Information on the MX800 Base Station from Spectra Engineering

General Info

The Mx800 is a great base station for amateur use. The 220 MHz versions are now on the surplus market from Passport trunking systems that have gone bust in the mid 2000's. Motorola OEM'd these systems as a standard part of their passport config.

As they were commercial stations, they are mostly narrow band FM only. Some are switchable, but most will require a filter change and re-calibration of the transmitter to work on 5 KHz deviation used by amateur radio. The manual has a procedure on how to convert the receiver if you have SMD rework equipment.

Most will require a firmware upgrade and you may wish to put a CTCSS/DCS decoder in them if you need that. My standard setup uses the CTCSS board, audio delay and Raspberry Pi based allstar controller. The advantage to the RA-35 interface is if the RPi goes offline it will fail over to in cabinet local repeat with ID on the built-in controller.

The jumpers, dip switches and nomenclature can be confusing. I've resorted to tracing out the diagrams to understand the logic inputs and have presented the settings here as my standard configuration. This may not work for everyone and there is certainly more telemetry and IO which can be done with the Mx800.

Mx800 decoding DCS
Mx800 decoding CTCSS
Mx800 Receiver Filters changed to wide band
Mx800 Receiver Filter
Mx800 PA
Mx800 PA closeup
Mx800 PA closeup
OEM compatible DCS/CTCSS module
== Known Issues ==
There has been one report of some of the electrolytic capacitors leaking, but I have not seen this
=== Power amp in the ham band ===
These 218 MHz amps are not happy doing less than about 25W. Some have displayed spurious emissions when operated out of this 25-50W envelope.
The below was a soft amp:
I've found the power out to drop off to less than 50 W (40W normal) at 225 MHz. Not sure what causes this, but I'll need to test further.
===
== Dip Switches and Jumpers==
=== SW 2 ===
SW2 sets several operational cases of the station. Of the most important there is a repeater controller enable built in. This should be disabled for ham use.
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SW 2
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Function
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Description
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Best for Ham
=== Jumpers ===
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Jumper
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Function / Description
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Default
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Position for
Ham use
This isn't really a "compressor" but an amp on the VF input.
Select either Wide Band or Wide Band filtered and limited or nil.
Wide Band filtered and limited means DC-4000 Hz and limited for deviation. This will have some processing on it.
Wide Band is a direct connection to modulator with no limiting.
Disables RX VF to line and TTR VF. The function polarity or nil can be selected.
This is the most convoluted description.
RX VF is the RX to line output. You want this output to be there regardless if there is a CTCSS/DCS tone detected by the repeater. Setting this to active low makes it output by default in conjunction with setting of Jumper 25.
The function polarity or nil can be selected. Note that this control is in parallel with DIP SW 2/3
All bussed bases are ‘listeners’ on the modem RS232 TX port. All bussed bases have their RS232 TX ports diode to the modem RX port.
No resistor fitted. D10 out of circuit.
4K7 resistor across D10.Configure at least one and no more than four MX800 in this mode when multiple units connected.
D10 fitted, no resistor. Configure balance of bussed units in this mode.
To use mute defeat remove JMP12 and fit JMP 25.
The control signal polarity can be inverted by changing the position of JMP25
This enables the routing of the Wide band input through a 300 Hz Low Pass filter. Ideal for an external CTCSS level
= Interfacing =
Most interfacing can be done with the DB-15 port on the back, known as CN1 - Line IO. This is mapped to SKH on the PCB.
== CN1 ==
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DB-15 Pin
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SKH Pin
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If you want TX VF input to be looped to the RX audio output when active set Jumper 9 to the appropriate position depending if input is high or low.
If this jumper 9 is not placed and jumper 26 is enabled, the filtered CTCSS from the receiver will be output on this pin. This can be used for other functions externally.
M-LEAD is what most hams want this will give an output when configured in MX tools that COS and PL/DPL are detected. If you want to have an external controller have a PL input you want this as the PL input.
DC-FM input (JMP8 in position 1-2)
Wide Band input: (JMP8 in position 2-3) AKA direct modulator input mode
CTCSS Input: (JMP27 in positions 1-2)
TX Subtone audio may be injected into this connection point. Input sensitivity is Fixed at 1Vp-p. AC coupled
The RF mute status may be monitored by reading this voltage. +5volt logic signal indicates mute status. This output is not CTCSS dependent. Output impedance approx 100ohms. The polarity is selectable via the internal jumper JMP17.
