FCC Narrow Band Ruling

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Zaputil
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FCC Narrow Band Ruling

Post by Zaputil »

The FCC finally issued a long-awaited ruling regarding narrowband applications. For the full story visit the APCO International website at :

http://www.apco911.org/frequency/narrowband_mandate.htm
Susan157
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Canada will only give 12.5Khz now

Post by Susan157 »

:wink:

W e have it here now.
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nmfire10
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Post by nmfire10 »

I've been wondering exactly what that just answered for me. Thanks!

Matt
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Post by ASTROMODAT »

Quite amazing and a very powerful affect! It says no new FCC certifications for equipment that can optionally operate at one voice channel per 25 kHz after Jan 1, 2005 (less than 2 years from now). Then, consider that the ASTRO Spectra and the Quantar were released in 1993 (10 years ago). Their product lifecycles are almost up. And, unless Motorola comes out with replacements in the next 18 months or so, then how are Gov't Agencies supposed to get by until 2018? The realistic effect is that they will need to upgrade a heck of a lot sooner. This is very inconsistent!

Larry

P.S. Also screws Hams since they will have to use boat anchors. Very doubtful that they will have 12.5 kHz repeaters anytime soon, so no more way to dual use late model commercial gear on commercial and ham bands.
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Post by alex »

ASTROMODAT wrote:P.S. Also screws Hams since they will have to use boat anchors. Very doubtful that they will have 12.5 kHz repeaters anytime soon, so no more way to dual use late model commercial gear on commercial and ham bands.


Larry - Where in that document does it specificly mention amateur radio. I might be tired, but I can't find the work amateur or ham anywhere in it.

"we" might be exempt. While I think it would be good to see a lot of the repeaters replaced out there - hams might get with some of the newer and cool technology.... I just don't see how this ruling effects them specificly - at least as of yet.

-Alex
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Post by jcobb »

The gov't agencies are under a much tighter time frame to go to narrow band. The ruling to only type accept equipment for narrow band only will not hurt them.

It looks like, on first read-thru, that it gives them time to do their usual budgeting for new equipment. I think I remember that they can still use the wide/narrow capable equipment for a while - and they will be on narrow band channels so it won't hurt them.

And it might benefit hams in that if the gov't agencies only buy narrow band compliant newly type accepted stuff, the wide/narrow band equipment will trickle down to the hams that much quicker. But I don't see that many hams using old gov't stuff anyway, not with the affordable ham equipment that's out there.

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Post by ASTROMODAT »

Alex, regarding Hams, I'm saying that they will be relegated to boat anchors soon (if they want to use commercial gear) since new radios type accepted in the next 18 months or so will not be capable of 25 kHz ops. And, Hams won't have 12.5 kHz repeaters operating in the next 18 months or so. Thus, they will be relegated to boat anchors, kind of like the bad old days.

Larry
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Post by N9LLO »

As far as hams go I see it completley different. It will flood the used market with late model gear (anything newer than a MastrII
or Micor in ham terms) that will have no commercial value. This will
cause a major upgrade in the ham repeater infrastructure. Around here that consists of mainly the type of radios mentioned above.
Not that there is anything wrong with Micors and Mastr II's they are still very attractive due to ease of service and lots of spares etc. but keeping the Motrac Compas and the Mastr Pros running is
starting to get old. Threre are still many of these in ham service.

Chris N9LLO
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alex
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Post by alex »

ASTROMODAT wrote:Alex, regarding Hams, I'm saying that they will be relegated to boat anchors soon (if they want to use commercial gear) since new radios type accepted in the next 18 months or so will not be capable of 25 kHz ops. And, Hams won't have 12.5 kHz repeaters operating in the next 18 months or so. Thus, they will be relegated to boat anchors, kind of like the bad old days.


(I was up early this morning, so pardon me if I am a bit off here)

Your saying all the equipment that will come out of these upgrardes will go straight to boat anchors? Government looks like they have the first deadline to meet....

I think a lot of the stuff will goto the business sector still, and then back to the hams/general public.

I don't think it'll see an express route to the trashcan.

I also wonder if the'll stick to the schedule or not. Think about how many times the HDTV stuff has changed :roll:

-Alex
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Post by ASTROMODAT »

Excellent point, Alex. History says these "deadlines" have a tendency to get slipped out.

