[Yaesu] FT-900 Modification for Variable "RF" Gain Control
donald.s.tucker@exgate.tek.com
donald.s.tucker@exgate.tek.com
Thu, 17 Jun 1999 15:06:04 -0700
I have a copy of the noise blanker TB but it is a single page sheet. The
only note of consequence in it is it states that the value "may be any value
between 6.8K and 10K, some clipping of the desired signal may occur with
some condition." When they sent me the TB they sent a 10K with it and this
is what I installed. Nothing about any procedure! It seems to work OK and
I don't notice any clipping. In any follow up phone call with one of the
techs, was a suggestion that a slightly higher value might also be
appropriate. Did not experiment. If your TB has more information than
this, would like a copy of it. My TB is dated 18 October 1994 by the way, I
received it in Jan 1996.
The res value change worked wonders and I have no ignition noise other than
a strange low level 'hash' (S1/2) which only appears when the ignition is in
the operating position prior to engaging the starter (past the accessory
position)or when the engine is operating (same switch position). Also have
a low level hash which is tied to car movement (tire rotation). No roll, no
noise except something is at a particular point, slow roll, very obvious
noise synced with some rotating component. Particularly bad on 17M when
combined with the other hash (S3). Not hardly noticeable on other bands.
Anyone have some suggestions would appreciate it. Don't think the fixed
hash is fuel pump, but could be wrong. (Plymouth grand voyager)
Only have to pull off the road with the really weak signals.
Where does one find a Collins filter to replace the standard 2.6 kHz ceramic
filter.
And does anyone have a SP-6 Yaesu speaker for sale?
-----Original Message-----
From: David G. Maley [mailto:dgmaley@soli.inav.net]
Sent: Thursday, June 17, 1999 2:31 PM
To: Tucker, Donald S
Cc: wa3gin@erols.com; yaesutech@worldnet.att.net; yaesu@contesting.com
Subject: RE: [Yaesu] FT-900 Modification for Variable "RF" Gain Control
Don;
I placed my rig on my bench and went through the factory test select
procedure for this resistor. Do you have a copy of the service
bulletin? Basically it says to keep increasing this resistor value
until you notice a SLIGHT audio distortion on the voice peaks.
Install that resistor value. I used a resistor dec. box. I also made
it a little too high, so a do get a little distortion on strong signals.
I consider it worth the trade. My radio ended up using a 9.7K resistor.
On the additional filter. Suggest you install the Collins mechanical
filter instead. What you will hear is better audio (no filter ringing),
and less filter leakage.
73 Dave WA0ZZG
On Thu, 17 Jun 1999 donald.s.tucker@exgate.tek.com wrote:
>
> 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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