FT736 & 9600 Baud Operation
                    ---------------------------
                       by James Miller G3RUH

These notes tell you where to get FM RX audio direct from the
discriminator, and where to modulate the FM TX varactor directly.  These
modifications are non-destructive and take no more than a few minutes. 
The signals bypass the "DATA SOCKET" for high grade FM operations.

The RX mod is suitable for:

 *  UOSAT-D 9600 baud downlink and terrestrial links
 *  1200 baud AFSK/FM Standard Packet - BUT IT'S UNSQUELCHED.

The TX mod is suitable for:

 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink direct FSK and terrestrial links
 *  1200 baud AFSK/FM Standard Packet.

                            ---****---

FT736 -  FM Direct from Discriminator
-------------------------------------
Detected FM direct from the receiver discriminator is available from the
RX UNIT at the junction of R91 and C83.  These components are shown in the
top right-hand corner of the schematic.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. RX Unit is the vertical module on the left.
 4. Locate R91 which is about 25mm from the top, 50mm from the radio rear. 
    the resistor is "on-end", and near a couple of glass diodes.
 5. Scrape any paint off R91's free end and wet with solder.
 6. Your RXaudio lead should be a fine screened cable;  connect the inner
    to R91, and the outer braid to a ground point (e.g. can of TO09)
 7. Route the cable out though any convenient aperture in the case.
 8. The discriminator sensitivity (FM Normal) as about 6 kHz/volt.

Important note on 9600 Baud Use
-------------------------------
Some FT736 receivers are fitted with an LFH12-S IF filter for FM. (CF01 at
the top front of the RX Unit).  This is a 12 kHz bandwidth filter which is
a little too narrow for 9600 bps FSK operation.  It is recommended you
change this to 15 kHz or better still for UOSAT-D use, 20 kHz bandwidth
which will allow more tolerance for doppler shift, and give a far better
"eye".  Suitable filters are: LFH-15S / CFW455E, and LFH-20S / CFW455D. 

                            ---****---

FT736  DIRECT VARACTOR FM MODULATION
------------------------------------
Refer to the circuit diagram; inject your TXaudio at the junction of
R32/C29 on the TX Unit.  The signal level at this point should be 800 mV
peak-peak, and will give +/- 3 kHz deviation.  DO NOT EXCEED THIS LEVEL. 
Set Mic Gain to min.

Modulating the FM transmitter this way you get an LF response down to 18
Hz (at which point the associated synthesiser PLL begins to track the
modulation), and an HF response which is flat to some 10 kHz.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. TX Unit is the module flat on the left (not the one tucked down the
    side vertically).
 4. R32 is just to the left of the rectangular shielded enclosure.  The
    resistor is "on end".  Scrape any paint off the free leg.
 5. Your TXaudio lead should be a fine screened cable;  connect the inner
    to R32, and the outer braid to the adjacent enclosure. 
 6. Route the cable out though any convenient aperture in the case.

 7a. 1200 BAUD PSK MODEM: TXAudio of 800 mV pk-pk can be obtained by
    adjusting the components C9= 1uf, R3=47k, R5=infinity (i.e. remove). 
    C10 stays at 10nf (0.01uf).

 7b. 9600 BAUD FSK MODEM:  Adjust TXAudio level with VR1.  Use TXEPROM
     selection number 10 (ten) for UO-14, i.e.  JMP1,3 ON, JMP2,4 OFF


Tidy Installation
-----------------
I found it neat to make up a little aluminium bracket to affix under 
the rear left lid screw.  This bracket carries a 5-pin DIN socket, 
and the TX RX and PTT wires are terminated here.  This saves having 
leads dangling out of the interior. (Tnx EI6EH).

 Notes compiled by G3RUH @ GB7DDX 1990 Mar 16, rev 1991 Sep 20
<EOF>

Msg Nr.     : 32411 
Da          : LU7AKC
Per         : NET9K6@WW      
Tipo/status : B$
Data/ora    : 0815/0258
Dimensione  :10172
Titolo      : FT736 & 9600 Bps
Bid (Mid)   : 12251_LU7AKC

                    FT736 & 9600 Baud Operation
                    ---------------------------
                       by James Miller G3RUH

These notes tell you where to get FM RX audio direct from the discriminator,
and where to modulate the FM TX varactor directly.  These mods are
non-destructive and take no more than a few minutes.  The signal bypass the
"DATA SOCKET" for high grade FM operations.

The RX mod is suitable for:

 *  UOSAT-D 9600 baud downlink and terrestrial links
 *  1200 baud AFSK/FM Standard Packet - BUT IT'S UNSQUELCHED.

The TX mod is suitable for:

 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink direct FSK and terrestrial links
 *  1200 baud AFSK/FM Standard Packet.


FT736 -  FM Direct from Discriminator
-------------------------------------
Detected FM direct from the receiver discriminator is available from the RX
UNIT at the junction of R91 and C83.  These components are shown in the top
right-hand corner of the schematic.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. RX Unit is the vertical module on the left.
 4. Locate R91 which is about 25mm from the top, 50mm from the radio rear. the
    resistor is "on-end", and near a couple of glass diodes.
 5. Scrape any paint off R91's free end and wet with solder.
 6. Your RXaudio lead should be a fine screened cable;  connect the inner to
    R91, and the outer braid to a ground point (e.g. can of TO09)
 7. Route the cable out though any convenient aperture in the case.
 8. The discriminator sensitivity (FM Normal) as about 6 kHz/volt.


