[RTTY] Wow - thanks Dr Flowers!

Thu Dec 26 15:15:46 EST 2013

Hi Al,
Baud rate does NOT limit BW, except for 2-tone FSK RTTY.
Actually, two tone FSK RTTY is the ONLY digital modulation that currently has a 
defacto BW limit under FCC rules. Those limits are 300 baud and 1000 Hz maximum 
spacing between tones, which would occupy 1500 Hz. No one uses that, but it is a 
limit.

On the other hand, I can legally use, for example, 16 carriers (or 32 or 64) 
spaced 1 kHz each, with each carrier containing QAM encoding, and as long as I 
strobe the ensemble of those carriers at less than 300 baud, I'm legal - and 
occupying more than 18 kHz (or 34kHz or 66 kHz) BW.  It's a crappy modulation 
but LEGAL today! The FSK shift limit doesn't apply because it's not FSK!

The ONLY thing limiting modulations like the crappy ones I listed above is that 
VERY FEW receivers out there can handle a bandwidth of 18 kHz (or 34 kHz or 
more).  Most radios can handle less than 2400 Hz of phase and amplitude-linear 
BW suitable for modern modulations.

PACTOR-4 (which occupies about 2200 Hz BW, just like PACTOR 3 which is in use 
today) would indeed be permissible once the 300 baud symbol rate is removed.

A sore point for me is that the PACTOR (3 and 4) encoding and decoding are not 
publicly available -unless you actually buy their modem. That is wrong, but that 
is the status quo, and RM-11708 has nothing to do with it one way or the other.

Kai, KE4PT

On 12/26/2013 12:44 PM, Al Kozakiewicz wrote:
> As I said in my own comment, this is a straw-man argument.  The symbol rate has the effect (intended or not) of capping the bandwidth.  Although you are technically correct that the current regulations stop no one from sending 45.45 baud RTTY using 120 kHz of bandwidth, NOBODY does!
>
> Also, I thought that when the ARRL amended their filing to drop the reference to "unspecified digital modes", that effectively removed Pactor 4 as a permissible mode on amateur band HF if the proposed rule was adopted.  That's not true?
>
> Al
> AB2ZY
>
> -----Original Message-----
> From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Kai
> Sent: Thursday, December 26, 2013 10:47 AM
> To: rtty at contesting.com
> Subject: Re: [RTTY] Wow - thanks Dr Flowers!
>
> Hi Chen
> What a tortured argument he made!!
>
> BIG error here:
> *"**So, before the FCC removes the symbol rate and allow higher bandwidths ..."*
>
> Higher bandwidths ARE already permitted, or more precisely HIGHER BANDWIDTHS ARE NOT PROHIBITED TODAY, with the exception of two tone FSK ("RTTY"), which is limited at about 1.5 kHz BW. [My emphasis!].
> Today, hams can use 2.8 kHz, 6 kHz, 12 kHz or 120 kHz or higher bandwidths as long as the symbol rate is below
> 300 baud, and the emission is confined to the ham band. The ARRL proposal would limit the BW to 2.8 kHz where none exists today (well below the 6 kHz permitted in Canada).
>
> 73
> Kai, KE4PT
>
> On 12/26/2013 5:42 AM, Kok Chen wrote:
>> On Dec 25, 2013, at 10:35 PM, Rex Maner wrote:
>>
>>> I'm glad I know how to press the ENTER key.  I sure don't have any
>>> idea what this person is talking about , but it sure sounds
>>> informed.( I Think )
>> I believe some of the points that Andy made are (I paraphrase, and also drill down a bit):
>>
>> 1) the Symbol Rate is not about the ARRL strawman of "spectral efficiency." The ARRL themselves have in the past said that spectrum efficiency is not a goal of amateur radio (and neither does §97.1(a-e)), and now the ARRL petition claims that it is, when arguing for wider bandwidths.
>>
>> 2) based on past FCC rulings, the Symbol Rate is never about bandwidth either, but about hams being able to self regulate.
>>     a) self regulation means that everyone else has to be able to "read the mail," (literally :-)
>>     b) this means that I should be able to copy a signal even when conditions are poor,
>>     c) well, if that is so, high symbol rates simply don't work anyway, since the symbol rate has to be kept low even though the path between the two parties is good, so that a third party (like an OO) can still monitor the conversation.
>>     d) by complaining that Pactor-3 is not efficient, the ARRL obviously don't even understand how the ionosphere works (Andy cites the Maslin book).
>>
>> 3) modern digital modes use what are called (by Harris, for example) "Serial Tone" modems.
>>     a)  you cannot use low SYMBOL rates (like the 100 baud in Pactor 3) and keep adding subcarriers to get higher DATA rates,
>>     b)  so, you use something like 64-QAM (QAM is a mix of PSK and amplitude modulation -- ASK), and you run at really high symbol rates,
>>     c)  to get high symbol rates through HF propagation when conditions are poor, the Serial Tone modems equalizes the channel,
>>     d)  to do equalization, they periodically send a long pseudo preamble (PN) sequence (example Andy gave is 176 bits long, used in STANAG 4285) .
>>     e)  the receiver takes the PN preamble and performs an autocorrelation, and from that derives a real time equalization of ionospheric distortion.
>>     f)  but here is the crux: unless the PN generator is openly published, it is equivalent to encryption, (which serves a dual purpose with the mil STANAG modems)
>>     g)  so we are back to hams not being able to self regulate again, since we cannot read the effectively encrypted mail.
>>
>> So, before the FCC removes the symbol rate and allow higher bandwidths, they should make sure that Amateurs have the tools to read the mail.  By citing Pactor-4 in the petition, the ARRL must think that Pactor-4 satisfy the "read the mail" condition, but Andy thinks that it does not.  Pactor-4 does not satisfy the conditions needed to be used in the Amateur service.
>>
>> Andy also points to the fallacy with people who expect privacy when they use the Amateur service to forward email, since Amateur Radio principals have been that messages that are carried by the service must be transparent.  By making encryption open, these email users will at least not be misled that they have any privacy when they use the Amateur service to forward their email.  Since the principal is already embedded in §97.309(a), the FCC need not make a new ruling but just re-affirm it, since "it is obviously a point of confusion" to many parties.
>>
>> Andy also called the 2.8 kHz part of the petition "strange," and added that the ARRL has not specifically said why they think there is a "tangible need" for it.  In my own comment, I had used "arbitrary and capricious" to describe the 2.8 kHz number -- in lawyerese, a rule is arbitrary if it is not supported by logic or the necessary facts; a rule is capricious if it is adopted without thought or reason or is irrational (http://definitions.uslegal.com/a/arbitrary-and-capricious/ ).
>>
>> 73
>> Chen, W7AY
>>
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