car antenna

[geraldchainsaw]

when I installed a electric antenna,   I loss some of my radio stations,  with the orig antenna theres no problems,  the electric is grounded,   any advice what might be wrong?,    the only thing I can think of is,  when the antenna extends it loses contact  somehow,   thanks     jerry

[glr7533]

Here is some information from another site that might help you.

There wouldn't be any operational issues using a newer "power antenna" to the American's tube type radio. Currently available power antennas ( which are all of telescoping design ) will typically max out to about 33 " at full height. This may reduce reception slightly as compared to older antenna which likely will extend further, but the real world difference is negligible. If you decide to use a currently available fixed mast antenna you'll find that it will work just fine.
You can "tweak" most AM radios to fine tune the radio's circuitry to the antenna length to maximize AM reception. Usually there's an "antenna trimmer" adjustment screw on most radios. You can usually find this adjustment near the antenna jack . Sometimes it protrudes from the case like a set screw and sometimes the adjustment is a straight slot screw head recessed behind a hole in the radio case. Most vintage GM-Delco radios have the "trimmer" adjustment accessible from the front of the radio. It's hidden behind the tuning knob. Pull the tuning knob(s) off and you'll likely find the adjustment is behind a small hole. To tweak the adjustment do as follows:
Set your antenna to the desired height. Turn on the radio and tune it to an AM station near the far right of the dial. If it's a tube type radio let it warm up for a few minutes. Slowly turn the trimmer adjustment back and forth to max out or peak the volume level of the selected station. If you have a single, favorite AM station that you always tune that station in and tweak the trimmer accordingly though this method will reduce the radio's sensitivity to other stations.
Two other things to keep in mind. One: the trimmer has no affect on FM reception. Two: Keep in mind that on an AM radio or when on the AM band of an AM/FM and there's a bad or no antenna connection you will hear silence when trying to tune to a station. This could lead you to believe that you have a bad radio or bad speaker. This is unlike the FM band that where you'll normally hear a hissing or whooshing sound when tuning between stations or when there's no antenna connection.

[geraldchainsaw]

thanks,  I'll ck it out.

[Ford Blue blood]

33" is the nominal length for the best FM reception.  It is approximately 1/2 wave length for FM stations in the middle of the frequency range.  AM requires a much longer antenna for optimum reception.  As discussed the older radios had "trimer adjusters" that were designed to make the antenna "look" longer for the much longer wave length of that frequency band.

The tuning instruction grl7533 provided works perfect for a desired radio station.  To get the best reception over the entire band width select a station that is mid range, on the weak side and tweak the trimmer.  That trimmer is used to "match" the antenna to the workings on the AM band.

[mustang6984]

Just for thought...
FM signals are "airborne" meaning they are up above us more so than the AM signals which are considered to be ground biased, meaning they hug the earth more-so.
So, when tuning your antenna, do it with which sort of use will be dominate, FM or AM, and then go from there.

[Ford Blue blood]

Please forgive me for getting in the weeds a little bit with the radio frequency thing. FM radio is considered "line of sight".  The frequency is 88 - 108 MHz, RF energy in that range and higher will propagate in a straight line.  AM is 535 - 1700 KHz and will bend around with the earth's surface because it's wavelength is in multiple meters.  AM signals will also duct and refract, caused by the nature of our upper-level atmosphere.  The result of that was the "clear channel" AM broadcast of days gone by (WSM, WGH, WLS, WHO and so on) that were so easy to listen to at night. The higher frequency of FM also becomes attenuated much faster, primarily because of it's short wavelength, by rain and atmospheric moisture/temperature.