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[Yaesu] IRAD IF mod + possible problem

To: <yaesu@contesting.com>
Subject: [Yaesu] IRAD IF mod + possible problem
From: rwalters@mailhost.magicnet.net (Ron Walters)
Date: Mon, 25 May 1998 14:28:14 -0400
Potential Trouble w/IRAD IF mod Kit and my impressions.

Some background, Vintage of my rig is 12/95,  installed variable power
mod and also some of the technical mod for spurious outputs when using
the rig on 15 Meters.  Before I describe the problem I ran into, let me
first comment on the IRAD IF kit mod.

When I installed the IRAD IF mod kit it lived up to all of my
expectations, I do not have the extensive test equipment that many of
you may, but I can say that the following subjective observations were

Was able to reduce the 9-1 menu IF gain from a setting of 13 to 9 with a
noticeable reduction in IF noise.  I am the second Owner of this rig and
when I first reviewed the 9-1 menu setting it was set for 31 or the
max.  I don't know if this is the way it came form Yaesu but I doubt it
and believe it was adjusted by the previous Owner.  I re-adjusted it to
a setting of 13 which improved the performance and the noise floor.

One of most noticeable improvements was the noise blanker.  One of major
disappointments when I first used the rig was the effectiveness of the
noise blanker compared to my old Kenwood TS-940SAT which did an
outstanding job at noise reduction.  I really haven?t had a chance to
analyzes the circuits for were the noise sampling is done, would
appreciate any feedback, should this mod had any impact?  I can only
report that the noise reduction circuits are now working up to my
expectations and have a noticeable impact when engaged.

The second improvement, and this is also subjective, seems to be the
effectiveness of the EDSP functions, I believe that the effectiveness of
the EDSP has improved, again it is only subjective and it maybe that my
hearing has improved.  However now when I engage the EDSP many of the
signals jump out of the noise, like they should, and there is a definite
impact with the S/N ratio of the received signal.

Now for the negative, this old vintage rig had the dreaded spurious
emissions after heating up or when used with the internal antenna tuner
when operating 15 meters.  I've read on the reflector of similar
problems with spurious emissions from the 18 and 24.5Mhz positions as
well as 21Mhz.  Yaesu printed a 5/31/96 tech mod to correct this
problem.  After I installed the mod except for new coils on the RF unit
and careful routing of two cables my rig no longer exhibited this
dreaded problem.  No problem for over six months.

When installing the IRAD mod on the AF unit one of the cables that was
re-routed by the Yaesu mod had to be extended about 1 1/2 inches which
caused the cable to re-rout over the RF unit.  This cable is plugged
into a socket next to L1086 on the RF unit.  I didn't think to much
about this until recently  on fifteen (15m) I got the chance to work a
rare DX station and the dreaded spurious emissions with break up of the
15 meter SSB signal once again occurred.  It dawned on me that possibly
the cable on the RF unit had moved.  I checked it, and yes it had, since
to install the IRAD mod I had to increase the length of connecting cable
form the old location to the new IRAD kit location.

Once again I took the covers off, lifted the fan and power unit up and
away and sure enough there was the cable now moved back over the RF unit
and not outside of the shielded area like Yaesu first suggested.  The
simple thing would to replace the cable with a little longer one but I
decided to re-route the cable 180 degrees from the Yaesu suggestion.  I
ran the cable on top of the BPF unit enclosure, which is located in the
center of the RF unit, and secured it in place using some copper tape.
The cable now runs across the BPF shield enclosure and then up through a
opening to the AF unit.  I reassembled the rig and fired it up.

So far I haven?t noticed any spurious emissions or encounter any
difficulties. "Knock on wood". Have had the rig on for over three hours
with out any problems.  Probably most of the rigs built after May of 96
will not have this problem if you choose to install the IRAD mod and I
would recommend to everyone that this IRAD mod is well worth the cost.
My advice regardless of the manufactured date is to treat these cables
with kid cloves and if the problem occurs you won?t be surprised.

A final comment, I installed the audio capacitor mod that was supplied
with the IRAD mod but I feel with this vintage rig that there was a
negative improvement to the audio quality.  I was unable to read the
existing capacitor value as suggested by the author of the mod so for
some it maybe trial and error.  Again its subjective.


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