ZEN and the art of making a great AM/FM antenna
Mobile One makes AM antennas for Cars,Trains, Boats,Caravans & Buildings.
The most important aspect of any low frequency antenna is the antenna impedance
Car radios have an antenna impedance of 75 ~ 100 Ohms which make it easy to use external antennas
However many desktop radios have a 300 Ohm or higher AM antenna input
impedance (Kenwood) or use
an internal ferrite core antenna and have no simple way of including a external antenna.
Note: Kenwood brand radios are notorious for having high impedance antennas which make it
impossible to have external antennas, these type of radios usually come with a twisted wire external antenna
in the shape of a square using plastic covered twisted wire.
You cannot easily improve the reception without the use of a balun.
The next most important aspect is the antenna feed line or cable cable capacitance, It is important that
when including an external antenna you use Low Capacitance coax such as RG62, Do NOT use
CB coax RG58 as this will attenuate the AM signal, It will not however attenuate your FM signal.
If impedance and capacitance are not right then the AM signal will be greatly reduced
IN A NUTSHELL - A $25 old second hand AM/FM car radio bought at a trash & treasure will out perform
a $500 Kenwood or similar desktop radio on AM anytime.
The Longer The Antenna The Better The Performance
Look at where you plan to put the antenna then measure the maximum length you can use,
then get the longest antenna that will match your requirements.
Cable Lengths Are Not Critical
Unlike UHF CB antennas, the length of cable is not critical but should still remain as short as required
There Are Different Types Of Coatings For AM/FM Antennas
PVC - A thick coat of PVC plastic and is suitable for most applications, available in Black or White.
Polyolefin - A thick coat of Polyolefin rubber, for high quality & very long
lasting finish, available in all colours.
Some Do's & Don't's
With AM/FM Antennas
Do - |
Test
for shorts or open circuit if possible with an multi meter |
Do - |
Mount
the antenna high as possible |
Do - |
Use
a spring even if mounted on a bull bar to absorb vibration from the engine |
Do - |
Use
a wire strap to earth the base if necessary
|
Don't - |
Mount
the antenna close along side any metal object or antenna |
The
Main Causes For Poor Performance With AM/FM Antenna
Poor ground plane |
You
need a suitable ground plane at least the length of the antenna as
the radius of the ground plane in area. |
Antenna too short |
The
longer the antenna the better the performance - in many aspects
|
Antenna too low |
Antennas
need to be as high as possible |
Antenna to close |
Antennas
will simply not work if they are running up along any metal object
such as headlights, bull bars or brick walls |
|
Click here to go to Mobile One's range of Broadcast Band Antennas