Hugh Blemings's Blog

Hugh Blemings's Blog, A Diary and Miscellaneous ramblings

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    Sun, 06 Mar 2005


    Have managed to clean up the transmit signal by relocating some of the internal wiring in the enclosure so it's a bit further from the transmitter PCB. Also re-routed the coax to the TX antenna and GPS antenna so they're as far apart as possible. Ran for about half an hour today and every transmission sounded clean and was picked up by the APRS network. Promising.

    Enlisted Rachaels help and we finished off the wiring harness and LED assembly which I've just put on the bike. Have managed to locate it so its in my normal field of view but not to the point of being a nuisance. Few photos starting here. Will see how it all goes on the ride in to work tomorrow, all going well you'll be able to track me here.

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    Sat, 05 Mar 2005


    Have had the PocketTracker off the Trike for the last month or so. Trial runs I did back in February went well so all that remained was to finish putting bits together properly. The time to do so was elusive however!

    I put together a battery pack out of 6 NiMH AA cells, 2300mA capacity should allow for around 20 hours continuous operation. This ought to be enough for a normal weeks worth of commuting between charges. Battery pack has a resettable thermal fues in line to protect against shorts - don't fancy things getting too hot...

    A waterproof multi pin connector allows for charging the battery without removing it from the trike as well as configure the Pockettrack unit via a serial port. A switch adjacent to the connector switches the Pockettrack between the serial port and the GPS module.

    A 3.3V rail is continually powered from the battery pack to provide a backup supply to the GPS module. This allows it to retain ephemeris data and keep the real time clock running for a faster restart/relock when power comes back up. Since this only needed to be a few uA I was going to just use a zener and a current limiting resistor but after talking to Gavin, a longtime friend and electronics/firmware/software hacker extraordinare, I went for an ultra low standby current 3 terminal regulator instead.

    Final bit of circuitry was a switch to allow the status LEDs to be either dimmed or switched off. The need for this became clear after being all but blinded by them on an after dark ride one time :)

    Last night I put it all together - bolting the connectors, switches and battery pack in to the box and wiring it all up. Quick test on the bench looked encouraging and continued pottering with it this afternoon. Put some photos up to this point starting here.

    Michael dropped over as I was bolting the unit back on, and we wheeled the Trike outside to do some real world tests.

    Unfortunately it seems there is some RF feedback or distortion of the transmitted signal so need to do a bit of digging into that. This had occured once before and was able to cure it with internal shielding so fairly sure can be sorted. Following a hunch of Michaels am suspecting RF is being coupled in through the GPS antenna cable as it was in close proximity to the transmit antenna coax.

    Aside from sorting out said interference all that remains is putting together a more permanent wiring harness for the status LEDs, hoping to enlist Rachael's help with that again so she gets some soldering practice :)

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    Sun, 27 Feb 2005


    Last weekends trip to Wyong was fun, felt varying degrees of blah thanks to the aforementioned cold but that was forgotten for the most part courtesy of the fun had. Bought a few bits and pieces (read: junk) and after some deliberation, rather to Michael's amusement I think, a new radio for the shack at home. Had done quite a bit of reading up of the reviews at on the Yaesu FT-897 and when the vendors had them discounted by AU$300 seemed too good an opportunity to miss.

    One of the attractions of the FT-897 is that it has a very similar menuing system/UI to the FT-817 that I already own. Main differences being rather higher output power (100W on HF, 50W on 2m and 20W on 70cm) and, basically, more knobs and buttons to make it easier to drive quickly. Picked up a 13.8V/20A switchmode power supply to run it as well as some Anderson "Powerpole" connectors so can have some sort of order in my DC connections. All works nicely nicely, talked to two stations in the Ukraine this afternoon (UX0IB and UR0MC) on 20m (14MHz) with 70W into the vertical on the roof.

    Have been tending to leave the rig scanning the local 2m and 70cm repeaters when I'm in the office so have had a few nice chats with local ham friends too. Nice to be back on air :)

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    Sat, 19 Feb 2005

    Off to Wyong

    Heading off this afternoon with Michael to the Central Coast Amateur Radio Club Field Day, better known colloquially as Wyong Field Day This is by far the largest Amateur Radio meet/field day/junk sale in Australia - first time I've got organised to go. Will be cool to do a road trip too :)

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    Thu, 03 Feb 2005


    Some further reading and research brought me to the conclusion that all that had happened on Monday was the GPS hadn't got a fix and so stopped outputting data after a timeout. There seems to be a facility to set this with the configuration tool for the module. In the meantime the solution is simply to give it a few minutes while getting ready to lock up. Suspect adding the aforementioned backup supply will help a lot as module can then do a warm start instead. Hoping to do the backup supply and real battery pack on the weekend.