The context of my "boat anchor" coment is that today a Ham can buy a state-of-the-art commercial radio. In 18 months or so, this will NEVER again be the case. At that point, the NEWEST/most technically current radio radio they will be able to buy would be an ASTRO Spectra or XTS portable, radios designed in the mid to late 1980s. And, as time goes by, these radios will only get more and more ancient. I don't see Hams switching their repeaters to narrowband anytime this century, so they will not be able to use the 12.5 kHz only commercial radios.

One really interesting issue here is that it appears that Motorola will now be forced to get ASTRO M & P replacements (and a Quantar replacement) type accepted NLT Dec 31, 2004 to meet the deadline. This new line would be the last 25 kHz capable FCC Type Accepted series of Motorola analog/digital hybrid radios (25 kHz analog capable and 12.5 kHz IMBE). This series would complete the current phase of transition from FM 25 kHz analog to P25 Phase I. This way, Motorola could milk the new ASTRO replacement product line for 13 years (2005 - 2018), which is not unlike the product lifecycle of the current ASTRO line (1993 - 2004 is 11 years). Suggests to me that we should see ASTRO replacements pretty soon!

Like xmo said on this board: "Analog----What's that?!"

It will also be interesting to see how they carry out the mandate to not be 25 kHz capable. Remember the scanner stuff where you could cut one diode and it opened up the prohibited cellular bands? Then, the FCC had to revamp their regulatory language to preclude theses simple mods. So, you wonder if Motorola might have a FLASHport upgrade so that once you blow the dongle (sounds perverse) then the radio would no longer be capable of 25 kHz operations, and perhaps it would no longer accept a previous codeplug with 25 kHz capabilities, etc.

It reminds me of a prediction that Bob Galvin made. He was a featured speaker at the famous Motorola "Winds of Change" seminars (early 1990's) and he predicted that within 20 years, Motorola would reap more than 50% of its Land Mobile Sector's profits from software, as opposed to hardware. Recall that FLASHport was the really big deal being flaunted at the "Winds of Change" seminars. Maybe he foresaw stuff like these narrowband mandates. But, it's sure obvious that Motorola makes a ton of dough from FLASHports (which are generally non-discountable, and never cheap). What a cash cow---once you recover your R&D, it's all gravy!

Larry
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Narrowband mandate..

Post by Hartley »

Hi Y'all,

I don't see why:

1. Motorola would need to have a Quantar/Astro Spectra replacement Type Certified by 1/1/2005? These radios are already Certified, and could be sold until 1/1/2008. If they wanted to sell 'em after that, they would have to mod the software to prohibit wideband operation - not difficult, IMHO. Any NEW radio they were looking at Type Certifying after 1/1/2005 would have to to be narrowband only, of course.

2. Why the FCC shouldn't mandate narrowband technology for Part 90 licensees because it would affect the availablity of high-grade equipment for wideband-bound amateur radio ops? (seems like a miniscule market to me!) I also think the hams will transition to narrowband faster once the equipment is more available..(and works/sounds better)

73 DE Hartley
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Post by ASTROMODAT »

1. The reason why Motorola needs to act prior to Dec 2004 with a replacement for the aging ASTRO line is that the last 25 kHz FCC Type Accepted radio will need to meet the needs of Public Safety Agencies (that require a 25 kHz option) through 2018. This is too long for the aging ASTRO line, desinged in the 1980s, to realistically stay up to date. Remember, Motorola has one last window of opportunity to get a next generation hybrid radio FCC certified, and that date is well under 2 years from now. On the other hand, this next generation radio can be sold to Public Safety until 2018. The point is that Motorola has to be close to replacing the ASTRO line anyway (since it's so old now), but they now have a clock ticking on its replacement to gain FCC Type Acceptance (asuming it will support 25 kHz oprerations) for one last product series.

If Motorola were to miss this impending final FCC certification date, they will have two HORRIBLE choices for supporting Public Safety customers who may continue to need legacy 25 kHz operations and NEW and recently designed/modern radios: A) Keep selling a 1980's designed radio until 2018 (not realistic), or B) not be allowed to ever again gain type acceptance for an ASTRO replacement radio that can also support legacy 25 kHz.

