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Why 1/2 watt for ch 8-14


jc1240
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Hi all.  I'm new both here and with 2-way radios in general (outside of have some bow archaic FRS radios from the late 90s or early 2000s. 

 

I received my GMRS license last week (and am studying for the Amateur Technical). I have a question that I searched for, but didn't find the answer.

 

With the re-alignment of FRS/GMRS frequencies and the increased power for a chunk of them on the FRS side, why are ch 8-14 still limited to 1/2 watt for both?

 

Is there something unique about those frequencies and the possibility of causing interference on some other service?

 

 

EDIT:  Also, does the fact that FRS and GMRS have different bandwidths mean that they cannot talk to each other?

I found the answer at https://midlandusa.com/why-gmrs-for-two-way-radio-communication/  They can communicate with each other.

 

EDIT2:  I didn't even notice the reply below before I added the Midland link.  I was using a cached version of the page I think.

 

Thanks,

John

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Ok, Great questions and while I am half asleep I'll try to get a reasonable answer to you.

Channel 8-14 are limited to .5 watts power and 12.5kHz bandwidth due to them being close to the repeater input channels. By limiting TX power and narrow banding those channels, it reduces the chance of interference with repeater users.

 

FRS is narrow band (12.5kHz) all the way through, and most bubblepack radios will be set up this way. GMRS uses wide band (20kHz.) They can talk to one another if on the same channel, though there will be some degradation of audio (narrow band transmissions will sound quiet on wide band channels, and wide band transmissions may clip or sound over-modulated when heard on a narrow band channel)

Bandwidth is the total amount of frequency space a signal is allowed to take up. A 12.5kHz signal can take up as much as 6.25kHz of frequency space on either side of the center frequency. A 20kHz signal can take up to 10kHz on either side. So when a wide band radio is listening to a narrow band transmitter, it is expecting a 10kHz signal on either side of the center frequency, however since the narrow band radio only sends out 6.25 on either side, the audio output becomes quieter. On the flip side, a narrow band radio is expecting a 6.25 signal on either side of the frequency, however when it receives a 10kHz signal, the radio is hit with an extra 3.75kHz of signal and will either over-modulate, or overload the front end (in rare cases however usually worse when very close to one another.) 

I'm sure some of the other radio heads could explain it better, but thats the fundamentals. Narrow band and wide band radios can talk to one another which a few minor issues, but will work in a pinch. and the .5W TX power is simply to help prevent interference with repeater users.

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Thank you WRAK968.  I must have been on a cached version of the page and edited my original with info I found that they can talk before I saw your reply (but Midland's didn't have the warnings you provided)

 

The explanations are great.  Any more technical at this point and my head would start to hurt, so your level of explanation is perfect.

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Thank you WRAK968.  I must have been on a cached version of the page and edited my original with info I found that they can talk before I saw your reply (but Midland's didn't have the warnings you provided)

 

The explanations are great.  Any more technical at this point and my head would start to hurt, so your level of explanation is perfect.

Anytime. The guys and girls on this site can answer almost any question. Many are Ham/Emergency Communications techs, and we all started out somewhere :) Any other questions you have feel free to research/ask them.

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