mmckenna
I ♥ Ø
I recently installed a VHF mobile in my wife's new truck. I used a Larsen NMOQ 1/4 wave VHF whip permanently installed in the center of the truck roof. I have an Agilent spectrum analyzer with tracking generator that I borrowed from work to test it before I called it done.
Often hams will ask about various dual band antennas. I've pointed out a few times that a 1/4 wave VHF whip will act as a 3/4 wave on UHF. It is important to point out that a 1/4 wave VHF whip will have a nice radiation pattern on 2 meters, and it'll also have a funky radiation pattern on 70cm, often with major lobes above the horizon. Not a great solution for dual band use, but it is an option if you don't frequent UHF often. Still, a dual band antenna is probably going to serve you better.
But, while I had the test gear at home, I decided to run a sweep not only on the VHF band, but also UHF, just for giggles.
Here's the VHF sweep on a Larsen NMOQ cut for about 148MHz. You can see that a standard 1/4 wave permanent mount on the center of a truck roof will give a nice low SWR across the VHF band:
Here's the UHF band on the same antenna, a Larsen NMOQ cut for 148MHz:
-Remember, on the UHF band, this antenna is going to toss radiation lobes up above the horizon. Not ideal if you are out on the plains, but probably going to work well enough in the mountains where a repeater may be well above the horizon. I ran a Kenwood TM-D710 with a similar antenna for years.
Point is, the SWR is more than acceptable across a nice chunk of useable UHF spectrum. Easy enough to cover the 70 centimeter band, but also GMRS.
So, not trying to sell you anything, just sharing some screen shots for discussion. I still think a dedicated dual band antenna is probably your best choice for 2 meter/70 centimeter use, but using a simple 1/4 wave VHF antenna isn't going to result in damage to your radio, at least not from high SWR.
Here's a sweep of everything from 136-500MHz:
Center of the roof, ideal ground plane, no regrets.
Often hams will ask about various dual band antennas. I've pointed out a few times that a 1/4 wave VHF whip will act as a 3/4 wave on UHF. It is important to point out that a 1/4 wave VHF whip will have a nice radiation pattern on 2 meters, and it'll also have a funky radiation pattern on 70cm, often with major lobes above the horizon. Not a great solution for dual band use, but it is an option if you don't frequent UHF often. Still, a dual band antenna is probably going to serve you better.
But, while I had the test gear at home, I decided to run a sweep not only on the VHF band, but also UHF, just for giggles.
Here's the VHF sweep on a Larsen NMOQ cut for about 148MHz. You can see that a standard 1/4 wave permanent mount on the center of a truck roof will give a nice low SWR across the VHF band:
Here's the UHF band on the same antenna, a Larsen NMOQ cut for 148MHz:
-Remember, on the UHF band, this antenna is going to toss radiation lobes up above the horizon. Not ideal if you are out on the plains, but probably going to work well enough in the mountains where a repeater may be well above the horizon. I ran a Kenwood TM-D710 with a similar antenna for years.
Point is, the SWR is more than acceptable across a nice chunk of useable UHF spectrum. Easy enough to cover the 70 centimeter band, but also GMRS.
So, not trying to sell you anything, just sharing some screen shots for discussion. I still think a dedicated dual band antenna is probably your best choice for 2 meter/70 centimeter use, but using a simple 1/4 wave VHF antenna isn't going to result in damage to your radio, at least not from high SWR.
Here's a sweep of everything from 136-500MHz:
Center of the roof, ideal ground plane, no regrets.