Modifications for the ICOM - RogerK

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19-07-1998(IC-275) PSK Transmit Audio Modification for ICOM IC275 & IC271From AMSAT-Australia Newsletter #59 (Graham Ratcliff, VK5AGR)After reading a FUJI-OSCAR-20-PRBBS message from James, G3RUH, regarding the modifications he made to his Yaesu FT736 toimprove the PSK transmit audio, I decided to investigate the situation on my ICOM IC275H to see if the same problem existed. Iwas certainly less than satisfied with the results I was getting in the first few days with FO-20 Mode JD. I was feeding the TXaudio in at the front microphone socket and results on the uplink were quite poor but my downlink copy was 100%.The first change I made was to move the Tx audio to the rear connector, ACC1. Results improved but I was still not satisfied.Some scoping around the Varicap diode, D40, revealed considerable distortion of the PSK audio. To prove if this was the cause ofmy problem I studied the IC275 circuit to see how I could feed the TX audio in as close to the Varicap modulator diode, D40, aspossible.In the IC275H there are several Audio feeds to D40, including 3 via Q33, and in my unit one of these, the feed from the ToneSquelch is unused. P46 normally plugs into the Tone Sq card but as this option is not installed it is left unterminated inside therug. I also found that Pin 1 on ACC1 was unused so a shielded wire from P46, pins TSTN and GND to ACC1, Pins 1 and 2 wouldgive easy access from outside the rig to D40 and NOT alter any of the existing functions of the IC275H.The installation of the wiring is not as easy as it sounds however:(1) You have to find a way to connect P46. I stripped a small amount of insulation from the wires just behind the plug housingand soldered the extension wire there.(2) To gain access to ACC1 you must remove the PLL PCB that it is mounted on. With the board removed I soldered theextension wire to the underside of the board taking care not to short out any surrounding tracks. The whole exercise took about30 minutes.You will probably need more audio level from you PSK modem (see changes recommended by G3RUH in his FT-736 discussion).You can then use the pot, F151, in the IC275H to set the TX modulation level.Results from making this change have been outstanding with many less retries on the uplink than previously. The waveformbeing applied to the Varicap diode is now identical to the output from the modem.Performance via LUSAT and PACSAT digipeaters have been equally pleasing. EXTRA hint: Use DWAIT=0 RESPTIME=0 and startTXDELAY=100 ms and reduce to as low as possible for your radio - I use 30 ms.A similar change could be performed on the ICOM IC271 by wiring to J12 on the Main Board. J12 is normally unused inAustralian IC271's.Since the above article referred to G3RUH's FT-736 discussion, I sent a message to James Miller G3RUH on FO20 and asked himto repost it on the bird. I had lost the copy I downloaded since I did not anticipate any need for it.Jack - the notes about mods to the FT736R were specific to that machine, and won't be relevant to the IC735.1. What you need to do is work out a way to belt the varactor directly. Then inject a square wave (1200 hz will do) andmeasure the deviation that results.2. You can do this measurement with either a proper deviation instrument or more likely with a monitor RX, by looking at theoutput from it's discriminator.3. You can calibrate the monitor RX quite easily, Tune in a steady unmodulated carrier and note the discriminator DC outputvoltage Change the RX frequency by 1 Khz (knob on the RX front) and note the change in DC voltage. That gives you themonitor RX sensitivity in volts per Khz.4. Now return to the TX, and adjust that driving square wave to give you approx +/- 3 kHz, you want to see about 6x voltspeak to peak square wave on the monitor. (Somewhere between 4x and 6x will do, no more.)5. Now return to the modem and juggle about with the TXAudio output components to achieve this level of drive signal, andlook at the monitor RX too.6. When you have done this, which should take you all of 30 minutes, you should be in business. If you can't get squarewaves TX to produce squarish waves out of the monitor RX, then the varactor dept. must be suspect, and so on.All is fairly logical. Hope useful. Let me know the results.73 de James G3RUH @ GB7SPV 1990 Mar 28Since I am not going to be able to try the mods until I return from a vacation I won't be able to give you an answer as towhether they work or not. But it is my opinion they will. What is happening is that between the mic connector and the varactorthe digital signal is being badly distorted and the bird does not respond to the digital signal. This would not make muchdifference on voice but on a digital signal it makes all the difference in the world.Please feel free to contact me further if I can be of any further help.Best regards Jack W9FMW