Receiver audio output from op-amp. Default nominal line level is set to -10dBm. Unbalanced output with common return to analog Earth.
= DCS Decoder =
IC18 is the output latch for the LEDs and pin 12 will go high when M-LEAD is active. This is a convenient place to get an active high for DCS/CTCSS active.
= W9CR alignment procedure and setup with Allstar =
== Initial Alignment ==
It's important to align the Mx800 before trying to integrate the external controller or audio delay board in the unit.
All audio levels are calibrated for -10 dBm (600 ohm) as line level.
You'll need a DB-15 connector with an DC blocking cap for testing.
Study the procedure on the pages 77-82 of the manual as this is used for the majority of the alignment.
=== Procedure ===
Setup the following channels:
If aligning for a specific frequency, use that in place of 224.400
==== Model Number ====
Using the access code "solderadv" in MxTools, set the model number to 25 KHz channel width.
==== PA Calibation ====
Set the sliders to lock for all channels and enable realtime updates.
With the power out slider set to maximum in the channel display of MxTools, adjust the three tuning capacitors on the PA for maximum power output.
Preform a PA calibration after this from MxTools.
Now set the power to the desired power in the channel config. Typically it's best to set this at 25-50W
==== Peak Deviation and Modulation Adjustment ====
For Wide Band with CTCSS '''use a peak deviation of 4.400 KHz.'''
'''JMP8 needs to be set to 1-2 for the Wide Band Input.'''
When complete, select OK on the channel screen and then write the channel data to the Mx800
==== TX Center Frequency Alignment ====
==== TX Line Input Level and Nominal Deviation Alignment ====
JMP- Ensure the VF compressor is enabled.
JMP-8 set in position 1-2
===== Setup limiter gain =====
===== Setup line audio input gain =====
For some fucking reason they call this TX VF gain in the manual.
Ensure the VF compressor JMP-4 is in position 1-2 (enabled)
General idea is -10 dBm should give 60% deviation (3khz).
===== Setup repeat audio gain =====
For some reason they call this TTR gain. I think they just want to be different in .au
===== RX Line Output Level Adjustment =====
==== Squelch Threshold Setting ====
Again they call this "mute" for some reason. It's the squelch setting.
This should complete the basic alignment and your station should be set to -10 dBm line level for 60% deviation on receive and transmit. Channel 1 is setup to duplex and Channel 3 is setup to repeat.
== Integration of the audio delay ==
I find wire wrap wire works well for connecting from the audio delay to this SKK connector
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SKK
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ARS
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Fuction
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Color
The below shows the hookup using this color code to the audio delay board.
Set the level control for the same input as output, this will ensure the rest of the station alignment stays the same.
The delay may be adjusted, but I find 50-100 ms is more then sufficient. The delay board from Spectra Engineering is only 40 ms and not configurable.
Double sided tape can be used to secure the delay board in the unit. Try not to route wires close to the CPU or other digital parts.
== Audio interface board and Pi setup ==
=== Physical install of parts ===
The board and Pi will sit on the exciter and receiver as shown using adhesive standoffs. Ensure you don't have any screw heads hitting the underside of the board.
The Cat5 cable is routed out the back of the unit through the square hole under the power connector.
==== Wiring up the audio interface ====
Wire up following the table below. I remove the DB-9 on the RA-35 interface to make it easier.
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RA-35
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Location
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Function
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Color
East of uP
SIP-1 pin 8
These pictures show how everything is wired up. Since this is all internal the DB-15 is still usable for external interfacing if needed.
Audio IO mx800 SKH
PL Active High (M-Lead) tap point
Selection for Fail-Safe to channel 3

Configuration of Mx800 MxTools settings

Ensure the jumpers on the controller board are configured properly.

Hardware settings

TX Reference - 13 MHz
RX IF 90.0
RX Low injection
Delayed audio option checked - only added tail time into hang calculations.
Local Remote function: enabled
Subtone DCS option: installed
LED settings: Standard
Microphone not installed
Digital IO port active state: Low
Channel spacing: 25 KHz

Alarm settings

Power supply monitor: out of range shutdown enabled
Temperature settings: Fan on 35c, Over temp shut down 85c
RF low power alarm, 25W -- Make sure this is below the actual setting for the channel if you set it to less the 50W
Low voltage Alarm, Trip point 11v, clear point 12v
VSWR trip point: 3:1
Alarm tone to air: enabled

Alarm Out 1

This should be greyed out as we're using this as a M-lead for CTCSS/DCS decode status

