Was building up an interface RS-232 for Lamar WA7LT where I do some
contesting. Ran into a problem that took me quite a while to figure out
so I thought I would document it for the group(s). Using the Max-232
device which is about as easy as almost anything I discovered that some
FT-1000's and 990's as well use an emitter follower on their serial out
line.
I noticed this but never thought about it when building transistor FSK
interfaces as I just used a substitution box until things keyed or
diddled. You won't notice this on Opto circuits of course.
But since the Max 232 is a TTL gate it doesn't have enough load. I added
a 1.5K resistor to gnd in the interface box (one could fix it in the
radio which Yaesu did in later runs but easier in my little box) did the
trick. You can measure the CAT coming from the radio Pin 1 to Pin 2
(ttl out) and if its less than 5K add a resistor.
Total price for the Max232 Yaesu box was $6 plus a little box which I
had. (Actually $3 less as I got the Max 232 chips as samples from Maxium).
Jay WS7I
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