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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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