Also, keep in mind how fast PCs are changing, as compared to a radio designed in the 1980s. At some point, an entirely new internal data structure will be needed in their radios, and at some point the 1980s ASTRO will be out of gas in this regards. I would think that Motorola's ASTRO series replacement radios will take this into account and have a more robust upgrade path so as to be able to more gracefully evolve with new PCs, as compared to the nearly antiquated ASTRO line.

Seems pretty obvious that Motorola has got to move on this!

2. I never meant to imply that the FCC is concerned about the effect of this ruling on Hams! The issue is simply that it DOES negatively affect Hams. Then again, they can continue to 1) buy rice rockets and/or 2) continue to use boat anchors. Point is, they will no longer have the option of new/state-of-the-art commercial gear. Of course, that is strictly their problem, and most certainly not an issue for the FCC to worry about!

Hope this clarifies.

Larry
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Post by nmfire10 »

As for Ham repeaters.... Any manufacturer can make a 25Khz repeater for ham even after 2005. It simply can not be type accepted for use OUTSIDE the ham radio band. It would have to be a Ham Radio ONLY repeater.
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Narrowband..

Post by Hartley »

Hi Y'all,

Larry, thanks for the clarification - and I do see what you mean!

I suspect the rather draconian language in this Proposal is due to two things - one, they are VERY frustrated with the situation at present - where Industry and PS seem to be ignoring narrowbanding, yet continue to bombard the FCC with demands for "more spectrum" for their needs.
Two, they know they will be pressured to modify this proposal, and I bet they figure that "starting high" is the way to go!

Thanks es 73,

Hartley
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Post by ASTROMODAT »

Yes, ALL Ham rice rockets (portable, mobile and repeaters) can continue to operate on 25 kHz humongous channels ad infinitum. We are talking about COMMERCIAL gear--- that is the issue.

Keep in mind that Ham repeaters are NOT FCC Type Accepted anyways. (Except foer the innocuous Part 15 aspect.)

Larry
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Post by Mike B »

Even if the FCC does not mandate narrow band for HAMs, they may need to migrate anyway to avoid an image as inefficient spectrum hogs and to help keep possible HAM spectrum reallocation at bay. After the currently mandated narrow band transition is complete, one hopes it will reduce some of the spectrum use pressure by increasing the number of available channels. However, if HAMs have been sitting on their laurels ignoring narrow band for all those years, as soon as these old band use pressures build back up again HAMs might find themselves in a really bad spot. Someone is bound to push the idea of cutting the FM VHF/UHF HAM band allocations in half, and then finally forcing HAMs into narrow band to “make up for the reduced allocation”. HAM frequency segments full of old wide band spaced channels would look seriously underutilized and ripe for the taking. If HAMs wait too long to voluntarily change over, it will be too late to react and defend their band allocations.

In order for HAMs to make the VHF/UHF narrow band transition, they will need mobile and handheld radios that can do mixed 25 KHz and 12.5 KHz on a per channel basis. Because the repeater owners do not own the majority of the mobile and handheld radios used on their radio systems, and users do not restrict themselves to a single repeater or radio system, flexible radios will be required to facilitate the change. If a radio is not capable of easily mixed wide and narrow band operation, it will not be useful to a HAMs that have to use both during a transition period. Presumably, the FCC will keep accepting new 25 KHz capable HAM radios, so there should not be any regulatory problem.

If the manufacturers would view this as a long-term opportunity to eventually replace every existing HAM radio, it might look like a slightly bigger than miniscule market :).
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re: FCC, see...

Post by Woody_99 »

Yeah, what's up with that... I had another ham nearly bite my head off over the FCC type acceptance thing... Last I checked, ham gear doesn't require an FCC ID. (of course they all have one since the transmitter section is also used in the commercial version of the radios.)
I thought that the only reason we see the "not FCC approved as yet" disclaimers on ham radio ads is simply due to the fact that since the transmitter section will be used in the commercial radios too, the company can't sell it until acceptance is acquired, no matter what 'model' radio its used in.
I see how that confuses the hams I suppose...?
input?
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Ham "Type Acceptance"

Post by Hartley »

Hi Woody,

The only Certification required of ham radios is Part 15, which is still time-consuming (and expensive). But all they're looking for with that is incidental and spurious radiation - they aren't checking for much of anything else.