Note:From Bill K7RIEICOM has not tried this mod nor have we verified this problem.This modification is read 724 times.top of page19-07-1998(IC-275) IC-275 Freq. steps mod.Titolo: Tuning steps change for all mode Icom IC-275/475/575/1275The IC-275/475 FM-Step selectmatrix use these diodes on the front unit: (type 1SS53) D41, D42, D43, D44, (D45), D46Note: diode D45 is not present but solder holes exist for it on the board just between D44 e D46installed diodes are marked with X :(*) (*)D41 D42 D43 D44 D45 D46 D48 Steps DB4 DB5 DB6 DB7. . . . . . . 10.0 Hz. . . X . . . 100.0 Hz 1 0 0 0. X . . . . . 1.0 KHz 0 0 1 0X . X . 5.0 KHz 1 0 1 0. . . . X . . 10.0 KHz 0 1 0 0. . . (*) X X . 12.5 KHz (*) 1 1 0. . . . . . X 25.0 KHz 0 0 0 1X . X . . . . 1.0 MHz 0 1 0 1(*)To set a step of 12.5 KHz in FM mode (TS button off) it is not necessary disconnect the diode D44, just insert the diode D45(IN4148 or similar) near D44 and "voil? les jeux sont faits".Unscrew the two lateral screws and unlock the front panel.Remove also all the connectors of the front board and after that unscrew ALL the screws of the metallic shield covering the frontboard. It seems too much complicated insert the diodes from the component side of the front board, so it is better insert D45from the solder side.This modification is read 812 times.top of page19-07-1998(IC-275) Band Expand for ICOM IC-275E/H and IC-275A/HTo expand RX range delete D 44To expand TX range delete D 27 install D 43Range 138-174 MHz TX not in full range PLL lockoutThis modification is read 952 times.top of page19-07-1998(IC-275) IC amplifier oscillatesNote:This service bulletin is meant for technical personnelwith experience working on solid state communicationsequipment. Damage caused by improperlyinstalling this modification may causeICOM to charge for subsequent repairs to theproduct. ICOM does not warrant this modification.Bulletin #: 588-001Subject:If the IC amplifier oscillates when the noiseblanker is turned on and the FL-83 CW narrow filteris installedProcedure
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Modifications for the ICOMcreated 2
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(IC-271)(IC-271)(IC-271)(IC-2710)(I
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(IC-475)(IC-475)(IC-475)(IC-475)(IC
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(IC-756pro) Expand tx-freqeuncy for
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(IC-W2E)(IC-W31)(IC-W31)(IC-W31)(IC
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2. After about 0.5 second, press st
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21-10-1999(AT-500) ICOM AT-500 Tune
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4. Program the radio to the local w
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19-07-1998(IC-03) ICOM 02/03/04 & V
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This modification is read 553 times
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6. Reinstall the RAM board into the
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27-10-1998(IC-1275) Power control m
Page 25 and 26: 27-10-1998(IC-1275) Modification of
Page 27 and 28: ●Connect the short plug end with
Page 29 and 30: This modification is read 1316 time
Page 31 and 32: 50MHz to something like 204MHz cont
Page 33 and 34: 26-07-2001(IC-207) Band Expansion f
Page 35 and 36: This modification is read 4219 time
Page 37 and 38: Fig. 3: The circuit extract from IC
Page 39 and 40: 19-07-1998(IC-22) Icom IC22S Packet
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Page 43 and 44: More detailed:In the true spirit of
Page 45 and 46: 19-07-1998(IC-229) IC-229H Fix CPU/
Page 47 and 48: In addition, if you want to put an
Page 49 and 50: By diode:●●Remove D17 diode on
Page 51 and 52: 1. Remove diode D14 (if there is an
Page 53 and 54: cut... I'm guessing, but it could b
Page 55 and 56: 19-07-1998(IC-24) IC-24AT enabling
Page 57 and 58: 19-07-1998(IC-24) Tip to to functio
Page 59 and 60: This complete the mods done with su
Page 63 and 64: Comment:These TRX is accorded to my
Page 65 and 66: this mod of use as I have.Any comme
Page 67 and 68: other wires come in. Take the cable
Page 69 and 70: 17-11-2000(IC-2700) Enabling ICOM 2
Page 71 and 72: 19-07-1998(IC-271) IC-271 / 471 fue
Page 73 and 74: RAM card version B images:This modi
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Page 79 and 80: 19-07-1998(IC-275) Improve the stab
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Page 83 and 84: Note: a strong signal will be serio
Page 85 and 86: 19-07-1998(IC-28) The long, noisy s
Page 87 and 88: not a hard mod to do,..........but
Page 89 and 90: 02-04-2000(IC-2800) IC-2800H cross
Page 91 and 92: 19-07-1998(IC-281) Extended Receive
Page 93 and 94: encased it in shrink-tube. The oper
Page 95 and 96: push buttonswitch ^ ^| |___________
Page 97 and 98: 19-07-1998(IC-2IA) IC-2IA lousey xm
Page 99 and 100: 1. Change to RECEIVER MODE (not rec
Page 101 and 102: 13.0V 5.0W12.0V 5.0W11.0V 5.0W10.0V
Page 105 and 106: MODIFICATION (Refer to figure 1.)1.
