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VHF antenna lengths

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MrGobsy

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Hello,

During my work I have to use multiple radios in the VHF low band and with each radio we have a combination of antennas, each antenna will work with any of the frequencies used on these radios.

My question is, what are the benefits of using either the shorter or longer antennas that I have available?

(Frequency band is 30mhz to 87.975mhz and antenna size is 80cm to 150cm, power is 0.1, 1, 2 and 5watt)
 

prcguy

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For the frequency range you are using, a full length 1/4 wave whip antenna would range from 2.37m at 30MHz to about 81cm at 87.975Mhz. When you shorten an antenna considerably its efficiency goes way down, so a whip closer to its natural full 1/4 wavelength and with no lossy matching circuits would work the best.

Since you are using what sounds like VHF lo band FM military radios with 25KHz channel spacing, antennas for these come in various sizes and have some complex matching circuits in them to cover the wide frequency range and those circuits can be quite lossy, further degrading the antenna performance.

Even though all your antennas are rated for the entire frequency range, for best performance use the longest one (150cm) when your operating frequencies are in the 30-60MHz range, the 80cm long antenna when you are in the 70-90MHz range and if you have one in between size use that around the 50 to 70Mhz range.

I play a lot with similar radios to yours and at 50Mhz where a 1m long antenna on a hand held radio can communicate 30mi to a mountain top, switching to a 33cm long antenna just doesn't work at all.

If you were using radios in the higher VHF band like 136 to 174Mhz where a full 1/4 wave antenna is much smaller and around 41 to 52cm, you can use a full size 1/4 antenna with no lossy matching circuits and get very good performance.

Height is also important in the frequency range you are using and getting the antenna up high in the air will have the most impact on increasing range with your radios.
prcguy

Hello,

During my work I have to use multiple radios in the VHF low band and with each radio we have a combination of antennas, each antenna will work with any of the frequencies used on these radios.

My question is, what are the benefits of using either the shorter or longer antennas that I have available?

(Frequency band is 30mhz to 87.975mhz and antenna size is 80cm to 150cm, power is 0.1, 1, 2 and 5watt)
 

jwt873

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As pointed out above.. The lower the frequency, the longer the wavelength. So, a quarter wave antenna for 30 Mhz will be longer than a quarter wave antenna made for 80 Mhz.

While generally antenna lengths get shorter as the frequency increase, you can't judge the frequency they're made for simply by looking at the length.

Antennas can be cut to different wavelengths.. For instance, you can have 1/4 wave or 5/8 wave or 1/2 wave antenna. Not only that, but coils can be added to make shorter antennas appear longer to radio waves. You can use coils to make co-linear vertical antennas which are multiple wavelengths stacked on top of each other.

You need to use the correct antenna for the application. You can't necessarily judge which would be the correct antenna by simply looking at its length.
 

prcguy

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Since he is using military radios and probably the matching wide band antennas, they will all cover the entire frequency range. Its just a matter of choosing the longer one for best performance on the lower freqs and that would also work fine for the higher ones. Going to the shorter one for the highest frequency range would probably work a little better, but using the shortest one at 30MHz would limit the range.
prcguy

As pointed out above.. The lower the frequency, the longer the wavelength. So, a quarter wave antenna for 30 Mhz will be longer than a quarter wave antenna made for 80 Mhz.

While generally antenna lengths get shorter as the frequency increase, you can't judge the frequency they're made for simply by looking at the length.

Antennas can be cut to different wavelengths.. For instance, you can have 1/4 wave or 5/8 wave or 1/2 wave antenna. Not only that, but coils can be added to make shorter antennas appear longer to radio waves. You can use coils to make co-linear vertical antennas which are multiple wavelengths stacked on top of each other.

You need to use the correct antenna for the application. You can't necessarily judge which would be the correct antenna by simply looking at its length.
 

jwt873

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That's true.. He did say the all the antennas work on all the frequencies..

