Antenna for GMRS repeater?

[WRTC928]

I know I'm likely to get a lot of differing opinions, but that's okay.

If you were putting up a GMRS repeater, what antenna would you use, assuming that for the time being, you're going to put it on a 30' telescoping flagpole?

[SteveShannon]

14 minutes ago, WRTC928 said:

Do you mean one higher than the other on separate masts, or one directly above the other on the same mast? My understanding is that the latter can be done, but it requires some fancy calculations.

Same mast. No fancy calculations needed, just increase the distance if you detect interference.

[WRYZ926]

I'll add to what @SteveShannon said. It is sometimes easier to keep antennas separated vertically versus keeping them separated horizontally. A lot will depend on your locating and setup.

Think of the radiation pattern of vertical antennas as a beach ball. The lower the antenna gain the rounder the pattern will be. The higher the gain, the flatter the pattern will be. An example would be comparing the pattern of a 5 dBd antenna and a 9 dBD antenna. The pattern with the 5 dBD antenna will look like a donut while the pattern of the 9 dBd antenna will look like a thick pancake.

Keeping the antennas separated vertically works. As Steve said, you can always move the lower antenna down some if you do get some interference.

 

 

[WRUE951]

On 3/18/2025 at 3:43 PM, WRTC928 said:

I know I'm likely to get a lot of differing opinions, but that's okay.

If you were putting up a GMRS repeater, what antenna would you use, assuming that for the time being, you're going to put it on a 30' telescoping flagpole?

There are a lot of other questions you have to figure out.   I use a home brew copper J-Pole on my portable repeater set up. That antenna mounts on a 30' telescoping flagpole mounted on my RV ladder.  The J-Pole does not require a ground plane or a ground however i would still ground the antenna regardless..   The J-Pole is also fairly light and won't overweight the flagpole unless you get a good wind.  There is no way i would mount a dipole on the flagpole as the added weight and length will overwhelm the pole.  You need something light and nimble,  consider wither a copper j-pole or a twin lead J-pole like the Ed Fong J-pole antenna..    

[WSEZ864]

I have two ground planes mounted above one another on a single PVC mast mounted to my chimney. The top antenna is for 2 meters and the lower one is for GMRS. The top of the lower antenna is about 12" below the bottom of the upper antenna. No noticeable interaction.

[WSHH887]

Keep talking guys I am learning a lot. The bit about gain effecting the pattern is new to me. 
So if using a 6db antenna and a 3 db antenna you would mount the 6 db lower since its pattern is "thinner"?

[OffRoaderX]

1 minute ago, WSHH887 said:

So if using a 6db antenna and a 3 db antenna you would mount the 6 db lower since its pattern is "thinner"?

Unless you are trying to bounce your signals off the moon, no.. Just mount the antenna wherever you can and enjoy talking to your friends on your radio.  If you want to over-complicate things, look into getting a H.A.M.s radios license.

[GreggInFL]

On 3/20/2025 at 3:24 PM, SteveShannon said:

I struggle to even skim through it. I mean it’s so far over my head that I don’t even know where to start...

I struggle to understand Steve, so don't ask me any technical questions.

[SteveShannon]

3 hours ago, GreggInFL said:

I struggle to understand Steve, so don't ask me any technical questions.

So do most people!

[WRTC928]

23 hours ago, WRUE951 said:

You need something light and nimble,  consider wither a copper j-pole or a twin lead J-pole like the Ed Fong J-pole antenna..    

That's not really a consideration at present, because this will be a fixed installation. I'll keep it in mind, though.

[Socalgmrs]

Comet 712efc because it doesn’t need tuning, hears everything and tx over 200miles and its only $40 more then other junk