[RTTY] Wow - thanks Dr Flowers!

[Kai]

Hi Chen,
Right you are - P4 is 2400 Hz BW, not 2200 Hz.  So the 2200 of P3 has already 
crept up to 2400 Hz.  The data from your URL further also makes my point:

"Special importance was given during the development of PACTOR-4 that this 
*could be used without problem on industry standard transceivers with a 2.4 kHz 
IF bandwidth ("amateur radio transceiver")*. Due to the adaptive equalizer, the 
form of the IF filter curve (as compared against OFDM, PACTOR-3) is non 
critical. PACTOR-4 requires only slightly more SNR in order to equalize even 
"heavily bent" IF filter curves."

In other words, *it is only 2400 Hz because of today's equipment limitations!*
They tuned it to the typical ham transceiver BW (just like they did PACTOR-3). 
THAT is why we need a limit! Ham radios, especially SDR units, will be able to 
handle higher BWs - let's get the limit in place NOW.

73
Kai

On 12/26/2013 4:01 PM, Kok Chen wrote:
> On Dec 26, 2013, at 12:15 PM, Kai wrote:
>
>> 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.
> Pactor-3 has 2200 Hz bandwidth (2K20J2D), but Pactor-4 is 2400 Hz, per SCS, not 2200 Hz.  See
>
> http://www.p4dragon.com/en/PACTOR-4.html
>
> Pactor-4 SL1 has two subcarriers.  Pactor-4 SL2 through SL10 are all single carrier, at 1800 baud.  SL9 and SL10 are 16-QAM and 32-QAM, thus 1800*4 (7200) and 1800*5 (9000) bits/second raw data rate.  See
>
> http://www.medav.de/fileadmin/redaktion/documents/English/vd_PACTOR_demodulator.pdf
>
> So, the ITU emission mode of Pactor-4 actually changes as you switch SL levels.  But the bandwidth of Pactor-4 does not change to same the degree as the bandwidth change for Pactor-3 (from 500 Hz to 2200 Hz).
>
> Further, notice that SL2 through SL4 have a spreading factor, so the 1800 baud actually produces lower than 1800 bits/second raw data (bit) rate.
>
> It is going to be interesting to see if Pactor-4 SL2, 3, and 4 can be legal on ham bands since they involve some sort of spreading.  DQPSK is often implemented with a direct sequence spreader.  If/when they reveal the details (to work around "unspecified codes") we will know if these SL levels are mathematically equivalent to direct sequence spread spectrum.
>
> Lawyers, start your billable hours clocks :-).
>
> 73
> Chen, W7AY
>
>