Questions about Antennas

[rmidle0095]

Here is a pic of two antennas I got with a xts 2500 VHF.

As you can tell the one on the left looks to be a 800MHZ antenna. It only 5" and the thick one on the right is 4". Can anyone tell me what these antennas are designed for?

[bezking]

The one on the right could conceivably be a VHF stubby antenna (VHF stubs have particularly bad issues, I would avoid them), but there's no way the one on the left is a valid VHF antenna - it looks like a UHF whip.

[JRUTA]

The one on the right could conceivably be a VHF stubby antenna (VHF stubs have particularly bad issues, I would avoid them), but there's no way the one on the left is a valid VHF antenna - it looks like a UHF whip.

Bezking, what particular issues do the stubby vhfs have? I just ordered a legit, Moto one. Now I'm concerned.

Thanks

[bezking]

Well I've never sat down and worked out the numbers, but I was told a few times by different people to stay away from the VHF stubby antennas. I believe it was something about how they are designed internally in relation to VHF radiation characteristics.

[Tom in D.C.]

The answer is all in the wavelength of the frequency in use. A VHF "stubby" antenna is a wound coil, because you can't have an 18-inch or so wire attached to the radio, 18 inches being a rough VHF quarter wave. Making that 18 inches into a coil provides a radiator that is much less efficient than having the straight 18-inch wire. OTOH, a UHF quarter wave is about six inches, so the UHF antenna can be just a straight wire of about that length. Same thing goes for 800 mHz. However, the same rule applies when you go to UHF; you make the antenna into a coil and its performance gets worse than the straight six-inch antenna. Getting back to VHF, the common shortened antenna for VHF is about six or seven inches, which is bad enough, but when you shorten it further to, say, three or four inches its efficiency really suffers. So, if you electrically shorten the antenna for any band the performance is inferior to an antenna that is actually a quarter-wave long. In practice, say with workers communicating at short distances, the antenna length/type doesn't matter all that much, but at greater distances (simplex or into a repeater) the antenna will definitely make a difference.

[Bill_G]

Neither antenna is VHF. The one on the left is hard to say, but my guess is 800. It's too short to be a UHF. The one on the right is a helical UHF.

[FireCpt809]

good indicator is looking at the color ring in the base of the SMA.. Its not 100% but on Motorola antennas its a good chance

[RadioSouth]

Assuming the antenna on the Left is OEM 5 &1/4" and has a white insulator it's a wideband UHF Jedi/XTS series they seem kinda short for their application but are what Motorola sells.
The antenna on the Right looks exactly like a Jedi/XTS VHF stubby (REX4994 ? going from memory) This particular antenna is quite different from the other antenna's Motorola sells. Don't know where they source it from but it is devoid of any Motorola markings and is the only one I've seen that has a plated (chrome or nickle?) connector. Should have a white insulator and measure a shade over 3 &1/2" If I didn't receive mine directly from Motorola parts I would have thought this to be a knockoff.

[rmidle0095]

On both sma connectors the color is a dark red. I believe none of these came from motorola.

[RadioSouth]

No way to tell on a knockoff, a lot of Chinese stuff is made to sell with no regard for function. Wouldn't risk the finals on XTS with an unknown antenna.
Some members have dissected some of these and posted there findings, the innards were laughable.
Pick up an OEM it's cheap insurance for your high end radio,

[rmidle0095]

yah im trading both these in for a real oem one.

[Astro Spectra]

This would help you ID what you have:

http://batboard.batlabs.com/viewtopic.p ... 60&start=0