I would also beg to differ regarding the "transmitter sections are the same" statement - if you look, almost all amateur radios are spec'd at 10 ppm (an uncompensated crystal ocsillator) while even wideband Part 90 stuff is required to be at least 5 ppm. Also, you'll notice that very few amateur spec sheets use the phrase "Measured using EIA/TIA-603" - which means the specs could mean just about anything they want them to. A good example: the Yaesu FT-817 and FT-897 radios have an optional TCXO available - until recently, the spec sheet for it just said "0.5 ppm" - but here's what it REALLY meant: "0.5 ppm per hour at 25 degrees C after warmup" (found in a recent FT-897 brochure). The stock TCXO has a similar weasel-worded definition.. Caveat Emptor!

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Post by nmfire10 »

This has me thinking.. I never thought of this before.

On all the Ham radios that I have, mainly a Kenwood TH79a portable and Icom IC-2800 Mobile, you can enter the frequency 440.6125. Because the radio is allowing me to enter that, does that mean the TX/RX is going to be actual narrow band or is it going to be wideband on a narrowband frequency?
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Ham Radios

Post by Hartley »

Hi Matt,

I'm quite sure it would still be in wideband mode. Some of the newer ham rigs do offer a "narrowband" mode - some even change the receiver IF filtering for it - but it is usually selected via a menu option or other control separate from the frequency selector.

After all, if you programmed your Maxtrac/Spectra/HT1000 on 440.6125, it wouldn't automatically switch to narrowband, would it? :-) Even the HT1000 (which has narrowband capability) needs to be told which bandwidth to use.

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Post by nmfire10 »

Thats what I was afraid of. When I put some narrow band channels in my MTS2000, I always assumed that the radio assumed. Then I noticed that under "F9 More Options" you had to tell it to use 12.5Kz.
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Post by ASTROMODAT »

Some off-shore Ham radios are definately capable of 12.5 kHz operations. For example, the Kenwood D700E APRS European version curerently has narrowband TX/RX capabilities. I think the Ham manufacturers can easily go narrow band, if they see some incentive for it. The point about Ham spectrum utilization pressures is an excellent one!

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Post by larryepage »

Or not...

The move to narrow-band channels may just end up being one of the more short-sighted changes made in two-way radio communication.

The reason? Well...the short answer is that the cost just does not match the benefits. Why? If you look at almost any dual channel-width radio available, you will note that there is a performance cost of 10 dB to move to the narrower channel. If you compare other "equivalent" grade radios, you will also see this 10 dB differential.

This 10 dB cost comes with only a 3 dB benefit (a doubling of channel capacity). (10dB cuts communications range by more than half, by the way.)

Additionally, people with insufficient technical knowledge have assumed that the only impact here is that we have to put new input filters in place and turn the transmit deviation down. This is simply not true. In addition to reducing modulation levels, it is necessary to reduce the maximum frequency used to modulate the signal in order to reduce sidebands to fit nin the new channels. While there is generally not a lot of energy in these higher frequencies, they are where important intelligibility information is contained. This is especially true when trying to listen in noisy or difficult environments. As a result, Motorola and others generally add quite a bit of processing to the modulating signal to try to preserve this intelligibility.

And...while I would like to see amateurs as a group move to better equipment than what they typically use, I believe that their strength and value may be better served if they do not move away from 25 kHz channels. Why? Because as agencies move to systems that are more technology and infrastructure dependent, it is going to be ever more important that someone be able to come in with a basic working system that can restore functionality when the big emergency occurs and the fancy system quits working.

And...I'm not just making all this up. If you will permit me to digress a little bit, I'll tell you that a few weeks ago, I had the privilege of participating with the Columbia debris recovery effort as an amateur operator. Multiple agencies had lots of fancy equipment on site. One major manufacturer provided a vehicle equipped as a "first responder interoperability vehicle." The working communication was still done using amateur operators and amateur equipment. As near as I could tell, there were a couple of reasons for this. First...no one had bothered to bring the necessary programming information necessary to make the interoperability vehicle work. Second, even if they had, the individual agencies who could make their communications systems work (primarily Texas Department of Public Safety) had their channels so full with their own communications that they had no room left for interoperability traffic.

