Any AFSK through a SDR TX differs fundamentally with the assumed and
suggested 3kHz criteria.
ARRL infirmation package http://www.arrl.org/rm-11708-faq limits the bad
width to 2.8kHz.
3kHz is a different number,
I need to understand the specification; what is now on the table?
The http://www.arrl.org/rm-11708-faq says 2.8kHz maximum but now I am
reading some verbal expression that is subject for the amateurs to
scrutinize.
Nobody on the reflector is not necessarily a happy guineapig accepting any
specification that is written and merely based on good amateur practice. We
do not understand where it leads to.
A clear number, like 2.8kHz for band width is acceptable.
3.0kHz is barely acceptable.
Through unclear specifying, I see a development to increasing data rate or
decreasing BER.
Those shortwave links would be established using SDR.
That specification could exceed 10kHz. Easily.
The guys who would make that can say it is necessary and is based on the
newest, absolute best amateur practices.
Please, specify a set of the critical specification using numbers so we can
discuss this engineering topic in a way we can take the necessary good
amateur and engineering practices.
As there is a way the maximum band width would exceed 2.8kHz, people have a
good reason to be unhappy.
73,
Jukka OH6LI
2016-08-25 16:37 GMT+03:00 Ward Silver <hwardsil@gmail.com>:
> Here some facts to consider and then I'll get busy with my comments to the
> NPRM:
>
> Any mode that uses AFSK modulation of an SSB radio will be no wider than 3
> kHz, obviously. If the radio could be modified with wider filters, the
> signals could get wider, too, but the phase/amplitude characteristics of
> the transmit chain needs to have much cleaner characteristics than for
> voice. (Direct FSK has different limiting issues.) It would take a whole
> new modulation/transmission scheme to do wider-band data and that would
> demand an SDR with very low IMD in the amplifier chain. The SDR part is
> straightforward since that's mostly math and FPGA programming. The RF
> amplifier part is not so easy and will require advanced techniques from the
> wireless data industry such as adaptive pre-distortion. (One benefit to
> SSB/CW operation from such an adaptation would be cleaner transmitters.)
>
> We should take some comfort in the fact that there aren't many wideband
> data signals on shortwave commercial or military channels. If wideband
> data was easy, they would be doing it now. They are not. Here is an
> extensive table of characteristics for many known HF data modes, including
> military and commercial signals: http://www.sigidwiki.com/wiki/Category:HF
>
> The widest signal in the table that is not a radar or a jammer is DRM
> (Digital Radio Mondiale) at 20 kHz and that's a "phone" signal for hi-fi
> audio. The data version of DRM is much narrower and has been used on the
> ham bands for SSTV in the image sub-bands. The widest pure data signal in
> the table has a 6 kHz bandwidth. We might be concerned about the
> authorization of spread spectrum and wideband OFDM techniques but neither
> of those are authorized emissions below 30 MHz. So...even if the FCC
> declines to put a bandwidth limit of 6 or even 10 kHz on amateur signals,
> we're not going to see a big influx of roaring, high-speed data anywhere on
> HF. The physics of propagation just doesn't work and it takes a lot of
> engineering and equipment to make even the narrower modes perform. I think
> they ought to keep a bandwidth limit because the HF bands are a shared
> resource but that's a behavioral concern.
>
> = = =
>
> What kind of a need is there for regional HF digital in emcomm? Well,
> earthquakes and hurricanes, for starters. The Pacific NW just had their
> big tsunami/earthquake drill (The Great ShakeOut) and having lived there
> for a long time I can tell you it is not wild speculation that comms could
> be taken out for several million people in three states over several
> hundred miles along the I-5 corridor between Grants Pass, OR and Vancouver,
> BC. VHF/UHF ain't gonna get 'er done. The emergency groups up there are
> prepared to use HF (either Winlink systems or NBEMS) to coordinate on a
> state-wide basis. Drill traffic is often passed over HF, sometimes through
> mailboxes hundreds or thousands of miles from the area due to the skip zone.
>
> We have enjoyed a ten-year hiatus in big hurricanes hitting the southeast
> U.S. but HF is a prime resource for recovery from really big storms. Here
> in Missouri, we have localized disasters (mostly) but there is no
> state-wide VHF+ system to support communications with the state Office of
> Emergency Services. So the need is real.
>
> = = =
>
> The concern about session-based protocols (including AX.25) being hard to
> monitor is certainly valid. PACTOR modes do support the ability to monitor
> the packets (with another PACTOR modem) for station ID. The data is
> usually compressed, so unless you capture everything perfectly, you won't
> be able to tell what is being sent. (I can't decipher cyrillic or katakana
> morse, either...) Here's a possible solution - create an network of PACTOR
> modems that listen to the various signals in monitor mode and post the
> station IDs and any other associated data online like the RBN system. A
> "mode deciphering monitor" program that runs on one's personal SDR would be
> a worthy project, too. Simple matter of programming :-)
>
> The "hidden transmitter" problem is always a concern, even on CW/RTTY
> where a station who can't hear me tries to communicate with a station I can
> hear. Yes, the channel-busy detectors could be better, but the operators
> have to engage. This is why I lobbied (successfully) for a set of new
> questions in the General Class pool that directly address the requirements
> of a control operator to listen before initiating contact with a
> remote-control station. Will they do it? Some will and some won't, but at
> least they've had to learn about the requirement.
>
> I've been clobbered by phone, RTTY, SSTV, and even CW signals from
> stations who could clearly hear my signal and just didn't care. What did a
> famous phone contester once say, "A clear frequency is where the needle
> comes off the right-hand peg a little bit." Data stations aren't the only
> offenders in this regard.
>
> = = =
>
> There is some historical precedent as to the benefits of loosening
> restrictions on amateur data experimentation. The FCC NPRMs in the late
> 1970s and early 1990s liberalizing amateur data modes resulted in a huge
> explosion of amateur innovation such as packet radio, various TOR modes,
> and other interesting developments. This is generally viewed as a good
> thing. Your cell phone, by the way, probably includes at a deep level some
> data protocols developed for amateur radio that were adapted for commercial
> use. (This is described in "A History of QST, Volume 1 - Technology,"
> published in 2014.) We have mostly forgotten what "data" was like
> (non-existent) in the days before hams could use ASCII.
>
> = = =
>
> Opening up bandwidths is just not going to be the calamity some of us are
> concerned about. There will be some irritation (including mine) as we
> adjust to new patterns of band use (and the kids will play on our lawns)
> but I am willing to accept the risk, support innovation that responds to
> new needs, use my big knob, and move on.
>
> 73, Ward N0AX
>
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