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Author Topic: Another new part 90 narrowband question...  (Read 4581 times)
KT0DD
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Posts: 277




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« on: December 09, 2012, 09:10:47 AM »

I know the new part 90 rules require 12.5khz channels for narrowband compliance. My FT60 and FT270 have 12.5 khz channel step selection. Is this on receive only or does it affect transmit as well? If it does affect transmit, why don't the big 3 try and get part 90 certification on their gear? The new chinese rigs are getting it.
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KC0RZW
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Posts: 29




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« Reply #1 on: December 09, 2012, 09:15:24 AM »

I suspect they don't because it is not cost effective to pay for that certification when they already have a commercial line.
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AJ3O
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Posts: 124




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« Reply #2 on: December 27, 2012, 12:47:10 PM »

12.5khz is the old standard for narrowband requirements. The new part 90 calls for 2.5 khz steps. It won't affect Hams unless you try to scan the public service frequencies. You will still be able to hear them, it will just sound quieter or muffled.
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N1CX
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Posts: 119




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« Reply #3 on: December 27, 2012, 04:27:34 PM »

The old was 25 khz steps and is now 12.5, you can occupy multiple 2.5 khz channels inside a channel only if digital I believe.

The standard now however is 12.5 khz bandwidth.
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AJ3O
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« Reply #4 on: December 27, 2012, 05:37:22 PM »

My apologies, you are correct. Embarrassed
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N1CX
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« Reply #5 on: December 30, 2012, 06:23:53 AM »

I'm in the business Smiley
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KCJ9091
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« Reply #6 on: December 30, 2012, 07:24:59 AM »

Deviation?
Splinter channels?
Occupied bandwidth?

It was not that long ago that 25 kHz FM was Narrow band. Does that make 12.5 kHz FM Ultra Narrow?  What will 6.25 kHz FM be called Super Narrow? 

Just how narrow can FM go and still possess decent audio quality?
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AA4HA
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Posts: 1377




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« Reply #7 on: December 30, 2012, 10:51:38 AM »

Deviation?
Splinter channels?
Occupied bandwidth?

It was not that long ago that 25 kHz FM was Narrow band. Does that make 12.5 kHz FM Ultra Narrow?  What will 6.25 kHz FM be called Super Narrow?  

Just how narrow can FM go and still possess decent audio quality?

When you do not have sufficient FM deviation to convey human speech.

For example, telco grade circuits are rated from 300-3000 Hz. There is significant roll off of performance above 3000 Hz for speech. The range of 300-3000 is more than adequate to convey a human voice. Think of how we are limited on SSB to around 2.7 KHz (well, most nice hams do).

If we had to, we should be just fine on a 6.25 KHz channel spacing with only some minor loss of high frequency response.

Running on narrower channel spacing with less FM deviation would require that we have better frequency stability and more precise oscillators so everyone stays on the center frequency. Also the linearity of the signal is important and proper pre-de emphasis.

You do not need to be in a digital mode for this to work. Digital CODEC's take an analog speech signal and run it through a D/A converter, run compression on the digital stream and zap the digital stream across the air with a more advanced modulation technique.
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There is a great deal of hype about how "different" narrowbanding will be for public safety agencies. Lots of manufacturers are using this to push the $5000 HT that is capable of all sorts of digital modes, trunking and encryption. One municipality I was consulting for was concerned about replacing >300 alert receivers in the local schools because the Bat-Wing people said "they would not support narrowband analog". I talked myself blue in the face that they did not need to spend a quarter million dollars in replacing those receivers but the manufacturer would not relent and did the full court press because they are in the business of selling equipment, not common sense.

The VHF FM receiver that was set up for 25 KHz channels will work just fine when receiving a transmitter that is putting out 12.5 KHz deviation. The only thing they will notice is that the recovered audio is quieter. The solution, turn up the volume control. If you want to sell them something then make it radio service to go through and peak the receivers for optimal performance from a 12.5 KHz signal.
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Back in 1980 we were aligning telemetry radios to operate with 1.5 KHz deviation on VHF splinter (6.25 KHz spacing), 2.5 KHz deviation on UHF. It was simple FSK modem operation at 600 baud but it worked just fine.
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Do this test at home (or on your computer). Listen to a voice broadcast like the news from an FM station. Use the equalizer and chop off everything above 3000 Hz. It will not sound musical but the speech is perfectly intelligible.
« Last Edit: December 30, 2012, 11:06:49 AM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KM3F
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Posts: 494




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« Reply #8 on: January 10, 2013, 02:21:00 PM »

On just Deviation alone, the normal FM dedicated ham radio is limited to 5000 HZ audio.
FM repeaters normally are not any wider and most often even less.
Ever hear an FM station that is obnoxiously loud?
Your hearing over deviation to the point the repeater is clipping the excess deviation along with the loudness.
The rest is channel spacing has been reduced along with the deviation for com application.
Below 10 meters, FM deviation has to be reduced even more by part 97 rule.
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WB5ITT
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Posts: 100




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« Reply #9 on: February 17, 2013, 04:28:37 PM »

Deviation?
Splinter channels?
Occupied bandwidth?

