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Date: Sun, 18 Jan 2009 21:04:58 +0000
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
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Subject: Re: LF: PSK CONTACT G4JNT - M0BMU
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Amateur bands are typically 2 to 10% of their centre frequency, so
lets take a figure of 5%, giving a useable band 95uHz wide.  Allow a
waveform that criutically fits inside this bandwidth - OFDM or MFSK
fit the bill nicely as they both have 'brick wall' frequency spectra,
so with really good coding we ought to be able to fit in about  100 -
200 u Bits/s, or one bit per 500 - 10000s.  Say one bit per hour.

We will use a codebook based approach to coding callsigns and reports
so as to compress a message into the smallest space possible:  say a
maximum of 256 stations on the band in the world,  means 8 bits need
to be allocated to callsign, and four possible reports
(poor/marginal/OK/strong) gives 10 bits per QSO.  Add two more bits
for QSO formatting and we end up with 12 bits of data per frame .   We
will need good error correction, so make it a convolutional rate half
code - 24 bits in total.  A QSO needs a minimum of two overs each for
full acknowledgement each way so at least 96 bits need to be
exchanged.   If no further overhead is used, the QSO could therefore
be completed in four days.


Andy  G4JNT
www.g4jnt.com



2009/1/18 Wolfgang B=FCscher <dl4yhf@freenet.de>:
> John wrote:
>>
>> 1.9mhz - now what sort of signalling rate can you get on 160Gm?
>>
>> John F5VLF
>>
>>
>
> ;o)
> Need a pretty decent antenna length for that, right ?
> And just consider the 1/f noise in the milliHertz receiver - use liquid
> helium cooling for the frontend ;-)
>
>
>