Hello Jim,
Thank you.
I ran the circuit unattended over night with a somewhat cautious feeling
but the system is still fine ;-) Now beeing here on the Grabber PC again
and watch how it works in operation. Nearly perfect.
There are some transient overshootings when rapidly reaching the
resonance point. Two short impulses occurr when crossing the resonance
point (to far beyond the optimal point, then a bit back and a smaller
bit back again) This happens since i had to reduce the 33 Ohm resistor
because the engine stucked yesterday in the evening. The engines
stucking may have to do with different meachanical forces at different
coil angles and just the cold outside. So now i could simply decrease
the gain a bit, ie. increase the dead band. But what i want to do is to
make the resistor smaller and reduce the output voltage a bit, making
the behaviour of the source come closer to an ideal voltage source
instead of a current source. I will simply add a 7808 or 7806 and a
1000uF cap in front of the 7667. Then i have to add a voltage divider in
front of the 7667 to keep the input voltage below the supply voltage.
Also this will make the inpit LOW level a bit closer to 0V.
I found some further minor things that could be changed or optimised in
the circuit.
-Of course i do not need 2x a 680 Ohm resistor for the LEDs, one is enough.
-Also ordinary 1N4148 diodes instead of the BAT42 will work as well.
Matching is uncritical.
-A RC circuit with a time constant of about 1 ms (10n, 100k) between
output of the amp stage and the comparators may help to reduce unwanted
short active impulses during pressing or releasing the PTT (sometimes
seen here).
BTW i observed no EMC problems here with the circuit. The functionality
is the same at 1% or 100% TX power.
73, Stefan/DK7FC
Am 23.12.2011 12:17, schrieb James Moritz:
Dear Stefan,
That is a nice simple circuit - I may well try something very similar
at my QTH over the Christmas holiday, if time allows...
I suppose one advantage of a passive, "signal powered" phase detector
for this scheme is that the phase detector output automatically
becomes zero when the transmit signal is not present, which will
prevent unwanted tuner operation on receive. As well as the BAT42
diodes providing a dead zone in servo operation close to the resonance
point, I guess the inertia of the motor and gearbox will produce some
hysteresis, moving the variometer to a very slightly over-adjusted
position after the motor drive is removed, which will also help to
prevent the system continuously searching around the correct tuning
point. I expect one can optimise the resistor in series with the
motor, as well as the amplifier gain, to get the best operation of
this feature.
Cheers, Jim Moritz
73 de M0BMU
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