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  Spectra Dual Radio
Configuration Procedure

By Josh Wallace KD5QCZ
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I had done a from-the-ground-up Spectra dual-radio write-up a while back and never posted it. This was done a couple of years ago for a friend who wanted a dual-radio kit for his space-limited mobile install using a pair of un-hacked normal A9 mid-power radios as the building blocks. However, since you will be writing completely new MOFLAG strings into both radios you can use any A4/5/7/9 Spectra radio. The only radio that cannot be used (ironically enough) is a factory A3 radio, as it uses a different MLM and a different inter-connect board.

Before we begin, let me preface this by saying that both of my radios were black-tagged and had version 6.xx MLMs. Dual-radio/SIU capability does not seem to be tied to a specific MLM version as has been opined previously but it may well require version 6.xx or later. Maybe one day I'll haul out a version 5.xx C9 800 trunking radio and try it; who knows?

You will need the following items:

We'll start with building cables to go from the radios to the SIU box from stock HKN4536 Spectra remote-mount cables. You can use external ASN boxes as per the original setup, but again it simplifies things to just use a straight-through cable. I don't know if the SIU will let you drive internal SecureNet via the switch on the HHCH; it's worth investigating. The length probably doesn't matter but to conserve space I kept mine under 3 feet.

Factory DB25FColor (Use)New DB25M
1Black/Green (PTT)NC
5White (SB9600 Bus+)2
9Black/Brown (Detected Audio)NC
10Shield for 9 (Analog Ground)NC
11Shield for 12 (Mic Hi-)12
12Black/Yellow (Mic Hi+)13
13Purple (Emergency)NC
14Black (SB9600 Bus-)3
16Brown (Spare 1)NC
17Red (Spare 2)NC
18Blue (Digital Ground)9 and 18
19Black/Orange (Reset)1
21Bare (SB9600 shield carrier)11
22Yellow (Sw B+)14
23Black/Red (SB9600 Busy)4
24Green (Speaker-)24
25Orange (Speaker+)23

Editor's Note: The SB9600 BUS+ (pin 5) and SB9600 BUS- (pin 14) wires are a shielded pair with the shield going to pin 21. Some Motorola documentation shows these wires as in the table above, while other diagrams show the white and black wires swapped as in a twisted pair. Ohm out all wires to make sure they go to the desired pins.

Now comes the fun part: hacking and programming the Spectra radios. This complete process will have to be performed on both radios you plan on using.

  1. Start by programming all of your modes, frequencies, MDC IDs, scan lists, etc. with normal Spectra RSS and writing to each radio with it connected to your working A9 head. Leave the mode names at default since you won't need them later. Save that code plug with normal RSS and LAB RSS in case you flub a step later and need to start over.
  2. With the radio and A9 head still connected to the programming setup, go into Lab RSS but don't read it.
  3. Go into BitBanger and write the following string to the following locations. The first column deals with data in the MLM, and the second column deals with data in the Command Board. You must write the same string into both the MLM and the Command Board memory. All values are hexadecimal.


    When you exit out it will automatically write the radio, which will then display FAIL 01/82. Don't worry, this is normal, caused by a checksum mismatch with the new feature strings you just wrote.

  4. Exit out of Lab RSS and go back into normal RSS. With the A9 head still attached, read and write back to the radio without changing anything in the programming. It should now display no fail codes and appear to be operating normally.
  5. Go back to Lab RSS, read the radio, then go into the MOFLAG menu.
  6. Look for and change the following settings:
    1. Moflag 4, Bit 4 - Mode_names - Set to "Disabled"
    2. Moflag 8, Bit 5 - S9k_control_head - Set to "Disabled"
    3. Moflag 9, Bit 0 - multi_radio_system - Set to "Enabled"
    4. Moflag 13, Bit 5 - SIU - Set to "Enabled"
    5. Do not change anything else.
  7. Exit out to the main menu and write to the radio. You may get the warning that the feature set doesn't match the radio, blah, blah, blah; just go ahead and write it. If everything is going right so far, the code plug size should drop from about 40-50 blocks down to about 5-12. This is because it isn't writing to the A9 head anymore. If the code plug size is still 40-50 blocks, you missed a step somewhere; go back and double-check your work.
  8. Go back to regular Spectra RSS. Go to F9 (Setup), then F4 (RSS Configuration) and set "Multiple Radios" to "Enabled." Hit F8 (Save) then F10 to exit.
  9. With the A9 head still connected to the radio, go to your new F2 (Radio/ASN Group Conversion) menu. Hit F2 (Read Radio Type). "Current Radio Group" should display as "Normal."
  10. If you want your setup to match the factory labeling on the HHCH, you will need to set your UHF radio to "Main" and your VHF radio to "Aux." This is done with up/down arrow keys.
  11. Once the correct type is selected, hit F7 (Conv Radio). If you followed everything correctly, the "Current Radio Group" field will change to whatever you just selected after a brief program cycle. If it doesn't and still displays "Normal" then you missed a step somewhere; go back and double-check your work.
  12. You may now disconnect the A9 head and connect the radio to the SIU.

Use the Radio 1 port on the SIU for your "Main" radio and the Radio 2 port for the "Aux" radio. If you reverse them, transmit mike audio will not pass. On the HHCH end of the HHCH cable there are three plugs; the orange/green plug is for Radio 1's speaker and the black/black/red plug is for Radio 2's speaker. The 6-pin plug with 4 pins populated is for a DTMF pad that I haven't seen the documentation for. The orange and green wires on the SIU end of the HHCH cable work identically to a normal Spectra's ignition sense leads; green is constant 12V (for RX control) and orange is switched (for TX control). Or you can connect them both to constant 12V and control it from the Off/VHF/UHF switch on the HHCH. I also strongly advise running either braid or 14-gauge wire between the SIU box and the chassis of one (or preferably) both of your Spectra radio drawers to beef up the SIU's flimsy grounding. Additionally, the HHCH cable may have a stray black wire coming off the HHCH end; it's connected to two shields in the cable and can be connected to chassis ground if you're having problems with alternator whine or other noise in your transmit audio.

The SIU RSS programs using the same Spectra high-power cable and RIB you used for the radio programming, and can be connected to either radio to read/write. Its only function is to program mode names over 99. If neither of your radios goes over 99 channels, you don't need it at all, even when using a NIB/unused SIU. You can use it to program your channels with MaxTrac-style trunking labels if desired, like 1A, 2C, etc.

One final note: the SIU and HHCH can be used with any single A9 radio as-is. The MOFLAG work is only necessary to use two radios in a dual-radio configuration.

Acknowledgements and Credits:

Credit goes to BatBoard user natedogg223 for the original MOFLAG documentation and to BatBoard user Jim202 for the cable pin-out.

Contact Information:

The author can be contacted at: hishy [ at ] mototaku [ dot ] net.

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This page originally compiled 14-Jan-12.

Article text © Copyright 2012 By Josh Wallace KD5QCZ.
Converted to HTML and Repeater-Builder format by Robert W. Meister WA1MIK.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.