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TCP-group 1994


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Re: Patents and AX.25



Actually, I had HF in mind when I wrote that, although the same
principle certainly applies on other bands. Although I'd like to see
bandwidth limits eliminated in favor of automatic power control on ALL
bands, the present limits on VHF/UHF aren't nearly as
counterproductive as those currently in effect for HF.

Given the common HF practice of sending audio through a SSB
transceiver, a power-controlled 3 Khz wide (but spectrally efficient)
data emission can be implemented right now in external DSP, with no
radio modifications. Much like Clover, but without the gratuitous 500
Hz bandwidth restriction.

The current QEX has an interesting article on Clover test results.  It
turns out that Clover requires something like 10-15 dB more Eb/N0 to
provide data and error rates comparable to those of a NATO standard HF
modem running in a 3 Khz bandwidth. If it weren't for the FCC's artificial
bandwidth constraints, we could not only be able to reduce transmitter power
by a factor of 10-15 dB for the same data rate but what power is sent could be
spread out over 6 times as much bandwidth. Thus the total spectral density
in watts/hz could be reduced by as much as 20 dB, a factor of 100. Such a
signal would be far less prone to interference, and it would also cause much
less interference to others trying to reuse the same channel at a distance.

Phil





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