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Re: Inquiry



 Roy Welch writes:

> Is there is anyone out there who has built a radio tuning circuit which
> senses the FM radio discriminator voltage as input and provides mic up/down
> key click tuning as output.

Herewith a couple of items from the G3RWL crypt: first part is the circuitry
to go with a G3RUH 1200 bps modem (because it has rig control circuitry); 
second part is the relevent parts of that modem (since not many folks have 
one of these any more). Most of the first part came from G8TZJ.

This (first) article was published in December 1990, in Oscar News,
the journal of Amsat-UK.

The circuit shown below is for automatic receiver tuning for 9600 baud
operation, provided you have the G3RUH 1200 PSK board. This PSK board will
interface to the majority of rigs that have up / down lines. If you don't
have this board, then it would be easy to build the part of the PSK circuit
from U5 through to the 70 cms rig's control lines. In the PSK board the
error voltage from the PLL is a measure of how far the rig is off-tune.
This is amplified in U5 and so pulls the rig back onto frequency,
compensating for doppler. In 9600 baud FSK operation the frequency error
can be detected from the dc level at your receivers discriminator output.

                                             \
                             100k           / 1M
                         +--/\/\/\/-----/\/\/\/----+
                         |                / PR1    |
                         |                         |
                         |            | |          |
                         +------------| |----------+    IC1=TL082 / TL072
Input                    |            | | 100nF    |
>From 70 cm Rx            |     | \                 |
Discriminator            |     |   \  +---- +12v   |
                         |    6|     \| 8          |
>--------------/\/\/\/---+-----| -     \           |
                100k           |  IC1a   \------+--+-----------------+
+12v ----+                    5|         / 7    |                    |
         |    +-----------+----| +     /        /                    |
         /    |           |    |     /     10k  \                    |
    10k  \    |         -----  |   /            /                    |
         /    |         -----  | /              \                    |
         \    |      10nF |          10k        |         +-- +12v   |
         |    |           |  +-----/\/\/\-------+         |          |
         |    |  +--------+  |                  |         |          |
         /    |  |           |           / |    |         \          |
   100k  \    |  |           |         /   |    |         / 100k     |
   PR2   /<---+  |           |       /     |2   |         \          |
         \       |           |     /     - |----+         /          |
         /       |           | 1 /         |              |          |
         |       |         +-+-- \  IC1b   |3             |          |
         |       |         |       \     + |----+-------+-+          |
         /       |         |       4 \     |    |       |            |
    10k  \       |         |         | \   |  -----     /            |
         /       |         |         |   \ |  -----     \ 100k       |
         \       |         |         |          | 10nF  /            |
         |       |         |         |          |       \            |
         |       |         |         |          |       |            |
  0v  ---+-------+-----    |   ------+----------+-------+-- 0v       |
                           |                                         |
                           +--------------------*    *---------------+
                                               B    /  A
                              \               LK1  *
               R25           /                     | C
           +--/\/\/\/-----/\/\/\/----+             |
           |               / VR3     |             |
           |                         |             /
           |             | |         |             \  100K
           +-------------| |---------+             /
           |        C18  | |         |             \
           |                  / |    |             |
           |                /   |    |             |
           |              /     |    |      /*-----+               Input
           |            /     - |----+----*/  SW1      R24         from U11
           |          /         |            *----+---/\/\/\-----< 1200 PSK
       ----+--------/    U5     |                 |                Modem
                     \        + |----+            |
                       \        |    |          -----
                         \      |    |          ----- 10nF
                           \    |    |            |
                             \  |                 |
                               \             -----+---- 0v

                            CIRCUIT DESCRIPTION
                            -------------------

The 70 cms receiver's discriminator is connected via a 100 k resistor to
IC1a, half of a TL082 (072) op-amp, where the 9600 data + dc level, is
amplified and the 9600 baud data filtered out. If the circuit looks
familiar, it is because it is almost a copy of U5 from the G3RUH 1200 PSK
board. The signal is inverted in IC1b so that at points A & B there are
normal and inverted polarities that may be selected by LK1 to feed to U5.
The link is selected so that as the received frequency falls the rig is
tuned down to follow. If the wrong link is selected then the circuit will
do it's best to off-tune the receiver. PR1 adjusts the gain of the circuit
and PR2 adjusts the dc off-set to correct the centre tune position. SW1
selects 1200 PSK or 9600 FSK auto frequency control. Note the addition of a
10 nF capacitor to ground between R24 and the switch. This removes the
ripple content in the signal from U11, so the wiring from R24 to the switch
will not radiate a signal.

