Cheap Antenna Solution for FRS walkie talkie

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ericcarson
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Cheap Antenna Solution for FRS walkie talkie

Post by ericcarson » Tue Mar 05, 2002 11:17 am

Hey, I have a really tiny motorola talkabout FRS radio :)

Alan87I
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Re: Cheap Antenna Solution for FRS walkie talkie

Post by Alan87I » Wed Mar 06, 2002 4:33 am

Those radios work on 462 to 467 MHz . In RF the higher the frequency the shorter the antenna.
The length in feet of the radio wave is determinded by dividing 936 by the frequency for a full wave length . this gives roughly 2 feet. In most radio applications antennas are built in either full wave length / 1/2 wave length or 1/4 wave length . under 1/4 wave length usuall requires some sort of loading coil to make up the elictrical differance , to at least 1/4 wave . I've not yet opened a frs antenna to see if it has a loading coil,If you attached either a 6 inch 1 foot or 2 foot antenna to your radio you should see some improvement. Another experiment is connect a mini female uhf connector and hook it to your ready made TV antenna , Witch is a directional beem . Point it where you talk the most. TV frequencys are very close to the frs frequencys. With a beem the the range is improved in both tx and rx> I'd try it my self but the wind destroyed my tv antenna years ago. Allan

ericcarson
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Re: Cheap Antenna Solution for FRS walkie talkie

Post by ericcarson » Wed Mar 06, 2002 6:13 am

Thanks a bunch Allan! This will help alot! :D

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jollyrgr
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Re: Cheap Antenna Solution for FRS walkie talkie

Post by jollyrgr » Wed Mar 06, 2002 4:31 pm

If you want to follow rules, you will NOT modify your FRS radio to accept an external antenna connector or a different antenna. This is against the rules of this service. In fact the transmitter circuit cannot be mounted separate from the antenna. There are a couple models (car mobile units) that have an external magnet mount antenna. But the "trick" here is that the radio is actually in the base of the unit and the speaker, microphone, and channel selector/indicator are in a separate unit inside the car.<p>But speaking from a "theoretical" or "technical" point this is basically a half watt GMRS radio. In fact the first seven channels of the FRS radio is shared with GMRS. What is GMRS? It is the General Mobile Radio Service, a LICENSED radio service. With GMRS you are allowed to add external antennas. These antennas could be amateur radio (or ham radio, another licensed service) 440MHz (70CM) antennas cut down slightly. Both ham and GMRS radios have provisions on most of their handhelds to have a "rubber ducky" that has a MALE BNC antenna attached to them. The GMRS and ham radios have a FEMALE BNC connector on them. If you desire in these services you can take off the "rubber ducky" and connect a 50 ohm piece of coax with a BNC connector (or apropriate adaptors) and use an externally mounted antenna. Antennas on FRS are somewhat interesting. On a number of FRS radios the antenna is a coil/spring that slips inside the hollow rubber tube. In other words the antenna is soldered directly to the main board and is just a coil of wire. The rubber "antenna" is fastend to the case and the "coil" antenna is slipped up inside the tube when the radio is assembled. (I snagged the picture from off the web; it is not mine. It is from the following web site: http://www.whiteson.org/boxster/mods/frs/#)<p>;) . <p>So what does this mean? Even though you COULD open up the radio replace the antenna with a FEMALE BNC connector. And you COULD use a "rubber ducky" with BNC for handheld use and an external antenna for MOBILE/BASE work. You LEGALLY cannot do this.<p>[ March 06, 2002: Message edited by: Jolly Roger ]<p>[ March 06, 2002: Message edited by: Jolly Roger ]<p>[ March 07, 2002: Message edited by: Jolly Roger ]</p>
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

HomeBrew
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Re: Cheap Antenna Solution for FRS walkie talkie

Post by HomeBrew » Thu Mar 07, 2002 1:39 am

The TV antenna will work especially if you happen to still be using 300 ohn twin lead. I have used this many times with various types of low power transmitters and if your in the path of the front end of the antenna, you might be suprised at the range you can get. The 75 ohm will work,but my results were not as good.

Alan87I
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Re: Cheap Antenna Solution for FRS walkie talkie

Post by Alan87I » Thu Mar 07, 2002 5:12 am

If the TV antenna was modified . Insulate it it from the mast and connect the common lead to the mast and positive conductor to the the antenna. The system would also benifit from the use of a matching network or tuner. MFJ makes some nice units. But the expence would most likely out weigh the gain. The sugestion of the Gmrs units is a good idea these radios have more power and some models will work some of the frequencys in the frs band. But they are expencive as well. As mentioned the 300 ohm feed line worked better, the feed line has to match the impendance that the radio has on it's output circuit. their stock antenna is most likely far from a common 50 or 75 ohm circuit. I bet a good Ham tuner in line would get some impressive results . Allan

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