[NLRS] Re: Digital modes

[Dr. Gerald N. Johnson, electrical engineer]

The audio fed to the phase modulator has a modified spectrum so the
result comes out FM. In digital data that spectral modification
accomplished by a simple RC network destroys the phase coherence of the
1s and 0s and makes that data not usable. Ears are NOT sensitive to the
relative phase of harmonics, but square waves are very sensitive to the
relative phase of harmonics. So what works for voice often destroys
data.

Many radios inject voice into the PLL VCO control line. The phase
changes caused by the low pass filter of the loop don't damage voice but
destroy data. Hence many commercial radios that claim to run 9600 baud
FSK have horrible error rates at any signal strength. A part in 1000
error rate isn't quite good enough to pass one packet.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.