Wednesday, February 27, 2013


I posted a link to the Advanced Repeater Systems Webpage, titled No Ham Narrowband FM on twitter. Subtitled: "If you're not upgrading to digital, don't downgrade to Narrowband FM!"

For the most part I agree with it.  Mostly I liked the technical analysis of the issue.

I received a tweet back, asking if I was for or against narrowbanding on Ham bands.  He seemed to think I would be for it, being more of a tech guy.

I responded I think we need to go wider.

Several years back, I explained why I feel this on my VOIP/DV page.

Hams are not bound by these narrowband rules, refarming nor will there ever likely even ever be a rebanding.  We have oodles of spectrum available to us, most of it un-used.
What is actually disappointing about D-Star is that  it's only a 4800 baud total data stream equivalent signal.  2400 bps is reserved for actual digital voice, 1200 bps is reserved for FEC (forward error correction)  on the digital voice.  (This is for callsign and short message data.)  1200 baud is reserved for serial data low speed digital data .  (This is for APRS, and text messages/text query's.)  The sad part is 1200 baud data is what we were doing in the 1980's. 
So if 4800 baud can fit into a 6kHz bandwidth, we could have had a 12800 (12.8k) baud total data stream equivalent signal fit into our existing 16 kHz bandwidth plans.  This could have left us with 9.2k left for data.  Or at the very least more could have been given for the digital voice codec, so that we could use other license free-codecs that sound more natural.

Less far back, I blogged about the problems with frequency coordination.

What bothers me is that most of the VHF-UHF bands are inundated with mostly inactive repeaters.

The problem is frequency coordinators have broken the bands into channels most fairly narrow in width, with conventional input and outputs. I think this image/model discourages potential other use, that may not fit the convention.
And my last blog was about a potential rules re-write to encourage some new developments in the hobby.

Ham radio has always used hand-me-down gear from the commercial world.  And I would be absolutely irate if some coordination body told me as an existing repeater owner that I had to narrow band.

I think a some guidelines would be;

-If you are putting a new analog repeater on the air, if it's narrow band capable, it should be.   To start a 5-year phase-in plan for 6.25kHz channel centers and mandatory 2.5 kHz narrowband FM deviation on analog. 

-The number of wide band and narrow band analog channels needs to be rationed.  I'd like to see some effort to slowly over time (via attrition)  clear out and reserve some wider channels on the VHF and UHF bands for new techniques.

-I think when it comes to coordination requests, newer modes should be given priority.  If there are 10 analog repeaters in a given area, and someone proposes to put up a P25 system, but there are no channels available... back to rationing space for older modes.

Of all the VHF/UHF digital radio modes I have played with.  I like TETRA the most, as it's the most versatile.   The biggest problem is price.

It supports 4 TDMA channels in a 25 kHz bandwidth channel.  Mototrbo/DMR does 2 TDMA channels in a 12.5 kHz bandwidth channel.

The main reason I like it is because it doesn't sound digital.  It sound like a telephone grade voice path.  This is because the radios also function like mobile phones.  There is Asterisk SIP tie in support.

And for IP packet data services, DMR offers a throughput of 2.0 kb/s per timeslot, whereas TETRA offers 3.5 kb/s per timeslot.  So if you code an application for DMR that uses both slots, the max is 4 kb/s.  With TETRA 4 timeslots can be combined into a single data channel to achieve higher rates.

And if you are not in range of the repeater system, DMO mode allows you to repeat though a sequence of one or more TETRA terminals as relays to reach your destination.  (Think same-band crossband using alternate time slots)

So in summary, narrow banding just so we can have more of the same (under used analog repeaters) is just plumb stupid in my opinion.

Here are some relation observations that I made early in 2011:

During an interview, the Beaver Valley ARA revealed that ARRL President, Kay Craigie, N3KN got licensed in 1983 because she was jealous of all the fun her husband was having with ham radio. She was a computer hobbyist at the time and became a ham just when computers were starting to be integrated with amateur radio.

So it would seem natural to assume her stance on the future of digital communications is strong.

Brennan Price, N4QX is the new Technical Relations Manager filling the vacancy created by the retirement of Paul Rinaldo, W4RI.

It was Paul, W4RI's recommendation (back in 2001), to the Board that  the HSMM Working Group be founded and he has written many-many articles over the years on packet radio and other digital aspects.

I don't know much about Brennan, N4QX, other that his stated goal is  to "defend Amateur Radio spectrum. So it would seem that encouraging new uses and techniques would be logical.

I fell strongly about the ARRL Technology Task Force. I hope he can  fill the shoes as well as Paul did.

So far I haven't really seen anything happen at the league level that affirms my above assumptions of these two.  I kind of expected these jokers to file comments to the FCC along the lines of what Bruce Perens did in terms of getting some rules relaxed to help move things forward.

1 comment:

James said...

hear hear!
I feel less knowledgeable than I should be but it strikes me as weird that people can make telephone modems that can go 33.6K and up over a 3khz telephone connection and not do something similar over radio. I know radio has to worry about the signal strength over distance though. Still, it seems like the nominal bandwidth has been frozen for the past 30+ years. It's even such a low concern to some people that apparently the team designing D-Star didn't think that people might want to use the whole 4800 baud channel for data. You don't even get 1200 baud, in the end it's 791 baud. And you get to waste time, energy and transmitter power by transmitting empty voice frames at the same time. Beyond stupid.
I didn't know TETRA would let you do a sort of in-band crossdomain repeat. That's pretty cool. If we had fast enough packet then maybe people could digipeat voice across the country with codec2.
Personally, I'd like to see (or develop) a sort of smart radio technology. Give people a base that they can work from and see what they build with it. Apple was going to keep the iphone locked down and require that people build webapps to visit in the browser afterall. Then someone jailbroke it and figured out how to write binary apps, Apple embraced that and became a huge beneficiary of all of that activity.