Receiver Noise Modification by W7SV
Problem: Receiver Noise generated by the
Solution: Here is a copy of the original
Yaesu FT1000MP service bulletin about the "IMD" fix which they put out after I
told them about how to fix the noise problem on the original FT1000D. IMD is
part of the problem, but the main part of the fix is to reduce the reverse
flowing electrons in the switching diode by using a PIN diode with an intrinsic
layer between the "P" and "N" layers.
Click here to view the Yaesu Service Bulletin
This reduces the reverse electron flow by a factor of > 1000. The reverse
flowing electrons in the original standard switching diodes are amplified (by
approx 120 db) by the RF and IF and Audio stages and manifest themselves as
NOISE in the receiver!! So putting the pins in place of the standard switching
diodes really does 2 things... reduces noise as explained above AND reduces
intermod on strong signals.
You will note that the signals sound cleaner after you do the pin diode mod.
Yaesu already used PINs(1SV196)(surface mount devices) on the leading edge of
the front end bandpass filters, so there is not much to be gained by replacing
them with the better HP5082-3081 diodes.
I also replace the switching diodes around the various RF amps and the IPO
switch to eliminate that source of noise. SO.. the diodes to replace on the
RF/IF board are:
Bandpass switching diodes (14):
D1004, D1009, D1010, D1015, D1019, D1026, D1030, D1036, D1040, D1044, D1047,
D1049, D1054, D1057
RF AMP / IPO SWITCH diodes (8);
D1001, D1002 IPO SWITCH
D1006, D1014 Low Band Preamp
D1032, D1037 Mid band Preamp
D1041, D1043 High Band Preamp
I think you will note a big reduction in internally generated noise and the
signals will also sound cleaner after you do the mod.
Download Pictures of the FT1000MP disassembly procedure thanks to Lutz, W4/DH7LK
for this basic procedure for dis-assembling the FT1000MP to do the pin diode
mod. Kirby, W7SV
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