Important note on 9600 Baud Use
-------------------------------
Some FT736 receivers are fitted with an LFH12-S IF filter for FM. (CF01 at the
top front of the RX Unit).  This is a 12 kHz bandwidth filter which is a little
too narrow for 9600 bps FSK operation.  It is recommended you change this to 15
kHz or better still for UOSAT-D use, 20 kHz bandwidth which will allow more
tolerance for doppler shift, and give a far better "eye".  Suitable filters
are: LFH-15S or CFW455E, and LFH-20S or CFW455D.


FT736  DIRECT VARACTOR FM MODULATION
------------------------------------
Refer to the circuit diagram; inject your TXaudio at the junction of R32/C29 on
the TX Unit.  The signal level at this point should be 800 mV peak-peak, and
will give +/- 3 kHz deviation.  DO NOT EXCEED THIS LEVEL. Set Mic Gain to min.

Modulating the FM transmitter this way you get an LF response down to 18 Hz (at
which point the associated synthesiser PLL begins to track the modulation), and
an HF response which is flat to some 10 kHz.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. TX Unit is the module flat on the left (not the one tucked down the side
    vertically).
 4. R32 is just to the left of the rectangular shielded enclosure.  The
    resistor is "on end".  Scrape any paint off the free leg.
 5. Your TXaudio lead should be a fine screened cable;  connect the inner to
    R32, and the outer braid to the adjacent enclosure.
 6. Route the cable out though any convenient aperture in the case.
 7a. 1200 BAUD PSK MODEM: TXAudio of 800 mV pk-pk can be obtained by adjusting
    the components C9= 1uf, R3=47k, R5=infinity (i.e. remove). C10 stays at
    10nf (0.01uf).
 7b. 9600 BAUD FSK MODEM: Adjust TXAudio level with VR1

 Notes compiled by G3RUH @ GB7DDX 1990 Mar 16
===============================================================================
 Yaesu FT-736R TAPR PSK Modem freq shift prob

    I bought a Yaesu FT736 about 6 months ago.  It's a great radio but one
thing annoyed me about it.  When I used in on FO-20 or the microsats with my
TAPR PSK modem, the PSK modem adjusts to the doppler frequency shift by sending
pulses to the up/down buttons on the microphone.  Only problem is, everytime it
sent a pulse the radio went BEEP.  This beep didn't come thru the speaker,
instead it was emitted from a separate buzzer.  As a result, even when using
the headphomes, the beep would disturb the whole house.  This was a particular
problem on late night passes.  Thanks to a suggestion from WB2IBO and the folks
at Yaesu, I've discovered you can fix the problem.

    If you remove the top cover you will find a circuit board right behind the
front panel.  As you are facing the front of the radio on the top left corner
you will see capacitor C63 identified on the board with a red wire going into
the circuit board next to it.  Clip the red wire and no more beep. You won't
actually see the beeper.  To find the beeper you have to remove the top and
bottom covers (see the manual) and then loosen the screws on either side of the
frnt pa~el (see sectio~ 3.5.4 in the ma~ual).  At the bottm left f the
circuit bard is the black buzzer, about the si~e f a quarter.  The red ire
yu ~eed to clip starts frm here.  You dn't actually have t remove the
bottom cover if you clip it where it goes back into the circuit board on the
top, however.

   You could rig up a switch to turn the buzzer off and on, but I don't why
anyone would ever want to turn it back on.  73 de WA0PTV @WA0PTV

(Message originated at NS1N from KC1HO reqMOD Server v2.0)
===============================================================================
TX-PLL Modification
YAESU FT-736R 9600 Mod

Modification to the Yaesu FT-736R. G4WFQ 12/1/92.

This modification was given to me by Zeno Wahl, G0NJC/VE3LMX (U.O.S)

The modification lowers the frequency response to 3 HZ, and gives a far better
"eye" by reducing L.F flutter.

Proceed thus.

Locate "TXPLL UNIT" (Vertical board on Tx unit).

Locate R01 (Scrape any paint off. Wet component with FINE solder.

Solder 560ohm Resistor on R01 (end nearest to pll board)  Solder 47micro fara
tantalum in series with 560R. Take (-) negative leg of Cap to Gnd, eg case of
Txpll unit.

73 Dave G4WFQ.
===============================================================================

                       Better UO-22 Decoding
                       -=-=-=-=-=-=-=-=-=-=-

Dave - you are right.  UO-22 is less than optimum.  The problem starts in the
satellite which does not have a transmit spectrum extending to DC, nor ewen to
the desirable 30 Hz.  In fact it is 3db down at 100 Hz.  The effect of this is
to cause "droop" on short runs of 1s or 0s.  It can clearly be seen on a scope.
Display the eye diagram, and slow the sweep speed down so that a dozen or so
bits is visible.  Looked at another way, the poor LF performance introduces
wobble on the trace, and this blurrs the eye.  So if the receive system was
so-so (say with UO-14) then it may well be very error prone from UO-22.

