How to tell what an antenna is tuned to?

Status
Not open for further replies.

k9-cop

Member
Joined
Jul 14, 2006
Messages
36
I have several mobile antennas that I have aquired but I am not sure what band they are tuned to for transmitting and receiving. What pieces of equipment would I need to test these antennas? How do they work?
 

af5rn

Member
Joined
Apr 4, 2008
Messages
1,059
Location
N. Tex / S. Fla
Man, this used to be easy. But these days it's not always easy, with all the dual-band, collinear, and cell look-alike designs out there. If these are straight whips without loads, then it's a simple matter of measuring them with a tape measure and figuring the wavelength. Probably no such luck though. Like Code3 said, we'd probably have to just eyeball them and compare them to known antennas on the market. A lot of people here have a lot of antennas, so post some pics and I bet we can help you solve the mystery.
 

k9-cop

Member
Joined
Jul 14, 2006
Messages
36
Yeah that is the problem is that I have several different styles that I have aquired over the last few years. I only work with radios in the public safety bands, no hams or anything like that. So there is no one piece of equipment that I can purchase and hook the antennas up to for tuning etc.?
 

KE5MC

Member
Premium Subscriber
Joined
Dec 19, 2002
Messages
848
Location
Lewisville, TX
k9-cop said:
Yeah that is the problem is that I have several different styles that I have aquired over the last few years. I only work with radios in the public safety bands, no hams or anything like that. So there is no one piece of equipment that I can purchase and hook the antennas up to for tuning etc.?
Grid-Dip meter was or still is common for checking resonate circuits.

Oscillator with switchable tuning coils for different frequency ranges. Depending on if the circuit is series or parallel resonate the meter would peak or dip and you could read the frequency off the dial indicator. Bring the coil in close to the circuit under test affects the Q of the oscillator and changed the meter reading.

I don't know how well it would work for antennas.
 

af5rn

Member
Joined
Apr 4, 2008
Messages
1,059
Location
N. Tex / S. Fla
If all you are dealing with is professional LMR radio, that simplifies things greatly. Most all of it can be readily identified on sight by nomenclature. Post some pics and whip lengths, and let us take a shot at it. Sounds like a fun exercise. Then you can tell us how accurate we were after you test them.

As for the machine, a test monitor and/or an SWR meter should do the trick. Transmit through the antenna in the four different bands until you find the band with the lowest SWR, and there ya go. Then you can fine tune to find the actual resonant frequency of that particular antenna for a more precise determination. For example, finding out that it is UHF is the easy part. But determining whether it is cut for the federal band (401-420ish), the LMR band (450-470ish), or the UHF-T band (482-512ish) will take a little more time and testing. Definitely doable though, without much hassle or expensive equipment. Good luck!
 

k9-cop

Member
Joined
Jul 14, 2006
Messages
36
Forgive my ignorance but I am looking for a machine on Ebay to accomplish what I am looking for to test my UHF/VHF antennas. Will this machine work for what I want to do?

http://cgi.ebay.com/SWR-14-SWR-Power-Meter-CB-used-to-tune-antenna_W0QQitemZ180235997899QQihZ008QQcategoryZ48699QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

If not would someone post some ebay links for me for what I need? If there is something a little better than what I posted could you post it as well? Thanks for the time and patients.
 

mancow

Member
Database Admin
Joined
Feb 19, 2003
Messages
5,940
Location
N.E. Kansas
No, but this will do it through 470 Mhz.

http://tinyurl.com/5emqev



k9-cop said:
Forgive my ignorance but I am looking for a machine on Ebay to accomplish what I am looking for to test my UHF/VHF antennas. Will this machine work for what I want to do?

http://cgi.ebay.com/SWR-14-SWR-Power-Meter-CB-used-to-tune-antenna_W0QQitemZ180235997899QQihZ008QQcategoryZ48699QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

If not would someone post some ebay links for me for what I need? If there is something a little better than what I posted could you post it as well? Thanks for the time and patients.
 

k9-cop

Member
Joined
Jul 14, 2006
Messages
36
Yikes that is spendy! Any non digital ones that are on the cheaper end?
 

zz0468

QRT
Joined
Feb 6, 2007
Messages
6,029
It seems kind of silly to spend a bunch of money to determine what frequency some unknown antennas are. Especially if you don't have the technical skills to operate the equipment or interpret the results. And if you don't know what the meters and displays are telling you, the answers you get will be meaningless.

A semi-skilled technician could determine what they are with a signal generator, a directional coupler, and a detector. That's the simple way. The cheap way is with the device that mancow linked to. The fun way is with a network analyzer.

In your case, if you need antennas, you're better off either buying new, or taking what you have to someone who already has what they need. If you don't need antennas and are just curious, there's a better and more logical way of acquiring the knowledge you seek.
 

af5rn

Member
Joined
Apr 4, 2008
Messages
1,059
Location
N. Tex / S. Fla
k9-cop said:
Yikes that is spendy! Any non digital ones that are on the cheaper end?
LOL! That IS the cheaper end! When you said you "work" with radios in the public safety band, I thought you meant professionally. I've never known a professional radio shop or tech to not have a service monitor, and they cost a couple grand on the low end (without spectrum analyser).

If you're not quite ready to drop a couple hundred on the cheapest possible solution, then yeah... we're back to posting some pics and lengths so we can help you identify them.
 

k9-cop

Member
Joined
Jul 14, 2006
Messages
36
You are correct, when I say that I work with radios more of what I meant is that I am in charge of the inventory of radios for our department. I also do all of the programming of our radios. That is the extent of what I do......
 
Status
Not open for further replies.
Top