Re: Abolition of symbol rate restriction
Hi Charles and group.
I have been following this thread for some time. Here is my 2 cents worth.
You are so right that the SHF bands are at risk to being lost due to under-use, and that they can carry wide band width signals.ï¿½ As for your question of Why some amateurs are obsessed with running wide signals on HF bands where they are (A) inappropriate) and (B) not needed is a mystery. - Can you explain it?
For disaster communications, HF communications are VERY appropriate and NEEDED! Also, MARS is using HF Pactor for data communications. Usingï¿½ SHF in a large disaster zone (think Katrina),ï¿½ would take thousands of SHF repeaters in a very large Mesh network to effectively cover a large disaster zone that could be covered with ONE HF transceiver using N.V.I.S. propagation mode.ï¿½
With a change in the FCC regulations, Amateur Radio could truly develop new and useful Emergency Communications tools. With the development of SDR radio platforms, we could do what has been done for years by the military by using BOTHï¿½ USB and LSB at the same time from one HF transceiver, voice on USB and data on LSB. This would be no wider in band width than a vintage AM signal. With a 3 KHz bandwidth for data, truly useful modes like PACTOR 4 could be utilized.ï¿½
By the way, did you know that Pactor 4 can work just fine on 2 meter SSB! We have done it with Red Cross using Pactor 3 over a 65 mile obstructed mountainousï¿½ path from San Diego Red Cross, (50 Watts to 13 element horizontal Yagi),ï¿½ to a solar powered portable station in the desert, using knife edge refraction.ï¿½ We passed large messages with color map attachments back and forth over this path and then did the same thing with 40 meter N.V.I.S. We have found that both of these modes will work well in a disaster zone. The 2 meter signals bounce very well up the canyons and valleys we have in San Diego, day or night.
The added benefit of using Pactor 3 or 4 on 2 meters, is security of transmissions. They are on the low end of 2 meters on unknown frequencies around 144.1 - .27 MHz, using Horizontal antennas, with infrequent intermittent transmissions, and even if someone stumbled on to the transmissions they would need a $1300 Pactor modem that was LINKED to get copy. ï¿½
Why is Amateur Radio so slow to adopt or develop new technologies? Way back in 1995 I worked for Coded Communications. They developed a radio modem that communicated over VHF/UHF radio's at 9600 BPs. They developed a plug in chip that put a reverse curve to the radio's audio bandpass. I am no engineer, but as I remember it, they used a 4 phase clock running QPSK.ï¿½ï¿½ The modem was so fast and reliable that an ACK would come back before you could get your finger off the send button! Taxis in Los Vegas were sending credit card info & status reports over their radio's with this modem. In Coded's mobile data terminals, they stored user forms in EEPROM so only the typed fields the user entered were sent. The other receiving modem would know, by the header information, what form was being used. When I left the company, they were developing a modem that would run 19.2 KBPs, that would work on VHF radio's.ï¿½ Such a system in use by Amateur Radio could support Red Cross, RACES, ARES communications, during disasters. Forms like the ICS213 forms could be preloaded,ï¿½ to shorten the data stream sent.
Meanwhile in 2013, Amateur Radio pokes along at 1200 BPs packet. ï¿½
73 Bruceï¿½ WA6DNT
On 7/29/2013 6:08 PM, Charles Brabham wrote:
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