The cure is to make the receive system have as good an HF performance as
possible, and a good LF performance.  Having a good HF response ensures a good
eye, and thus a better margin to cope with the LF wobble.  And having a good LF
response minimises and additional self noise from the RX/modem interface.

On the modem increase C25 to 1 uf.  This is the RXAudio input coupling
capacitor.

On an FT736R:
 1. Use a CFW455B (or C or D) IF filter in the RX UNIT.

 2. On the RX UNIT, remove C82.  This is a little ceramic capacitor tucked in
    close to the grey cube marked "455D".  Bend it back and forth until the
    legs snap off.  You can reach it by removing the radio lid only.  DO THIS!

When you have done these changes, TX selection 10 transmitting to an FT736R
gives a virtually perfect eye.  Since UO-22 also transmits selection 10, you
can see the extent of the LF aberration as a blurring at the "eye" convergence
point.  However you should now have reliable decoding.

Other radios seem not to be as reluctant as the FT736R, probably because they
have a better basic HF response.  However, changing modem C25 should help.

I am evaluating the feasibilty of implementing LF equaliser to rectify the
UO-22 LF problem.  The perfect project for all you DSP freaks.  I'm on holiday
for two weeks.  I expect one of you lot to have done it by the time I get back.
No kidding.

73 de James G3RUH @ GB7DDX.#22.GBR.EU

Msg Nr.     : 32411 
Da          : LU7AKC
Per         : NET9K6@WW      
Tipo/status : B$
Data/ora    : 0815/0258
Dimensione  :10172
Titolo      : FT736 & 9600 Bps
Bid (Mid)   : 12251_LU7AKC

                    FT736 & 9600 Baud Operation
                    ---------------------------
                       by James Miller G3RUH

These notes tell you where to get FM RX audio direct from the discriminator,
and where to modulate the FM TX varactor directly.  These mods are
non-destructive and take no more than a few minutes.  The signal bypass the
"DATA SOCKET" for high grade FM operations.

The RX mod is suitable for:

 *  UOSAT-D 9600 baud downlink and terrestrial links
 *  1200 baud AFSK/FM Standard Packet - BUT IT'S UNSQUELCHED.

The TX mod is suitable for:

 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink direct FSK and terrestrial links
 *  1200 baud AFSK/FM Standard Packet.


FT736 -  FM Direct from Discriminator
-------------------------------------
Detected FM direct from the receiver discriminator is available from the RX
UNIT at the junction of R91 and C83.  These components are shown in the top
right-hand corner of the schematic.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. RX Unit is the vertical module on the left.
 4. Locate R91 which is about 25mm from the top, 50mm from the radio rear. the
    resistor is "on-end", and near a couple of glass diodes.
 5. Scrape any paint off R91's free end and wet with solder.
 6. Your RXaudio lead should be a fine screened cable;  connect the inner to
    R91, and the outer braid to a ground point (e.g. can of TO09)
 7. Route the cable out though any convenient aperture in the case.
 8. The discriminator sensitivity (FM Normal) as about 6 kHz/volt.


Important note on 9600 Baud Use
-------------------------------
Some FT736 receivers are fitted with an LFH12-S IF filter for FM. (CF01 at the
top front of the RX Unit).  This is a 12 kHz bandwidth filter which is a little
too narrow for 9600 bps FSK operation.  It is recommended you change this to 15
kHz or better still for UOSAT-D use, 20 kHz bandwidth which will allow more
tolerance for doppler shift, and give a far better "eye".  Suitable filters
are: LFH-15S or CFW455E, and LFH-20S or CFW455D.


FT736  DIRECT VARACTOR FM MODULATION
------------------------------------
Refer to the circuit diagram; inject your TXaudio at the junction of R32/C29 on
the TX Unit.  The signal level at this point should be 800 mV peak-peak, and
will give +/- 3 kHz deviation.  DO NOT EXCEED THIS LEVEL. Set Mic Gain to min.

Modulating the FM transmitter this way you get an LF response down to 18 Hz (at
which point the associated synthesiser PLL begins to track the modulation), and
an HF response which is flat to some 10 kHz.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. TX Unit is the module flat on the left (not the one tucked down the side
    vertically).
 4. R32 is just to the left of the rectangular shielded enclosure.  The
    resistor is "on end".  Scrape any paint off the free leg.
 5. Your TXaudio lead should be a fine screened cable;  connect the inner to
    R32, and the outer braid to the adjacent enclosure.
 6. Route the cable out though any convenient aperture in the case.
 7a. 1200 BAUD PSK MODEM: TXAudio of 800 mV pk-pk can be obtained by adjusting
    the components C9= 1uf, R3=47k, R5=infinity (i.e. remove). C10 stays at
    10nf (0.01uf).
 7b. 9600 BAUD FSK MODEM: Adjust TXAudio level with VR1

 Notes compiled by G3RUH @ GB7DDX 1990 Mar 16
===============================================================================
 Yaesu FT-736R TAPR PSK Modem freq shift prob

    I bought a Yaesu FT736 about 6 months ago.  It's a great radio but one
thing annoyed me about it.  When I used in on FO-20 or the microsats with my
TAPR PSK modem, the PSK modem adjusts to the doppler frequency shift by sending
pulses to the up/down buttons on the microphone.  Only problem is, everytime it
sent a pulse the radio went BEEP.  This beep didn't come thru the speaker,
instead it was emitted from a separate buzzer.  As a result, even when using
the headphomes, the beep would disturb the whole house.  This was a particular
problem on late night passes.  Thanks to a suggestion from WB2IBO and the folks
at Yaesu, I've discovered you can fix the problem.

