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Sunday, 22 November 2015

How to get a Leixen VV-898 to transmit and recieve on APRS

Just exactly how do you get a Leixen VV-898 to transmit and receive on APRS? This is how it is done.

Firstly you need to find the pinout for the mic, a Google search will bring it up in no time, using my method you may also need to find an Ethernet pinout as well, but be aware that the pin numbering may be opposite to that of the VV-898 mic plug diagram, it remains for you to match and note the colours.

Next you need an interface, I already had one lying around but my shack computer has no physical COM port onboard so a USB to Serial adaptor had to be used, the one I have is a Prolific type, be aware that these may need older drivers as newer drivers reject some cheap programming cables that are allegedly based on a Prolific chip but it is in fact a non-genuine chip, and the Serial adaptors may have one of these rather than a genuine Prolific chip, my serial adaptor appears to have a genuine chip in it unlike my mass of programming cables and TTL lead, my interface is wired up to pin 7 on the serial plug (RTS) though you can wire it to pin 4 (DTR).

On your computer you need to install a sound card TNC, I use UZ7HO's Soundmodem, there is a high speed version as well but we do not want this for APRS, it needs no installation, just extract from the zip file to a convenient folder (desktop on my shack computer with the icon pinned to the taskbar), set up the modem as required (APRS is 1200 baud AFSK), then set it up for the PTT on your COM port, in my case this was COM 7 but yours may differ, unless you have a physical COM port which is always COM 1 (modern computers rarely have more than 1 onboard COM port)

Next you need to set up your APRS client, I use APRSIS32, this client can be used without a radio to connect to the Internet, and also as an iGate or digipeater, but we don't need that functionality and it would require the appropriate NoV and a full license from what I understand, it needs to be able to talk to sound card TNC, this is found on localhost (unless the machine you're running the client on is on your network separately from sound card TNC), if you have a second sound card in your computer (I do) then ensure that is set up in the sound card TNC first so your main sound card can be used for other things like Echolink for example, plug a lead into the back of the VV-898, I placed a ground-loop isolator on this line to eliminate unwanted noise, power it up, and tune to the APRS frequency (in the UK this is 144.800 MHz, in other European countries it should be the same, but check first before you transmit), ensure you have disabled the APRS-IS side of APRSIS32, and it is not set up as an iGate or digipeater (turn off options for RF to IS and IS to RF and if you wish disable Internet access entirely), if the soundmodem is working and APRSIS32 is talking to it you should see a list of callsigns and other items scrolling on the top left of the window.

Now you can test your interface, tune the rig to a clear frequency or connect it to a dummy load, and connect the circuit to the mic socket, the rig should do nothing, if the red light comes on and it has gone into transmit this indicates a problem with the interface wiring, if not you're good to go.

At this stage don't plug the audio feed into the computer, if you are doing this into a dummy load there should be no need to identify, you should still be able to listen on a handheld placed close to the dummy load and tuned to the same frequency, you will also need to get the volume set up correctly, you can use existing APRS transmissions as a reference, if your interface is built with a potentiometer, as mine is, you may need to adjust this, too quiet the iGate and other stations won't receive the transmissions properly, too loud is just as bad and may cause interference, once you have it right, connect your rig back to the antenna and send a packet to APRS, if it is heard by an iGate you should appear on aprs.fi, if not your packet was not received properly by the iGate if at all, in this case check all your settings carefully.

Once it all works give yourself a pat on the back, you've got a radio with no TNC port to transmit APRS packets successfully.

Though if you are in my situation and want to use the same rig for voice, just disconnect the leads and reconnect the mic, job done.

73 de M6RSQ

(note that this isn't an exact guide, the full ins and outs are a lot more detailed)

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