signal before it even
gets to your Receiver !! RG-58 and RG-59 Coax Cable is the
worst ones to use, yet most Scanner and Television Antenna
installations use those types of cables most often. Any installation
exceeding 50 feet of coax cable can often improve their overall
performance by simply upgrading the type of coax being used.
For installations that are 100 feet and more, the improved
performance may be quite surprising. Losses in Coaxial cable
equally affect the receiving and transmitting performance. For
more information on commonly used Coax Cables,
Select : COAX-LOSSES
*** USE OF PRE-AMPLIFIERS ***
Do They Help You, OR, Do They Make It Worse? If you live in
a Metropolitan Area, you will generally find that when you put a
pre-amp on your Television or Scanner antenna, your reception
will actually get worse! This is caused by nearby transmitters
which, even though they are on different frequencies than what
you are trying to get, will over-load the pre-amp and/or the front-
end of your receiver, and, will cause much more mixing of the
stronger signals (pager transmitters are a good example), which
will cause those signals to appear on many other frequencies you
are trying to receive on. You are better off using a better antenna
and coax for your installation. If you live more than 5 to 10 miles
from any strong Radio/FM/Television/Pager/Land-Mobile
communications transmitter, then the possibility of a pre-amp
could help your reception performance. There are some
manufacturers of Filters (or Traps) that are designed to reduce
FM Broadcast or Pager Interference that could be inserted in your
coax, but for best results, those filters should be on the antenna
side of your pre-amp. The mixing of strong signals in your Receiver
is called INTERMOD and is very annoying.
*** WEATHER PROOFING ***
How to Keep It Working like it was when it was new.
Radio Frequency (RF) Signals/Power, and WATER, DO NOT MIX !
*** SAFETY ***
Power Lines, Wind and Lightning.
No Antenna should be installed in a location, whereas, if it fell down it
could come into contact with any electrical power lines. Any Antenna
Installation IS ONLY AS STRONG AS ITS WEAKEST POINT !
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** NEW ** - TV CHANNELS - BROADCAST - 300 MILE RANGE |
The following Web Page is provided to those who may not be aware that
RULES DO EXIST for the Citizens-Band: Citizens-Band
Some Information Concerning Family Radio Service (FRS): FRS
( Web Masters Note: )
Planning to add quite a bit more information on this and other
Hint Pages. Keep Checking for additional information.
HOME - Northern Ohio Amateur Radio Development
www.noard.com
Northern Ohio Amateur Radio Development - Rick Wells, K8SCI
PH: (330) 225-7373
E-Mail
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Brunswick, Ohio is 20 Miles Southwest of Cleveland, Ohio
Updated 01/20/2008
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