As for an external magnetic mounted antenna cut to the railroad band, with a BASE loading coil designed to include the railroad band. (160-162 MHZ) recommend using 160.890 as the frequency to cut the 5/8 wave antenna whip to. Quality antennas come with a cutting chart so that the proper length of the antenna whip can be obtained for the desired frequencies. 160.890 is in the center of the railroad band. Here is the Larsen Antenna cutting chart: [www.larsen-antennas.com]

Highly recommend that you not use an antenna designed for anything outside the 144-174 MHZ band range, unless you want your Radio Shack scanner to pick up more birdies, and noise than you can stand, possibly even reject weak signals you want to hear from the railroad band. An antenna designed to work in the 160-162 MHZ range is best.

This same frequency range is improtant in choosing the base loading coil, at the bottom of the antenna whip. A base loading coil increases antenna gain. To some extent it helps reject frequencies outside of what you want to hear, while making the antenna more sensative to the proper frequencies. In other words you don't need a multi-band antenna that just does a fair job on all frequencies, if you are serious about listening to railroad frequencies. An antenna cut for the railroad band will still work for other than railroad frequencies in the VHF high band, just not as well.

Recommend placing the magnetic mount antenna in the center of the vehicle's roof, or on the trunk lid, to provide the best possible ground plane. A good ground plane helps reflect signals to your antenna whip. There are antennas designed to work without a ground plane such as Larsen's OM150CK for 144-174 MHZ. The initial post mentioned a rubber duck antenna on a magnetic mount. While this does not sound like a good idea for a a vehicle, for hand held scanners there are rubber duck type antennas manufactured for the railroad band. These noticeably improve performance. Larsen offers them in various frequency ranges and with various connectors: [www.larsen-antennas.com]
The helical type has served well.

Having resistor type spark plugs and resistor type spark plug wires helps cut down on background interference and noise. There are also filters that can be installed to reduce alternator whine. However, I have only had to do that on two older 70's era automobiles.

Finally I would warn all objectors the information presented here has been learned over 39 years of railroad radio listening, along with a few concepts learned while working with the Santa Fe's Communications Dept technicians. You are of course entitled to disagree, just remember that this information is offered in an attempt to help others. I am certainly not an radio expert.

While Radio Shack scanners have improved over the years, it is doubtful that the antennas they may offer are of the same high quality as Larsen Antennas. In my opinion Larsen Antennas are the best. The railroad industry continues to use Larsen products. With the internet Larsen Antennas are not as difficult to obtain as they used to be. Here is their catalog: [www.larsen-antennas.com] Recommend their LM150 series.

When reading the Larsen catalog always remember that the railroad band is 159-162 MHZ, and don't order anything that does not include that range. If you can find a Larsen dealer who is knowledgeable about commercial and ham radio, they should be willing to help you find the package or separate parts you need. Their home page is [www.larsen-antennas.com]