Tuesday, March 03, 2015

Cross Country HF APRS

Anyone that has visited my mobile ops gallery on my website knows that my mobile is set up for FM APRS mobile operations.
My main transceiver for APRS is the Kenwood TM-D710A, which may be the best choice there is for working conventional FM APRS.
Having said that, the best aprs system that you can have is only as good as how well you get in to the aprs network.  The aprs network is made up of digipeaters and I-gates strategically placed throughout the country. In large parts of Alberta the aprs network gives good coverage, however there are vast areas of eastern Alberta where I travel down roads less travelled where my beacons go unheard by the network due to lack of coverage.

To the west along the foothills that lie on the eastern slope of the Rockies, and within the Rockies themselves, the coverage for aprs is spotty at best. I began investigating in to the possibility of running HF APRS in my mobile allowing me to connect from remote areas of Alberta.
The HF APRS network that resides in North America is on the high end of 30 meters
This band is open day and night with the range on average being anywhere from 800 kilometers to 3200 kilometers or more depending on the time of day and band conditions.
Many APRS stations are silently monitoring this channel for beacons and will gate transmissions heard to the aprs Internet system.

You can easily get aprs position reports to aprs.fi and to individual Internet connected aprs users from the remotest corners of North America, and this means all and every part of Alberta.
With time spent at my computer doing research, I slowly formulated a plan for putting together an HF APRS system in my mobile.
Wanting more than just being able to be placed on a map and tracked as I moved about, I also wanted the capability to have a fully bidirectional system capable of messaging with other HF APRS stations across North America.

Conventional APRS activity on HF uses 300-baud 200-Hz-shift FSK AX.25 packet.
From my research I discovered that this form of packet that has been around for decades is a rather poor mode for HF, as the 300 changes/sec symbol rate, combined with no form of redundancy or forward error correction in the packets, makes conventional packet extremely susceptible to the noise pops, static crashes, and interference from other stations on HF unlike FM APRS.
While doing research I discovered that there is now another form of packet being used that uses a form of PSK-31 that transmits about 30 symbols per second compared to 300 for the classic FSK packet.

This new form is using PSK-63, a faster variant of PSK31, and this is what I decided to base my new HF APRS mobile station on.
After more research I decided to use APRS Messenger an application developed by Chris Moulding G4HYG located in the UK.
This program uses PSK63 to send and receive APRS beacons and messages.
I already had the HF rig that being my Kenwood TS-480HX.
The next piece of equipment required besides my 480 HF transceiver was a computer, and I already had that in the form of my Toshiba netbook that I use with my Kenwood D710A while mobile.

With APRS Messenger being a soundcard application, I could have utilized the soundcard that resides within my netbook, but I didn't want to have more cables than I had to cluttering up the inside of my mobile, and besides my Kenwood 480 has a data port available that would only require one cable.
I was aware of the terrific external soundcard device in the form of the Tigertronics Signallink USB and soon ordered one from Tigertronics in Oregon.
Once I received the SignalLink USB, it was a simple matter of connecting the data cable included to the data port on the Kenwood 480, and then connecting the USB cable from the SignalLink to the netbook, and windows 7 loaded the drivers and I was good to go.
Well maybe not quite, as I also had to purchase a GPS antenna that could be utilized with my netbook.
The GPS must provide an industry-standard NMEA-0183 output at either a physical or virtual (i.e. from a serial<-->USB dongle) RS-232 serial COM port.  The GPS must be set to operate at the NMEA-standard 4800 baud output.
After checking out the various options available to me, I selected the Model BU-353S4.GlobalSat BU353S4 SiRF Star IV USB GPS Receiver as seen mounted on my radio stack.

With everything connected up it was only a short time before I had the SignalLink device set properly and communicating with APRS Messenger. I soon had APRS Messenger set up the way I liked, and in short order I began to see my mobile VE6AB-63 symbol appear on the map at aprs.fi.
Upon checking the raw packets for VE6AB-63 on aprs.fi, it was very cool to see that I was being heard and I-Gated  by stations located in Montana, Iowa, and Washington state. I was good to go!

Those of you using conventional FM APRS, know that the biggest SSID that you can use is 15.
Because I am running HF APRS, and in particular PSK-63 APRS, I am able to use the SSID 63 (VE6AB-63) that indicates that I am an HF PSK-63 APRS station
So the next time you see my VE6AB-63 APRS symbol on the map, you know that I am running HF APRS Mobile.
Note...everything going on in the photos of the radio stack in my mobile are temporally positioned, as I wanted to show you all the devices that make up my HF APRS mobile station.
Also, my netbook shows both APRSIS32 as well as APRS Messenger running at the same time, as both my Kenwood TM-D710A, and my Kenwood TS-480HX are simultaneously connected to my netbook running the two applications.

Now I covered the basic's in this post on assembling an HF APRS system, however there is a bit more to it than that, for example under no circumstances do you want to set a path in APRS Messenger asking to be digipeated.
Set a path of WIDE2-1 and call it done, as you don't need or want to be digipeated causing hate and discontent across the continent and beyond.
With the path set for WIDE2-1 you will be heard and I-Gated in to the Internet.

Also with PSK-63 you do not want to use more than 15 or 20 watts, as PSK-63 is two simultaneous tones, and the average power output of your radio has to be kept under 25 watts to prevent severe intermodulation distortion of the two tones.
There are also a few other things you need to do with the settings, so if you decide to go HF APRS mobile and have questions drop me an email.

One final note, although my 10/80 meter gearmotor antenna covers the 30 meter band, I built a new 30 meter monobander coil especially for 30 meter HF APRS mobile.

Note...all photos expand....


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