1. The most important aspect of any low frequency antenna is the antenna impedance, Car radios have an antenna impedance of 75 to 100 Ohms which make it easy to use external antennas, Desktop radios and Hi Fi sound systems (Panasonic, Kenwood, etc) have a 300 Ohm or higher AM antenna input
impedance or they may use an internal ferrite core antenna and have no simple way of including an external antenna.
Note: Kenwood and Panasonic desktop brand Hi Fi systems or 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 small square using plastic covered twisted wire. You cannot easily improve the reception without the use of a balun.
2. 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.
IN A NUTSHELL - A $25 old second hand AM/FM car radio bought at a trash & treasure can out perform a $500 indoor desktop stereo system radio & cd player on AM anytime.
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, by far the best antenna is the M160 for FM and the M1 for AM
Unlike UHF CB antennas, the length of cable is not critical but should still remain as short as required, excess cable should never be coiled.
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.
DO - Test
for shorts or open circuit if possible with an multi meter
DO - Mount the antenna high as possible - This can improve the signal and reduce any background noise.
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 - but make sure it is secured
DON'T - Mount the antenna close along side any metal object or antenna
1. The discone is a wide band receiving antenna that can work on an enormous bandwith, allowing you to scan 25MHz to 1.3gHz continuously with equal performance, this is ok for general listening but the drawback is that there is no gain on any frequency or band. Mobile One makes an antenna that is similar to a discone in theory the GPFM or GPAM Antennas.
2. The other antenna is a standard transmitting type of antenna that has been designed for particular frequency and or bands, this antenna does not work equally well throughout 25MHz to 1.3gHz but has highs and lows of performance throughout 25MHz to 1.3gHz, this allows the antenna to have gain on various bands, Mobile One makes such an antenna called a SCATX, this name implies the antenna is a combined scanning and transmitting antenna.
Some digital radios and TV's that are currently available, can have either a F Connector (Large Push In type) or a standard TV Type plug these digital radios and TV's may require a 75 Ohm Antenna, however, there are other smaller DAB+ Radios that require a tiny screw in connector called a SMA connector , these require a 50 Ohm Antenna.