Modifications for the ICOM - RogerK

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 W9FMWNote:From Bill K7RIEICOM has not tried this mod nor have we verified this problem.This modification is read 731 times.top of page19-07-1998(IC-271) VOX of an IC-271,471,1271 usable for FMHow to make the VOX of an IC-271,471,1271 usable for FM :1'st type of 'main-board' :The only thing to be done is to add a diode such as 1n4148 or bax13 on the MAIN board on the position D74When D74 is inserted ... the vox works in FM also.The diode is on the shematic diagram of the Main board but is not mounted on the pcb in the factory.73's de stefaanON4BY @ ON4HU16/03/1990 18.31 h2'nd type :(On this board a D74 is present (near PA- and RF-YGR- Unit))(It might be not present in the plans !)Disconnect the cathode of D69 from it's old postition. It's new position is the cathode of D50 or D51name ! position on main board ! (old) function !D69 ! near 'CW-DELAY'. ! 'FM -VOX-OFF' ! FM 8VD50 ! near 'RF-YGR-Unit' ! 'USB-VOX-ON' ! USB8VD51 ! near 'RF-YGR-Unit' ! 'LSB-VOX-ON' ! LSB8V20/03/1990This modification is read 685 times.top of page