Hello Rud, In asynchronous ARQ mode, in all cases, it is necessary to bit synchronize the receiver as the receiver does not know when teh next frame is going to be transmitted (reversely, in synchronous ARQ mode this is not necessary as the RX knows exactly the time of the reception of the next frame). For bit synchronization, it is necessary to send previously a sequence of symbols (which solves this problem of VOX even if it was not done for this...).
For example, here is an extract of the ARQ FAE protocol. 28 symbols to synchronize can seem much but the S/N can be very low (down to -13 dB). As you see in ARQ FAE in ALE400, there is a delay of 0.56 second before transmitting any useful symbol. 73 Patrick ARQ FAE synchronization sequence In 125 bauds Before each FAE frame, it is transmitted 28 symbols, alternately on the lowest frequency and then on the highest frequency, so for a duration of about 0.224 second (28/125 s). This is aimed: * to cover the necessary delay to switch the transceiver (128 ms maximum, with a standard delay of about 40 ms), * to permit the symbol synchronization just before the frame reception (96 ms). - In 50 bauds It is also transmitted 28 symbols, alternately on the lowest frequency and then on the highest frequency, so for a duration of about 0.56 second (28/50 s). This is also aimed to: * to cover the necessary delay to switch the transceiver (128 ms maximum, with a standard delay of about 40 ms), * to permit the symbol synchronization just before the frame reception (432 ms). ----- Original Message ----- From: "Rud Merriam" <[EMAIL PROTECTED]> To: <digitalradio@yahoogroups.com> Sent: Wednesday, August 27, 2008 12:25 AM Subject: RE: [digitalradio] Re: Signalink No Good for ARQ Modes > Or the protocol implementers need to recognize the need to generate a tone > to trigger the VOX. This would be analogous to the delay they provide for > transmitter keying. > > > - 73 - > Rud Merriam K5RUD > ARES AEC Montgomery County, TX > http://TheHamNetwork.net > > >> -----Original Message----- >> From: digitalradio@yahoogroups.com >> [mailto:[EMAIL PROTECTED] On Behalf Of expeditionradio >> Sent: Tuesday, August 26, 2008 1:26 PM >> To: digitalradio@yahoogroups.com >> Subject: [digitalradio] Re: Signalink No Good for ARQ Modes >> >> >> > Sholto Fisher wrote: >> > I can't believe it makes any significant >> > difference at least for ALE400 FAE. >> >> Hi Sholto, >> >> Whether you believe it or not, that's >> up to you. But the math doesn't lie, >> and neither does the oscilloscope. >> >> IMHO, any interface that chops off part of your >> transmission, for whatever mode, should >> be returned to the manufacturer for refund :) >> >> 73 Bonnie VR2/KQ6XA >> >> >> ------------------------------------ >> >> Announce your digital presence via our Interactive Sked Page >> at http://www.obriensweb.com/sked >> >> Check our other Yahoo Groups.... http://groups.yahoo.com/group/dxlist/ >> http://groups.yahoo.com/group/contesting >> http://groups.yahoo.com/group/themixwgroup >> Yahoo! Groups Links >> >> >> > > > ------------------------------------ > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/sked > > Check our other Yahoo Groups.... > http://groups.yahoo.com/group/dxlist/ > http://groups.yahoo.com/group/contesting > http://groups.yahoo.com/group/themixwgroup > Yahoo! Groups Links > > > > >
