What is the difference in 1/4 wave and 5/8 wave nmo mount antennas?

[dcfrmp255]

As said above. I'm kinda new to nmo mount antennas. Which one gets better reception? I'm gonna be transmitting with 45 watts. I have both, I'm just wondering what the difference is and, which one to put on my truck. Any help would be appreciated. Thanks

 

[Lt.214]

Hi,


The difference between the 2 antennas is a 1/4 wave antenna does not produce any gain and is a smaller antenna in height. The 5/8 wave antenna will be taller in height and add gain to the power the radio is putting out.


For VHF(150 Mhz) you usually get about 2db gain from a 5/8 wave antenna. What this means is say you have a 50 watt radio connected to your 1/4 wave antenna, it puts 50 watts out of the antenna(in a perfect world). If you replace the 1/4 antenna and connect the 5/8 wave antenna with the 2db gain rating, it would now be similar to connecting your 1/4 wave antenna to a 100 watt radio.


Since the antenna is longer, there is more antenna to radiate the 50 watts coming out of it, so its similar to having a more powerful radio connected to a smaller antenna, and improves the performance and potentially the range of your radio.


This is the simple explanation without getting into all the tech stuff.


Hope this helps,


Chris

 

[dcfrmp255]

Thanks for the info. I'm prolly gonna go with the 1/4 wave because, I dont want that long whip from the 5/8 wave sticking up from my cab.

 

[NPS Ranger]

Actually if you got 100 watts of effective radiated power with the new antenna compared to 50 watts with the old, that would be a 3 dB gain, not 2.


dB gain = 10*log(Power out/Power in)


An antenna with twice the effective radiated power would therefore have a gain of 10*log(2/1) = 3dB.

 

[WS224]

What is the difference in 1/4 wave and 5/8 wave nmo mount antennas?

This one was pretty easy. I actually did it in my head.


The answer is 3/8.

 

[Lt.214]

I was merely giving the OP a basic idea of the diference. I am well aware of the theory of ERP and the math behind it. Since NPS felt the need to post the math behind ERP to prove his point then yes he is correct in his numbers, before you factor in db loss in the coax, if there is a poor SWR match on the antenna, loose connections creating a poor ground etc.


All are antenna tech items that I was attempting not to confuse the OP with since the OP stated their knowledge was very limited with antennas.


Chris

 

[NPS Ranger]

Haha OK, point taken. But my point was the following:

If you replace the 1/4 antenna and connect the 5/8 wave antenna with the 2db gain rating, it would now be similar to connecting your 1/4 wave antenna to a 100 watt radio.

If you factor in what you said in your second post:

before you factor in db loss in the coax, if there is a poor SWR match on the antenna, loose connections creating a poor ground etc

then if you replace the 1/4 antenna and connect the 5/8 wave antenna with the 2db gain rating, it would now be similar to connecting your 1/4 wave antenna to about a 65 watt radio.

Just breakin yer balls. :lol:

 

[Lt.214]

Well I mean if we are going this far, might as well discuss the reverse flow of the 1.21 Gigawatts needed to excite the flux capacitor through the kanuetor valve that drives the dylithium crystals in the power amp to produce the wattage needed to make the math work!


Chris

 

[Newberry13]

Well I mean if we are going this far, might as well discuss the reverse flow of the 1.21 Gigawatts needed to excite the flux capacitor through the kanuetor valve that drives the dylithium crystals in the power amp to produce the wattage needed to make the math work!


Chris

:ugeek: Here I thought I was good at math and science. Thanks for destroying my dreams of working for NASA and going into space. :mrgreen:

 

[Lt.214]

Radios aren't rocket science, you should do fine. I mean we have been putting men and women in space for decades using low bid parts and space craft. :lol:

 

[SlickTop Solutions]

Radios aren't rocket science, you should do fine. I mean we have been putting men and women in space for decades using low bid parts and space craft. :lol:

Not to mention the weapon I carried in the Army, the Humvee I rode in and the uniforms I wore were all produced by the lowest bidder.