    If you remove the top cover you will find a circuit board right behind the
front panel.  As you are facing the front of the radio on the top left corner
you will see capacitor C63 identified on the board with a red wire going into
the circuit board next to it.  Clip the red wire and no more beep. You won't
actually see the beeper.  To find the beeper you have to remove the top and
bottom covers (see the manual) and then loosen the screws on either side of the
frnt pa~el (see sectio~ 3.5.4 in the ma~ual).  At the bottm left f the
circuit bard is the black buzzer, about the si~e f a quarter.  The red ire
yu ~eed to clip starts frm here.  You dn't actually have t remove the
bottom cover if you clip it where it goes back into the circuit board on the
top, however.

   You could rig up a switch to turn the buzzer off and on, but I don't why
anyone would ever want to turn it back on.  73 de WA0PTV @WA0PTV

(Message originated at NS1N from KC1HO reqMOD Server v2.0)
===============================================================================
TX-PLL Modification
YAESU FT-736R 9600 Mod

Modification to the Yaesu FT-736R. G4WFQ 12/1/92.

This modification was given to me by Zeno Wahl, G0NJC/VE3LMX (U.O.S)

The modification lowers the frequency response to 3 HZ, and gives a far better
"eye" by reducing L.F flutter.

Proceed thus.

Locate "TXPLL UNIT" (Vertical board on Tx unit).

Locate R01 (Scrape any paint off. Wet component with FINE solder.

Solder 560ohm Resistor on R01 (end nearest to pll board)  Solder 47micro fara
tantalum in series with 560R. Take (-) negative leg of Cap to Gnd, eg case of
Txpll unit.

73 Dave G4WFQ.
===============================================================================

                       Better UO-22 Decoding
                       -=-=-=-=-=-=-=-=-=-=-

Dave - you are right.  UO-22 is less than optimum.  The problem starts in the
satellite which does not have a transmit spectrum extending to DC, nor ewen to
the desirable 30 Hz.  In fact it is 3db down at 100 Hz.  The effect of this is
to cause "droop" on short runs of 1s or 0s.  It can clearly be seen on a scope.
Display the eye diagram, and slow the sweep speed down so that a dozen or so
bits is visible.  Looked at another way, the poor LF performance introduces
wobble on the trace, and this blurrs the eye.  So if the receive system was
so-so (say with UO-14) then it may well be very error prone from UO-22.

The cure is to make the receive system have as good an HF performance as
possible, and a good LF performance.  Having a good HF response ensures a good
eye, and thus a better margin to cope with the LF wobble.  And having a good LF
response minimises and additional self noise from the RX/modem interface.

On the modem increase C25 to 1 uf.  This is the RXAudio input coupling
capacitor.

On an FT736R:
 1. Use a CFW455B (or C or D) IF filter in the RX UNIT.

 2. On the RX UNIT, remove C82.  This is a little ceramic capacitor tucked in
    close to the grey cube marked "455D".  Bend it back and forth until the
    legs snap off.  You can reach it by removing the radio lid only.  DO THIS!

When you have done these changes, TX selection 10 transmitting to an FT736R
gives a virtually perfect eye.  Since UO-22 also transmits selection 10, you
can see the extent of the LF aberration as a blurring at the "eye" convergence
point.  However you should now have reliable decoding.

Other radios seem not to be as reluctant as the FT736R, probably because they
have a better basic HF response.  However, changing modem C25 should help.

I am evaluating the feasibilty of implementing LF equaliser to rectify the
UO-22 LF problem.  The perfect project for all you DSP freaks.  I'm on holiday
for two weeks.  I expect one of you lot to have done it by the time I get back.
No kidding.

73 de James G3RUH @ GB7DDX.#22.GBR.EU

Msg Nr.     : 73651 
Da          : IW4DGM
Per         : 9600  @ITA     
Tipo/status : BF
Data/ora    : 1201/1636
Dimensione  : 4374
Titolo      : Modifica 9600 baud per l'FT 736
Bid (Mid)   : 20905_IW4CEA

  FT736r a 9600 Baud
 --------------------

I segnali bypassano il "CONNETTORE DATI" per una maggior qualita' di FM.

La modifica RX e' adatta per:
 *  UOSAT-D 9600 baud downlink e collegamenti terrestri
 *  1200 baud AFSK/FM Standard Packet - MA NON E' A SQUELCH APERTO.

La modifica TX e' adatta per:
 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink diretto FSK e collegamenti terrestri
 *  1200 baud AFSK/FM Standard Packet.


FT736  RX-FM direttamente dal Discriminatore
--------------------------------------------
Il prelievo della ricezione FM direttamente dal discriminatore e' possibile
farlo nella RX UNIT alla giunzione di R91 con C83. Questi componenti sono
visibili nell'angolo in alto a destra dello schema.

