Icom IC-575 (IC 575 IC575) transceiver mods reviews software and diagrams

   
 
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18 April 2014, 21:47 UTC 


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Icom IC-575 (IC 575 IC575)
IC-575
Programming interface schematics for Icom:
Programming software for Icom IC-575 (IC 575 IC575) :
PDF User Manual for Icom IC-575 (IC 575 IC575) :
PDF Service Manual with schematics for Icom IC-575 (IC 575 IC575) :

Mods for Icom IC-575 (IC 575 IC575) :
    Icom IC-575 (IC 575 IC575) General Coverage TX Modification
    Icom IC-575 (IC 575 IC575) Pass band Tuning Modification
    Icom IC-575 (IC 575 IC575) Power control modification
    Icom IC-575 (IC 575 IC575) Restoration of pass band tuning
    Icom IC-575 (IC 575 IC575) Splitting into RX- and TX paths
    Icom IC-575 (IC 575 IC575) Modification of cw pass band (BFO)
    Icom IC-575 (IC 575 IC575) Disabling of SBB squelch
    Icom IC-575 (IC 575 IC575) Very fast AGC
    Icom IC-575 (IC 575 IC575) SSB RF Gain
    Icom IC-575 (IC 575 IC575) Tuning speed
    Icom IC-575 (IC 575 IC575) Frequency range & CTCSS tones
    Icom IC-575 (IC 575 IC575) Freq. steps mod

Icom IC-575 (IC 575 IC575) technical specifications :  Icom IC-575 (IC 575 IC575) technical specifications

com IC-575 (IC 575 IC575) Power control modification

Problem:

The power control circuit in IC-x75 is an ALC circuit. ALC circuits suffers from several drawbacks:
  • slow reaction time due to time constants

  • insufficient regulation due to low feed-back factor

These factors gives the problem that if the average power has been set to a low value (e.g. for driving a HPA), peak power can still be in the order of 3-4 dB higher. This leads to either considerable side band distortion or a low average power output.

note: If you are always using your transceiver barefoot, without connecting any PA or transverter, this modification will offer no benefit.


Solution:

The solution to these problems is to use a simple forward gain regulation without the feed back circuit of the ALC. The original ALC is still kept for SWR protection only.

The ALC is working on gate 1 of Q13, which is a IF amplifier (9 or 10.75 MHz). The new power regulation uses gate 2 of Q13. Therefore the two circuits can exist in parallel.

The modification should also give you a bigger dynamic range in the power regulation (lowest power < 5W on the IC-x75H).


Implementation:
  • replace R87 (470k) with 100k

  • cut "POCO" wire (pin 3, P1/J1, MAIN, orange) at the plug (P1)

  • connect the "POCO" wire to gate 2 of Q13 (e.g. via top of R87)

  • adjust R250 (SWR protection), R256 (low power level) & R259 (high power level) fully counter-clockwise. (this will give you full SWR protection, but cancels the ALC in normal operation).

  • put the front plate RF PWR in full output position (clockwise) and adjust R82 (Q13 output attenuator) until you have the nominal output power (initially the output power will be higher because you removed the regulation, but the PA will be saturated).

  • the balance between FM, CW & SSB output can be adjusted with R137 (CW carrier level) & R105 (FM carrier level).

  • other interesting adjustments: R135 (mixer balance i.e. SSB carrier suppression), R133 (TX BFO output level).


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