Jump to content
  • 0

GMRS NFM or FM


jrogers2
 Share

Question

Our radio club has a GMRS repeater that we want to use for emergency communication. We have two members, each an "expert" with FRS/GMRS rules and equipment. The problem is one says that GMRS is Narrow Band while the other says it Wide Band.

 

I need to know which is correct and the Part 95 FCC rules that addresses this issue.

Link to comment
Share on other sites

9 answers to this question

Recommended Posts

  • 0

Despite what Midland Marketing would like the world to believe, by marketing non compliant radios, GMRS is wide band baby.

 

The modulation is +/- 5.0 KHz, the channel bandwidth is 20 KHz and the channel spacing is 25 KHz. Example 462.600 and 467.600 MHz. The exception are the GMRS interstitial channels at 467 MHz which are narrow band +/- 2.5 KHz, on 12.5 KHz channel spacing.  Example 467.5875 MHz when used by GMRS radios.

 

All FRS interstitial channels 462 and 467 MHz are narrowband. Example 462.5875 and 467.5875 MHz when used with FRS radios.

 

Wide band is what the God of FM Radio Major Edwin Armstrong intended:

 

https://en.wikipedia.org/wiki/Edwin_Howard_Armstrong#Wide-band_FM_radio

 

Wideband is tremendously better than narrowband: 3 dB better which translates to much greater area reliability.  If you have a narrowband radio trying to use a wideband repeater or simply talking directly, the loss is greater ~ 6 dB.

 

YOUR REPEATER SYSTEM WILL PERFORM MUCH BETTER IF ALL COMPLY WITH WIDEBAND AS INTENDED. THERE WAS NEVER AN FCC NARROW BAND MANDATE FOR GMRS NOR WILL THERE EVER BE AS FRS ALREADY OCCUPIES THE INTERSTITIALS.

 

See the maps wide vs narrow. Green good, yellow nope.

 

http://www.leikhim.com/page13.php

 

FCC Rules:

 

§ 95.1773 GMRS authorized bandwidths.
Each GMRS transmitter type must be designed
such that the occupied bandwidth does not exceed
the authorized bandwidth for the channels used.
Operation of GMRS stations must also be in
compliance with these requirements.
(a ) Main channels. The authorized bandwidth is
20 kHz for GMRS transmitters operating on any of
the 462 MHz main channels (see § 95.1763(a )) or
any of the 467 MHz main channels (see
§ 95.1763(c )).
(b ) Interstitial channels. The authorized
bandwidth is 20 kHz for GMRS transmitters
operating on any of the 462 MHz interstitial
channels (see § 95.1763(b )and is 12.5 kHz for
GMRS transmitters operating on any of the
467 MHz interstitial channels (see § 95.1763(d )).
(c ) Digital data transmissions. Digital data
transmissions are limited to the 462 MHz main
channels and interstitial channels in the 462 MHz
and 467 MHz bands.

 

§ 95.1775 GMRS modulation requirements.
Each GMRS transmitter type must be designed to
satisfy the modulation requirements in this section.
Operation of GMRS stations must also be in
compliance with these requirements.
(a ) Main channels. The peak frequency deviation
for emissions to be transmitted on the main
channels must not exceed ± 5 kHz.
(b ) 462 MHz interstitial channels. The peak
frequency deviation for emissions to be transmitted
on the 462 MHz interstitial channels must not
exceed ± 5 kHz.
(c ) 467 MHz interstitial channels. The peak
frequency deviation for emissions to be transmitted

on the 467 MHz interstitial channels must not
exceed ± 2.5 kHz, and the highest audio frequency
contributing substantially to modulation must not
exceed 3.125 kHz.
(d ) Overmodulation. Each GMRS transmitter
type, except for a mobile station transmitter type
with a transmitter power output of 2.5 W or less,
must automatically prevent a higher than normal
audio level from causing overmodulation.
(e ) Audio filter. Each GMRS transmitter type
must include audio frequency low pass filtering,
unless it complies with the applicable paragraphs
of § 95.1779 (without filtering).
(1) The filter must be between the modulation
limiter and the modulated stage of the transmitter.
(2) At any frequency (f in kHz) between 3 and
20 kHz, the filter must have an attenuation of at
least 60 log (f/3) dB more than the attenuation at
1 kHz. Above 20 kHz, it must have an attenuation
of at least 50 dB more than the attenuation at
1 kHz.

Link to comment
Share on other sites

  • 0

While the information above is useful - there is no correct answer to whether the FCC considers GMRS to be wideband or narrowband. The FCC simply does not care which bandwidth you use, either one is acceptable to them.

 

Most high profile repeater systems do use wideband - for the increased performance noted above.

 

There are valid reasons why people might want to use narrowband, mainly due to available equipment or interference.

