[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) --------------------------------
FROM: RAINER L R ARNDT
SM5LBR
KOLARVAEGEN 18
SE-74492 HUDDUNGEBY
SWEDEN
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
TO: YAESU REFLECTOR BY THREAD
RE: SUPPOSED/CLAIMED NOISE PROBLEM WITH THE YAESU FT-990
========================================================
Gentlemen:
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
performance.
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
States.
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
problem.
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
FT-1000.
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
RAINER (RAY) ARNDT
SM5LBR
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