> However, directly taping to the trigger point
> with the controller loads down the whole thing
> and nothing is received. I've tried using
> a radio shack mps2222a transistor to make a
> transistor switch and still, it loads it down.
The transistor required current to turn it on.
Pulling current from the radio circuit, appears
to be a no-no.
Try using a VN10KM (also known as VN10LP at digi
key)(also known as a 2N7000) or any generic
switching fet. The fet requires a few + volts
(about 4) with no current draw, to turn it on.
You can use the fet to key a proper size (small)
relay from + radio supply voltage to the drain
if you want/need one.
Radio Shaft (Shack) sells a number of basic fets.
Just about any switching fet they sell will
probably work ok.
Ground the Source Lead, use the Drain lead as
your logic function/source.
Provide a high value resistor from the gate to
the source to allow the fet gate to drain (shut
off). 470K is a good value. Also add some 200pf
caps (gate and drain to ground/source) for rf
problem prevention. The value can be anything
from .1 down to 200pf.
Get a 500K pot, place one end to your squelch
gate ckt, the other end to ground. See if your
squelch gate ckt functions as you normally expect.
If not you can try a higher 1 meg trim pot.
Tie the trim pot wiper (center) lead to the
2N7000/VN10KM fet gate through a 47k ohm
resistor (don't forget the 470K gate to
source "drain down" resistor and generic
bypass disc ceramic cap.
Adjust the pot so the fet drain goes to ground
with the desired squelch gate action. A volt meter
on the squelch circuit before starting will tell
you if the min require ~ +4 volts is available
to turn on a fet.
> I'm thinking now of using a quad buffer/line
> driver or something like that, but thats going
> to use a lot of space.
An op amp circuit is a high impedance input,
same thing as the fet ckt described above.
> I'd prefer to just use a transistor or something.
> Something that I can solder flat to the PC
> board and not have to run a pile of wires
> and add a circuit board.
> Does anyone have any ideas --- know of any
> transistors that could be used that will not load
> down the gate/squelch? I need something that
> is almost transparrent to the gate trigger.
See the above, get away from the devices which
require current to turn them on... ie transistors.
Try a fet, a voltage controlled device that doesn't
require significant current to turn on. FETs or
op amp/comparator circuits are a good choice.
> Thanks
> Dave
> N9NLU
cheers
skipp
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