Procedere in questo modo:
 1. Interrompere l'alimentazione al FT736.
 2. Togliete solo il coperchio superiore.
 3. L'unita' RX e' nel modulo verticale sulla sinistra.
 4. Localizzate R91 che e' circa a 25mm dal bordo, 50mm dalla parte posteriore
    della radio. La resistenza e' in verticale (on-end), e vicino a molti diodi
    di vetro.
 5. Raschiate la vernice dal terminale libero della R91 e "rinfrescatelo"
    con un po' di stagno.
 6. Per il segnale audio RX usate un cavetto schermato molto sottile; collegate
    il centrale a R91, e la calza ad un punto di massa (es. carcassa di TO09).
 7. Fate passare il cavetto attraverso una qualche apertura dell'apparato.
 8. La sensibilita' del discriminatore (FM Normale) e' circa 6 kHz/volt.

Nota importante per l'uso a 9600 Baud
-------------------------------------
Il ricevitore di alcuni FT736 e' equipaggiato con un filtro IF LFH12-S per FM.
(CF01 proprio in cima alla parte frontale della RX Unit). E' un filtro a 12 kHz
di larghezza di banda ed e' un po' troppo stretto per operare a 9600 bps FSK.
Si raccomanda di cambiarlo con un altro da 15 kHz o ancora migliore per uso
UOSAT-D, i 20 kHz di larghezza di banda ci lasceranno piu' tolleranza per lo
shift doppler, ed otterremo un "occhio" di gran lunga migliore.
I filtri adatti sono: LFH-15S / CFW455E, e LFH-20S / CFW455D.


FT736  TX-MODULAZIONE direttamente al Diodo Varicup
---------------------------------------------------
Riferendoci al circuito elettrico; iniettate l'audio TX alla giunzione di
R32/C29 nella TX Unit. Il livello di segnale in questo punto dovrebbe essere
800 mV pico-pico, e dovrebbe dare +/- 3 kHz di deviazione.
 NON OLTREPASSARE QUESTO LIVELLO. 
Portare il Mic Gain al minimo.

Modulando il trasmettitore FM in questo modo  avrete una risposta in LF
sotto ai 18Hz (e' a questo punto che il sintetizzatore PLL incomincia a
rivelare la modulazione), ed una risposta in HF piatta fino a circa 10 kHz.

Procedere in questo modo:
 1. Interrompere l'alimentazione al FT736.
 2. Togliete solo il coperchio superiore.
 3. L'Unita' TX e' il modulo piatto sulla sinistra (non quello piegato giu'
    verticalmente lungo il fianco).
 4. R32 e' proprio a sinistra del contenitore rettangolare schermato.
    La resistenza e' in verticale. Raschiate la vernice dal terminale libero.
 5. Per il segnale audio TX usate un cavetto schermato molto sottile; collegate
    il centrale a R32, e la calza al contenitore vicino.
 6. Fate passare il cavetto attraverso una qualche apertura dell'apparato.

 7a. MODEM 1200 BAUD PSK: Si puo' ottenere un TXAudio di 800 mV pico-pico
     cambiando i componenti C9= 1uf, R3=47k, R5=infinito (eliminare). 
     C10 rimane 10nf (0.01uf).
 7b. MODEM 9600 BAUD FSK: Tarare il livello TXAudio con VR1. Nella TXEPROM
     selezionare il numero 10 per UO-14, cioe' JMP1,3 ON, JMP2,4 OFF


Installazione piu' pulita
-------------------------
Per un lavoro piu' pulito si puo' usare una piccola staffa di alluminio da
fissare sotto la vite a sinistra.
Questa staffa ospitera' una presa DIN a 5-pin a cui verranno collegati
i cavetti con i segnali TX RX e PTT.
Cosi' da non avere cavetti vaganti all'interno dell'apparato. (Grazie EI6EH).


 James Miller G3RUH @GB7DDX  16 Marzo 1990, rev 20 Settembre 1991
---------------------
 traduzione di
 Paolo IW4DGM @IW4CEA

Msg Nr.     : 32816 
Da          : IW3GRX
Per         : IW3GRX
Tipo/status : PN
Data/ora    : 0417/2111
Dimensione  : 3892
Titolo      : Modifica 9600 baud per FT736
Bid (Mid)   : 32816_IW3GRX

ÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜ

                     -==> PY4SM@PY4SM.BRA.SA <==-
ÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜ
MODIFICACIONES 736 U22
 -------------------------------------------------
                    FT736 & 9600 Baud Operation
                    ---------------------------
                       by James Miller G3RUH

These notes tell you where to get FM RX audio direct from the
discriminator, and where to modulate the FM TX varactor directly.  These
mods are non-destructive and take no more than a few minutes.  The signal
bypass the "DATA SOCKET" for high grade FM operations.

The RX mod is suitable for:

 *  UOSAT-D 9600 baud downlink and terrestrial links
 *  1200 baud AFSK/FM Standard Packet - BUT IT'S UNSQUELCHED.

The TX mod is suitable for:

 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink direct FSK and terrestrial links
 *  1200 baud AFSK/FM Standard Packet.

