[Yaesu] FT-990 NOISE FT-990 NOISE

Kok Chen kchen@apple.com
Thu, 19 Sep 1996 08:34:27 -0700

Ray, SM5LBR (ERAC.ERARAT@memo.ericsson.se), has asked if I could help 
him post the following message since his attemped posting didn't seem 
to have made it through.

---------------------- (snip, snip) --------------------------------
             KOLARVAEGEN 18
             SE-74492 HUDDUNGEBY
             Phone home +4622496127
             Phone mobile +46705493900
             Phone office +4687570877
             Fax office +4687571350
             email: rainer.arndtéera.ericsson.se
             homepage: www.angelfire.com/pages0/sm5lbr/index.html
             packet: SM5LBRÉSK5DB.C.SWE.EU




       Having finally come across the Reflector and having studied
       the different inputs regarding this matter, I believe it's
       about time to "jump in" and give you some background as
       well as my views.

       1. BACKGROUND
          I have been on the air since 1979. The first set of SW
          radio I owned was a Drake C-line which I sold in early
          1995. (I'm still not sure whether this was a good
          decision...) At the end of the 80's I started to think
          about buying a solid state radio. During a visit in the
          states in '89 I purchased an IC-725, which after a
          relatively short time I found unsatisfactory in

          In '92 I bought an FT-890 which I found was great. It
          was this radio that really boosted my interest in modern
          radios and consequently I stopped using the Drake-line.
          Since I wanted something big I started thinking about an
          FT-990 (I thought an FT-1000 was too big in terms of
          cost for me.). So I bought a new FT-990 with very late
          serial number in December 1994 during a visit in the
          Coming home, the first thing that caught me was "this
          radio does not sound as quiet as my 890!"

       2. THE PROBLEM
          At that point in time the 20m band too seemed to be
          rather noisy, so I couldn't really determine where the
          noise was coming from. So I started to investigate.

          Since I work for a company that has world class
          competency in radio, I went to our lab with both radios
          and we started to measure and compare. It was not really
          easy, but my perception is that with equal signals into
          both radios, we had to increase the level to the FT-990
          with around 6 to 10dB in order to get the same good
          audibility/intelligibility as for the 890! There
          definitely seemed to be some noise underneath the
          signal, but it did, at that point in time, not sound as
          if it came from the radios RF or IF, rather from the AF.
          However, when I reduced the IF gain (There is a
          potentiometer on the IF-board.) the noise decreased sub-
          stantially, but so did the sensitivity too.

          I got in touch with Yaesu Europe who finally asked me to
          leave the radio with their service department in the UK
          (Just outside Heathrow Airport when I passed through on
          a biz trip.). The guys there were extremely nice and
          helpful and started to check. When I picked up the radio
          some days later, they told me "there's nothing wrong
          with your FT-990, it's within spec." However, they did
          not present any measurement results. Ok, I said to
          myself, I will have to live with this, in my eyes minor
          In 1995, visiting Dayton, I bumped into Chip Margelli
          K7JA at the Yaesu booth. Chip is said to be one of the
          persons that have contributed to the becoming of the
          FT-990. Whether in terms of hands-on design work or by
          defining the radio, I don't know. I discussed the
          problem with Chip and his, in a way diplomatic, answer
          was "I have always said that the digital filter should
          not have a switch to be turned off". This answer proofed
          to me that Yaesu are aware of the problem and that their
          only current suggestion would be to reduce this wideband
          noise or hiss by using the SC-filter. I then later was
          corresponding with Chip, but never got any further,
          besides that Chip praised this radio, told me on how
          many DX-peditions it had been used and so forth.

          Found an early review from 1992 RadCom (RSGB) where
          Peter Hart (In my eyes very competent and well
          respected.) had measured the FT-990. He was very pleased
          with the radio and got figures like -122dBm for the
          sensitivity in SSB on 14MHz. "Very good figures were
          measured for IP3, close-in dynamic range and reciprocal
          mixing. Indeed all these figures measured at a few dB
          better than the FT-1000 sample reviewed last June."
          (RadCom April 1992).
          N.B. Hart did not mention any noise problem.

          Today the FT-990 has an extremely good reputation in the
          UK and it is advertised as being equal to the

          Took home a Schlumberger Stabilock Radio Test Set
          and did som measurements. What disturbed me was the
          fact that I only could reach/verify Hart's figures when
          the SC-filter was used and both the lower and upper edge
          were optimized, i e both knobs in the region of 9 to 10
          o'clock. With the filter switched off, I lost about 6
          to 10dB in sensitivity!

          Got in touch with Hardy Landskov N7RT who was displayed
          on the cover of CQ Magazine June 96. Hardy was said to
          having done "all thinkable modifications to his FT-990".
          I received a very comprehensive answer from Hardy
          roughly a month ago. And indeed Hardy had done a lot of
          interesting things covering different areas of the
          radio. As far as the noise is concerned, Hardy wrote:
          "Added a 5.8kHz Collins mechanical filter on the output
          of T2023 to remove broadband hiss. This is what you are
          hearing with the SC filter off. This happens when the
          front end gain is low (as it should be for decent
          dynamic range) and the IF gain is high. The trouble
          comes because the IF bandwidth widens out with the use
          of the small 10mm tuned circuit transformers that have
          low Q.
          This filter addition removed most of the noise, but
          I still have to put the SC filter on to get rid of the
          remaining background hiss. This is not recommended for
          the faint of heart. It costs a lot of money and did not
          yield what I thought it would. Plus, it got complicated
          and difficult to squeeze the filter in there. Running
          the SC filter in all time solves the IF hiss problem."

       3. SO WHAT NOW?
          Well, it would be important to get more inputs. The
          thing is: I'm still waiting for to hear anything from
        the Yaesu designers in Japan.
          Still, I think this is a great radio and I will not sell
          it (Unless I come across an FT-1000 at a reasonable
          price.) I have never owned a radio that performed so
          well on 40m nighttimes, which is a very tough band here
          in Europe.

       Best regards and hope to hear from you


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