And normally longer is better, but I'd at least want to know the gain and radiation pattern of each antenna. It could make a difference depending on the specific application.

Most antenna manufacturers have that information online.
 

MrGobsy

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Bristol
Each antenna is listed as a omni directional, vertically polarised broadband antenna

Sent from my SM-G935F using Tapatalk
 

hill

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Location
Middle River, MD
He never stated he was using military radios, since his location of Bristol looks like it could be overseas like somewhere in the U.K.

They have different allocations then we do in USA for those range of frequencies and I think they some public safety in those going from memory.

I await MrGobsy's to tell us what his using.
 

MrGobsy

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Location
Bristol
Military is correct, I'm using the UK prc 354 and UK prc/vrc 355 through to 359 (an updated version of the American SINCGARS radio)
 

prcguy

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His comment of radios specifically covering 30 to 87.975Mhz could be nothing other than military radios. I have never used the PRC-354 and related series, apparently they are newer and not very common on the surplus market yet. I have used or owned many others. Thanks MrGosby for filling us in on the type of radio.
prcguy

He never stated he was using military radios, since his location of Bristol looks like it could be overseas like somewhere in the U.K.

They have different allocations then we do in USA for those range of frequencies and I think they some public safety in those going from memory.

I await MrGobsy's to tell us what his using.
 

mass-man

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Parker Co., TX
COOL...

VHF radios[edit]
VPT - a UK Type 1 (Pritchel) encrypted section to platoon-level UK/PRC354 5W VHF Portable Transceiver (VPT)
ADR+ - an enhanced and improved 'Bowmanised' version of ITT Corporation's company/squadron-level SINCGARS (Single Channel Ground and Airborne Radio System) frequency-hopping radio with a 30-88 MHz frequency range. Depending on its configuration, the ADR+ is variously designated UK/PRC355 (5 W manpack), UK/PRC356 (16 W ground-role manpack), UK/VRC357 (16 W vehicle clip-in radio), UK/VRC358 (16 W low-power vehicle radio), or UK/VRC359 (50 W vehicle-mounted high-power radio).
The manpack version of the ADR+ has an Automatic Situational Awareness Module inserted in BCIP 5.2 which enables Own Station Position Reports to be broadcast without the presence of an associated computer.

Under the terms of the baseline contract, ITT Defence delivered some 26,000 ADR+ radios and 8,000 VPTs, complemented by 580 examples of the UK/ARC341 VHF aircraft role radio (a derivative of the company's SINCGARS AN/ARC-201D airborne transceiver) for helicopter platforms.
 

prcguy

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If they have Type 1 encryption they will never legitimately make it to the surplus market.
prcguy

COOL...

VHF radios[edit]
VPT - a UK Type 1 (Pritchel) encrypted section to platoon-level UK/PRC354 5W VHF Portable Transceiver (VPT)
ADR+ - an enhanced and improved 'Bowmanised' version of ITT Corporation's company/squadron-level SINCGARS (Single Channel Ground and Airborne Radio System) frequency-hopping radio with a 30-88 MHz frequency range. Depending on its configuration, the ADR+ is variously designated UK/PRC355 (5 W manpack), UK/PRC356 (16 W ground-role manpack), UK/VRC357 (16 W vehicle clip-in radio), UK/VRC358 (16 W low-power vehicle radio), or UK/VRC359 (50 W vehicle-mounted high-power radio).
The manpack version of the ADR+ has an Automatic Situational Awareness Module inserted in BCIP 5.2 which enables Own Station Position Reports to be broadcast without the presence of an associated computer.

Under the terms of the baseline contract, ITT Defence delivered some 26,000 ADR+ radios and 8,000 VPTs, complemented by 580 examples of the UK/ARC341 VHF aircraft role radio (a derivative of the company's SINCGARS AN/ARC-201D airborne transceiver) for helicopter platforms.
 
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