[Yaesu] FT-1000MP: main rx AF hiss - Thanks

[WD8ARZ]

Hello George, thanks for posting again about the work your doing into the
IF signal to noise ratio modification for the FT1000MP.  I am following
your comments with great interest and would be glad to put one of your
boards to a test on this end......and return the board to you if you wish
with the results of that test. 

With the broadband nature of todays radios, I would be concerned about
increasing front end RF/IF gain in the presence of local strong
transmitters. I seemed to remember one of the goals set for the design of
the FT1000MP was to improve performance in just this area, and to keep
distortion and overload situations to a minimum.

I am concerned that not every radio will behave well with a modification of
this type and would be very eager to hear from Yaesu their opinion as to
the benificial gain this will bring to the 'overall performance'  and any
trade offs to their design goals. I would be disappointed in Yaesu if this
is actually a flaw in their design for a rig in this performance and cost
range. It would be should a basic error to defy their engineering
resources. 

At the least, those making this modification will need to realign/calibrate
the entire radio to put the S meter and dymnamic performance objectives
back into optimum, but my biggest concern would be the performance factors
in strong RF field areas.

Your input is greatly appreciated and I am looking forward to any and all
modifications for refining this terrific transceiver.

73 from Bill - WD8ARZ
E-Mail Reply to:
wd8arz@null.net

----------
> From: George Cutsogeorge <w2vjn@rosenet.net>
> To: Steven J. Franke <sfranke@uiwpls.ece.uiuc.edu>; yaesu@contesting.com
> Cc: sfranke@uiwpls.ece.uiuc.edu
> Subject: Re: [Yaesu] FT-1000MP: main rx AF hiss
> Date: Wednesday, December 17, 1997 1:40 PM
> 
> Hi Steve and the list,
> 
> Some time ago I posted a message about the "audio hiss" which answers
some
> of the questions that have recently come up.  The previous msg is
repeated
> below.  Since that time I've built a prototype and run some dynamic range
> tests on the modified receiver.  The net effect due to the increased
> sensitivity is actually a small increase in dynamic range.  Yaesu was
kind
> enough to sell me some connectors and cables, so I am laying out a PC
> board.
> 
> George, W2VJN
> 
> ----------
> 11/24/97
> 
> 
> I have been looking into the problem and have what I believe to be a good
> solution.  The noise coming out of the receiver is mostly IF noise.  This
> can be verified by removing a pair of filters, one in each IF, and
> measuring the audio output noise and setting a reference on the meter. 
> Then, return the filters and take another measure.  Any additional noise
> will be coming from the front end of the radio.  The front end noise must
> over ride the IF (and audio) generated noise or the receiver noise floor
> will be degraded.  The result of my test showed from 0 to +2 dB of
> additional noise with various filter combinations.  This is not enough to
> over ride the IF noise and shows that the gain before the second IF is
too
> low.
> 
> The RF gain reduces the noise because it operates on the agc buss which
> reduces the IF gain as well as the RF gain.  Another way to observe the
> problem is to switch in front end attenuation.  You will notice that the
> noise heard out of the radio does not reduce very much.  If the noise
were
> coming from the antenna, attenuation would reduce it.  This is not a
> problem on 10 meters when the tuned front end is employed as the dual
gate
> mosfet has more gain than the push pull RF stage used on the lower bands.

> You will notice more front end noise on 10 meters for this reason.
> 
> In my unit I have installed a small, high dynamic range amplifier with a
> few dB of gain at the 70 MHz input to the IF board.  It doesn't take much
> gain to over ride the IF noise and excessive gain would reduce the strong
> signal capabilities of the radio.  The measured noise floor of my radio
has
> improved 3 to 4 dB and it really sounds good to me now.  Antenna noise is
> very apparent and I have been able to reduce the IF gain using menu item
> 9-1 by about 3 dB.  This further reduces the IF hiss problem by an
> equivalent amount.
> 
> After the WW contest I'll measure the dynamic range of the modified radio
> and maybe adjust the gain a bit.
> 
> The amplifier is very simple.  A major problem is that I have not found a
> supplier for the pc mounted coax connectors used in the radio.  If I can
> come up with connectors, I intend to make a mod kit available through
> International Radio.  
> 
> George
> w2vjn@rosenet.net


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