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[Ham-80211] HSMM: 420-430 MHz

kb9mwr at gmail.com kb9mwr at gmail.com
Fri Mar 4 19:00:33 UTC 2011


You are correct there is a 56 kilobauds speed or maximum bandwidth of
100 kHz for 222-450 MHz.  (On all frequencies 902 MHz and above there
are no speed or bandwidth limits.)  However for 70 cm there is no
bandwidth limit for image communications.

Interestingly enough the ATSC digital TV standard uses Coded
orthogonal frequency-division multiplex (COFDM)

A 802.11a/g OFDM modem would be a J2C (fax) or J2F (video) emission.
The word image encompasses both television and facsimile.  Basically
the rules permits you to transmit images information using essentially
any modulation method.

John Stevensen, KD6OZH was the first that I know of to start
development of a 70 cm OFDM Modem see:

K8OCL & KD6OZH "28 kbps to 9 Mbps UHF Modems for Amateur Raio
Stations," QEX Mar/Apr 2005

Since I have a camera on my tower, I am willing to push the envelope
on some rather antique rules and bandplans at the expense of helping
show that some experimental uses can help bring new life to
underutilized spectrum.



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