New antenna

[Jmit5425]

Purchasing a new mag mount antenna and i thought i read it's best to cut the length to 7.5" for getting the best performance for railroads. Can anyone confirm that for me?
Thanks
Jeff

 

[mmckenna]

Purchasing a new mag mount antenna and i thought i read it's best to cut the length to 7.5" for getting the best performance for railroads. Can anyone confirm that for me?
Thanks
Jeff

Antenna length is related to frequency and antenna design. Without knowing the specific antenna you are purchasing and which frequencies you want to listen to, we can't answer your question.

 

[Jmit5425]

Railroad frequencies.

 

[mmckenna]

Railroad frequencies.

I'm assuming you mean the 160MHz VHF band, not any of the other bands they use?

Antenna length also depends on the exact type of antenna. A 1/4 wave will be a different length than a 1/2 wave, and that'll be a different length from a 5/8th's wave.

Without knowing EXACTLY what model antenna you have, no one can provide a length.

More than happy to help you out here and walk you through the process, but you haven't provided enough information to give you a proper answer. Fill in the blanks for us and we can help. We can't guess at what you have.

 

[Jmit5425]

Makes total sense. I just thought that since i mentioned railroad frequencies that would suffice. Here's what I'm buying,

ProComm JBC-290M/BN Mini-Mobile Magnet​

I thought i read on another site that 17.5" was the right length for the 160mhz frequencies.
Any thoughts?

 

[Hdc30474]

That antenna's whip seems to be 18 inches in length if I looked up the right one. It appears to be a 1/4 wave magnetic mount.

The length of a 1/4 wave antenna element is 234/frequency = length in feet.

At 160 MHz that is 17.55 inches. Unless you are transmitting and actually check transmit VSWR, do not cut that antenna. For 160 MHz the antenna at 18 inches (156 MHz) instead of 17.55 is not going to make any difference for receive.

 

[Jmit5425]

Ok. That's a great answer. At least now i know. I appreciate your response.
Thanks
Jeff

 

[Hdc30474]

Ok. That's a great answer. At least now i know. I appreciate your response.
Thanks
Jeff

If I do understand what that antenna is, it should work fine from probably 140 MHz all the way to 174 MHz for receive. And even fairly well down to 118 Mhz for receive. If you plan to mount it on a car or truck. If just sitting on something non metallic, it will not work nearly as well. It neads to be on a fairly good size piece of metal. 12 inches across or more.

 

[Jmit5425]

Got it, thanks

 

[mmckenna]

Yeah, that's squarely in the middle of "not going to be noticeable" if you cut it.

Earlier, you said 7.5" which threw me off quite a bit. 17.5" is close enough to 1/4 wave for what you are doing.