                            ---****---

FT736 -  FM Direct from Discriminator
-------------------------------------
Detected FM direct from the receiver discriminator is available from the
RX UNIT at the junction of R91 and C83.  These components are shown in the
top right-hand corner of the schematic.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. RX Unit is the vertical module on the left.
 4. Locate R91 which is about 25mm from the top, 50mm from the radio rear.
    the resistor is "on-end", and near a couple of glass diodes.
 5. Scrape any paint off R91's free end and wet with solder.
 6. Your RXaudio lead should be a fine screened cable;  connect the inner
    to R91, and the outer braid to a ground point (e.g. can of TO09)
 7. Route the cable out though any convenient aperture in the case.
 8. The discriminator sensitivity (FM Normal) as about 6 kHz/volt.

Important note on 9600 Baud Use
-------------------------------
Some FT736 receivers are fitted with an LFH12-S IF filter for FM. (CF01 at
the top front of the RX Unit).  This is a 12 kHz bandwidth filter which is
a little too narrow for 9600 bps FSK operation.  It is recommended you
change this to 15 kHz or better still for UOSAT-D use, 20 kHz bandwidth
which will allow more tolerance for doppler shift, and give a far better
"eye".  Suitable filters are: LFH-15S or CFW455E, and LFH-20S or CFW455D.
The first of these is a Yaesu spare part, and is often already fitted.

                            ---****---

FT736  DIRECT VARACTOR FM MODULATION
------------------------------------
Refer to the circuit diagram; inject your TXaudio at the junction of
R32/C29 on the TX Unit.  The signal level at this point should be 800 mV
peak-peak, and will give +/- 3 kHz deviation.  DO NOT EXCEED THIS LEVEL.
Set Mic Gain to min.

Modulating the FM transmitter this way you get an LF response down to 18
Hz (at which point the associated synthesiser PLL begins to track the
modulation), and an HF response which is flat to some 10 kHz.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. TX Unit is the module flat on the left (not the one tucked down the
    side vertically).
 4. R32 is just to the left of the rectangular shielded enclosure.  The
    resistor is "on end".  Scrape any paint off the free leg.
 5. Your TXaudio lead should be a fine screened cable;  connect the inner
    to R32, and the outer braid to the adjacent enclosure.
 6. Route the cable out though any convenient aperture in the case.

 7a. 1200 BAUD PSK MODEM: TXAudio of 800 mV pk-pk can be obtained by
    adjusting the components C9= 1uf, R3=47k, R5=infinity (i.e. remove).
    C10 stays at 10nf (0.01uf).

 7b. 9600 BAUD FSK MODEM: Adjust TXAudio level with VR1

 Notes compiled by G3RUH @ GB7SPV 1990 Mar 16


Msg Nr.     : 142574
Da          : IW3GRX
Per         : TEMP  
Tipo/status : PN
Data/ora    : 0129/1237
Dimensione  :12496
Bid (Mid)   : 11502_IW3GRX
Titolo      : Modifica 9600 baud per l'FT736

***************************************************************************

From: LU7AKC@LU7AKC.#COL.CF.ARG.SOAM
To  : NET9K6@WW

                    FT736 & 9600 Baud Operation
                    ---------------------------
                       by James Miller G3RUH

These notes tell you where to get FM RX audio direct from the discriminator,
and where to modulate the FM TX varactor directly.  These mods are
non-destructive and take no more than a few minutes.  The signal bypass the
"DATA SOCKET" for high grade FM operations.

The RX mod is suitable for:

 *  UOSAT-D 9600 baud downlink and terrestrial links
 *  1200 baud AFSK/FM Standard Packet - BUT IT'S UNSQUELCHED.

The TX mod is suitable for:

 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink direct FSK and terrestrial links
 *  1200 baud AFSK/FM Standard Packet.


FT736 -  FM Direct from Discriminator
-------------------------------------
Detected FM direct from the receiver discriminator is available from the RX
UNIT at the junction of R91 and C83.  These components are shown in the top
right-hand corner of the schematic.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. RX Unit is the vertical module on the left.
 4. Locate R91 which is about 25mm from the top, 50mm from the radio rear. the
    resistor is "on-end", and near a couple of glass diodes.
 5. Scrape any paint off R91's free end and wet with solder.
 6. Your RXaudio lead should be a fine screened cable;  connect the inner to
    R91, and the outer braid to a ground point (e.g. can of TO09)
 7. Route the cable out though any convenient aperture in the case.
 8. The discriminator sensitivity (FM Normal) as about 6 kHz/volt.


Important note on 9600 Baud Use
-------------------------------
Some FT736 receivers are fitted with an LFH12-S IF filter for FM. (CF01 at the
top front of the RX Unit).  This is a 12 kHz bandwidth filter which is a little
too narrow for 9600 bps FSK operation.  It is recommended you change this to 15
kHz or better still for UOSAT-D use, 20 kHz bandwidth which will allow more
tolerance for doppler shift, and give a far better "eye".  Suitable filters
are: LFH-15S or CFW455E, and LFH-20S or CFW455D.


