How to tell what an antenna is tuned to?
- Thread starter k9-cop
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RolnCode3
Member
There's no marking on them? Can you compare them to photos of antennas on TESSCO or some other website? Pictures often help with identifying as well.
af5rn
Member
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.
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.?
k9-cop said:
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
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!
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!
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-Powe...ryZ48699QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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.
http://cgi.ebay.com/SWR-14-SWR-Powe...ryZ48699QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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.
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.
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
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).k9-cop said:
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.
hoser147
Member
Check with whoever does your commercial radio work, after all they probably supplied the radio's and antenna's to your dept. Hoser
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