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[Ham-80211] HSMM: 420-430 MHz

Brian Webster bwebster at wirelessmapping.com
Fri Mar 4 20:12:29 UTC 2011


While I would agree that it is nice to push the limits, I would further look
at the rules to determine what modes or modulation formats are allowed for
image communications just to make sure they don't specifically state them.

Thank You,
Brian N2KGC

-----Original Message-----
From: ham-80211-bounces at tapr.org [mailto:ham-80211-bounces at tapr.org] On
Behalf Of kb9mwr at gmail.com
Sent: Friday, March 04, 2011 2:01 PM
To: ham-80211 at tapr.org
Subject: Re: [Ham-80211] HSMM: 420-430 MHz

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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