Null-modem cable: interface description, functions, wiring

Producers of satellite receivers periodically release updates to the software of their equipment, fix errors in it, and improve performance or add some new features.

In order to update the firmware of the device, you must first download it to a personal computer, and then connect the receiver to the PC and restart the program. A null-modem cable is used to connect the computer to the satellite receiver. If you do not have such an interface, you can buy it in computer stores, though not always there is this product. In any case, you have a choice: to look for a ready solution or to make a null-modem cable yourself. The latter option will be much cheaper.

How to make a null-modem RS-232 cable?

For its manufacture we need a four-wire cable (length is determined by the user) and two connectors of the type RS 232 ("mother"). These connectors can be found in any radio store, they are very popular, since they are present in virtually every personal computer as a COM port. Cable can be a twisted pair. For this we twist together each of the veins and get four conductors. Next, you need to wiring the connectors. In this case, it is necessary to prevent accidental closure, as this will lead to failure of the equipment. Such a null modem cable Will work stably with a wire length of up to 50 meters.

Recommendations for soldering

This manual is not mandatory, but it is tested by practice:

1. It is not recommended to cut off excess leads at the connector.

2. Connecting the connector housings is necessary to relieve tension, since the housing touches the device. Otherwise, there is a risk of burning the COM interface on the computer or receiver. This connection is not required if all equipment is grounded.

3. It is preferable to use a shielded cable, since it works better.

4. In all tuners of the satellite signal, only three contacts are used.

5. In some receiving devices there is no MAX232 chip (it is assumed that it will be in the external adapter). In such devices, there are four outputs on the receiver's COM port, but at the output of the adapter there are the same three contacts. Therefore, before you connect the null modem cable, you need to study the documentation for your device in detail, you may first need to attach the adapter.

6. In some tuners, pins 2 and 3 on the connector are interchanged. In this case, you need a straight cable, not a cross cable. In order to determine what type of connector is on your receiver, you should study the documentation for it.

7. Cable is recommended to use stranded, as it is more resistant to mechanical influences. Soldered contacts should be filled with silicone to avoid short circuit.

Unpacking the null modem cable RS232

In the COM interface, only three contacts and the connector body should be soldered. In this cable, you must use 2, 3 and 5 pins. In the forward version of the null-modem cable, these contacts are soldered the same in both connectors, and in the cross-connect 2 and 3 they are interchanged.