Questions about suggested antenna

[WRJC636]

Fellow GMRS friends.  My rural neighbor gave me an old 30 foot aluminum tv ground anchored TV antenna and the huge concretre base.  It seems quite sturdy--he did not guy it, but I thought I would.   He used it before he went to a dish.  Its been laying in the weeds for several years and its been talking to me lately. I'm thinking that it would be perfect for an GMRS antenna that would go well with some of the new 50 watt GMRS mobile / base units I'm seeing for sale in the $300 to $400 range.  I live rural, but with rolling hills.  Closest GMRS repeaters are around 25 miles.  Any antenna suggestions?  Many thanks.  I a[[reciate anyone's time.  

[SteveShannon]

You referred to it as an antenna, but the rest of your question seems to indicate it might be a tower. I’ll answer it as if it is an antenna. My answer would be different for a tower. 
A picture of the antenna might help, but the things that come to mind first are as follows:

First I would put an antenna analyzer on it to see if it’s resonant anywhere close to the GMRS range of frequencies. Channels 2-13 were VHF (30-300 MHz), not UHF (300-3000 MHz). The UHF channels may have been covered by antenna also, but most TV antennas were targeted at VHF.

Second, TV antennas were designed to be 75 ohm. Most two way radio antennas are 50 ohm.  That’s not a bad problem, but may require some ingenuity.

Third, the structure of this antenna might be usable as a tower to raise a GMRS antenna.  That might be a useful thing!

Good luck!

 

[Lscott]

6 hours ago, WRJC636 said:

Its been laying in the weeds for several years

I would inspect it VERY THOROUGHLY AND CAREFULLY first. Depending on materials a cheap galvanized steel tower may have rusted through sections that can fail in a wind gust. Aluminum would be better.

Other things to look for are cracks in the main vertical supports.
 

Look at the welds where the zig-zag stiffing members attach to the main side supports. 

Another is at the top where the mast mounts to the tower.

Cheap towers are nice. But not when they fail, falling on the utility wires, house, garage or your ride. Maybe even you.

[Sab02r]

I like my Tram 1486 antenna...but mine is roof-mounted. 

Perhaps the longer Comet GP-6NC or GP-9NC might be a better use of your dedicated tower.

[WRXW945]

If you are only looking to hit the repeater and not simplex communication, maybe try a yagi antenna.  They are very directional so you would have to aim it at the repeater properly, but they offer substantial gain increases compared to omni directional antennas.  I don't have a ton of experience with them, but others here could probably offer up some suggestions on which one to buy.  

[WRXT271]

For GMRS I would only use an antenna similar to the one I use. It is cut for GMRS frequencies only. Tram Browning BR-6155 76inch fiberglass omnidirectional base 450-470MHz 5dBd antenna.

[WRYF638]

You can build a better antenna than any commercially manufactured one if you are handy. Search for homebrew ham antennas, and use a calculator to resize the elements for your preferred frequency.

https://www.hamuniverse.com/wb3aywcollinear.html

I built a 4-element collinear vertical antenna from copper tubing. It took a bit of tuning to get it perfect, but it was worth the effort. Total cost was about $60, and antenna gain is about 7 dBd (9 dBi). The difference between that and my dipole is amazing.

Edited September 10, 2023 by WRYF638