But if the path S/N is so poor that you cannot get the message across at
all, isn't the spectrum efficiency zero? ;-)
73 - Skip KH6TY
Rein Couperus wrote:
Spectrum efficiency must be measured in time necessary to get the info
across,
length of info transferred, and bandwidth.
((characters/second)/ bandwidth) or characters/(seconds * bandwidth).
The bandwidth includes a certain guard band(minimum distance between 2
different
signals), which for JT65 is quite small ... but the time is a large
factor...
To give a small example:
Pskmail using PSK500 ARQ has a spectrum efficiency of 23/500 = 0.046
CPS/Hz
... measured on 14094.0 kHz running 100 mW connected to SM0RWO
(>1000Miles) ...
The longest message in JT65 is 13 characters... and a message takes 48
seconds..
the bandwidth (according to the mode description) is 65 * 2.7 = 175 Hz
...which calculates to (13/48) / 175 = 0.001547619 CPS/Hz
I would say this is a pretty bad value... :)
Rein PA0R
>Bill N9DSJ decoded two stations within 24 Hz of each other, how is
>that for spectrum efficiency? I was transmitting 5 watts,
>
>I know many are already aware of this, but take a look
>
>N9DSJ-1 (EN52ti) Heard N6TE(DM12) on 3576.23 KHz -8dB at 03:32:00Z
using JT65A
>N9DSJ-1 (EN52ti) Heard K3UK(FN02) on 3575.99 KHz -5dB at 03:32:00Z
using JT65A
>
>Bill N9DSJ decoded two stations within 24 Hz of each other, how is
>that for spectrum efficiency? I was transmitting 5 watts,
>
>Andy K3UK
>
>
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