    Did the run with the mob yesterday morning and system worked really nicely. The ride home similarly worked well. Bucketed down rain though so filed that under "Character Building"

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    Mon, 31 Jan 2005

    Hardware Wierdness

    Ride home didn't fare so well, checked the unit half way home and no LEDs lit at all. Further investigation once home suggested that the GPS module may never have got a fix and so the PocketTrack gave up and shut itself down thinking something was amiss. Lack of standby supply means GPS unit has to do a cold start - has no idea of time or previous location and this takes longer if antenna is moving. Have some bits arriving tomorrow to rectify this so will see how that goes.

    Well chuffed with results from this morning though, if nothing else transmitter and antenna are doing the trick :)

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    Encouraging results

    Ride in this morning went well, good coverage on route through the back of Cook - down Heart Break Hill, will see how things go this afternoon on the route through the ANU and AIS.

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    Sun, 30 Jan 2005

    PocketTracker setup taking shape

    Spent some time working on the PocketTracker setup this afternoon. Made good progress and was even more enjoyable for Rachael helping out with some of it. She can now fairly claim to have stripped some Cat5 cable, soldered LEDs and have a rudimentary understanding of how it all fits together (little antenna gets position from satellites, bigger antenna transmits a signal saying where I am etc.)

    About a week back I'd mounted a commercially made ground independent antenna on the back of the trike. The one I'm using is of Australian design and manufacture an RFIndustries CD28-37. Have added a bit of bright orange surveyors tape to top so it can do double duty as a second flag :)

    Today was basically finishing up the elecronics package to connect to the antenna. Took a sequence of photos starting here which gives a pretty good guide to what I've ended up with.

    Assuming it runs well this week, final steps will be to mount the batteries in the lid of the waterproof enclosure, rig up the status LEDs so they're visible while riding and wire up the multipin connector to allow the batteries to be charged and unit to be programmed without removing it from the bike. Once again, more to follow!

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    Thu, 20 Jan 2005

    Update on the Pockettracker

    Pockettracker rig I mentioned earlier seemed to work quite well which is pleasing.

    Have dissassembled the system and over the last week bought various bits and pieces to allow a more permanent installation. More to follow!

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    Thu, 13 Jan 2005

    Pockettracker System Integration (!)

    Couple of nights back Michael dropped over and we great evening chatting and doing some electronics hacking. I think we concluded it was the first time in about ten years we'd done that kinda thing so was well overdue :)

    Spent a couple of hours fitting the Pockettrack PCB into the die cast enclosure I'd put a GPS receiver module in about a year ago. Bit of a squeeze but went in ok. Initial tests before closing the lid seemed encouraging, module quickly aquired the SVs and we were off and running getting good APRS signals into the local iGate.

    Final checkout wasn't so promising, most transmissions sounded "dirty" like there was some RF feedback or such. Further investigation this evening confirmed that when the two boards (GPS and Pockettrack) were within a few mm of each other the RF output went noisy. Found a suitable sized piece of copper shield (plastic coated) on an old floppy drive PCB and shoehorned that in over the transmitter and soldered it to the PCB groundplane. Bingo! Clean as a whistle.

    Will try it out on the trike tomorrow so hopefully you'll see me riding in to work around 8am here

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    Mon, 10 Jan 2005

    First Tracking Test Results

    First go with the rather jury-rigged APRS tracking arrangement described yesterday seemed to work quite well, here is some output from FindU from the ride home

    Also found that the FindU site will let you pass a scaling parameter to the query so you get a more useful level of detail. Here is the "breadcrumb" track and last known location displays scaled so you can see more of the city area.

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    Sun, 09 Jan 2005


    Back when we were in Austin I ordered a pair of PocketTracker kits. The intention being to use one as a portable tracking unit (along with a GPS receiver module I already had) and the other to transmit weather data from the block. The only difference between them is the firmware in one of the PIC microcontrollers. The units transmit APRS data at low power in the 2m (VHF) Ham band and are quite compact.

    Completed assembly of the tracking board this weekend. Was quite fun, Rachael helped by placing some components and applying solder as required. Nice to be able to do a bit of hardware hacking for a change too. Pleasingly the unit fired up first go with a nice clean transmit signal on the local frequency.

    The various configuration options are set with a little (freeware) PalmOS application called pTTConfig. Duly configured I gave it an on-air test and with assistance from Michael, VK1TMS a few kilometers away, was able to confirm that the signal was reasonable. A bit more tweaking of the digipeating path brought it up on FindU via the local iGate. iGate is a system that takes off air APRS data and sends it to a central server on the 'net.

    Spent a couple of hours jury rigging it up on the trike using my Garmin handheld for a GPS. Permanent arrangement will be more black box style and involve less gaffa tape :) Took the temporary setup out for a quick spin just now, light setup on GT3 worked nicely, and thus encouraged will give it a go on the way to work tomorrow. With any luck you'll be able to follow my progress here

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