Will a 70cm antenna work well enough for GMRS?

[SpiritOfRadio]

I am starting to get sucked into the rabbit hole of antennas for vehicles and handhelds.  But there seem to be far more antennas available for the 70 cm band than specifically for GMRS which is about 64 cm per my calculations.

Any problems or downsides to using a 70cm antenna for GMRS?  I don't intend on using any other bands for now.

And if you have personally tested a 70cm antenna for GMRS and have recommendations, that would be awesome!

[WyoJoe]

Many, but certainly not all, antennas are tunable. If you can find a 70cm antenna that is tunable, you can trim a little off the length to retune it for GMRS. As you mentioned, the wavelength for GMRS is shorter than it is for the 70cm ham band, so this is a relatively easy thing to do. Using a 70cm antenna without retuning will cause some of your power to be reflected back to the radio due to an SWR mismatch. How much so will very much depend on the specific antenna. This also may or may not be problematic depending on the specific situation.

With that said, when I'm shopping for GMRS antennas, I try to find either GMRS specific or UHF business band antennas that are designed for the 450 to 470 MHz spectrum. They are out there and not too hard to find, but because they are less common, you may have to look in other places than where you'd look for a ham radio antenna. Buytwowayradios.com is one place I've found them, and theantennafarm.com is another.

[mbrun]

I am starting to get sucked into the rabbit hole of antennas for vehicles and handhelds.  But there seem to be far more antennas available for the 70 cm band than specifically for GMRS which is about 64 cm per my calculations.
Any problems or downsides to using a 70cm antenna for GMRS?  I don't intend on using any other bands for now.
And if you have personally tested a 70cm antenna for GMRS and have recommendations, that would be awesome!

While I don’t use a 70cm antenna for use on GMRS, I know from posts on this forum that some do. Technically you can transmit into any antenna designed for any band, but how long your radio will last doing so is a complete unknown. If your 70cm antenna has a sufficiently wide bandwidth as to present an SWR that is acceptable to you (and your radio) you can use it. An SWR of 2.0:1 or less is acceptable in many circles, including mine. Even some GMRS antenna manufacturers state their SWR is
A wise thing one can do when transmitting into an antenna with a higher-than-optimum SWR is to back the Tx power down. Doing so reduces the actual amount of reflected power to an amount that lessens the probability of radio damage.

I just now re-measured the Comet high-gain dual band antenna I use for amateur work and its SWR ranged from 1.6:1 in the 462.xxxx band to a high of 2.3:1 in the 467.xxx band. Your mileage may very.


Michael
WRHS965
KE8PLM

[wayoverthere]

On 8/8/2021 at 5:09 AM, mbrun said:

While I don’t use a 70cm antenna for use on GMRS, I know from posts on this forum that some do. Technically you can transmit into any antenna designed for any band, but how long your radio will last doing so is a complete unknown. If your 70cm antenna has a sufficiently wide bandwidth as to present an SWR that is acceptable to you (and your radio) you can use it. An SWR of 2.0:1 or less is acceptable in many circles, including mine. Even some GMRS antenna manufacturers state their SWR is
A wise thing one can do when transmitting into an antenna with a higher-than-optimum SWR is to back the Tx power down. Doing so reduces the actual amount of reflected power to an amount that lessens the probability of radio damage.

I just now re-measured the Comet high-gain dual band antenna I use for amateur work and its SWR ranged from 1.6:1 in the 462.xxxx band to a high of 2.3:1 in the 467.xxx band. Your mileage may very.


Michael
WRHS965
KE8PLM

I saw similar with the dual band gp1 I have for the ham side, 2.1 ish in 462 and above 3 to 1 on 467. Similarly less than optimal results with the Midland 5/8 wave gmrs antenna for 70cm.

That said, my mobile is a 5/8 over 5/8 wave browning uhf antenna, rated for 410-490mhz, rather than a gmrs specific antenna...when I checked that one recently related to another topic, it showed 1.1 in 462 (462.5625, 462.725), and 1.12 on 467.725

[OldRadioGuy]

I have tested several of my 70cm ham antennas on my GMRS and the SWR looks fine on all of them.  Under 2:1 in all cases and usually about 1.5 which is just fine.  Most of them are dual band 2m/70cm.  Many of the ham antennas are dual band so this gives you a lot to choose from.

Since 465MHz is a shorter wavelength than the ham 70cm you probably could trim the antenna down very slightly to improve SWR but you'd want to be very careful and use a very short coax with a good SWR meter for your testing.  I do not see the need for this.   You only lose about 10% of your power or .5dB with a 2:1 SWR.

There is a huge selection of 70cm ham antennas so it really is a nice option to have.

Vince

[MichaelLAX]

When I purchased my Anytone AT-779UV mobile radio from Let's Get Ready, I had them throw in a mag-mount antenna for an additional $20.

I presume it was a Ham mag mount.

The antenna works well on all three bands: 2 meters, 70 cms and GMRS, and I typically scan all of my simplex and repeater freqs for all three bands at will.

And the Anytone also works well with my Comet 2 meter, 1.25 mtr and 70 cm antenna on my rooftop.