GM340 for telemetry: modem, connector and channel data rate
Motorola GM340 has long been the workhorse of radio channels of telemechanics: the station stands in a cabinet on a bush of wells, a pump or a substation and transmits data to the control room. We understand what is connected to it and how to set up a bundle.
Why do you need a radio if you have a cellular connection?
Remote facilities—well bushes, water intakes, pumps, and substations—are often located where cellular communication is not available or reliable. Own VHF-radio channel does not depend on the operator: the station at the facility communicates with the central station at the control center directly, and if necessary through the repeater.
Data in telemechanics a little - pressure, level, position of valves, signals of accident. They have the speed of an analog station with a modem, so the GM340 still works in such systems.
What is connected to the GM340
The station itself transmits sound, and the data turns into an audio signal external modem. It connects to the station's rear accessory connector through accessory connector HLN9457. For a modem, you need these lines:
| Contact | Signal. | Why a modem? |
|---|---|---|
| 3 | PTT | switches on the transmitter during the parcel |
| 4 | carrier-detector | It shows that the channel is busy. |
| 5 | modulator | This is the modem signal. |
| 7 | land | wire |
| 11 | receiver | from here the modem accepts the parcel |
| 15 | signal level (RSSI) | diagnosing channel quality |
Numbering contacts before assembly of the tourniquet must be called: an inverted connector is a common reason for "no communication" with serviceable stations and modems.
It is impossible to power the modem from the station: there is +13.2 V on the connector, but through a current-limiting resistor it is tens of milliamperes. The modem is connected to the power supply unit of the cabinet.
What modems work with GM340
GM340 is directly named in the documentation of Russian modems of telemechanics. R9-03M (PIC Progress) and MD-V.23M2 (SKB "Promavtomatika"). Manufacturers specify signal levels and switch positions for it, so the bundle is assembled according to documentation, not selection.
If there are few objects and you do not want to collect a bundle, there is an option "station and modem in one building" - Motorola GM DATABOX.
What to set up in CPS
- Contact 3 – External PTT mode for data; without this setting, the modulator input is not connected to the transmission path.
- Contact 4 is a carrier detector.
- The output of the receiver on contact 11 - without filtration and without noise suppressor.
- On the data channel, turn off predations, CTCSS/DCS subtones, compander and transmission restriction timer.
The signal level of the modem at the modulator input is set according to the deviometer: start from a small level and raise to a working deviation. The congested input expands the spectrum and interferes with neighboring channels.
What speed to wait
The speed rests on the width of the channel, not on the station:
- 1200 bits/s - always works, the most stable mode at distant points;
- up to 2400 bits/s in a narrow channel of 12.5 kHz;
- up to 4800 bits/s - 25 kHz channel.
9600 bits / s in a narrow channel through the sound path do not physically pass. To survey several dozen sensors once a minute, these speeds are enough with a margin.
Antenna, mast and lightning protection
The distance of the radio channel determines the height of the antenna, not the power. They put it on the site. BC-100 base antenna The mast is above the roofs and trees, and in the rupture of the feeder in front of the cabinet, storm-discharger LP-350. The mast and the cabinet are grounded.
Frequencies for data transmission
Voice permission does not always cover data transmission: telephony and data have different radiation classes. If the stations are transferred to telemechanics, the registration documents for them are reissued - it is worth laying in the terms of the project.
What to send for calculation
The number of objects and control points, the distance between them, the range of your frequencies, the modem (if already selected) and what is on the masts. We will respond with a letter with a set: stations, connectors, antennas and lightning protection.
Agree on specific products for the project
Send the radio model, external equipment and project specification. The station, DATABOX and accessory connector are indicated by different lines; they are not interchangeable products. The specific configuration, compatibility scheme and actual kit contents are agreed upon according to your project documentation.
Request a quote · +7 381 249-00-02Please email us. Provide the full models, quantity and address of receipt; composition, current availability and deadline will be agreed in the response.