So we may just have to wait and see how this all plays out. Right now, I'm not particularly optimistic that it's going to be the good deal that everyone seems to be expecting.
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Post by Alan »

If you look at almost any dual channel-width radio available, you will note that there is a performance cost of 10 dB to move to the narrower channel.


Where do you get this from?

We have been running narrowband (12.5 KHz) for 3-4 years now. Our experience is the end user notices very little difference (2 to 5% range reduction).
We have conducted extensive testing with public safety users and they are always hard pressed to hear the difference between wide band (25 KHz0 and narrowband (12.5 KHz).
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Post by larryepage »

The arithmetic is fairly simple:

3 dB loss of recovered audio due to reduced deviation
2 dB increased insertion loss of tighter receiver filters (You can argue this one a little either way)

Then...

1 or 2 dB increased insertion loss for tighter combiners required in multi-transmitter locations
1 or 2 dB increased noise floor due to the larger number of transmitters in an area and increased cross-modulation or intermodulation products
1 dB or so increased susceptibility to QRN (interference from natural sources) against the narrower signal

There may also be insertion loss or noise increase for audio processors (like Motorola's HearClear) inserted in the path to try to restore fidelity.

So...some of the degradation won't be heard until the denser band is fully populated. And while I can't claim to know how you run your listenability tests, I would want to verify that radios are really working completely within 12.5 kHz parameters, and not just with reduced deviation on transmitters... And again...when all neighboring sysems are fully built out, I'd be interested in seeing the test results again.
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Post by Alan »

The old link to this article was in correct. (Error 404)
Here is the new link:

http://www.apco911.org/frequency/narrowbandmandate.htm
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so

Post by sglass »

This will effect GMRS as well?
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Post by Jonathan KC8RYW »

I don't see hams going to 12.5 KHz. I'm sorry, I just don't see that happening here in the USA.

Hams have invested quite a bit in radios. And these radios are for hobby use. In other words, we don't make a dime off of what we do.

Is there a crowding problem on the ham bands? I haven't noticed it, if there is.

Just my two cents.
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Post by ricciticcitembo »

Only in Cali. :P
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Post by ASTROMODAT »

Mike B got it exactly right. If Hams have plenty of room within their allocations and continue to use (no, make that HOG) 25 kHz channels, then I hope the Gov't takes away 50% of their spectrum. There's no reason they should be able to use these spectrum which is worth untold billions of dollars and continue to use 1950's analog FM 25 kHz technology. If they still have plenty of room, take away another 50% until they learn to be efficient , like the commercial boys. I say this as a Ham myself who believes that ALL of Ham spectrum will soon be taken if we don't wake up and see what is happening based on the economics of spectrum.

How are Hams use of the spectrum advancing the state-of-the-art when they continue to use 1950s analog FM technology where a single voice conversation requires a 25 kHz channel (almost no digital voice use, no narrow band, no trunking). Oh, yeah, I almost forgot---there are a handful of Hams using PK31 on their PCs (and 1,000 times that many still using CW!).

Larry
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Post by Jonathan KC8RYW »

Wait a second!

FCC Part 97 [ham radio] only places very loose restrictions on bandwidth.

“No amateur station transmission shall occupy more bandwidth than necessary for the information rate and emmission type being transmitted, in accordance with good amateur practice.” - 97.307a
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Post by Mike B »

The "1 or 2 dB increased insertion loss for tighter combiners required in multi-transmitter locations" does not make any sense to me. I do not know of any filter or combiner that can effectively resolve/filter a 12.5 KHz overall frequency difference at VHF or higher frequencies. The filter response skirts are just not steep enough. The immediate adjacent channel frequency rejection/selectivity must come primarily from the receiver itself. I do not see anything effective that can be done differently with repeater combiners, filters, notches, cans, etc. for a 12.5 KHz channel spacing vs. a 25 KHz channel spacing.

The 12.5 KHz spacing will not allow tighter spacing of multiple transmitter frequencies at a single repeater site, unless a better filter technology comes along.

I really do not know if the 12.5 KHz receiver filters have increased signal loss or not. Even if it does, filter loss is always present no matter what channel spacing is used. Each individual receiver design has to wrestle with filter loss vs. amplification, so a slight increase in filter loss all by itself is not an inherent disadvantage. Additional loss would be a problem with retrofitting a 25 KHz radio with a tighter 12.5 KHz filter.