FT736  DIRECT VARACTOR FM MODULATION
------------------------------------
Refer to the circuit diagram; inject your TXaudio at the junction of R32/C29 on
the TX Unit.  The signal level at this point should be 800 mV peak-peak, and
will give +/- 3 kHz deviation.  DO NOT EXCEED THIS LEVEL. Set Mic Gain to min.

Modulating the FM transmitter this way you get an LF response down to 18 Hz (at
which point the associated synthesiser PLL begins to track the modulation), and
an HF response which is flat to some 10 kHz.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. TX Unit is the module flat on the left (not the one tucked down the side
    vertically).
 4. R32 is just to the left of the rectangular shielded enclosure.  The
    resistor is "on end".  Scrape any paint off the free leg.
 5. Your TXaudio lead should be a fine screened cable;  connect the inner to
    R32, and the outer braid to the adjacent enclosure.
 6. Route the cable out though any convenient aperture in the case.
 7a. 1200 BAUD PSK MODEM: TXAudio of 800 mV pk-pk can be obtained by adjusting
    the components C9= 1uf, R3=47k, R5=infinity (i.e. remove). C10 stays at
    10nf (0.01uf).
 7b. 9600 BAUD FSK MODEM: Adjust TXAudio level with VR1

 Notes compiled by G3RUH @ GB7DDX 1990 Mar 16
===============================================================================
 Yaesu FT-736R TAPR PSK Modem freq shift prob

    I bought a Yaesu FT736 about 6 months ago.  It's a great radio but one
thing annoyed me about it.  When I used in on FO-20 or the microsats with my
TAPR PSK modem, the PSK modem adjusts to the doppler frequency shift by sending
pulses to the up/down buttons on the microphone.  Only problem is, everytime it
sent a pulse the radio went BEEP.  This beep didn't come thru the speaker,
instead it was emitted from a separate buzzer.  As a result, even when using
the headphomes, the beep would disturb the whole house.  This was a particular
problem on late night passes.  Thanks to a suggestion from WB2IBO and the folks
at Yaesu, I've discovered you can fix the problem.

    If you remove the top cover you will find a circuit board right behind the
front panel.  As you are facing the front of the radio on the top left corner
you will see capacitor C63 identified on the board with a red wire going into
the circuit board next to it.  Clip the red wire and no more beep. You won't
actually see the beeper.  To find the beeper you have to remove the top and
bottom covers (see the manual) and then loosen the screws on either side of the
front panel (see section 3.5.4 in the manual).  At the bottom left of the
circuit board is the black buzzer, about the size of a quarter.  The red wire
you need to clip starts from here.  You don't actually have to remove the
bottom cover if you clip it where it goes back into the circuit board on the
top, however.

   You could rig up a switch to turn the buzzer off and on, but I don't why
anyone would ever want to turn it back on.  73 de WA0PTV @WA0PTV

(Message originated at NS1N from KC1HO reqMOD Server v2.0)
===============================================================================
TX-PLL Modification
YAESU FT-736R 9600 Mod

Modification to the Yaesu FT-736R. G4WFQ 12/1/92.

This modification was given to me by Zeno Wahl, G0NJC/VE3LMX (U.O.S)

The modification lowers the frequency response to 3 HZ, and gives a far better
"eye" by reducing L.F flutter.

Proceed thus.

Locate "TXPLL UNIT" (Vertical board on Tx unit).

Locate R01 (Scrape any paint off. Wet component with FINE solder.

Solder 560ohm Resistor on R01 (end nearest to pll board)  Solder 47micro fara
tantalum in series with 560R. Take (-) negative leg of Cap to Gnd, eg case of
Txpll unit.

73 Dave G4WFQ.
===============================================================================

                       Better UO-22 Decoding
                       -=-=-=-=-=-=-=-=-=-=-

Dave - you are right.  UO-22 is less than optimum.  The problem starts in the
satellite which does not have a transmit spectrum extending to DC, nor even to
the desirable 30 Hz.  In fact it is 3db down at 100 Hz.  The effect of this is
to cause "droop" on short runs of 1s or 0s.  It can clearly be seen on a scope.
Display the eye diagram, and slow the sweep speed down so that a dozen or so
bits is visible.  Looked at another way, the poor LF performance introduces
wobble on the trace, and this blurrs the eye.  So if the receive system was
so-so (say with UO-14) then it may well be very error prone from UO-22.

The cure is to make the receive system have as good an HF performance as
possible, and a good LF performance.  Having a good HF response ensures a good
eye, and thus a better margin to cope with the LF wobble.  And having a good LF
response minimises and additional self noise from the RX/modem interface.

On the modem increase C25 to 1 uf.  This is the RXAudio input coupling
capacitor.

On an FT736R:
 1. Use a CFW455B (or C or D) IF filter in the RX UNIT.

 2. On the RX UNIT, remove C82.  This is a little ceramic capacitor tucked in
    close to the grey cube marked "455D".  Bend it back and forth until the
    legs snap off.  You can reach it by removing the radio lid only.  DO THIS!

When you have done these changes, TX selection 10 transmitting to an FT736R
gives a virtually perfect eye.  Since UO-22 also transmits selection 10, you
can see the extent of the LF aberration as a blurring at the "eye" convergence
point.  However you should now have reliable decoding.

Other radios seem not to be as reluctant as the FT736R, probably because they
have a better basic HF response.  However, changing modem C25 should help.

