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Frequency bandwidth

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gezafisch

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Hi guys!

I went to google before i posted on here but couldn't find anything that I could make sense of, so I decided to ask here.

How does frequency bandwidth (wide/narrow) effect radio Tx/Rx? Does it extend range at all?

Thanks!
gezafisch
 

jwt873

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It's difficult to answer a general theoretical question in less than 10 paragraphs. :)

What specifically are you thinking about? (Like why is there a wide and narrow band FM setting on your scanner).
 

jonwienke

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How does frequency bandwidth (wide/narrow) effect radio Tx/Rx? Does it extend range at all?
It depends. IF your radio uses a narrow (12.5KHz) IF filter for narrowband channels, then the usable range difference in range is fairly minimal. But a lot of cheaper radios use the same 25KHz IF filter for wide and narrow channels, and just turn up the receiver gain to compensate for the lower deviation of narrowband. That does decrease max range, because the receiver still has to deal with all of the noise in the 25KHz slice of bandwidth it is listening to, but the signal is only modulated enough to stay within a 12.5KHz channel width.
 

902

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In theory, it doesn't. Your power remains the same for either 20K0F3E or 11K2F3E emissions. However, the speech intelligibility changes in marginal areas. There are several forums which indicate maybe a 6 dB difference in intelligibility. If that were correlated to power, a 100 W wideband signal would be about as intelligible as a 25 W wideband signal - if it were narrowband (if you followed that analogy).

There are some schemes to recover audio. Most are proprietary, like Motorola's and Kenwoods comapndoring. They each work within their respective brands, but are not compatible with each other in between brands.

This is also a selling point for digital, as in digital, instead of your brain straining to make out words, a computer chip uses digital signal processing and error correction to deliver what it thinks is the output to the speaker. A narrow digital signal is about as intelligible as a wide analog signal... maybe more so under certain conditions.
 

KC3ECJ

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I've had a range improvement with narrow analog over wide analog on input to a repeater.
 

jim202

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I've had a range improvement with narrow analog over wide analog on input to a repeater.
I find that hard to believe with all the comments that have come back from Public Safety agencies when they changed from wide to narrow band operation some years back. In most cases they saw from 10 to 15 minimum percent range degradation in narrow operation over their original wide band operation.
 

902

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I find that hard to believe with all the comments that have come back from Public Safety agencies when they changed from wide to narrow band operation some years back. In most cases they saw from 10 to 15 minimum percent range degradation in narrow operation over their original wide band operation.
I'm thinking the narrowbanding may have reduced some sort of interference to his repeater input. Something changed. Everything I've heard concurs with what you have.
 

jonwienke

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Narrowbanding a GMRS repeater eliminates adjacent-channel interference from FRS users, because FRS channels are only 12.5KHz from the GMRS channels.
 

RFI-EMI-GUY

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Hi guys!

I went to google before i posted on here but couldn't find anything that I could make sense of, so I decided to ask here.

How does frequency bandwidth (wide/narrow) effect radio Tx/Rx? Does it extend range at all?

Thanks!
gezafisch
See the page at this link. Scroll down for the table and maps. For analog FM there is a 6 dB PENALTY when you go from wide band 25 KHz channels to narrow band 12.5 KHz channels.

Digital modes like P25 and DMR provide relief, but if this is GMRS you don't have that option, so stick with wide band mode where deviation is +/- 5 KHz like the FCC rules intended.


LEIKHIM AND ASSOCIATES LLC - VHF-UHF Narrowbanding
 

RFI-EMI-GUY

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I've had a range improvement with narrow analog over wide analog on input to a repeater.
I find that interesting to say the least. Normally the reduction in receiver bandwidth does improve receiver noise figure, however the reduction in transmitter deviation seriously impacts the received signal to noise ratio,

Why might going narrow band apparently provide improvements?

1) The subscriber radios were already narrow-band and the receiver noise figure was improved and bandwidth and AF gain now properly match.

2) The subscriber radios are wide band and the receiver noise figure was improved and AF gain increased. (this also means the radios are over deviating the receiver filter bans width and potentially distorted on voice peaks)

3) Some persistent adjacent channel interference that was mitigated by going narrow-band.

Pound for pound leaving GMRS or Amateur services wide band will result in better performance. It is one of those many cases where something that seems "outdated" is actually quite better.
 
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