MIDLAND 70-1630A on 70CM'S
by Brad Wooding VK3TAE

Last update 11-03-2005

The Midland 70-1630A is a 403 to 420Mhz ant he 70-1630B ia a 440 to 470Mhz radio.  The radios can be converted to 430 to 440 Mhz with a bit of time and patients.  These radios are 22 ch and have an option for 99ch with an addition of an extra board.

In Feb 2002 there came a lot of these units available from the Royal District Nursing Service.  The radios came with an extra modification.  The Emergency button function was added to the unit.  The scan button was removed and a Red push button was fitted in its place.

Scan  After removal of the emergency function board the red button can then be used for a scan button without any mods to the head.  You must program the Scan in Group 2 as Group 1 uses the Call Button.  This is done in the Freq entry page

Audio Mods When removing the Emergency function board you remove the power to the audio line that runs the 9.5v to drive the mic amp in the mic hand set.  You have to replace R401, a 270 ohm resistor. This was removed when the controller board was installed.

To save the removal of the whole RF board which takes quite some time to unscrew the 21 screws, links and plugs.  I have came up with a board mod to do from the top of the radio.

The photos shows the empty slot for R401.  Note the pin size, through hole that goes to the upper side of the board. This is underneath the RF Board.

           
   R401 is removed and Through Hole                                This mod is done for the contl'r/selcall unit.  

                    Not used in a std config, no need to remove it as it goes to J408/3 which is N/C

The resistor is soldered into the through hole and then to Pin 6 of J410 providing 9 volts for the mic audio.
The through hole is located next to a surface mount resistor and a transistor just below the trim pot.

Downloads

Schematic Diag     1630a-cct01.pdf    (626kb)
Sch Audio Fix Diag 1630a-cct02.pdf  (105kb)
Power Connector  1630apwr.pdf          (42kb)

Programming Manual Edit

The radio is programmed by a PC and a serial/TTL converter cable.   The radio uses the normal XTR software.
(don't ask me for a copy of the S/W).  The S/W will not allow out of band 430 to 440Mhz band so all frequencies have to be programmed by the manual edit function in the S/W.

Programming Out of Band software mod.

The xtr.chl file contains the band limits.  Before you edit this file I recommend you make a copy of the file and call it oldorig.chl.  Edit the xtr.chl using xtgold or a text editor. Simply change the 4500 to 4300 B Band or 4300 to 4400 A Band.  Other bands can be altered to suit your needs.  Then save the changes and run the xtr.exe program.  Remember the VCO will only go out of band so far so a 10Mhz limit should do any more and you are pushing it.  The VCO is usually at rock bottom at the 10Mhz out range.

I would like to remind you all, that the above information is used at your own risk.

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11/03/2005 KEY-COM COMMUNICATIONS (C) 2002                     keycom.com.au