Newsgroup: it.hobby.radioamatori
Titolo: Informazioni su modifiche RX ICOM ICR-71

    Cerco informazioni su informazioni su modifiche RX ICOM ICR-71 ed in
particolare riguardanti la riprogrammazione della ram per poter scendere al
di sotto dei 100Khz.
    Gradite risposte possibilmente tramite e-mail
    Adolfo IW6DMQ
 
ka...@bepop.it

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articolo.
              73,Roberto
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Ciao,
visto l'argomento di interesse generale rilancio un messaggio
pubblicato su rec.radio.shortwave; le informazioni e le modifiche
reperibili nel messaggio e nella documentazione on-line sono piuttosto
interessanti e consentono, tra l'altro, di espandere la gamma
operativa del '71 da 0 (anche se conviene farlo partire da almeno 10
kHz) fino a 37 MHz circa.
73
Fabrizio Magrone, IK4MTG
NOSPAM....@mbox.queen.it
   (Togliere NOSPAM.)
-----------------------< cut here >--------------------
MEMORY BOARD / BATTERY:
About ten years ago I built a simple interface and wrote a very basic
program to read and write to the Icom memory boards.  I used this to
set the upper and lower band limits in my R71A, and to adjust the
frequency display offset versus mode.  Both of my R71As now tune from
10kHz to 35MHz and display the exact "zero-beat" frequency on the
display for all modes.  For example, in CW the display reads 10.000.0
with WWV's carrier in the center of the CW filter's pass at my
favorite beat frequency.  Also, with the BFO optimally set for the
narrow SSB filters, both USB and LSB read 10.000.0 when I zero beat
WWV. 
The circuit uses a CD4040 to generate the address bits and a 78L05
voltage regulator.  It interfaces to any standard bidirectional
parallel port.  I have also included a "factory" file for the R71A
memory board.
73,
Andrew
N2CBU
Icom RAM Module Editor and R71A Modification Info:
http://www.geocities.com/Eureka/Business/4247/Icom/ICOMRAM.ZIP
R71 FM-Unit Manual (EX-257):
http://www.geocities.com/Eureka/Business/4247/Icom/ex257.pdf
R71 Component Placement Diagrams (Large - 5MB):
http://www.geocities.com/Eureka/Business/4247/Icom/layout.zip
Manual for EX309:
http://www.geocities.com/Eureka/Business/4247/Icom/EX309.PDF
Manual for UX14:
http://www.geocities.com/Eureka/Business/4247/Icom/UX14.PDF
Manual for RC11:
http://www.geocities.com/Eureka/Business/4247/Icom/RC11.PDF
Notes on replacing the plastic trim caps on the VCO board:
CERAMIC TRIMMERS:
Ceramic trim caps are available from Digikey (
www.digikey.com
) for
considerably less than from Icom.  For my R71A  receivers I used
Digikey part numbers "SG5R015" (2-5pF) and "SG10015" (3-10pF.)  Note
that for the R71A Icom recommends replacing C97 with a larger value
trimmer, therefore you need ONE of the 2-5pF trimmers and THREE of the
3-10pF trimmers.  I also replaced the plastic trimcap in the notch
filter circuit with one of the 3-10pF units and I plan to replace the
plastic trimcap in the BFO as well.
My receivers did not exhibit any problems before replacing the
trimmers, but I performed the operation anyway.  Afterwards I found
that the receiver was "quieter" than it had been and the MDS is indeed
lower by several dB (better sensitivity.)  I did not make any
measurements before replacing the trimmers since I was not expecting
any side-effects.  I assume this is due to less phase noise being
generated in the VCO because the ceramic trimmers likely have a higher
Q-factor then the original plastic trimmers.  If this is indeed a
side-benefit then perhaps it would be worthwhile investigating higher
Q-factor sapphire trimmers from Voltronics or Johanson.  I do see that
after replacing the trimcap in the notch filter circuit the notch is
deeper and sharper (and a little touchier to tune.)
Note- I found that it was easier to unsolder and remove the shielding
box surrounding the VCO from the PLL-Unit circuit board than to
unsolder the box's cover.