I am evaluating the feasibilty of implementing LF equaliser to rectify the
UO-22 LF problem.  The perfect project for all you DSP freaks.  I'm on holiday
for two weeks.  I expect one of you lot to have done it by the time I get back.
No kidding.

73 de James G3RUH @ GB7DDX.#22.GBR.EU

***************************************************************************

  FT736r a 9600 Baud
 --------------------

I segnali bypassano il "CONNETTORE DATI" per una maggior qualita' di FM.

La modifica RX e' adatta per:
 *  UOSAT-D 9600 baud downlink e collegamenti terrestri
 *  1200 baud AFSK/FM Standard Packet - MA NON E' A SQUELCH APERTO.

La modifica TX e' adatta per:
 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink diretto FSK e collegamenti terrestri
 *  1200 baud AFSK/FM Standard Packet.


FT736  RX-FM direttamente dal Discriminatore
--------------------------------------------
Il prelievo della ricezione FM direttamente dal discriminatore e' possibile
farlo nella RX UNIT alla giunzione di R91 con C83. Questi componenti sono
visibili nell'angolo in alto a destra dello schema.

Procedere in questo modo:
 1. Interrompere l'alimentazione al FT736.
 2. Togliete solo il coperchio superiore.
 3. L'unita' RX e' nel modulo verticale sulla sinistra.
 4. Localizzate R91 che e' circa a 25mm dal bordo, 50mm dalla parte posteriore
    della radio. La resistenza e' in verticale (on-end), e vicino a molti diodi
    di vetro.
 5. Raschiate la vernice dal terminale libero della R91 e "rinfrescatelo"
    con un po' di stagno.
 6. Per il segnale audio RX usate un cavetto schermato molto sottile; collegate
    il centrale a R91, e la calza ad un punto di massa (es. carcassa di TO09).
 7. Fate passare il cavetto attraverso una qualche apertura dell'apparato.
 8. La sensibilita' del discriminatore (FM Normale) e' circa 6 kHz/volt.

Nota importante per l'uso a 9600 Baud
-------------------------------------
Il ricevitore di alcuni FT736 e' equipaggiato con un filtro IF LFH12-S per FM.
(CF01 proprio in cima alla parte frontale della RX Unit). E' un filtro a 12 kHz
di larghezza di banda ed e' un po' troppo stretto per operare a 9600 bps FSK.
Si raccomanda di cambiarlo con un altro da 15 kHz o ancora migliore per uso
UOSAT-D, i 20 kHz di larghezza di banda ci lasceranno piu' tolleranza per lo
shift doppler, ed otterremo un "occhio" di gran lunga migliore.
I filtri adatti sono: LFH-15S / CFW455E, e LFH-20S / CFW455D.


FT736  TX-MODULAZIONE direttamente al Diodo Varicup
---------------------------------------------------
Riferendoci al circuito elettrico; iniettate l'audio TX alla giunzione di
R32/C29 nella TX Unit. Il livello di segnale in questo punto dovrebbe essere
800 mV pico-pico, e dovrebbe dare +/- 3 kHz di deviazione.
 NON OLTREPASSARE QUESTO LIVELLO. 
Portare il Mic Gain al minimo.

Modulando il trasmettitore FM in questo modo  avrete una risposta in LF
sotto ai 18Hz (e' a questo punto che il sintetizzatore PLL incomincia a
rivelare la modulazione), ed una risposta in HF piatta fino a circa 10 kHz.

Procedere in questo modo:
 1. Interrompere l'alimentazione al FT736.
 2. Togliete solo il coperchio superiore.
 3. L'Unita' TX e' il modulo piatto sulla sinistra (non quello piegato giu'
    verticalmente lungo il fianco).
 4. R32 e' proprio a sinistra del contenitore rettangolare schermato.
    La resistenza e' in verticale. Raschiate la vernice dal terminale libero.
 5. Per il segnale audio TX usate un cavetto schermato molto sottile; collegate
    il centrale a R32, e la calza al contenitore vicino.
 6. Fate passare il cavetto attraverso una qualche apertura dell'apparato.

 7a. MODEM 1200 BAUD PSK: Si puo' ottenere un TXAudio di 800 mV pico-pico
     cambiando i componenti C9= 1uf, R3=47k, R5=infinito (eliminare). 
     C10 rimane 10nf (0.01uf).
 7b. MODEM 9600 BAUD FSK: Tarare il livello TXAudio con VR1. Nella TXEPROM
     selezionare il numero 10 per UO-14, cioe' JMP1,3 ON, JMP2,4 OFF


Installazione piu' pulita
-------------------------
Per un lavoro piu' pulito si puo' usare una piccola staffa di alluminio da
fissare sotto la vite a sinistra.
Questa staffa ospitera' una presa DIN a 5-pin a cui verranno collegati
i cavetti con i segnali TX RX e PTT.
Cosi' da non avere cavetti vaganti all'interno dell'apparato. (Grazie EI6EH).


 James Miller G3RUH @GB7DDX  16 Marzo 1990, rev 20 Settembre 1991
---------------------
 traduzione di
 Paolo IW4DGM @IW4CEA

******************************************************************************