For your amusement and consternation here are my latest thoughts on doing an
OFDM protocol.
Symbol rate: 62.5 Hz(128 samples @ 8000 Hz)
Guard interval: 2, 4, 8 ms adaptive to conditions
Subchannels: 8 (62.5 125 187.5 250 312.5 375 437.5 500)
Bandwidth: 437.5 Hz
Raw BPS: 1778, 1600, 1333
30m has some commercial and govt. junk on it on this side of the pond
not to mention the bootlegger fishing boats. Rich k2tft
In digitalradio@yahoogroups.com, Sholto Fisher [EMAIL PROTECTED] wrote:
Can anyone record a minute or two for me to have a listen please?
Sholto KE7HPV.
The Fall Fling
Feld-Hell Club Fall Fling Rules:
Object: To contact as many other stations as
possible using the Feld-Hell digital mode. The contest is open to all
licensed amateurs and SWL participants.
Date:
Differential PSK should be more reliable in the presence of frequency drift and
Doppler spread. There are two ways to do this: 1) compare the phase with the
previous phase of the same subcarrier or 2) compare the phase with the phase of
the next higher or lower subcarrier. In the first case,
John,
Are there any cases where any of the current amateur radio digital modes
do not use differential keying?
Based on your comments on 8PSK, is this why it is the base waveform used
in the MIL-STD/FED-STD/STANAG modems?
What is your view on single tone modems as used in those standards vs.
As far as I know, most OFDM implementations use differential keying either in
time or frequency. HamDRM uses multiple pilot carriers as phase references. I
think that there is one pilot carrier for every 4-5 data carriers. I assume
that 8PSK is used in the federal standards because of the
Rud:
What language are you developing in? I have some software that generates and
receives OFDM with 8PSK subcarriers using .wav files containing I and Q
samples. The source code is about 1500 lines of Delphi (Pascal). It's fairly
slow as it uses a DFT and IDFT and floating point arithmentic,
Rud,
The Lyons book is a good introduction to the FFT and FIR filters but I haven't
read the other book. Multirate Signal Processing (ISBN 0-13-146511-2) has
information on more complex DSP systems. Digital Communications (ISBN
0-07-051726) is fairly old, but a good introductory book and there