Page 107 and 108: Procedure1. Remove the covers from
Page 109 and 110: 19-07-1998(IC-3200) Fix for IC-3200
Page 111 and 112: 4. select a frequency of 150.000Mhz
Page 113 and 114: 19-07-1998(IC-3220) How to iface Ic
Page 115 and 116: Now power on and type in the freque
Page 117 and 118: One note on the above - the BNC con
Page 119 and 120: e shorted to ground and cause PLL u
Page 121 and 122: 19-07-1998(IC-451) IC-451 aus 9600F
Page 123 and 124: 3. If by accident you lose power to
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Problem:This is a general transceiv
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Note: a strong signal will be serio
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Das spart einen mords Haufen Arbeit
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Dieses ist mit dieser Schaltung als
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X . X . 5.0 KHz 1 0 1 0. . . . X .
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Remove the back cover. If you place
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27-10-1998(IC-575) SSB RF GainProbl
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26-06-2001(IC-575) Pass band Tuning
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The trimpot leads will need to bent
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19-07-1998(IC-706) Info/mods for IC
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¦ ¦¦ ¦¦ ¦¦ ¦¦ ¦----------
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●●●●●●●●●●●
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From: gary@ke4zv.atl.ga.us (Gary Co
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Mehr Dynamik in der Modulation beko
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Operation:Be sure to read the manua
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Alternative zum modifizierten PC St
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●●●●●(Another receiver wi
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| IC31 uPD4094BG || |1 2 3 4 |5 6 7
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D116 and D118 are responsible for o
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Transmit power output after modific
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This information and photos was sup
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22-02-2002(IC-706MKII) IC-706MKIIG
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This modification is read 2320 time
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Delete cap. CT14 at pin 6 of IC3 on
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18-06-2000(IC-729) Using two Icom r
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19-07-1998(IC-735) IC-735 Remote Wo
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19-07-1998(IC-736) Icom IC-736 DDS/
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Also probably would apply to IC 735
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RAM card version B images:This modi
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John Schmitz NS8EAdditional informa
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13-01-2002(IC-746) Monitor Audio Ou
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19-07-1998(IC-751) IC-751 Bad Cap P
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inspect your job to be sure that th
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28-01-2002(IC-751) ICOM IC-751 Dual
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Step 8: Turn the radio off and inst
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To be neater you could remove the s
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[W804] | |Remove=>[W805] | CHIP |[W
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Date: 23-02-2002 User comment From:
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less.The second way to adjust the I
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23-11-2001(IC-756pro2) IC-756PRO2 T
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19-07-1998(IC-765) Icom IC-765 Pass
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19-07-1998(IC-775) New product info
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70% AM.My personal findings are tha
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11. Re-install board and all cables
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The Yaesu FT726R first appeared ten
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There seemed to be no way of changi
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Add a diode on the blank position b
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---- gar keine Diode ----Breitband
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To disable the x-band repeater just
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Well this should make things verry
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Set radio in VFO mode, and select f
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27-05-2001(IC-910) Expanded functio
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●●●350-470 MHz RX/TX800-950 M
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1. You're completely successful.2.
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●●●●●●●●●Für Han
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28-03-1999(IC-Q7) Modifying the ICO
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●●●●●●●●Desoldering
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You should now have the RF board co
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BOOT:Attenuator protecs strong sign
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1. Use an ohmmeter to determine whi
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2. Remove battery cover and battery
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Fig. 4. Receiving AO-40 (at MA=13)O
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This modification can also be found
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The Q and not Q outputs on this IC
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Date: 30-12-2001 User comment From:
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Removing 1F unit1. Pull the 2 knobs
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16-05-1999(IC-T8) Problem with the
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800 -
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Frequencyrange after modification:5
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Offset Freq: Hold [FUNC], Press [4]
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The Icom IC W21AT handi-talkie norm
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19-07-1998(IC-W2A) IC-W2A signal le
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19-07-1998(IC-W31) IC-W31E CROSS-BA
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15-10-2000(IC-W31) Cross Band Repea
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could always try it.Set VHF and UHF
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31-07-2001(IC-W32) Icom IC-W32A pro
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IC-4GAT - Turn the radio on, hold [
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IC-M9 - Hold [HI/LO] & [DW/SCAN] bu
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IC-275H 10IC-375A 12IC-471 22IC-475
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I have tested this mod with a ic-75
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How further up the hole is the bett
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Connect the NTC, FAN and power and
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5, 31, 48, and 79.4. Does the Prior
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19-07-1998(R-7000) Modify your ICOM
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1. C231 from 1000 pf to 68 pf.2. C2
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19-07-1998(R-71) Tricking the ICOM
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There are two wires which send logi
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A. Remove the top cover of the rece
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08-11-1998(R-7100) Modify your Icom
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17-03-2002(R-7100) Icom R7100 Discr
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23-08-1998(R-8500) Operating the Ic
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Modifications for the ICOM - RogerK

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