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Re: FT736 adjustment



----- Original Message -----
From: "Bob Schmidt" <bschmidt@ecdentalspecialists.com>
To: <amsat-bb@amsat.org>
Sent: Tuesday, June 13, 2006 5:05 PM
Subject: [amsat-bb] FT736 adjustment

> The tone quality when listening to USB vs LSB seems to be different in my
> FT736.  That is, one has lots of treble, while the other has lots of bass.
> Is there an adjustment to remedy this?
>
> Thanks
>
> Bob, WA9JDR

Hi Bob, WA9JDR

Generally speaking if the USB signal is placed to fall excessively in to
the low response of the lower slope of a passband filter than the lower
part of the  USB spectrum is greately attenuated and only the high part
of the USB spectrum is allowed to pass in to the filter with low
attenuation and you have lots of treble.

If the LSB signal is placed to fall excessively in to the low response of
the upper slope of the passband filter than the lower part of the LSB
spectrum is allowed to pass with small attenuation while the high part
of the spectrum is greately attenuated  and you have lot of bass.

I don't own a FT736 but I have a block diagram of it and if you look at
section RX UNIT F2887101 of your manual you will see that all received
signals are converted to 13.690 MHz and than they are introduced in to a
mixer with local crystal oscillator X3001 at 13.2335 MHz or X3002 at
13.2365 MHz

Now

13.690 - 13.2335 = 0.4565 MHz or 456.5 kHz

13.690 - 13.2365 = 0.4535 MHz or 453.5 kHz

456.5 kHz is the frequency in which must to fall the LSB signal in
to the high slope of the 455 kHz 8 pole filter CF3003 used for SSB
and CW

435.5 kHz is the frequency in which must to fall the USB signal
in to the low slope of the same 455 kHz 8 pole filter CF3003

It is possible that the crystal oscillators X3001 and X3002 are not
running exactly in their nominal frequencies so that adjustement of
the trimmer capacitor in parallel to each crystal is required.

If you have a precise frequency meter you can check it by instrument
but after taking note of the actual trimmers position for precaution
you can made the above adjustement by ear.

In any case the Technical Manual of any equipment should explain
step by step all calibrating and adjusting procedures.

Best 73" de

i8CVS Domenico
----
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