Railroad Spectra

General Information

This is a slightly different beast. Also known as the Spectra Clean Cab Radio. One of the specific model numbers is MB-R43KME1170AK. The MB denotes that the radio is supported by Motorola Canada. The "R" denotes railroad application. The railroad radio uses the low power programming cable and uses Spectra Railroad RSS, part number RVN4099B due to the special functions. The RSS Manual 68P02903A55 gives a good description of all the capabilities. It is important to note that you should not apply 12V to the programming cable lead (unless of course you want to blow up the radio).

The service manual for these radios is 6802902A82.

The radio has 99 independently selectable transmit and receive channels. These are normally programmed for the 97 standard AAR (Association of American Railroads) channel plan. In the US, this channel plan starts at Channel 07 (160.215) and goes up at 15 kHz intervals to Channel 97 (161.565). TX and RX frequency can be set independently by the user by selecting the proper number in the display (when monitoring, you'll often hear RR personnel saying things like "set both windows to 14", in reference to this). It has user selectable DTMF or AAR Single Tone signaling. It supports DTMF dialing from the keypad. The DTMF pad works without having to press the PTT button, also, but you may need to change the unkey time to prevent the transmitter from dropping out between key presses. It also supports up to 99 "Home" channels that will select a preprogrammed TX/RX channel pair and the signaling tones. This radio is not capable of scanning... the railroad has no use for scanning, the engineers know what channel that are supposed to be on, so that feature was never implemented.

You can add other than AAR freqs to it. Some RR's have repeater inputs that are out of the RR band (particularly Government owned RR's like Amtrak, Long Island RR, Metro North, NYCTA, etc.) and the RR Spectra accommodates that.

The RR Spectra RSS allows you to set the "pre-sets", DTMF tone sequences (transmitted when you push the DISP button), MDC tones, etc.

You can set P/L tones, but again, only on pre-set channels.

The presets are made up by tying individually programmed channels together after frequency information has been entered into them. If you don't need PL or DPL capability (which are accessed only through the Home mode configurations), you are free to do all sorts of weird stuff using the stand alone channel memories. For example, this has been done with amateur frequencies. You can program the radio such that channel "38 38" represents 146.52 simplex, and it works great. "38 36" could be programmed to let you transmit on 146.52 and monitor 146.49 (I know that would be bad operating practice, but the radio will let you do it). Of course, you have to remember what frequency (or frequencies) you put in each channel memory, because the radio will give you only the channel number. So before long, you will go back and set up Home modes for everything. Then, if you enter "Home" "3" "8", the display shows 146.520 and everything automatically works perfectly.

Now...apart from the capabilities of the radio, FCC Part 90 rules prohibit giving operators in those services the ability to access channels other than those licensed. Having direct access to repeater and simplex frequencies, and the ability of operators to build unintended operating configurations would be outside those rules. The radio can be programmed for "Home Mode Only" operation, however, which would make it work essentially like any dash mount Spectra, with access only to predetermined transmit/receive configurations.

You can set up as many as 99 preset, or "Home" channels. You move between the "Channel" and "Home" modes either by pressing the appropriate button and entering a number, or else by pressing and holding the desired mode button for about 3 seconds. If in "Home" mode, the radio remembers the previous channel setup, and if in "channel" mode, it remembers the last "Home" setup.

The RF part of the radio is a standard 146-174MHz 45W Spectra but the firmware and control interface is special. The Canadian versions of these radios are limited to 30W.

They also have an internal power supply capable of operating on 12VDC/72VDC (railroad standard).

Keep in mind that even though standard railroad channels are 15 kHz apart, these radios are intended to operate with 25 kHz channels (on an alternate channel basis).

Railroad Spectras are actually sort of wide-band units, primarily because Canadian railroads have traditionally used frequencies way outside the AAR channels at 160-161 MHz. The Railroad Spectra will, without modification or adjustment, do all amateur frequencies, as well as MARS/CAP, and will go at least to the upper 160s. It will probably go at least to 172 mHz. What it will not do is narrow bandwidth channels.

You will find that their most outstanding characteristics are their filtering of input DC power (locomotives are electrically hostile environments) and their overall audio performance, both on transmit and receive. (Locomotive cabs can be audibly hostile environments).

Connector Pinouts

The pinouts of the connectors on the radio go like this:

Power connector:

A --- +72 volts
B --- -13.8 volts
C --- - 72 volts
D --- +13.8 volts

Use only A and C for railroad 72 volt (nominal 64V supply) power, or B and D for 13.8 volt (nominal 12V supply). The 72 volt supply floats; the 13.8 volt supply is negative ground.

When using 72 volts to power this radio, the connections are as stated. However, since the battery system floats from the locomotive frame ground, it is necessary to use a 3 wire cable to make a power connection. The third wire goes to pin "B" on the power connector and to the frame ground at the other end. This connection is necessary to provide a proper RF ground for the radio.

12 pin Auxiliary Connector:

A --- Mic Audio
B --- Mic Ground (these either for electret or carbon mic)
C --- PTT
D --- Handset/PTT return
E --- Handset audio
F --- ?
G --- ?
H --- ?
J --- Hang-up return
K --- Hang-up
M --- Speaker Hi
N --- Speaker Lo

As with all Spectras, the audio amplifier is a direct coupled, floating type. DO NOT GROUND either speaker line or permanent damage to the radio may result. An audio transformer is available if necessary to utilize a nonstandard audio configuration. I do not have the part number.

6 pin "Hardwired Mic/Handset" Connector (on Front Panel Circuit board, P1005):

1 --- Handset mic audio (carbon or electret mic)
2 --- Ground
3 --- Handset PTT
4 --- Ground
5 --- Handset audio
6 --- Handset hangup

Some models have an optional hard-wired handset or palm microphone. These radios have a hole at the lower lefthand corner of the front bezel (the casting is slightly different, also) for the cable to pass through to the outside.

6 Pin Auxiliary Connector (J3003):

A --- Handset Mic Audio
B --- Mic Audio Ground
C --- Mic PTT
D --- Mic PTT Return
E --- Handset Audio
F --- Hangup

15 Pin Auxiliary/Programming Connector (DB15) (J3006, Service Data Port):

1 --- Reset
2 --- VIP Out 3
3 --- VIP Out 2
4 --- Unswitched A+
5 --- VIP In 1
6 --- Tx In
7 --- Data PTT
8 --- Ground
9 --- Busy
10 --- Bus-
11 --- Detector Audio
12 --- VIP Out 1
13 --- VIP In 2
14 --- Bus-
15 --- VIP In 3

Note that the Amphenol connectors can be obtained (except for the 12 pin bayonet style) from Connector World Supply in Seattle, WA. The 12 pin connector is about $90 from Motorola, unknown if it is still available.

If you have a Railroad radio with a microphone connector, the microphone plug is the same on all railroad radios, as part of the universal connector system. The pinout is as follows. Counter-clockwise from the bump in the ring where the pins are: 1.(on bump) mic hi, 2.spare (not used), 3."monitor", 4.PTT lo, 5.PTT, 6.mic lo.

If you look carefully at the pinout of the accessory connector on the back of the radio, you will see that it has everything you need to make a very simple TNC cable and either do amateur packet or commercial data. These are great radios for either application. In fact, the best ones for this application are the Canadian versions which are hard-limited to 30 watts output. Turns out that the reduced power is great for the higher duty cycle.