Wideband v.s Narrowband

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DaveS
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Wideband v.s Narrowband

Post by DaveS » Wed Apr 06, 2005 4:12 pm

I was searching the net trying to find an answer to something I have been curious about and found this very nice site you guys have here and thought I would register to ask this and probably many more questions in the future.What is the difference between wideband and narrowband transceivers? Just for example,if you used wideband on a band like FRS that is supposed to be narrow only,would other NB radios hear you and vice versa ? Would it interfere with anything or anyone? Is it illegal and why? I was told by a self appointed radio expert it does not matter but I had to disagree quietly for the moment because I know nothing about it! I would like some facts before I go back to tell this guy he is wrong or not.

k2hz
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Re: Wideband v.s Narrowband

Post by k2hz » Wed Apr 06, 2005 4:36 pm

DaveS wrote:I was searching the net trying to find an answer to something I have been curious about and found this very nice site you guys have here and thought I would register to ask this and probably many more questions in the future.What is the difference between wideband and narrowband transceivers? Just for example,if you used wideband on a band like FRS that is supposed to be narrow only,would other NB radios hear you and vice versa ? Would it interfere with anything or anyone? Is it illegal and why? I was told by a self appointed radio expert it does not matter but I had to disagree quietly for the moment because I know nothing about it! I would like some facts before I go back to tell this guy he is wrong or not.
You are correct and your "expert" is wrong.

An FRS transceiver and other radios operating in the narrow band mode
have an FCC authorized bandwidth of 11 kHz vs 16 kHz for wideband.

The effect of the excessive bandwidth of "wide" into "narrow" is that the signal simply does not "fit" into its assigned channel or the charachteristics of the associated receivers.

Attempts to use wideband equipment on a narrow band system produces 2 bad results -

The wideband signal is too wide to pass through the IF filters and discriminator in a properly designed narrow band radio receiver so it gets horribly distorted and the squelch tends to "pump" (chop out on voice peaks)

Your signal is wider that the FCC authorized channel so you are interferening with users on the adjacent channel. Also, your wideband receiver will experience interference from authorized adjacent channel users since its selectivity is too wide to properly reject the adjacent channels.

DaveS
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Post by DaveS » Wed Apr 06, 2005 10:08 pm

Wow,great response,that was exactly what I was looking for,thanks.

n5tbu
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Post by n5tbu » Mon Aug 08, 2005 6:26 am

11khz and 16 khz????? It should be:narrow band at +/- 2.5 khz and wideband at +/- 5 khz.
mod

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wowbagger
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Post by wowbagger » Mon Aug 08, 2005 10:05 am

n5tbu wrote:11kHz and 16 kHz????? It should be:narrow band at +/- 2.5 kHz and wideband at +/- 5 kHz.
mod
Not quite - you and he were not speaking of the same things.

You are speaking of the maximum instantaneous deviation - the amount the carrier will be displaced by a signal peak. For that, narrow band is usually accepted as 2.5 kHz and wideband as 5 kHz.

However, that is NOT the bandwidth of the signal. Since the modulating waveform is changing, this widens the signal more than the instantaneous deviation. In fact, the actual mathematical bandwidth of any FM signal is infinite - the result of FM is what is known as a Bessel function, which has components right out to F=infinity.

However, the magnitude of these components drops off rapidly as the distance from nominal carrier increases, and normally it is possible to bandwidth limit the resulting signal to only a couple of Bessel "lobes" with no real loss of fidelity.

The usual rule of thumb to compute the overall bandwidth of an FM signal is 2*(D+B) where D is the maximum instantaneous deviation of the signal, and B is the maximum frequency of the modulating waveform. For voice, B is usually taken as 3 kHz, so for narrowband:

2*(2500 + 3000) = 11000

and for wideband:
2*(5000 + 3000) = 16000

So, you are both right, but you are not both talking about the same thing.
If you have questions on the IFR COM-120[ABC] or 2975, I designed them. If you want manuals, calibration information, or pricing information, please contact Aeroflex directly.

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Boomer740
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Post by Boomer740 » Mon Aug 08, 2005 10:55 pm

I had never seen the math for that before. Thanks!

Paul

silverbk
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Post by silverbk » Tue Mar 28, 2006 1:25 am

I would also like to mention that if you attempt to use a narrowband radio on a wide system. You will get low audio on the wide receivers.

So in short you must use compatible equipment for both technical as well as legal reasons.

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No More Saddam
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Re: Wideband v.s Narrowband

Post by No More Saddam » Thu Feb 28, 2008 1:47 pm

Not to mention that you can only use type accpeted radios for FRS. They have to be built for that service or can be hybrids what conform to the FRS standards. FRS is limited to .5 watts and the radio cannot have a detachable antenna. So you cannot program your 45 watt Spectra on FRS and be legal.

Slimbob
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Re: Wideband v.s Narrowband

Post by Slimbob » Sun Feb 08, 2009 3:28 am

No More Saddam wrote:Not to mention that you can only use type accpeted radios for FRS. They have to be built for that service or can be hybrids what conform to the FRS standards. FRS is limited to .5 watts and the radio cannot have a detachable antenna. So you cannot program your 45 watt Spectra on FRS and be legal.
But, but, what about if I program that channel and only use it in the event of emergencies, you know, when the FCC rules don't apply?

/me ducks.

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