Question adout an antenna

KK4ELO

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For some reason it won't let me post another pic of the size. Says the file is too large. The whip is 16 inches, straight. Spring is 2 3/4 inches and the base coil is 1 3/4.
 

APX7500X2

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ecps92

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Correct it is a VHF and UHF, as PRCGuy indicates you trim/cut it to a specific frequency, there-by making it either VHF or UHF - not both
Ok.. I'm confused because it specifically says vhf AND uhf on the website.. Ok, so scanner antenna it is then thanks.
 

mmckenna

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Ok.. I'm confused because it specifically says vhf AND uhf on the website.. Ok, so scanner antenna it is then thanks.
How long is the whip?
If it's 1/4 wave, 18 or 19 inches or so will make it resonate on VHF. If it's around 6", it'll be resonate on the UHF band.
 

KK4ELO

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I know the quarter waves 19ish and 6ish, but they have no loading coil on them. I have a bunch. But this on has a loading coil in the base just like my Larson nmo 2/70.
 

mmckenna

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The base is not necessarily a loading coil.

What you have is a wide band 1/4 wave antenna. With the 16" whip and the length of the spring, it's tuned for likely the 154MHz range.

If it was resonate on the 2 meter band, it would act as a 3/4 wave UHF antenna on 70cm. Not a perfect dual band solution, but it will work with a funky radiation pattern on UHF. I've done it before with VHF quarter wave antennas.
 

mmckenna

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Looking at your last photo, that's VHF.

The nice thing about quarter wave antennas is that they are very broad banded. This one being a "wide band" version will do even better. If you have an SWR meter, give it a try on 2 meters and if the SWR is good, give it a try on 70cm.
 

KK4ELO

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I was gonna mount it in my truck for my dmr ht. I don't have an swr meter so it'll be a receive only antenna until I get a dual band. Don't want to burn out my ht. Thanks for the clarification
 

W5lz

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That frequency spread is not the usable bandwidth of the antenna. It -is- the frequency range it can be made to work on. That's typically done by adjusting the length for frequency. If it worked on your vehicle then it will work 'fixed' if you provide the "ground"/counterpoise/'other half' for it. Lots of ways to do that, ranging from a number of radials to a 'pie plate' (big pie!). Too big is typically better than too small, and 'close' counts fine. And "one size fits all" is still a dream...
 

dlwtrunked

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The base is not necessarily a loading coil.

What you have is a wide band 1/4 wave antenna. With the 16" whip and the length of the spring, it's tuned for likely the 154MHz range.

If it was resonate on the 2 meter band, it would act as a 3/4 wave UHF antenna on 70cm. Not a perfect dual band solution, but it will work with a funky radiation pattern on UHF. I've done it before with VHF quarter wave antennas.
It is definitely not a loading coil (else it would short out) but just a strain release.
 

K4RBT

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It looks like an Antennex B136 unity gain antenna. You cut the whip for the desired frequency. When the whip is cut, you have to allow for the height of the spring as it radiates as well. I think the heavy base is so they can make a robust antenna with a NMO mount.
I cannot find an Antennex website. I think it merged with Laird and they do not have generic mobile antennas anymore. Leaning toward public safety multi port antennas.
 
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