I would also like to see a real 12.5 KHz band segment that was packed with adjacent channels and heavily used. Forget the theory; show me the real McCoy :).

I am curious about what the new high frequency audio modulation limit for 12.5 KHz is. It was 3000 Hz. What is it now?

Motorola’s Hear Clear is supposed to also be about noise reduction. I think part of its design is based on companding, which is a proven noise reduction technique.
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Post by nmfire10 »

OK, now you've got me with another one here.

What is all this "Companding" stuff you keep talking about. Motorola calls it Hear Clear and I don't think Kenwood calls it anything but "Compander on or off".
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Post by Jonathan KC8RYW »

Compander... comes from combining a compressor and an expander.

Compression reduces dynamic range.

Expansion cuts noise.

Companding is nothing new... even AMPS uses companding, and that uses 30 KHz channels.
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Post by Mike B »

I think Hear Clear is supposed to be more complicated than just companding. There are lots of textbooks that do a better job of explaining companders than I can. However, I will take a shot at a short explanation.

First, the signal is compressed before it is transmitted. This compression involves taking the audio signal and both amplifying small signal levels and attenuating large signal levels. It kind of squeezes the signal levels over the entire audio bandwidth. This squeezed signal is transmitted at normal deviation levels when using FM. When the signal is transmitted, one would hope the noise floor in the transmission medium is in the small signal level range. In the receiver, the compressed signal has to be expanded so it sounds normal. This involves attenuating the small signal levels and amplifying the large signal levels (the reverse of compression). Well, if the noise that was picked up with the signal during transmission is in the small signal level range, this noise also gets attenuated by the receiver’s expansion process. If the noise is in the large signal level range, then you probably do not have enough signal to noise ratio to transmit anything intelligible anyway. Depending on the compression level and the transmission medium noise floor, companding can have dramatic noise reduction effects across the entire audio bandwidth.

It works on the principal that the noise present in the transmission medium (i.e. whatever it is the radio waves travel through) is a fixed level you have no control over. Therefore, you modify the audio signal sent through the transmission medium in such a way that this fixed amount of noise is actually reduced by the receiver in the process of recovering your audio signal.
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Post by nmfire10 »

Interesting. So what happens if you try to use that fuction on the reciever when the transmitting station is not using it?
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Post by Mike B »

Can you say distortion! I knew you could.

BTW, please do not confuse the term "noise" used in my previous post with judgments about the value of the content in some two-way radio communications. :)
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Post by perthcom »

Ok.. a riddle..
What is the word most often said in reply on a narrowband system?

Actually the above sentence is really a statement.. "what?" along with "can you repeat that?" "what did you say?" etc.

You need twice the channels, because it takes twice the airtime to get the same message through!

:cry:
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Post by nmfire10 »

perthcom wrote:Ok.. a riddle..
What is the word most often said in reply on a narrowband system?

Actually the above sentence is really a statement.. "what?" along with "can you repeat that?" "what did you say?" etc.

You need twice the channels, because it takes twice the airtime to get the same message through!

:cry:



I had "What is the most commonly spoken word on our Low Band system." on my AIM profile for a while. It confused the crap out of everyone. Until the got the little play on words.
"I'll eat you like a plate of bacon and eggs in the morning. "
- Some loser on rr.com

eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"

:-?
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Wes
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Post by Wes »

Will the new ruling effect Low Band systems too or only High Band and UHF????

Wes
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Cowthief
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Narrow band

Post by Cowthief »

Hello.

lots of new radios are able to narrow band, the kenwood TH-F6a has this in a menu option, you can even program it in channel profile, wide or narrow, along with CTCSS or DCS, power level, etc.

TNX
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Post by nmfire10 »

Yea, one of my friends just bought the VX-7R portable. It can do 12.5Khz and it is even waterproof. Yep! You can transmit UNDER WATER. LOL :P
"I'll eat you like a plate of bacon and eggs in the morning. "
- Some loser on rr.com

eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"

:-?
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Narrow band.

Post by Cowthief »

Hello.

