Hello again Steve, and Thank You for posting your very excellent and
informative reply ! It is really rare for someone to follow up an issue
from the begining to a satisfactory conclusion, much less to a fix or a
modification. Some of the previous message thread was cross posted on to a
FT1000MP email reflector at http://jehosophat.com/1000mp/ so I have put
a copy of this message there too.
Sometimes it is frustrating when trying to work out technical issues when
you cant put your hands on a users rig, or be there with them to see what
is missing or being overlooked in the information being exchanged. With
your FT1000MP possably being a mis-build, I wonder now if those that agreed
with your earlier assesment have the same problem ? Would be interesting to
hear from them after they follow up on the component value identifications
issue.
Will be looking forward to further postings from you about the FT1000MP in
the future.
73 from Bill Stamps - WD8ARZ
E-Mail Reply to:
wd8arz@null.net
----------
> From: Steve Franke <sfranke@uiwpls.ece.uiuc.edu>
> To: yaesu@contesting.com
> Subject: [Yaesu] FT-1000MP - main rx AF hiss - followup
To: <yaesu@contesting.com>
> Date: Tuesday, December 23, 1997 1:31 PM
>
> Hi All,
>
> I started this thread, so I thought that I should follow up with what I
> learned about my FT1000MP. After some fairly extensive tests, I decided
> that my transceiver is within specifications, and performs as the
designers
> intended. I also discovered that my perception of significantly more high
> frequency hiss on the main receiver output relative to the sub-receiver
> output (CW mode, EDSP demod OFF, 500 Hz filters) was correct, but I now
> have a better understanding of the constraints that led to this
performance
> characteristic. I should note that the audio sounded fine to me when
EDSP
> demodulation was turned ON.
>
> It turns out that the CW-mode AF low-pass filter is different on the main
> and sub receivers in my unit. The sub-receiver employs a filter with a
> slightly peaked low-pass response with the peak at about 700 Hz, whereas
> the main receiver has a low-pass filter with flat response out to about 1
> kHz or so. I discovered this only after inspecting the AF circuit board,
> as the schematic that came with my radio (and the service manual
schematic)
> showed identical analog AF CW filters in main/sub receivers.
>
> The net result, on my radio, when employing analog demodulation and with
> main and sub receiver AF gains set for equal total AF output powers, was
20
> dB higher noise spectral density level at 2 kHz on the main receiver.
This
> test was performed in CW mode, pitch frequency=550 Hz, 500 Hz IF filters,
> no antenna connected, on 21.040 MHz with FLAT preamp engaged.
>
> At least one reason for the use of a flatter and wider filter in the main
> receiver is to ensure flat performance over the entire range of audio
> "pitch" settings, which can place the center of the AF passband anywhere
> between 300 Hz and 1050 Hz. Since I listen to CW at a pitch of 550 Hz, I
> chose to modify my radio so that the main rx CW audio filter has the same
> type of peaked AF response as the sub-receiver. Compared to the
unmodified
> AF filter, the modified filter has larger response within the passband
> (peak at about 550 Hz), and lower response at the higher "hiss"
> frequencies. The net result, after the modification, is an improvement
> (i.e. decrease) of about 15 dB in the main-receiver "hiss" components at
2
> kHz when main/sub receivers are adjusted for equal AF outputs. In short,
I
> am now a happy camper.
>
> I cannot recommend the modification for everyone, as I chose to optimize
> the CW mode AF response of my radio for a specific CW pitch setting, and
> for use with the 500 Hz and 250 Hz IF filters. Also, the fact that the
> component values in my radio differed from the schematic suggest that not
> all 1000MP's are the same in this regard. That may account for the fact
> that responses to my original post ranged from "I agree" to "no problem
> here". In any case, for those who are interested, the relevant component
> values are as follows:
>
> AF CW low-pass filter is located on the AF board. Components that
> determine frequency response of the CW-mode AF low-pass filter are R3018,
> R3019, C3015, C3026.
>
> Schematic indicates:
> R3018=R3019=15K, C3015=.033uF C3026=.0047uF
>
> My radio came with the following values:
> R3018=R3019=12K, C3015=.015uF C3026=.0068uF
>
> I changed C3015 to .062uF by adding a .047uF capacitor in parallel with
the
> original .015uF cap.
>
> I should add that the modified filter is not in-line when EDSP
demodulation
> is selected. Thus, the modification did not alter the performance of the
> radio in that mode.
>
> Thanks to all who posted suggestions and who replied to me via direct
email.
>
> 73, Steve K9AN
> sfranke@uiwpls.ece.uiuc.edu
>
>
----------------------------------------------------------------------------
> Steven J. Franke | phone : 217.333.8128
> Space Science & Remote Sensing Lab. | fax : 217.244.5624
> 319 C.S.R.L. | email : sfranke@uiwpls.ece.uiuc.edu
> University of Illinois |
> 1308 W. Main Street |
> Urbana, Il 61801 USA |
>
----------------------------------------------------------------------------
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