MATEL 2C800 Field Phone
© Brooke Clarke 2014
This phone fits with my interest in telephones in general and military field phones in particular. The thing that's interesting about this unit is that you can have multiple phones on a single cable (Racal Acoustics Ltd. calls it a "highway") and call individual phones. It also supports priority override, conference calls as well as "all stations" calls.
These phones are marked: 2C800/42/1. I don't have the 2C803 terminators or the 2C806 Interface box and am looking for information about them.
The appearance is very similar to the TA-1 sound powered filed phone both in it's shape and in having a cord that terminates in a way to connect directly to a single pair of WD-1 field wire, or in the case of the 2C800 either a pair WD-1 or a pair WF16 field wire (redundant pairs), see Fig 2 below. Unlike the TA-1 the 2C800 is battery powered.
Photos
Fig 1 Overall View
Fig 2 Connection to WD1 or WF16 Field wire
You can use either WD1 or WF16 field wire, but in either case
the phone is only using a single pair.
Fig 5 Inside field wire connection box.
Fig 3 Back Operating Instructions
Fig 4 Four AA Batteries
After batteries are properly installed the red lamp lights when
the button with the battery icon is pressed.
Fig 6 Inside
Fig 7 Inside
Fig 8 Inside Note PCBs are bent (on purpose?)
The components on the PCB are:
Designation
Description
R1, R2
150 Ohm
R3, R4
15k Ohm
C1
2.2 uF
C2, C3
0.1 uF
D1, D2
Surge Protection?
C1 connected between R1 and R2. Outer ends of R1 and R2 go to phone line.
It's not clear where the rest are connected.
Photos supplied by Iain G0OZS.
Fig 20
Fig 21
Fig 22
Fig 23
Fig 24
The instructions say "the highway MUST be terminated at each end into a Highway Terminator type 2C803. I've read on the web that the termination matches the impedance of the line used (600 Ohms for field wire, 125 Ohms for LAN cable, 75 Ohms for TV coax, etc.). But, the resistance is split into two series resistors with a 2.2 uF cap in between them and the cap is shunted by a 27k resistor. I expect there are other components in the 2C803 terminator but don't have one to reverse engineer. If you know or have one please contact me.
The main terminating resistors are there to minimize reflections on the buss to allow good data fidelity. There's also a built-in-test feature that the phone knows it's connected to the "highway" and can detect if the "highway" has been disconnected. I expect that's the reason for the 2.2 uF cap and 27k resistor shunting the cap. The cap looks like a short to the data which just sees a terminated line. But the BIT circuit sees a much higher impedance with some type of signal or DC level across the 27k resistor.
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This page created on 25 June 2014Brooke's: PRC68, Alphanumeric index of web pages, Products for sale, Contact