Had to think.
Sometime in the 60s, the FCC made everyone go "narrow band".
The hams had a field day, huge amounts of equipment became surplus.
The problem was mostly one of frequency tolerance, or lack thereof.
hams simply set old progress line, or T-power, or Carfone radios up with a switch, narrow/wide, this set dev'/det' sens' to one of 2 levels, however, new equipment can easily be modded in software.
I think a solution could be, get hams to run digital trunking, it does not work in industry, perhaps we can make it work, first thing I would do, come up with something closer to AMPS, it works, and it is patent free.
The first radio trunking systems, IMTS, were not fast enough for 2 way radio, but AMPS was designed for PTT service, just the FCC was in fear that if the cellular carriers had PTT service, it would put local radio providers out of business, Fleetcall, now Nextel, is now in charge of that.

Thank You
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Post by Jonathan KC8RYW »

I know ham gear can be set to "narrow"... but... I suspect my Vx-5r [and probably other radios, too] only set the Tx to narrow, however, leave the audio at wide on Rx. Thus, you have to crank it up on Rx when hearing something narrow. Can anyone confirm this?
Last edited by Jonathan KC8RYW on Mon Mar 31, 2003 1:45 pm, edited 1 time in total.
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Tom in D.C.
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Wideband vx. narrowband, etc.

Post by Tom in D.C. »

From reading the very sketchy tech data in the VX-5R book it looks to me as if the "narrowband" option only reduces the transmit deviation and does nothing to the received signal width/passband.

I also wonder now what my VX900s do when I change the column in the program for each channel from "w" to "n." I'll find out, somehow, if it changes both RX and TX and post the answer so everyone will then know. (I set up the FRS channels on the UHF Vertex radio for "n" and it sounds really nice on the el-cheapo wrist radio I bought at Richmond in January for all of $20!)

Tom, W2NJS
...in D.C.
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Post by larryepage »

As mentioned before in this thread and in others...simply reducing the transmit deviation does not result in narrow band transmissions. FM Transmit bandwidth is determined by both the deviation and the 'important' (or first) sidebands. The calculation is that bandwidth = 2 x max deviation plus 2 x max modulating frequency. Standard FM transmitters without any audio processing (other than preemphasis) will modulate up to at least 3 kHz, and actually exceed that because the filter response slopes, and is not vertical.

So...for current radios with 5 kHz deviation, total bandwidth is 2 x 5 plus 2 x 3, or 16 kHz. If you want to fit that into a channel half as wide, then you have to cut the 16 kHz to 8 kHz. Doesn't much matter how you do it. You can go to 3 kHz deviation and 1 kHz max modulating frequency (and sound muffled like in the bottom of a well), or you can go to 2.5 kHz deviation and 1.5 kHz max frequency (which isn't much better), or you can somehow pre-process your signal and use other limits. Even if one moves to digital transmissions, the encode rate has to be cut to make the channel fit. And that isn't even a guarantee, because the sharp square wave-like transitions in digital signals turn out to have significant high-frequency content which will cause out of channel interference. (Can anyone say "Nextel?" Or HDTV?)

(By the way...Part 97 rules currently limit amateur FM transmitters to 4 kHz deviation, so cutting those channels in half is going to have an even bigger impact.)

In short...these changes are very likely going to be determined after the fact to be ill-advised at best and dangerous at worst. And I can tell you from the experience of working a few years ago with equivalent 800 MHz (wide) and 900 MHz (narrow) equipment side by side in a vehicle that in no way are the narrower channels able to deliver the same communication product as the wide ones, regardless of the use of expensive audio processing circuitry. The necessary information is simply not transmitted in the original signal.
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Post by Mike B »

Larrypage,

I asked before, but you did not answer. You appear to be saying that the old standard 300 to 3000 Hz audio bandwidth is not supported by the new narrow band modulation. Do you know any actual audio modulation bandwidth limits that are used with narrow band?

The suggestion of 1.5 KHz is ridiculous. So, I would assume only pre-processed modulation with different ???? higher limits is actually being used?