It was not that long ago that 25 kHz FM was Narrow band. Does that make 12.5 kHz FM Ultra Narrow?  What will 6.25 kHz FM be called Super Narrow?  

Just how narrow can FM go and still possess decent audio quality?

+/- 5kHz deviation FM (what has been called NBFM since the 60s) is 16kHz wide, not 25kHz. The b/w for analog FM is 2x (max deviation + max audio freq of modulation)...so 2x (5+3) = 16.
Originally two way FM use 15 kHz deviation and thus the channels were 60kHz spaced..when they cut the deviation to 5 kHz, they mistakenly cut the VHF Hi channels in half instead of 1/3 which would have made them 20kHz spaced (ironic that the lowband 30-50MHz channels ARE 20 kHz spaced and are not subject to the new narrowband rules...at least lowband got it right!!)
For optimum performance, plain analog FM needs to have a modulation index of at least 1..the MI is deviation / max freq of modulation..current amateur FM is 5/3 or 1.66 MI. DTMF and other signaling tones are 3 to 3.3kHz deviation, thus maintaining a decent MI.

FM below 29.0MHz is legal but it was formerly limited to 2.5kHz deviation (which is what the new Narrowband FM is limited to) and was called 'sliver band' in the 60-70s...Under the Plain English rewrite of 1994 of Part 97, this was changed for FM to where the max index could be a max of 1....since normal max audio in a FM transmitter 'peaks' at 3 kHz (the lowpass filter should cut off anything above that), you inject a 3K tone into the radio, set the deviation at 3kHz and you're legal...but FM on HF has phase distortion and other issues which is why it is not so popular (besides being a bandwidth hog). Above 29.0, you can run 5kHz deviation FM (and I THINK 15kHz is still legal...but WHY?) and thus the 10m rptr band is 20kHz stepped (though some folks have decided to go on the 10kHz odd channels due to the limited number of rptr pairs at 20k steps)

Analog FM at 6.25kHz spacing will not work; it will take a digital mode to accomplish that (TDMA and NXDN/ICAS being the front runners).....12.5kHz spaced analog FM (the new NB) has issues and requires in the radio compression/expandor (IE: compandor) chips to improve S/N issues....in the amateur gear, those chips are not installed....As to amateur gear not getting approved for commercial use, the audio paths actually can pass FCC requirements...but you cannot have a keyboard or front panel USER programmable radio in the commercial world...so thus the amateur versions of the commercial rigs are basically the same (My old FT711 on UHF was the same as the commercial version they sold...in fact, you could move some jumpers on the main CPU board, push a panel button and it would work as the commercial version with no band limits (but the memory channels would not show freq...and memory 10 was now memory 0!)
« Last Edit: February 17, 2013, 04:55:41 PM by WB5ITT » Logged
KCJ9091
Member

Posts: 0




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« Reply #10 on: February 18, 2013, 05:02:15 PM »

Deviation?
Splinter channels?
Occupied bandwidth?

It was not that long ago that 25 kHz FM was Narrow band. Does that make 12.5 kHz FM Ultra Narrow?  What will 6.25 kHz FM be called Super Narrow?  

Just how narrow can FM go and still possess decent audio quality?

+/- 5kHz deviation FM (what has been called NBFM since the 60s) is 16kHz wide, not 25kHz.

I was referring to the channel spacing and you know it as verified by this remark:

Analog FM at 6.25kHz spacing will not work;
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WB5ITT
Member

Posts: 100




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« Reply #11 on: February 22, 2013, 02:46:22 PM »

Deviation?
Splinter channels?
Occupied bandwidth?

It was not that long ago that 25 kHz FM was Narrow band. Does that make 12.5 kHz FM Ultra Narrow?  What will 6.25 kHz FM be called Super Narrow?  

Just how narrow can FM go and still possess decent audio quality?

+/- 5kHz deviation FM (what has been called NBFM since the 60s) is 16kHz wide, not 25kHz.

I was referring to the channel spacing and you know it as verified by this remark:

Analog FM at 6.25kHz spacing will not work;

25kHz spacing is only valid at UHF and 12.5 channel spacing has been used on UHF for quite some time....30/15 is the norm on VHF...so if you were referring to channel spacing, you were only partially right..
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