While I agree that keeping the rig away from bulkheads, etc. and allowing for adequate ventilation IS a good idea....
"PACTOR" is not really a "high-duty-cycle" mode...
Originally Posted by brianb00
Suggest you make sure it is well ventalated as pactor has a very high duty cycle.
a) PACTOR-I (which is FSK) IS a 100% duty-cycle mode, but is used only to signal/connect with a station ( a few seconds), and then you're going to be using PACTOR-II or PACTOR-III...
b) PACTOR-II is actually approx. a 50% duty-cycle mode (about what an SSB transmission
is with speech processing)...
c) PACTOR-III's duty-cycle varies, depending on connection quality (link s/n), with stronger signals being a very light duty-cycle of about 30%...and under very bad conditions, a duty-cycle of about 60%....
transmissions without any speech processing, are typically 25% - 35% duty-cycle....and with speech processing, about 50% - 60%....}
Again, ensuring adequate ventilation for the radio
IS important, but be aware that the "duty-cycle" of most sailors' PACTOR transmissions are not much different from an SSB transmission
with speech processing....and sometimes even lower...
After typing this last night....I wanted to find some supporting material, so as not cause an argument....so, I waited 'til I found an obvious source: Sailmail...
Here is directly from the Sailmail website:
FSK (frequency shift keying) is the transmission mode (used in Pactor-I) that the KAM+ uses all of the time, and that the SCS PTC-II uses briefly before it automatically switches to Pactor-II mode which uses PSK (phase shift keying). FSK mode has the potential to operate your radio continuously at maximum output. For engineers, its crest factor is 1.0 (i.e. the peak and average voltages of the modulating signal are the same).
PSK is the transmission mode used in Pactor-II and Pactor-III that is used by the SCS PTC-II after it connects with the SailMail station. When your radio is running at its peak output transmitting Pactor-II, its average power output will be half of its peak output. This is due to the properties of the PSK modulation, not due to any shortcoming of the radio. View this as an advantage of Pactor-II; it uses less power than does the FSK modulation used by Pactor-I (KAM+), and works over longer ranges at faster rates. For engineers, the voltage crest factor of the PSK used in Pactor-II is 1.45 (i.e. the peak to average voltage ratio is 1.45, which means that the peak to average power ratio is 1.45 squared, which is 2). A big advantage of Pactor-II, with its lower average power output, is that radios designed for voice duty can perform nearly as well as continuous-duty radios.
The crest factor of Pactor-III varies depending on how many tones the modem decides to use. Depending on the number of tones, the voltage crest factor for Pactor-III ranges from 1.24 to 1.93 (which corresponds to power crest factor of 1.9 dB to 3.7 dB). Remember by comparison that FSK has a voltage crest factor of 1.0 and Pactor-II had a voltage crest factor of 1.45. So in terrific conditions, Pactor-III, will use all 18 tones and will be very easy on your radio and only run your (150 watt peak power) radio at an average power of 40 watts. In lousy conditions Pactor-III will only use two tones, and with a 1.24 voltage crest factor will run your (150 watt peak power) radio at an average power of 97 watts.
I hope this helps...
s/v Annie Laurie