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RE: FT-847 9k6 deviation



Everyone just make sure you don't take th HPHONE out of the EVM and plug
that into pin 1 when in 9600 mode on the 847.  There isn't an AC coupling
cap to protect the IC that it does to and there 2+V of DC offset on the
HPHONE out jack!

Alan

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Mike73@aol.com
Sent: Wednesday, February 23, 2000 7:39 AM
To: amsat-bb@AMSAT.Org
Cc: w1emt@together.net
Subject: [amsat-bb] FT-847 9k6 deviation


Howdy,
Here's a little better explanation of what's going on with the FT-847 1k2
vs.
9k6 input level from ZL2AMD. Thanks Dave!

N1JEZ writes:

> If you look at the schematic the buffer amp is in circuit all the time but
a
> resistor is switched in and out in parallel with the feedback resistor
> around the amp. Looks like amp gain is being changed...... This is why I
had
> originally looked at changing the feedback resistor that was switched in
> for 9k6 to increase the gain and make it a bit easier to deviate at 9k6.

In a message dated 2/23/00 4:59:42 AM Eastern Standard Time,
lamontd@paradise.net.nz replied:

>  The amplifier gain is switched by the relay as you state.
>  When in the 1200 mode the gain of the op amp is 18 and any
>  signal over a very small amount is amplified and applied to Q1048
>   a peak detector, which conducts and inhibits any  9600 PTT from
>  occurring via the following transistor. Hence no uplink
>  Under 9600 mode the gain is insufficient to fire Q1048 and  the
>  audio is routed via R1150 to the varactor and normal  9600 PTT is
>  available.

73,
Mike, N1JEZ
AMSAT #29649
Local Area Coordinator
"A closed mouth gathers no feet."
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