I did the resistor value change (3.3K to a 10K)to the blanking circuit in my
FT-900. The improvement was enormous, but still was not sure it was as good
as it could be (also did the Yaesu suggested AM circuit change-forget the TB
number but have a copy if anyone interested). In talking with Yaesu on the
phone about the noise blanking mod, I learned that the best value to achieve
the most effective blanking was not necessarily 10K, but could be some value
less than, or even slightly more. Since I use my FT-900 exclusively in my
car, noise blanking is a prime issue. Wonder if anyone ever replaced the
fixed value with a variable value (a 10 or 12K pot) and literally set the
value to achieve the highest blanking efficiency?? If so think the FT-900
owners would be interested in your experience. Still a great rig, but never
had the SSB filter, which Yaesu no longer says is available. Understand
Irad (?) has one. Is the improvement worth the effort???
Don W7WLL
-----Original Message-----
From: Dave Jordan [mailto:wa3gin@erols.com]
Sent: Wednesday, June 16, 1999 7:36 PM
To: Yaesu Technical Support; yaesu@contesting.com
Subject: [Yaesu] FT-900 Modification for Variable "RF" Gain Control
Hi Folks,
When I first got my FT-900 brand new in the box I had reservations about
owning a rig that didn't have an "RF" gain control. It's been several
years
now and I'm still missing that "RF" gain control. I have a FT-1000 and
I'm just
used to cranking it back...it does make a difference in reception. SO,
back
then I asked Yaesu to give me location for the fixed resistor that
controlled the
RF gain.
Tonight I decided to open up the FT-900 and do the deed. I found
a free pin on the "CAT" socket that could be used to install a connector
with a
pot that I would parallel with the fixed resistor. So, I could unplug
the pot and
have the normal fixed setting or plug-it in and have some variability
over the
"RF" gain. As it turns out what Yaesu sent me as a mode was a technical
bulletin TB-9448-A, a fix to increase noise blanking performance, by
increasing the resistance of R2335 (on the back side of the xthe RF-Unit
board number F3251000C. I can scan in the location chart if anyone is
interested. R2335 was originally 3.3Kohms but can be increased up to 10K
ohms. I added another 3.3K ohms in series. Haven't got the box back
together yet but will report out on the results soon.
The question to the list and Yaesu technical support is simple. I need
the
location of the fixed resistor that is responsible for setting the "RF"
gain of
the FT-900. I would appreciate a fax or email enclosure of the specific
loation ASAP...
By the way, if you like the idea of a "RF" gain control but don't want
an outside connector with pot you could easily disable the sidetone
beeper
variable resistor and use it for this purpose. Another thought would be
to
simply use the pot to identify the favorite setting and use a fixed
resistor in
the plug. I've found that when I do crank back on the FT-1000 the
setting is always the same and the only time I turn it up these days is
to give a signal
report.
OK, that is it...thanks in advance for any assistance,
dave
WA3GIN
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--
FAQ on WWW: http://www.qsl.net/k7on/yaesu.html
Submissions: yaesu@contesting.com
Administrative requests: yaesu-REQUEST@contesting.com
Problems: owner-yaesu@contesting.com
Search: http://www.contesting.com/km9p/search.htm
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