Your examples are with like bandwidths. These channels were assigned for the purpose that you have mentioned, so any reduction in bandwidth would not provide any increase in efficiency. In other words you would still occupy the entire channel. With Amateur Radio this is not the case. We are not assigned channels (except 60 M) so any reduction in bandwidth may give us an increase in efficiency. Lets compare Pactor II and Pactor III under good conditions. http://www.scs-ptc.com/pactor.html tells us that on average PACTOR III give us a 3.5 X increase in data rate with 5 to 6 X the bandwidth. On good channels the increases are equal. This tells me that in the best case PACTOR II and PACTOR III are equally efficient, but on average Pactor II is more efficient. A single PIII QSO would occupy 2.4 KHz for less time than PII would occupy 400Hz of spectrum, if you calculate Hz/sec, PII will win in both the good channel and average channel case. Speed alone cannot be the only factor when considering efficiency. The wider bandwidth of PIII may make the transmission more robust. We also see that with Olivia and MT63, but we need to quantify that improvement. When we start spreading signals in a power limited system like Amateur Radio, we need to be aware of the affects of the Crest Factor (CF).
I think we will be able to use emissions with bandwidths greater than 500Hz in the RTTY/Data subbands, but it is very interesting to me to find how popular limiting the maximum occupied bandwidth to 500Hz actually is with the general ARS population.
73,
Mark N5RFX
Ah ha...well Bonnie I see that I am not the only one who is looking at the overall picture of band usage.__._,_.___
Here is an example of what I saw in the military...
SSB voice took 10 minutes to pass a 100 word message between really seasoned radio operators on an HF channel typical of most Q4-5 amateur radio QSOs.
When they went to 300 baud text data, they send the same message in 2 or 3 minutes and sometimes 3 or 4 when they had to repeat the message...this was again with Q4-5 signals. The modem was not much more than a Bell 103 modem.
With a MIL-STD-188-110 16 tone modem at 2400 baud, the message took 1 or 2 minutes and only every 5-6 messages was a it necessary to repeat a message.
The band/channel usage went from 1=10 to 9 0r 9=10...almost a ten fold increase in band/channel usage.
Today those same units are using 9600 BPS data and sending one page of text in a couple of minutes or sometimes "booking" messages and sending 20-50 messages at one time.
The higher the throughput and mode robust the mode, the less channel usage there is going to be at a fixed amount of data.
Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org
Other areas of interest:
The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/
DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion)
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