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Re: ICOM 821H and PSK-1...



At 08:03 PM 11/21/2000 -0500, Chris Souris wrote:


>I've tried to get the AFC working correctly with the PSK -1 and
>the ICOM 821H to track AO-40 correctly, but to no avail. It will
>auto-correct downward when turning the VFO to increase the freq, but when 
>turning the VFO to decrease the freq, the "up" LED on the PSK-1 flickers 
>ok, but the freq still goes downward even after I've stopped turning the 
>VFO, even with the "up" LED flickering.

Here is my experience with the G3RUH modem click tuning. Perhaps some of 
the information will apply to your PSK-1 problems.

ron w8gus

=====================================
The following may help in understanding the problems associated with click
tuning. It applies specifically to the G3RUH 400psk modem. The PSK-1
is probably similar in some respects.

The G3RUH modem has a 10 segment barLED which is essentially an audio
frequency meter. I measured the following using an audio generator
and counter.

     <---- lower rf(usb)     higher rf(usb) ---->
   1    2    3    4    5    6    7    8    9   10   bar# left to right
1620 1615 1610 1605 1595 1585 1575 1565 1555 1550  Hz
                  ^      ^       ^
                  |      |       |
                 UP     CTR     DOWN

The G3RUH modem works as follows. The correct tuning is when the
center bar is lit, actually 5 or 6 straddles the center. When the
received radio frequency drifts lower, assuming that the radio is set for
USB reception, the audio frequency becomes higher. When the #4 bar lights
an UP click pulse is generated which will move the radio frequecny
higher and the display back toward the center.

Conversely, if the frequency drifts higher, the audio frequency
is lower. When bar#7 lights a DOWN click pulse is generated which will
again correct the radio frequency and move the display back towards center.

The #4 and #7 bars are connected to optoisolators which enable the commands
to be communicated to the click pins of the radio microphone input.

Now comes the problems. We have three radio brands, Kenwood, Icom and Yaesu.
They implement mic click tuning in different ways. Also the click step size
varies with mode and model. You can see from the chart that the whole range
of the barLED is about +/- 35Hz. A step size of 10Hz is ideal. Although I
have not tried it, I think a step size of 50 or 100Hz may not work.

Here is some data I have gathered over the years. I would appreciate being
informed if there are any inaccuracies or additions. Since most radios only
display to 100Hz, it takes, with the FT-736, 10 clicks to change the last
frequency digit. Of course if you happen to be part way into the range you
may get some other number, like 6, the first time. Just keep clicking until
you observe a full range, which will be 10.

FT-736        10Hz
IC-275/475    10Hz  (data switch must be on)
IC-970        10Hz
FT-726        20Hz
TS-790        20Hz
IC-821        50Hz
IC-820       100Hz
IC-271/471   100Hz
TS-711/811     ??
FT-847         ??
IC-910H        ??
TS-2000        ??

On the Yaesu FT-736 the UP and DOWN pins are at +5Volts. Pressing
UP or DOWN connects the pin to COMMON. I have used my modem with
the FT-736 with complete success.

The TS-790 UP and DOWN pins connect to Ground when pressed. This
should not cause any problems. There are jumpers in the G3RUH modem
to set up for Kenwood or Yaesu.

Icom uses a different system, and I have not been able to make it
work with my G3RUH modem. A single pin on the mic connects to the UP
switch, and also to the DOWN switch through a 470 ohm resistor. The
open circuit voltage of this pin is 5Volts. Both switches connect to
Ground. The result is that a direct connection of UP to Ground i.e.
0Volts generates an UP command. When DOWN is pressed the voltage is
0.6Volts across the 470 ohm resistor. All Icom radios use this system
but there are variations. A different resistor value may be used. I
have seen 1.4Volts for DOWN.

In spite of setting the correct jumpers in the G3RUH modem and adding
the 470 ohm resistor, I have not been able to get the Icom system to work
with my IC-275. Let's just say I tried it and gave up. Maybe more work
would have solved the problem. I speculated that perhaps the opto-isolator
transistors were not being saturated; or that the 0.2 volts at saturation
would not permit the 0 or 0.6 volts that the system requires to be
achieved. Perhaps adding external DIP relays driven by the opto-isolators
would work. Another possible problem is the pulse length.

Finally what about radios with a larger step size. You might alter the
circuit in the G3RUH modem so that different bars are used to generate
the click, for example 3 and 8, but you don't want the frequency to
change so much that lock is lost. The manual says that lock will occur
for 1584Hz, plus or minus 80Hz. So perhaps range is not a problem.

If the radio has a large step size, but also has a PC serial port, you
might connect the modem clicks to a microprocessor and generate
frequency changes through the serial port.

Good luck. I hope this has been informative.




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