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General Information Radio Port Mgr . Edit TNC/modem Port . Edit Sound Card Port - Tuning Aid - Volume Settings . Edit Parameters New Port Setup Network TCP/IP Settings Radioport Sharing Auto Start Clients Other Settings Views Program Status Port Activity Status Shared Radio Ports AX.25 Status (Stations) Connected Programs Heard Stations List Monitor Other Features TCP/IP Over Radio . Driver Install . PE Pro Settings . Windows Settings Registration HTTP Interface Live Update Launch IE Browser Go to AGWsoft web site Send Error Report Tips, Tricks, & Trouble Tips and Tricks Problems? Sound Card Use . Sound Card Interface . HF Operations . 9600 Operations . Receive Problems . Transmit Problems
Help Date: 21 June 2004
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Sound Card InterfaceAn interface is the collection of wires and circuits used to connect your radio to the your computer's sound card. The interface needed for Packet Engine Pro is the same as those used for other sound card digital programs, such as PSK31, so you may already have a suitable interface. Typically an interface will have three (3) cables: The TX and PTT cables will need some circuitry/electrical components to match the radio and computer -- see below. Note the stereo channel capabilities of a sound card allow you to interface with two (2) radios at once! Kits/Ready-made InterfacesMany vendors sell ready-made interfaces or kits. Do a web search for "sound card interface" or "PSK31 interface". The quality, time savings, and relatively low cost of such interfaces make them worth considering. Build Your OwnYou can also build your own interface. You will find designs on this page or you can look for others by doing the "sound card interface" search on the internet.
If you build it yourself - General Info:
RX CableThis cable brings received audio from your radio (microphone, data, or speaker jack) to the sound card. Use the radio's data jack if available, since it usually has constant volume and squelch. If you use the microphone or speaker jack, remember that RX audio will be affected by the radio's volume and squelch knobs. 1. Using the sound card's LINE IN jack -- It is best to use the LINE IN jack of the sound card, if possible, since it is a better voltage match to the radio's output. If use the MIC jack of the sound card instead, you should use a simple circuit to reduce the voltage (see second drawing below).
2. Using the sound card's MIC jack -- If you use the sound card's microphone (MIC) jack instead of the LINE IN jack, then you will probably need to add an attenuation circuit on the RX audio line so that you do not overdrive the sound card. The exact attenuation will depend on the output voltage of your radio's RX line and the maximum allowed input voltage on the MIC jack. (Some examples: most Sound Blaster cards have a max. input voltage of 200 mV. The Kenwood TM-V7A outputs 500 mV on the 1200 baud RX pin in its data jack.) Here's a schematic for a 10:1 attenuation circuit:
Note: If you are planning a two port/ two radio cable, you can't use it and the MIC input jack. Typically, the ring in the MIC jack is used to provide a bias (+5V) voltage for electret microphones. It is not used for audio (right channel) input, so it couldn't be used for RX audio input from a second radio. Also note that while a mono plug could be used in a MIC jack, it is better to use a stereo plug; just leave the ring unwired. A mono plug will short circuit the ring (voltage) to the sleeve (ground), although the card's circuitry is designed to cope with this (a resistor severely limits current flow).
. TX CableThis cable brings audio to be transmitted from the sound card's LINE OUT jack to the radio's microphone or data jack. It needs some components to reduce the sound card voltage so that it matchs the maximum allowed voltage on radio's TX circuit. The exact attenuation will depend on your radio and sound card. An approximation is a 100:1 attenuation (40 dB) which will reduce the sound card output level (max. 2 Volt p-p) down to the level your radio normally would expect for microphone (often a max. of 20 milliVolt p-p ). For example, a 50:1 attenuation would be better if your radio's data jack which has a maximum input voltage of 40 mV p-p. 1. Here's the first option for an attenuation circuit:
The value of capacitor C1, if used, is often specified in the radio's user manual in the section on MIC/Speaker accessory plug wiring. 2. Here's a second option that combines a pot with a fixed resistor to give the pot a less delicate range of settings and makes it easier for you to adjust the total attenuation.
PTT CableFor the TX audio to be transmitted, you need a way to open the radio's PTT (Push to Talk/Transmit) circuit. If your radio has a VOX (Voice activated transmission) feature, then the TX audio will trigger the PTT. Two things to be careful of with VOX are that 1.) you must guard against room noise being transmitted when the VOX opens, and 2.) you may need a longer TXDelay because VOX may take longer to key up. If you don't have VOX, you can build a VOX circuit that does the same thing (do an internet search on "Tone Keyer") and there is at least one commercial tone keyer, Tigertronics SignaLink. The other alternative is to build PTT cable with a 'gate' circuit that opens the radio's PTT circuit. Packet Engine Pro provides for this by placing a voltage change on the RTS pin of your computer's RS-232 serial (COM) port or parallel (LPT) port when Packet Engine Pro has audio to transmit. Here's a schematic for a circuit which uses a phototransistor, or optocoupler, as the gate. The optocoupler is a special transistor that electrically isolates the radio from the sound card. A simple transistor does not do this.
Note that this circuit is used on the RTS pin if you are using the sound card in single port mode (left channel only). If you were using the card in dual port mode to control two radios, then a second circuit would attach to the DTR pin of the RS-232 port. RS-232 Connections for PTT circuit - If you have a DB9 Serial port (COM), the RTS (Request To Send) pin is # 7 and ground is pin #5
If your serial port has a DB25 COM connection (rarer), RTS is pin #4 and pin 7 for ground is pin #7. Note this is the diagram of a DB25 serial (COM) port not a DB25 parallel (LPT) port.
To use the parallel port (DB25 LTP) for PTT control, use LPT's Data Bit pins 2 or 3 for the PTT line and any pin 18 thru 25 for the GROUND.
Hints:
Using Two Radios with One Sound Card - Because sound cards have stereo -- two channel -- audio capabilities, you can use one sound card to interface with two radios. To do this, you'll need a more complicated interface with a second set of RX, TX and PTT cables. Note: this feature will not work if you use the MIC jack for RX audio. It will work if there is a LINE IN input jack. For the RX audio line, you will need to build a second cable -- with any necessary circuits -- that connects to the ring of the sound card jack (the right channel of the sound card). You will need to fit the RX audio line from both radio's into the stereo jack. You will need to do the same thing for the TX audio line -- a second cable with another attenuation circuit that attaches to the ring of the sound card jack (right channel). For PTT control, you will need to build a second PTT cable with a gate circuit that gets its signal from the DTR pin (Data Terminal Ready) in the RS-232 COM (serial) port or one of two Data Bit pins in the RS-232 LPT (parallel) connector. Here is where to find the DTR pin:
Remember that you will need to fit the PTT lines from both radio's into the RS-232 connector. Or you could make a more elaborate arrangement that lets you detach a cable when not in use (DB9 shown in this example; ground pins not shown but must be used):
You can find more information on this subject by doing an internet search for "sound card packet". Copyright 2004 SV2AGW George Rossopoulos . All rights reserved. |