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DB0FHN

[JN59NK Nuernberg]

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K0CQ   > 9K6      26.06.07 00:07l 32 Lines 1600 Bytes #999 (0) @ WW
BID : 36644_W0AK
Read: DG1VV GUEST DL8FO DJ9UI DL7ALE DG4YDF
Subj: Re: Hi speed transformer coupling?
Path: DB0FHN<DB0MRW<DK0WUE<DB0RES<IK2XDE<ON4HU<ON0BEL<N4ZKF<KQ0I<W0AK
Sent: 070618/0035Z @:W0AK.#CIA.IA.USA.NOAM #:36644 [Des Moines] $:36644_W0AK
From: K0CQ@W0AK.#CIA.IA.USA.NOAM
To  : 9K6@WW

Typically  the high speed techniques used for wire lines are  not 
used  in  amateur  radio,  or  as  far  as  I  know  for  any  RF 
application. Those techniques use multiple tones, not just two in 
order  to slow the signaling rate well below the data rate.  This 
conserves  bandwidth  but demands amplitude and  phase  stability 
(since  the  keying  scheme involves  both  amplitude  and  phase 
modulation) that is not available by radio. Further the modems go 
through  an  active  phase  and  frequency  compensation  at  the 
beginning  of  each  connection  which  would  have  to  be  done 
continuously by radio.

These  transformers rated for 28K or 64K are not for that wide  a 
signaling  bandwidth,  just the phase and frequency  response  is 
within compensating range while using an ordinary telephone  line 
which only allows 3 KHz or less audio bandwidth.

Running 9K6 packet we are using straight FSK, and to preserve the 
phase  of the data which has been run through a 4800 Hz low  pass 
filter  to  limit  the bandwidth, its necessary  to  connect  the 
modulation  direct to the transmitter frequency modulator and  to 
take  the received signal directly from the discriminator and  to 
avoid  any  of the audio processing in the  transceiver.  Further 
when  the  frequency modulator is in a phase  locked  synthesizer 
loop,  the loop bandwidth tends to destroy the data  making  many 
supposedly 9K6 radios workable only for very short distances  and 
even then with excess error rates.

73, Jerry, K0CQ @ W0AK.#CIA.IA.USA


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