Probably a dumb question - tuning a mobile 2m setup?

[Chazz Layne]

I've been searching the 'net for a couple days now in anticipation of getting my radio installed in the truck, but found nothing. In the past, on CB, the last step of an install was to hook a SWR meter inline and go back and forth from radio to antenna keying-up and tuning. Obviously this is bad practice to begin with, and even worse on HAM frequencies... how does one go about tuning in a 2m setup, or does this even need to be done?

[OU812]

This is not a dumb question and Ill try not to give a dumb answer. I just asked this question a week ago when I installed a 2m antenna in my Jeep. The answer that I got was pretty universally no you don’t need to tune it. You CAN tune it if you would like. But If you buy a 2m antenna and plug it into a 2m radio you will be fine. I got a diamond antenna from Ham Radio Outlet in Kearny Mesa for about $40 and so far it has been working great. I even took it to Big Bear and drug it thru the trees. So no you probably don't need to tune it unless you are having a problem. If you do decide that you want to tune it, know that you have to have a tuner that is capable of tuning in the 136MHz -176MHz range. A CB antenna tuner is made to work around 33MHz if I remember correctly. I priced them out at about $100 when I looked. But unturned I am getting the Keller Peak repeater from Oceanside. Hope this helps.

-Scott

PS feel free to correct me if I'm wrong.

[Chazz Layne]

Helps a ton, thanks... in that case I have everything I need on it's way from HamCity. I should be GTG for BorregoFest.

[sdnative]

You should connect up a SWR meter to it and make sure the reading is under 2.5 or so on the frequencies you plan on using to avoid damaging your rig. A SWR above 3 will most likely cause damage.

From what I understand, lower SWR does not necesarily directly correlate to better transmitter performance, so don't get caught up in trying to get the lowest possible SWR. If you're in the 1.5 to 2.0 range, you're fine.

HRO probably has one you can borrow. No need to even have the radio connected, as it just tests the antenna and feedline.

[DaveK]

Chazz:

Scott is correct, that you will most likely not need to tune anything. Even with a high SWR, most of the radios made today are built so that any SWR, above a certain point, will not damage the radio.

MFJ makes an antenna analyzer that can give you the SWR and many other measurements for your radio. It's a little pricy at about $250.00. If you will be at BF, you can use mine.

[Chazz Layne]

That would be much appreciated. $250 is a bit outside the budget this month, especially for a one-time use.

[sdnative]

A CB antenna tuner is made to work around 33MHz if I remember correctly

27mhz

MJR makes an antenna analyzer that can give you the SWR and many other measurements for your radio. It's a little pricy at about $250.00. If you will be at BF, you can use mine.

Just go into HRO and borrow theirs. They wont let you take it home, but you can test everything out in the parking lot.

[raYGunn]

If the SWR reading is high how do you lower it?

[OU812]

You can change the length of your antenna. I've only had to tune my CB antenna so far so I used this method from Firestick..

-If the SWR on channel 40 is greater than that on channel 1, your antenna is considered to be "LONG" and reduction of physical height and/or conductor length will correct this situation.

-If SWR on channel 1 is greater than that on channel 40, your antenna is considered to be "SHORT" and increasing the physical and/or electrical length of the antenna is required to correct this situation.

The site has some really useful information. Not all of it will apply to 2m but I am sure antenna tuning is about the same. Only difference is the wavelength.

-Scott
KJ6COB

[xtatik]

For a given frequency....lengthen to lower, shorten to raise. In most cases you won't need to tune a 2m/70cm antenna, except for a few of the loaded higher gain models....say 5/8 wave and greater. In that case, for FM just target a frequency that's roughly in the middle of the band. A resonant antenna will not only transmit better, it will hear better as well.