BTW, when you said "1 or 2 dB increased insertion loss for tighter combiners required in multi-transmitter locations ", did you really mean an increase in the overall isolation rating (such as when a repeater Tx has a higher power output) and not a "tighter" frequency rejection? As I already pointed out, an attempt at tighter adjacent frequency rejection based on narrow band vs. wide band does not make any sense to me. Some of the assumptions behind your 10 dB figure do not seem to pan out.
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Post by N9LLO »

[quote="larryepage"]1(By the way...Part 97 rules currently limit amateur FM transmitters to 4 kHz deviation, so cutting those channels in half is going to have an even bigger impact.)

What rule limits deviation to 4khz. I cant find it.

Chris N9LLO
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Post by larryepage »

Mike B--

I must have blown past your question before. Sorry.

Insertion loss generally tends to be higher for filters with narrow passbands. Because a bandpass filter is actually a low pass and high pass filter combined, when you narrow them up, both sides are attenuating to some extent the frequencies in between that you are really wanting to pass. So the insertion loss is greater. This becomes clear when you read the "Details of Operation" sections in the service manuals. At least in Motorola service manuals, these sections list gain for each stage and also insertion loss for each filter. It's very interesting to note the difference in attenuation for a wide vs. a narrow Saber, for example.

And yes...transceivers cannot suport a full 3 kHz audio bandwidth with narrowband equipment. The best you can do is to do some audio processing magic to make it sound sort of like they are. The cost is both to signal-to-noise ratio and to frequency response. Companding can help with S/N and the frequency response can be altered to help with the loss of higher frequencies, but the bottom line is that less information is being transmitted.

By the way, if you note carefully in the RSS manual for some of the later models, you will find that Motorola discourages use of the higher PL tone frequencies because they will not be completely removed from the receive audio and will be heard in the speaker. So one of the magic tricks to try to reduce the loss of audio is simply to install less effective filters.

As to my comment about combiners, etc., ... The whole point of moving to narrower channels is to allow more "non-interfering" simultaneous transmissions to occur in the same area. If you don't have all these additional transmissions, then you really don't need the additional channels and you don't need to move to narrower bandwidths.

Since the bulk of the repeaters serving a particular area usually tend to be clumped together in the few best locations, this means that there are going to be more systems in the same space. Most of these sites don't have a lot of room for additional antennas, so the new systems are going to have to share the antennas that are already there. These antennas are generally already serving multiple repeaters by using combiners to allow several systems to be share one antenna. These combiners are generally similar to duplexers. Since there will be more systems in the same overall frequency band, it follows that they will end up being closer together in frequency and will require combiners with narrower pass bands. Again, narrower filters generally come at the cost of greater insertion loss.

In summary...we will probably get past the problems and be able to communicate via the narrower channels. But it isn't going to come without a cost.

N9LLO - I don't believe that I am hallucinating about the 4k deviation restriction, especially at VHF or for audio transmissions. But I don't have the rules in front of me, so will have to wait to comment futher on that one until I've had a chance to look farther. Obviously that limitation would not apply to ATV or wideband data transmissions at UHF and above.
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Post by Mike B »

The Saber problem sounds like they used a wide band design receiver with an optional narrow filter. A better receiver design that takes the additional narrow filter loss into account would solve this problem. However, now I see your point, that given existing programmable wide/narrow receivers, we will tend to see the narrow band Rx performance compromised (less engineering effort, less complicated design). It may take a dedicated narrow receiver to easily overcome the problem and correctly balance the additional narrow filter loss with the various stage gains, etc.

I still think people are fooling themselves with the combiners. The filter slope is not steep enough to allow closer spaced Tx at a single site with narrow band vs. wide band. It appears they are actually being adjusted as small value on frequency attenuators to fudge the Rx rejection slightly higher (at the expense of Rx sensitivity). The combiner itself does not have a sharp enough response to address a 12.5 KHz difference. I think people will find that since combiner technology has not improved along with narrow band, that getting these "new" repeater sites working with lots more closely spaced Tx frequencies is a pipe dream :(. Implementing it with current combiner technology will be a repeater performance hit for an entire site (regardless of the Rx bandwidth). I see an artificial "marketing" connection between narrow radios and expectations of tighter spaced frequencies at any one repeater site.

Statically, the chance of having your mobile/portable in proximity with higher power mobiles that are close enough in frequency to totally desense your Rx, will probably be much higher with a more crowded band. Oh well, Nexthell is already training our public service providers not to depend on radio communications anyway :evil:.
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