We were fortunate that the radio club I belong to received a Yaesu FT-2500M as a donation. Since we have more modern VHF equipment, we decided to give the radio a new life by converting it into an APRS digipeater. If you’ve read other blog posts, you know I’m a huge fan of APRS, and as soon as I can get a new digipeater up and running, I get to work.
This radio is essentially a VHF single-band radio, meaning it operates on the 2-meter band. With a high output power of 50W, a medium power of 20W, and a low power of 5W, it offers good options depending on your needs. If you want to know more, you can consult the specifications page of the Yaesu FT-2500M.
As I always do in these cases, the first thing I started to investigate was how I could connect an APRS digipeater or a TNC to the radio in the most convenient way and that would allow me to work with the best possible performance.
For all the tests we’re going to do, first of all, we’ll need to be on your country’s VHF APRS frequency (in my case, 144.390 MHz). We’ll set the Time-out Timer (TOT) to 5 minutes and leave the Squelch fully open (so that we can hear the band noise).
We’re setting the TOT because if something fails in the TNC or Digipeater and the radio remains in transmit mode for too long, the radio itself will protect itself and shut down. Five minutes is the minimum TOT allowed on the Yaesu FT-2500M; I’d prefer something much shorter, like 10 seconds, but it’s what we have.
We leave the Squelch fully open for two reasons. The first is that the Squelch on some radios is very slow, and in the case of Packet Radio or APRS, this delay can cause us to lose information. The other reason is that by leaving the Squelch open we will be able to listen to the weakest stations, generally the mobile ones, which reach the limit of the digipeater.
Before starting work, I could see that the microphone connector could easily handle basically all the connections to the TNC. However, after consulting some forums, I found that sometimes the output audio level (generally known as SPK in the APRS/TNC world) can be very low and not perform well, so I had to look for alternatives.
Here we go.
APRS/Packet on a Yaesu FT-2500M using the microphone connector
If we’re lucky and our radio handles audio output levels suitable for APRS, we’ll be able to fully control the radio from this connector.
The following image shows the microphone connector pinout to get you started.
As we always say, we only need four wires to operate APRS or Packet Radio:
1-PTT
2-GND
3-MIC
4-SPK (RX Audio)
As you can see in the image, we can connect these four wires to the microphone connector, which is always the best option.
Why? The installation is much simpler, and with this type of connector, we can generally take the audio directly from the discriminator.
Audio taken directly from the discriminator isn’t processed by the different stages of the radio; therefore, it’s clean audio—the audio we actually receive through the antenna without any modifications.
For digital data, this is ideal because it allows the data to be processed more efficiently by the TNC or Digipeater.
What we should do is connect the radio to the TNC or digipeater using only these four cables, adjust the audio levels, and test if we can interpret the APRS packets.
If for some reason the APRS packets are not processed, we will go to option number two, taking the audio received directly from the speaker output.
APRS/Packet on a Yaesu FT-2500M using the microphone connector and Speaker plug
If we’re unlucky with the audio levels our digipeater can handle, we can take the audio received by the radio from the audio jack on the back.
I’m not the biggest fan of this option, but often it’s the only one we have left.
Doing this will result in a slightly bulkier cable with two parts. One part goes to the microphone connector (you can use an old computer patch cable) to operate the transmit function:
1-PTT
2-GND
3-MIC
And the other part of the cable goes to a mono plug on the back of the radio to handle the received audio:
4-MIC
5-GND (this is the same GND we took from the microphone connector)
With these two cables, we have to connect them to a single connector, in the case of the photo it’s a DB9, and solder the terminals according to the requirements of our TNC or digipeater.
As in the previous case, once everything is connected, we have to make the necessary audio adjustments to get it working correctly.
APRS with a Yaesu FT-2500M – general Recommendations
If your plan is to leave your radio permanently set up for APRS, I recommend you consider the following:
1- For fixed stations, using Wide2-2 as the path is more than sufficient in most cases.
2- If your digipeater also acts as an iGate, only forward messages from the internet to RF. Many people leave all their internet traffic to RF for unnecessary things.
3- Again, leave the squelch fully open to receive weaker stations.
4- It’s not necessary to use 50W of power; try with less to see the results—you might be surprised.
5- Don’t forget to leave the TOT (Time Out of Time) enabled.
In case you didn’t know, except for your main station (usually your home and in my case LU9CNS) in APRS it has an SSID. I leave you the following list so that you can take the one that fits what you are going to do:
-0 Your primary station usually fixed and message capable
-1 generic additional station, digi, mobile, wx, etc.
-2 generic additional station, digi, mobile, wx, etc
-3 generic additional station, digi, mobile, wx, etc
-4 generic additional station, digi, mobile, wx, etc.
-5 Other networks (Dstar, Iphones, Androids, Blackberry’s etc)
-6 Special activity, Satellite ops, camping or 6 meters, etc.
-7 walkie talkies, HT’s or other human portable
-8 boats, sailboats, RV’s or second main mobile
-9 Primary Mobile (usually message capable)
-10 internet, Igates, echolink, winlink, AVRS, APRN, etc.
-11 balloons, aircraft, spacecraft, etc.
-12 APRStt, DTMF, RFID, devices, one-way trackers*, etc.
-13 Weather stations
-14 Truckers or generally full time drivers
-15 generic additional station, digi, mobile, wx, etc
If you have any questions, please leave a comment. I love discussing APRS with colleagues from all over the world.
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