Link to comment
Share on other sites

  • 0

I think the core argument comes down to the fact the FCC has described the channel uses for GMRS repeater (and other main) channels as:

having an authorized bandwidth of 20 kHz and a peak frequency deviation not exceed ± 5 kHz.

 

However, the regulations go on describe

§ 95.1771 GMRS emission types.
Each GMRS transmitter type must be designed to satisfy the emission capability rules in this section. Operation of GMRS stations must also be in compliance with these rules.

(a) Each GMRS transmitter type must have the capability to transmit F3E or G3E emissions.
(B) Only emission types A1D, F1D, G1D, H1D, J1D, R1D, A3E, F3E, G3E, H3E, J3E, R3E, F2D, and G2D are authorized for use in the GMRS.

 

In practical terms the only two useful types are F3E (FM Voice) and G3E (Phase Modulated Voice), which are essentially the same to the receiver.  The other modes allow for AM and SSB and limited data, as permitted in the regulations. Personally, I have never heard on anyone operating AM or SSB on GMRS, but I guess it could happen.
 
So, the FCC has defined maximum channel bandwidth, deviation and transmission types. But, here is the issue, they have not mandated those. So, it is totally permissible to operate narrow band (NB) on any GMRS channel.
 
Now, in practical marketing terms, any company that only markets NB units for GMRS is obviously not going to push or promote wide band (WB) usage. However, since some GMRS channels are designated as NB, it is unlikely a WB only radio would be marketed as it could not transmit on the interstitial channels.
 
Which brings us back to the two experts.

...We have two members, each an "expert" with FRS/GMRS rules and equipment. The problem is one says that GMRS is Narrow Band while the other says it Wide Band. ...

In fact, if the statements of the two experts have been reported accurately, the answer should logically be neither or both.  If by "is" they mean can be used as, they are both correct. However, if they mean is mandated as, then both are wrong.

 

In fact, I would now say a true expert would not have defined GMRS in such a way and would have offered a better description as is provided by Part95E and the responses to the original question.  So, in my mind, the answer is neither expert is correct.

Link to comment
Share on other sites

  • 0

There is a very real engineering aspect to this in that narrow band radios and wide band radios are incompatible with each other.

 

They were never to co-exist. And legally, you can't tweak a narrow band radio to work better.

 

While "they might work", they are operating at widely different parameters.  There will be over-modulation received in one case and noisy weak modulation in the reverse. If you are expecting tone or digital squelch to work, they may not work.

 

Add a narrow band mobile and wide band repeater to the mix and the repeater often won't respond. This is a common thread by folks new to GMRS. They can't activate the repeater.

 

While I like the design of the Midland radios, they are creating a debacle by marketing radios (to the unwary) that have implications for a repeater operator, and users,  who hope to reap the entire benefit of GMRS's potential performance. 

 

GMRS main channels are 50 watts TPO, and +/- 5.0 KHz deviation. Always has been.

Link to comment
Share on other sites

  • 0

As stated here it can be what ever way you want it. It really boils down to what subscriber, radio you are going to use on it. If your plan is part 90 radios go wide. If they plan to by midland radios use NB. I have a mix of both due to the users on each.

Link to comment
Share on other sites

  • 0

As stated here it can be what ever way you want it. It really boils down to what subscriber, radio you are going to use on it. If your plan is part 90 radios go wide. If they plan to by midland radios use NB. I have a mix of both due to the users on each.

Keeping in mind, older part 90 radios are all wide band, while newer ones are narrow band. Though, some newer radios have the option to turn on narrow banding with appropriate software and/or permissions.
Link to comment
Share on other sites

  • 0

Keeping in mind, older part 90 radios are all wide band, while newer ones are narrow band. Though, some newer radios have the option to turn on narrow banding with appropriate software and/or permissions.

 

Correct. Unless your using pretty old programmable gear most stuff on the market supports both NM and WB. My radios are all programmed with both for this reason. Just know what is in your area and what you want to talk to. Knowing the gear you are buying is a plus. Most of the decent used gear that programs with windows does NB. There is still alot of old gear (GE MVS<MLS< Motorola GM/Maxtrac) stuff thats out there but normally a PITA to program so folks dont grab it like they used to. 

Link to comment
Share on other sites

  • 0

I have my Midland MXT400 set to use the 20kHz bandwidth on the channels on which it is allowed by Part 95E. I also have the local repeaters programmed into the slots meant for the channels reserved for the FRS handhelds.

 

The software and cable (DBR1)  is available.

Cable - https://midlandusa.com/product/dbr1-dual-band-radio-programming-cable/

Software - https://www.dropbox.com/s/eibap1ve5nnl5ju/MXT400_Setup_1.05.exe?dl=0

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use and Guidelines.