There is no bandwidth limit in the RTTY/data segments but there is a limit of
"no wider than a communications-quality DSB phone signal using the same
modulation type" in the phone/image segments from 160 to 1.25 meters. This is
interpreted as anything between 6 and 10 kHz by U.S. AM users but the European
governments have decided that 8 kHz is the upper limit on HF.
The rules specificly reference emission designators that authorize multiple
subcarriers so FDM modes are unlikely to beome illegal.
73,
John
KD6OZH
----- Original Message -----
From: Charles Brabham
To: digitalradio@yahoogroups.com
Sent: Wednesday, October 28, 2009 13:20 UTC
Subject: Re: [digitalradio] Why would anyone
From what I understand, we do not have an actual bandwidth limit on HF, but
we do have a practical one, based upon PART97 prohibitions against harmful
interference and of course the 300 baud limit.
The wider HF digital modes 'get around' the 300 baud limit by transmitting
multiple streams, each at less than 300 baud inividually but adding up to
something significantly higher. Q15x25 for example transmits fifteen PSK
streams for an effective 2.5 kb data rate. The transmitted signal is about the
same width as PACTOR III, around 2.5 kHz.
The legality of 'getting around' the 300 baud limit with multiple streams has
not been established. So far, the FCC has not put its foot down on the matter
but that is no guarantee that they will not decide to do so at some point in
the future, perhaps when and if they feel that the practice has gotten out of
hand.
The prohibition against deliberate harmful interference is the real limiting
factor. We must remember that saying "I didn't listen before transmitting, so I
didn't know I would interfere." is no defense whatsoever against a complaint of
deliberate interference. It does not take a rocket scientist to know that if
you transmit an ultra-wide signal on busy, crowded amateur radio spectrum
without taking pains to find a clear spot of the required size, that you will
most certainly end up crashing other hams QSOs.
In light of this, and the fact that our spectrum is shared spectrum where
nobody owns a frequency, you may wonder why we do not have a bandwidth limit on
HF. There are a number of reasons for this, but the main one is that we are
expected to experiment with radio technology, to push the envelope in various
ways that may require more bandwidth than usual. This is something to consider
if you are wondering why the FCC has not put their foot down so far on the 300
baud rule. They are giving us "leeway".
Playing with ultra-wide signals on an occasional, experimental basis is not
so difficult. As we all know, sometimes the HF bands are packed from one end to
the other, and at other times there are great, wide stretches of unused
spectrum out there. I'll mention here that the more useful and popular bits of
spectrum ( 20m for example ) are going to be unoccupied a lot less often than
17 or 15m for example. So, for a careful and thoughtful experimenter, finding a
stretch of open spectrum to play with a wide signal is not such a difficult
thing to do.
Not to mention VHF and UHF of course, the best and most reasonable place to
experiment by far.
Where we run into difficulties on HF is when we stop experimenting with wide
modes and start attempting to use them on a regular basis. This is because we
simply cannot realistically expect to find that much open HF spectrum on a
useful frequency, in the same spot, on a regular basis.
The problem is compounded when you attempt to utilize wide signals this way
with an unattended, automated server. With no human there to look for times
when the required amount of spectrum is open, we must depend upon 'signal
detection' software and there are limitations to signal detection that make it
progressively slower and uncertain as you sample a wider area for signals.
I think we can all take it for granted that WinLink's "to hell with our
fellow hams" approach of running wide signals with no signal detection
whatsoever is not acceptible, and may well bring on the crackdown upon signals
above 300 baud that I mentioned the possibility of, earlier. Thumbing their
noses at the amateur radio community and the PART97 regulations that way cannot
be realistically expected to return a good long-term outcome. They endanger us
all as they test the FCC's patience this way.
I have more to say about the inherent limits to signal detection but this
post is getting too long already.
So, we do not have a codified limit to bandwidth, but we do have a number of
practical ones that should be easy to stay out of trouble with, as long as we
play well with others and follow the rules. ( PART97 and The Amateurs Code )
Otherwise - we are asking for trouble and will not like the result that
follows.
73 DE Charles Brabham, N5PVL
Prefer to use radio for your amateur radio communications? - Stop by at
HamRadioNet.Org !
http://www.hamradionet.org
----- Original Message -----
From: Dave Sparks
To: digitalradio@yahoogroups.com
Sent: Tuesday, October 27, 2009 9:17 PM
Subject: Re: [digitalradio] Why would anyone
I'm not sure who suggested 50-100 khz. of B/W... But if someone can take
up 6 Khz of B/W just to transmit a human voice, why not something similar for
digital modes?
I'm not saying you SHOULD, or that it would be PRACTICAL, but if we're
setting limits ...
--
Dave Sparks
AF6AS
----- Original Message -----
From: DANNY DOUGLAS
To: digitalradio@yahoogroups.com
Sent: Tuesday, October 27, 2009 7:02 PM
Subject: Re: [digitalradio] Why would anyone
OH Wonderful! Some idiot would come up with something 50 or 100 kc wide,
and then be legal to wipe out dozens if not hundreds o QSOs. There MUST be
rules, because there is always going to be someone who will push the envelope
with so called "advances" which ignore the rights and wishes of others. Thats
why we have speed limits even the Germans have finally come around to realizing
you just cant let every Hans drive his own speed. By the way, 200 mph will
get you there (if it doesnt kill you and everyone else on the road), but 60
will get you there too, and a lot safer.
Danny Douglas
N7DC
ex WN5QMX ET2US WA5UKR ET3USA
SV0WPP VS6DD N7DC/YV5 G5CTB
All 2 years or more (except Novice)
short stints at: DA/PA/SU/HZ/7X/DU
CR9/7Y/KH7/5A/GW/GM/F
Pls QSL direct, buro, or LOTW preferred,
I Do not use, but as a courtesy do upload to eQSL for
those who do.
Moderator
DXandTALK
http://groups.yahoo.com/group/DXandTalk
dxandt...@yahoogroups.com
Moderator
Digital_modes
http://groups.yahoo.com/group/digital_modes/?yguid=341090159
----- Original Message -----
From: Dave Sparks
To: digitalradio@yahoogroups.com
Sent: Tuesday, October 27, 2009 9:55 PM
Subject: Re: [digitalradio] Why would anyone
----- Original Message -----
> From: Andy obrien
> To: digitalradio@yahoogroups.com
> Sent: Tuesday, October 27, 2009 3:57 PM
> Subject: Re: [digitalradio] Why would anyone
>
>
>
>
> I agree with Charles, mostly. I have mixed feelings about the whole
> "wide" versus "narrow" issue. While I tend to gravitate towards the
> narrow modes, I
> have to admit to sympathizing with those on this list who express
> frustration that they cannot experiment with some of the wider modes
> because they exceed
> baud rates and bandwidth limitations in the USA. Obviously, if I am
> parked on my narrow part of the spectrum having a nice chat, I would
be
> unhappy about
> someone with a 10 Khz wide signal zapping the entire band. I guess I
> would say that keeping the max under 2.7 Khz makes some sense.
>
> Andy K3UK
Hi Andy,
That limitation would only make sense if you were also willing to ban
DSB AM
transmissions, which take up over twice that bandwidth. What we really
need
is a rule that says you should use the minimum bandwidth needed to get
the
job done, just as we do with power.
--
Dave Sparks
AF6AS
