APRS Tracking quits

Discussion in 'Homebrew and Kit Projects' started by KD0FRT, Dec 15, 2008.

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  1. KD0FRT

    KD0FRT Ham Member QRZ Page

    I'm new to the operating of Ham radio but not by far new to radio and electronic hobbies. For some reason I have a sick obsession with building electronic things... And there it is.

    Bought an Argent Datasystems OpenTracker+ kit and assembled it, then went in to configure. My GPS solution had not presented itself at that point so I manually set my Long/Lat and selected do not require a fix. Ran into several issues getting my testing radio to operate properly.

    Using a RadioShack HTX-202 I bought off ebay for $30 to test this stuff with until I get it perfected then I have an OOOOOLD Kenwood 2m mobile for the perm. install in the selected vehicle. Oddly if I have the OpenTracker module powered up with a very well regulated power supply (I use ATX desktop PC power supply to power my electronic devices, afterall you can't get a WHOLE lot more regulated than those anywhere near the price. The unit Im using is rated 20 amps max @ +12vcd, 30 amps max @ +5vcd.)

    If the OpenTracker and HT are both powered by the same Power supply when the tracker keys up the transmitter it introduces a VERY bad hum which sounds similar to a 60hz buzz. Tried several different power supplies to no avail, so I'm just testing it with the battery pack on the HT. No big deal.

    Okay, so this sucker sends my data to the APRS network and my icon ends up on the OpenAPRS.com page right away.

    My GPS solution presented itself with something I already had laying around and never use. The "Microsoft GPS receiver" also known as the Pharos iGPS-360/500. More research yields the GPS receiver sends out a TTL signal instead of RS-232, so I built a TTL -> RS232 converter from a MAX232 chip and a few caps. Soldered the connections directly onto the exposed connector of the GPS unit and powered it all up. To my delight the OpenTracker+ was blinking red rapidly so I moved it outside and it locked onto a satellite signal very quickly. Attaching my transceiver again it located and sent my position to the APRS network.

    Now I understand theres a ham I found through a search that the iGPS wasn't a very reliable unit, so I'm thinking this is where my problem is. If I get in my car and drive, knowing good and well that I'm hitting the digipeters (driving right past several on a daily basis, if thats not enough of an indicator I don't know what is!!) after a few minutes of driving it no longer sends my location. I see the transmitter is keying on the intervals set, I can monitor and hear my data transmissions, but when I check my progress on OpenAPRS's map 99% of my trip is missing.

    Is there an easy way to diagnose that it is, infact the iGPS gizmo thats causing my problems? Something aside just replacement of that POS with a solid reliable receiver? :p

    Anyone have an Axiom Sandpiper II laying around they'd like to sell me? Didn't think so.... ;)

    -Scott
    KD0FRT
     
  2. KA1MDA

    KA1MDA Ham Member QRZ Page

    "I use ATX desktop PC power supply to power my electronic devices, afterall you can't get a WHOLE lot more regulated than those anywhere near the price. The unit Im using is rated 20 amps max @ +12vcd, 30 amps max @ +5vcd.)"

    Not always true! Many switch-mode power supplies need a minimum load to properly regulate, somewhere around 10% of their rated output. If under-loaded, regulation may go out the window. Many computer supplies also tend to regulate based primarily on the 5 volt rail, with the other voltages being fixed ratios of the 5 volts. I have seen lots of ATX supplies with great 5 volt regulation, but have seldom seen any with the output at 12 volts (most around 11.5 to 11.8). Even if the 12 volts was perfect, it's still short of the 13.8 volts required by most mobile devices.

    The hum is probably RFI from the transmitter getting into the power supply or audio lines if they are unshielded, unbypassed, or both.

    "(driving right past several on a daily basis, if thats not enough of an indicator I don't know what is!!)"

    Means absolutely nothing. APRS here is so overcrowded, the packet collisions are unreal. Many APRS digis are set to ignore position reports sent at intervals of less than 2 minutes. If you're beaconing every minute or less, the digi's could be throwing out all your packets as spam. Many digis have also stopped supporting the RELAY command. If you still have RELAY in your path setting, try taking it out.

    The only real way to diagnose what's happening is to monitor your own signal on another radio in close proximity and see if it's sending valid position data. If you know anyone with a Kenwood TM-D700 or 710 in their vehicle, ask them to follow you on a short trip and see if their radios are decoding your packets. You could also use a laptop running UI-VIew or something similar, decoding audio from an HT thru the sound card.

    Bottom line is you need to figure out a way to look at the APRS data before it goes through the digi to isolate if it's a GPS, radio, or digi issue.

    Tom, KA1MDA
    www.ka1mda.org
     
    Last edited: Dec 15, 2008
  3. KD0FRT

    KD0FRT Ham Member QRZ Page

    Now that you mention the transmission intervals I fail to remember what I set it at. The config I have saved on the computer is showing 300 seconds but I can't remember if I set it to 300, 120, or 90. The path it shows set in the software I left to default according to a wiki page it was what recommended anymore, which reads "WIDE2-2" so I'm pretty sure its not set to relay.

    Last night was the first time I've really attempted to go for a long drive and test it and I only got 3 miles or so before it crapped out. Will defiantly have to try and bring my notebook along and see what its sending.

    Thanks!
     
  4. KA1MDA

    KA1MDA Ham Member QRZ Page

    I forgot to mention, the radio's squelch setting can also have a huge effect on APRS coverage. If the squelch is set too high, the radio does not hear other APRS packets, and tries to transmit on top of them. If the squelch is set too low, the radio may never send an APRS packet as it thinks the frequency is busy. You may want to experiment with the squelch setting and make sure the tracker is properly responding.

    Tom, KA1MDA
     
  5. KD0FRT

    KD0FRT Ham Member QRZ Page

    Have another update.

    I've found what I've read about the HTX-202 for any kind of data transmissions it underperforms. Seems to be a great radio to carry as backup and talk on once in a while but just doesn't cut the cookie with packet.

    Finished making the cable to connect the OpenTracker to my Kenwood TR-7950 and slapped it in the car.

    Drove from My house in KC to Topeka and back, then checked my 4 hour history on openaprs.net. It shows my entire trip, but the trip is slightly... Well.. Skewed. What I read about the Pharos GPS receiver also seems true. Its pretty accurate for a few minutes then it starts to get way off in position. Noticed using that on the GPS dongle hooked to streets and trips a few years ago, but it didn't really occurr to me. Will be ordering a better quality GPS unit here in a few days.

    Still looking for the Sandpiper.. No luck... ;)
     
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