Information on the MX800 Base Station from Spectra Engineering

General Info

Most amps now are wide band, but I've seen a number that do not have the discrete driver transistor. They have a Mitsubishi power module as the first stage and three tuning capacitors. When peeked for maximum power (~60W) they have a 2% bandwidth. As they were tuned for 218 MHz from the factory it's worth retuning for amateur band operation. This will improve the match, which is important when followed with a duplexer.

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. The MX800 doesn't appear to have a loop power control. 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.

SW 2	Function	Description	Best for Ham
1	PTT Delay	Enables 50mS delay of PTT for use with simplex function.	OFF
2	Simplex Enable	Enables simplex function*	OFF
3	TX Timer	Sets programmable TX time out timer on.	OFF
4	Repeater Enable	Enables repeater function - only for in box repeat. External controller should be off. This is in parallel with the Repeater Enable on Pin 8 of the DB15 Line connector. If SW2/4 is OFF the function may be controlled through this external line. JMP 14 selects the control polarity in that case.	OFF *
5	TX VCO on	Switches TX VCO on continuously	ON
6	Scan on	Selects the receiver to enable the scanning of programmed scan channels	OFF

Jumpers

Jumpers set many operational aspects of the station and control audio routing. These can interplay and the nomenclature spectra engineering uses differs from what most people in North America are experienced too that it can be frustrating to figure out what really is going on.

Jumper	Function / Description	Default	Position for Ham use
1	Selects either default RUN or EMULATE mode for the micro processor.	Run	2-3
2	Enables the WATCHDOG auto reset function in the microprocessor.	Enabled	1-2
3	Enables or disables the PRE- EMPHASIS for the TX audio.	Enabled	1-2
4	Enables or disables the COMPRESSOR for the TX VF audio. This isn't really a "compressor" but an amp on the VF input.	Enabled	1-2
5	Enables or disables the HIGH PASS FILTER for the RX audio.	Enabled	2-3
6	Enables or disables the LOW PASS FILTER for the RX audio.	Enabled	2-3
7	Enables or disables the DE- EMPHASIS processing for the RX audio.	Enabled	2-3
8	Enables a direct connection to the TX modulator. 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.	DC-FM	1-2
9	TX VF Loopback control. Trunking LIFUISEN function.The function polarity or nil can be selected.	Active low	1-2
10	Controls the direction of the RS-232 TX and RX data.	Swap	2-3
11	Controls the direction of the RS-232 TX and RX data.	Swap	2-3
12	Trunking RX Talk function. 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.	Active low	REMOVED
13	Enables or disables the HIGH PASS FILTER for the TX audio.	Enabled	1-2
14	Repeater enable. Trunking LIFULOCEN function. The function polarity or nil can be selected. Note that this control is in parallel with DIP SW 2/3	Active low	1-2
15	Selects the connection for the common pin on the digital I/O connector to either Ground or + 5 volts.	ETH	2-3
16	Enables or disables the Low frequency HPF used for the Repeater VF routing.	Enabled	1-2
17	Selects the Mute / Squelch output polarity to either normally high or low.	Active low	1-2
18	Trunking TX Talk function. Disables TX VF to line and TTR VF. The function polarity or nil can be selected.	Active low	1-2
19	Selects either internal pull up to5V or internal pull down to ETH for digital input on D25 connector	Pull up	2-3
20	Not Placed
21	Not Placed
22	Microphone gain. Fit this jumper to increase Mic gain 33dB	Low gain	Not fitted
23	Enable tone to speaker. Fit this jumper to enable tone	Disabled	Not fitted
24	RS232 port termination. This jumper allows an internal termination to be selected or not for bussed RS232 connections. Up to 16 units may be bussed. 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.	Normal	1-2
	Normal: Non-bussed mode. No resistor fitted. D10 out of circuit.		1-2
	Master: Bussed mode. 4K7 resistor across D10.Configure at least one and no more than four MX800 in this mode when multiple units connected.		2-3
	Slave: Bussed mode. D10 fitted, no resistor. Configure balance of bussed units in this mode.		3-4
25	Mute defeat enable. Mute defeat cannot be used if RX TALK line is required. To use mute defeat remove JMP12 and fit JMP 25. The control signal polarity can be inverted by changing the position of JMP25	Disabled	Not fitted
	Active Low		2-3
	Active High		1-2
26	CTCSS output / TX VF Loopback control	TX VF Loopback	2-3
27	CTCSS input / WB DC-FM input This enables the routing of the Wide band input through a 300 Hz Low Pass filter. Ideal for an external CTCSS level	WB DC-FM input	2-3

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

DB-15 Pin	SKH Pin	Function
1	15	Alarm output #2 - Open Collector, "short to ground" when active
2	13	TX VF Loopback active or CTCSS output depending on jumpers 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.
3	11	Receiver audio from speaker amplifier. 4 ohm output.
4	9	Discrimator output, DC coupled, low impedance. You need a blocking capacitor on this output or you will destroy the amp.
5	7	Alarm output #3 - Open Collector, "short to ground" when active
6	5	Alarm output #1 OR M-LEAD - Open Collector, "short to ground" when active 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.
7	3	RX Talk - this enabled RX VF to the Line ouput and Repeater (TTR). This is needed if you want to have the RX output to line even if PL is not on it. Jumper 12 controls the polarity.
8	1	Internal Repeater Enable - On/Off of internal repeater function, polarity selectiable by Jumper 14
9	14	Transmit Audio Input 600 ohms. Transmitter audio input to op-amps etc.Nominal line input level is -10dBm. Can handle levels between -15dBm and+6dBm. Unbalanced input with common return to analog Earth.
10	12	Ground
11	10	TX TALK. Enables or disables TX VF from line as well as TTR VF. Thepolarity is selectable via the internal jumper JMP18. If this function is notrequired then remove jumper JMP18 or place it in position 1&2.
12	8	PTT - The standard PTT input is active low and may be driven from standard +5V logic outputs or open collector
13	6	TX DC-FM Input or Wideband Input. Select the internal jumperJMP8 to configure this input as either the DC-FM input or Wide Band input.Remove jumper if not used. DC-FM input (JMP8 in position 1-2) Audio or data may be connected to this point. In order to conform to transmitter bandwidth emissions limits, this input is hard limited to the peak deviation and Bessel filtered -3dB @ 3400Hz for minimum group delay distortion. Input impedance is >10k ohms. Input sensitivity is nominally 1Vp-p but depends upon RV2 adjustment. If this input is not used then jumper # JMP8 on the Micro Controller board should be removed to avoid any pickup of stray signals, or alternatively do not connect any wires to this pin. Avoid the use of ribbon cables longer than 30-50cm as this may result in excess coupling or crosstalk. Wide Band input: (JMP8 in position 2-3) AKA direct modulator input mode Wide band audio or data may be connected to this point. WARNING: In order to conform to transmitter bandwidth emissions limits, the signal MUST be prefiltered and level controlled, failure to do this WILL result in non-compliance of the TX emission spectrum. This input mode is not normally used except in special cases. 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
14	4	COR (called RX MUTE). 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.
15	2	RX Audio 600 Ohms output Receiver audio output from op-amp. Default nominal line level is set to -10dBm. Unbalanced output with common return to analog Earth.

DCS Decoder

The DCS decoder works, but the CTCSS led doesn't turn on if it's received. The only indication is the M-LEAD which can be configured to be ALARM-1 or M-LEAD. This output is open collector (shorts to ground) when squelch is open and a configured CTCSS or DCS tone is received.

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.

MX800-F 220 MHz Technical Brief

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