[Yaesu] FT757/linear interface

[rick@area.com]

I am trying to interface my FT757 to a linear.  The manual shows
non QSK linears are connected to PTT, which I measured with my
scope to have a 25 msec head start before RF comes out of the 
transceiver.  It shows QSK linears connected to "TX GND" on
the band info connector, which I measured to have a 5 msec
head start before RF appears.  It also shows an "Inhibit" connection
that the manual implies allows the linear to hold off the 
transmitter until its T/R relay has been activated.  There is
a "linear" switch that is supposed to be pushed if and only
if a QSK linear is used.  When this switch is in the non QSK position
it clearly shorts the inhibit input to ground on the inboard side
of a series diode. 

Here's the mystery.  The linear switch seems to have no effect
one way or the other, nor does the inhibit input.  On the schematic,
it shows the INH signal going from the local to the RF board at
which point it is grounded!  So it appears like the feature has
been defeated internally without changing the documentation to
reflect that.

Can anyone clear this up?

Rick Karlquist N6RK
rick@area.com



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