Interesting stuff and handy notes for amateur radio uperators
Interfacing between PC and radio equipment
Interfacing Your PC to radio equipment is a relatively simple thing to do but there are a few pitfalls to be aware of.
There are many unwanted side effects of directly connecting a PC to radio gear that may not be obvious at first but can cause all sorts of problems and spoil Your fun. These issues range from mildly annoying interference to causing expensive physical damage to Your PC or radio equipment.
Any direct electrical connection between PC and radio can provide a path for noise, cause ground loop faults and provide a path for RF ingress on cabling to damage sensitive components in the PC or radio equipment if the interface and cabling is not designed to protect against these potentially annoying and damaging conditions.
There are many commercially available 'off the shelf' sound cards, data cables and digi-mode interfaces that have good levels of isolation and protection built in, some are better than others. You would think it is just a case of avoiding the cheap ones but ther are many budget priced units that are well protected and expensive units that are poorly designed with little or no protection that can be easily damaged.
Interfacing can sound complex and commercial units are often given fancy names and dressed up with extra features that can be nice but are not really needed. Controlling a radio and piping audio between PC and radio does not have to be a complicated or expensive thing to do. Basic PTT control and audio interfacing is relatively simple to do. It does not cost much to do it safely with good levels of isolation and protection built into a simple interface. The most expensive part of most home made interface units will often be the project box or case it is housed in!
There are many unwanted side effects of directly connecting a PC to radio gear that may not be obvious at first but can cause all sorts of problems and spoil Your fun. These issues range from mildly annoying interference to causing expensive physical damage to Your PC or radio equipment.
Any direct electrical connection between PC and radio can provide a path for noise, cause ground loop faults and provide a path for RF ingress on cabling to damage sensitive components in the PC or radio equipment if the interface and cabling is not designed to protect against these potentially annoying and damaging conditions.
There are many commercially available 'off the shelf' sound cards, data cables and digi-mode interfaces that have good levels of isolation and protection built in, some are better than others. You would think it is just a case of avoiding the cheap ones but ther are many budget priced units that are well protected and expensive units that are poorly designed with little or no protection that can be easily damaged.
Interfacing can sound complex and commercial units are often given fancy names and dressed up with extra features that can be nice but are not really needed. Controlling a radio and piping audio between PC and radio does not have to be a complicated or expensive thing to do. Basic PTT control and audio interfacing is relatively simple to do. It does not cost much to do it safely with good levels of isolation and protection built into a simple interface. The most expensive part of most home made interface units will often be the project box or case it is housed in!
Safe & Simple PTT control using Opto-Isolator / Opto-Coupler
This quick and easy hardware interface uses the DTR pin on a standard RS232C serial port (SER / COM port) to switch radio transceivers between RX and TX modes controlled by software on the PC. This will work with any software that lets You set the DTR HIGH for TX. If You cannot use the DTR pin for whatever reason You can use the RTS pin instead.
Using an Opto-Isolator IC there is no direct electrical connection between the PC and the radio. This stops any potential difference or ground loop faults and provides a barrier against electrical noise travelling between the PC and radio. Most Opto-Isolator / Opto-Coupler ICs provide electrical separation up to a few thousand volts, this effectively stops induced voltage caused by RF ingress into cabling from getting into the PC which is a good idea especially for people who run RF amplifiers in the shack. Placing the Opto-Isolator IC inside the shell of the Serial port connector at the PC end of the cable maximises protection for the PC.
How it works.
The DTR pin on the RS232C port is normally held LOW (this is actually -V) and the radio will be in RX mode.
The input pins on the Optocoupler IC have a diode across them to protect the infra red LED inside the IC from reverse voltage when the serial port DTR pin is in the LOW state (-V)
To TX the software sets DTR to HIGH, the DTR pin changes state from LOW to HIGH (flips from -V to +V) The +V powers the IR LED inside the Optocoupler IC. This in turn makes the Phototransistor inside the Optocoupler IC conduct, effectively connecting the Output pins on the IC together.
The output pins on the IC simply connect the PTT control pin on the radio to the GND pin on the radio making it switch into TX mode.
When the software 'drops' PTT the DTR pin returns to the LOW state (-V) the IR LED turns OFF and the Phototransistor in the IC disconnects the PTT control pin from the GND pin on the radio and it goes back into RX mode.
The DTR pin on the RS232C port is normally held LOW (this is actually -V) and the radio will be in RX mode.
The input pins on the Optocoupler IC have a diode across them to protect the infra red LED inside the IC from reverse voltage when the serial port DTR pin is in the LOW state (-V)
To TX the software sets DTR to HIGH, the DTR pin changes state from LOW to HIGH (flips from -V to +V) The +V powers the IR LED inside the Optocoupler IC. This in turn makes the Phototransistor inside the Optocoupler IC conduct, effectively connecting the Output pins on the IC together.
The output pins on the IC simply connect the PTT control pin on the radio to the GND pin on the radio making it switch into TX mode.
When the software 'drops' PTT the DTR pin returns to the LOW state (-V) the IR LED turns OFF and the Phototransistor in the IC disconnects the PTT control pin from the GND pin on the radio and it goes back into RX mode.
Audio interfacing with isolating transformers.
Basic audio interface circuit using 600 OHM 1:1 audio isolating transformers removes the possibility of potential difference and ground loop fault conditions between the PC and radio. The audio OUTPUT level from the PC is easily adjusted using the POT (25K OHM variable resistor). This makes it easy to set the audio level into the radio for optimum performance. When using digital modes the audio level into the radio should be set using the POT so the ALC only just moves a fraction from Zero position.
NOTE: Make sure You do NOT have any connection between the two halves of the circuit. To ensure proper isolation and protection against ground loop faults the Grounds on either side of the transformers must NOT be connected together directly or indirectly through conductive housing. IE; If you build the circuit inside a metal box do NOT connect the Shield Ground from the PC audio plugs to the metal box.
Here are a few interesting and possibly useful videos from some people who know some handy stuff.
Dave Jones is an electronics engineer from Australia who makes loads of educational and interesting videos about a range of electronics related topics.
From component specifications & limitations to teardown & repairs of a wide range of devices, lab equipment and domestic electronic items.
These videos (and many more) are available on Dave's youtube channel.
Whether You are just getting into electronics or have been into it for years EEVblog is well worth having a look at.
From component specifications & limitations to teardown & repairs of a wide range of devices, lab equipment and domestic electronic items.
These videos (and many more) are available on Dave's youtube channel.
Whether You are just getting into electronics or have been into it for years EEVblog is well worth having a look at.
Transistor Zener Clamp Circuit. (EEVblog #1157)
|
Lithium Ion/Polymer battery charging tutorial. (EEVblog #176)
|
How do Transistors work? (EEVblog #748)
|
How NOT to Blow Up Your Oscilloscope. (EEVblog #279)
|
Paul Carlson is an electronics and radio communications enthusiast who makes interesting educational videos.
Well worth taking a look at his Mr Carlson's Lab Youtube channel.
Well worth taking a look at his Mr Carlson's Lab Youtube channel.
Transistor Identification and Testing. By Mr Carlson's Lab.
|
Radio Repair Tips. By Mr Carlson's Lab.
|
Zener Diode vs Vacuum Tube regulation and More. By Mr Carlson's Lab.
|
What Capacitor Do I Use?. By Mr Carlson's Lab.
|