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LF: Re: Frequency errors on PSK31

To: [email protected]
Subject: LF: Re: Frequency errors on PSK31
From: "Andy Talbot" <[email protected]>
Date: Sat, 11 Dec 2004 13:43:37 -0000
References: <[email protected]>
Reply-to: [email protected]
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As PSK31 uses differential coding, it is the phase change over the 32ms signalling period due to freqeuncy error that is important.  If for BPSK, we need to maintain the phase to less than 90 degrees to remove the ambiguity, so 90/360 / 32ms = 7.8Hz freq error permissible.
 
For noisy signals, the determination of correct phase becomes worse, so error rate will progressively worsen with tuning error.
 
Andy  G4JNT
 
----- Original Message -----
Sent: Saturday, December 11, 2004 10:12 AM
Subject: LF: Frequency errors on PSK31

Hello.
 
I'm trying to produce a small PSK31 beacon on a PIC chip using one port (and an XOR gate) to initiate phase change, and others to control the mark space ratio for driving a class D amplifier for the amplitude change.
 
Question:
 
With the currently available soundcard decoders, what frequency errors are permissable in the PSK31 waveform which will still decode successfully? Normally 32ms but what tolerance is OK?
Do the decoders lock, and then suddenly lose all decoding ability if the frequency is too far off, or do they just slowly increase their bit error rate with frequency error?
 
 
73
 
David


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