                   Adjusting the 9600 Auto-Tune Circuit
                   ------------------------------------

This procedure is based on the ICOM IC 471e's tuning step of 1 kHz. If your
rig tunes with different steps then it may take some experimentation to
find the correct procedure for your receiver. VR3 on the G3RUH 1200 PSK
board must firstly be set as stated in the alignment instructions for that
modem. If you have built the U5 circuitry separately then set VR3 to
minimum resistance. With the tune switch off (1200 PSK modem) set PR1 for
minimum resistance. Tune the rig to a clear channel and adjust PR2 so that
the 1200 PSK tune meter is centred. (High and Low LED's off.) Next using
the tune meter, tune in a local signal accurately (for instance a
repeater), then swing the rig's rit up and down to see how far off-tune you
have to be before the up or down LED lights. If greater than about 1 kHz
adjust PR1 to increase the gain, go to a free channel and re-adjust PR2, as
adjusting PR1 will alter the correct setting of PR2. Go back to the local
signal, swing the rig's rit up and down as done previously, noting the
frequency error when the LEDs light. Re-adjust PR1 and PR2 until the LEDs
light with an approximately +- 1 kHz error, and the tune meter is in the
centre when not receiving a signal. As a final check, tune in a signal (a
repeater), put the tune switch on and when you try to imitate doppler by
slowly tuning up or down the rig should be pulled back to the original
frequency.

End of File.


Part two ... self-tuner copied from the G3RUH 1200 baud modem diagram. This is
designed to suit all ICOM TRIO/KENWOOD and YAESU standards.
Component designations are those in the original diagram.


                         R25        VR3                  DCP = decouple with
                        100K      1M var                       10nF to ground;
from 1200bps        +--\/\/\/\----\/\/\/\----+      also to decouple all chips
   |                |                        |      Vdd = 5v feeds only U2 & U3
   |   1200/9600    +--------------||--------+      Vcc = 12v feeds the rest
   |   switch here  |        \     C18       |
   |            |   |        | \   100nF     |        U4, U5 = TL084
   |   R24      |   |        |   \           |           U10 = 4011B
   |  100K      |   |       2|     \         |     R26    U2 = 4049
   +-/\/\/\/----+---+--------| -     \  1    |    100K    U3 = 74LS05
                    |        |   U5    \-----+--/\/\/\/-+----------+
                   DCP       |         /     |          |          |
    +-------+----------------| +     /       |         +|          |
    |       |               3|     /         |     C23 ---         |
    |    CZ meter            |   /           |     1uF ---         |
    |    100 uA              | /     R32     |          |          |
    |       |                /       56K     |          |          |
    |       +----------------------/\/\/\/---+         gnd         |
    |                                                              |
    |stabilised at half Vcc                                        |
    +-------------------+------------------+                       |
                        |             /    |                       |
       R11 1M     pos1  |           / |    |                       |
 +Vcc--/\/\/\/--+----+  |         /   |    |                       |
       R2 270K  |    |  |       /     |9   |                       |
    +--/\/\/\/--+   DCP |     /     - |----+                       |
    |                   | 8 /         |                            |
 +--+-------------------+---   U4     |10                          |
 |  |  R4 270K              \       + |--+--------+  +Vcc          |
DCP +--/\/\/\/--+----+----+   \       |  |        |    |           |
       R12 1M   |    |    |     \     | DCP  +-/\/\/\/-+           |
    +--/\/\/\/--+   DCP  pos2     \   |      | VR2 1M var          |
    |                               \ |      |                     |
    |                                 \     gnd                    |
   gnd                                                             |
                                                                   |
   +---------------------------------------------------------------+
   |
   |          \
   |          | \
   |          |   \
   |         9|     \     "down" lamp
   |    pos1--| -     \         |         +---\
   |          |         \ 8     |        1|     \
   |          |   U5     -------+---------|       \          \
   |        10|         /                 |         \ 3     3| \ 2
   +----------| +     /                   |   U10    O-------|U2 O--- drive 1
   |          |     /                    2|         /        | /
   |          |   /                   +---|       /          /
   |          | /                     |   |     /
   |          /                       |   +---/
   |          R13 1M                  |
   |  +Vcc---/\/\/\/--------------+---+
   |                              |   |
   |          \       ground here |   |   +---\
   |          | \    via a switch-+   |  6|     \
   |          |   \    to disable     +---|       \          \
   |         6|     \   auto-tune         |         \ 4     5| \ 4
   +----------| -     \                   |   U10    O-------|U2 O--- drive 2
              |         \ 7              5|         /        | /
              |   U5     -------+---------|       /          /
             5|         /       |         |     /
        pos2--| +     /         |         +---/
              |     /       "up" lamp
              |   /
              | /
              /

