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
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