Active alarm out is conducting

Alarm Out 2

Trip ON:

Low fwd power
High refl power
Active alarm out is conducting

Alarm Out 3

Trip ON:

Low volts
High volts
Tx unlocked
RX unlocked
High temp
Active alarm out is conducting

Alarm LED

Trip on:

Low fwd power
High refl power
Low volts
High volts
Tx unlocked
RX unlocked
High temp
Active alarm: LED on

Software Settings

Repeater Settings:

Tone Tail length: 2000 ms
Tx Tail Length: 5000 ms
VF path: internal RX

PTT Hang time:

PTT hang time: enable
Tone tail length: 200 ms
TX tail length: 1000 ms

TX Subtone delay: 0

RX Reverse burst: 250 ms

RF mode:

RF Mode Port Bit : unchecked

Repeater Delay: 0 ms

Alarm 1 routing:

Qualified M Lead

Very important as it enables the alarm 1 output to be active low if squelch and CTCSS/DCS is decoded.

DCS Polarity, Normal/Normal

Ext Rx Subtone Disable: VF Only

Very important or the station will not pass audio to the Line output if set to tone squelch and only carrier squelch is active. If this doesn't pass the controller will not have audio when is carrier squelch mode.

Channel select input: Binary

This needs to to be binary for fail-safe output to work.

Tx Timeout Length: 0 disabled.

Morse Code Settings

This setting is configured to be used only in fail-safe repeat mode.

Word per Min : 25
Message Text : CALLSIGN, no other characters
Morse Code Mode: Auto ID on Inactivity
Auto id interval: 5 Min

Morse Code activation:

Morse enabled
Send only in repeat mode

Setup of asterisk

In modules.conf enable simpleusb and disable usbradio

simpleusb.conf

[general]
[usb44232]
eeprom = 1              ; EEPROM installed: 0,1
hdwtype = 0             ; Leave this set to 0 for USB sound fobs modified using

; Receiver parameters
rxboost = 0             ; 0 = 20db attenuator inserted 
ctcssfrom = no		; just for testing and alignment!
;ctcssfrom = usb        ; no,usb,usbinvert
deemphasis = no         ; no de-emphasis needed
plfilter = no           ; no PL filter

; Transmitter parameters
txmixa = voice          ; Left channel output (A): voice only (no tone)
txmixb = no		; nothing on channel b
txboost = 0		; no TX boost, it's too hot!
invertptt = 0           ; Invert PTT 0 = ground to transmit, 1 = open to transmit
preemphasis = 0         ; no need for 6db/octave pre-emphasis
duplex = 1              ; Full Duplex

rpt.conf

[44232]
rxchannel = SimpleUSB/usb44232  ; SimpleUSB

Testing

Start asterisk now and see if it loads up ok. You should have the levels set at default and hear some telemetry come over the repeater. The Mx800 should be on channel 1 now.

Setting audio levels on asterisk

Ensure subaudible tones are disabled in the Mx800 and asterisk.

Setup the Transmit audio levels first:

activate the test tone from asterisk function '*904'
check with 'simpleusb-tone-menu' that the tx tone level is set to 500.
adjust the tx tone level output from the RA-35 to -10 dBm. This is best done with the analog pot option on the board.
verify this is 3.0 KHz deviation on the service monitor
disable the test tone

Setup the Receive audio levels next:

Send a 1 KHz tone at 3 KHz deviation into the receiver.
verify this is -10 dBm on the line level
adjust the audio level on the RA-35 input
in 'simpleusb-tone-menu' adjust the level until the RX-VOICE-DISPLAY level is just under the 3 KHz mark.
save the settings and turn off the service monitor.

The audio interface is now calibrated for a -10 dBm level for 60% deviation. The audio via asterisk should sound the same level as in cabinet repeat audio now.

You may now enable PL in the channel settings in MxTools and enable PL in asterisk if you are using it. A setting of 6 in MxTools channel for PL should be used for wide band PL, and it will translate to ~500 Hz of modulation.

Docs

MX800 Technical Manual

Software

MXtools is the software used to manage the radios.

MXtools Revision History.txt

MXtools V3.1.8010

MXtools V3.1.8028 - Needed for >3.6.0 Firmware.

All these need a password to program the radios, and have different access based on the password used.

  'solder' -  basic password, lowest access
  'solderall' - more advanced password
  'solderadv' - more advanced, looks like you can change the model number using this and the channels from narrow/wide
  'solderusa' - not sure
  'solderalllc' - looks to be the best