                                    +Vdd
                               R8     |     R39
                               4K7    |     47K
                         +---/\/\/\/--+--/\/\/\/---+     gnd-----J3
                  \      |             \           |
drive 1          1| \ 2  |           13| \ 12      |
-+----------------|U3 O--+-------------|U3 O-------+-------------J1
 |                | /                  | /                       down
 |                /                    /
 |                                                               /|\
 |                                  +Vdd                          |
 |                             R9     |     R38               +ve going
 |                             4K7    |     47K                 pulse
 |                       +---/\/\/\/--+--/\/\/\/---+              |
 |                \      |             \           |             \|/
 |   drive 2     3| \ 4  |           11| \ 10      |
 | ---------------|U3 O--+-------------|U3 O-------+-------------J2
 |                | /                  | /                       up
 |                /                    /
 |                            R37       
 |                 +Vdd-----/\/\/\/-------------+
 |                            47K      \        |
 |                                    9| \ 8    |               down
 +-------------------------------------|U3 O----+---------+------J4
                                       | /                |
                                       /                  o     /|\
                                                  Link 1  o      |
                              R36                         |  -ve going
                   +Vdd-----\/\/\/\-----------+--/\/\/\/--+     pulse
                              47K      \      |   R40            |
     drive 2                          5| \ 6  |   470R          \|/
---------------------------------------|U3 O--+------------------J5
                                       | /                       up
                                       /


Drivers for up/down LED's:



drive from U5 pins 7 and 8
  |                                1K5
  |                          +---/\/\/\/---|<---Vcc
  |                         /              LED
  |     68K              |/
  +---/\/\/\/--+---------|
               |   BC107 |\
               |           _\|
               +-/\/\/\/-----+
                   15K       |
                            gnd


Explanation from the book:

... tuning voltage is amplified by U5 pins 2 and 3 which has gain adjustable
from x1 to x10 by VR3. (This op-amp also drives a centre-zero tuning meter.)
After filtering by R26/C23 the voltage (which increases for falling frequency)
is offered to two comparators, with upper and lower thresholds set by resistor
chain R11/2/4/12, 1.28v above and below the 6v reference. When exactly on tune
outputs U5 pins 7 and 8 are low. If off tune, then the appropriate comparator
output goes high.

U10 pins 1,2,5,6, if enabled by the "Tune-ON" switch, pass the signal via 12v
to 5v level shifter U2 to the open-collector hex-inverter U3 which creates two
pairs of signals. These are high-going up/down tune signals at J1 and J2, and
low-going signals at J4 and J5. Each line can sink up to 8mA.

You have to chose which tuning signals suit your rig by reference to the
equipment's handbook. For example the FT726R needs high-going signals, while
the FT790R uses low-going. ICOM have a special bi-level standard for the IC741
and similar rigs where 0v signals UP, 1.3v signals DOWN, and neither (about
4.2v) means no action. So for ICOM rigs connect link 1 and use J5 ... unless
the microphone is left connected; in this case the link can be omitted because
an R40 will be connected inside the mic housing.

For many rigs that use low-going pulses the pull-ups R36-R39 can be omitted.

73
Richard W L Limebear G3RWL
g3rwl@amsat.org
FOC # 1188

          So many beautiful girls ..... (sob) so little time
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