LoRa GPS Tracker

LoRa is a newish Internet Of Things communications technology.  It promises long range (LoRa), transmits a small amount of power and is designed for sensors that may need to operate from batteries for very long periods of time.  The air protocol works at very low received signal levels, with down to -148 dBm claimed with low data rate transfers.

There are several LoRa modules available for very reasonable prices from Ebay.  I purchased 3 x AIThinker RA-02 modules for $20.  These modules use the Semtech SX1278 chip which packs in an amazing amount of functionality.  The module is capable of +17dBm transmit, with a boost mode for +20dBm (100mW).

One of the LoRa bands is 433MHz, in the 70cm amateur band.  With an interest in a low power GPS tracker that could be used as the “last mile” for APRS and hiking, a test transmitter and receiver were designed and assembled.

LoRa is intended to work in a network topology with nodes that talk to field units (LoRaWAN), but there is a peer to peer mode using the LoRa protocol that has been made available by the Radiohead driver collection.  I used Arduinos for the control side of things as there are many drivers and sample applications available.  The GPS is a UBlox 6M unit, not the smallest, but works well.

The system was set up for a 125kHz bandwidth and a spreading factor of 11, which gives a data rate of 500 bits/sec.  Initially, I tried a spreading factor of 7, giving a 5000bit/sec. data rate and this worked for a couple of kilometres with the receiver sitting on the car dash.

For a more controlled test, I set up the transmitting unit in the back yard connected to a mobile whip that was about 3 metres above the ground.   The receiver was packaged up in a small speaker enclosure and fitted with an LCD display so I could see the decoded packets.

I went for a ride on the bike with the receiver and chose a distance 5km from the transmitter that was non line of sight to see what would happen.  To my surprise, packets were decoded, a few were missed depending on antenna orientation (a 70cm portable rubber duck).

Here is an elevation plot of the radio path:

 

 

 

As you can see, it is not line of site.

Here is the GPS tracker:

GPS Tracker

LoRa Receiver

Here is the receiver:

Power for the tracker is supplied from a single 18650 LiPo cell.  A 3.3 volt supply is used for the Arduino Pro Mini, Neo 6M GPS and RA-02 LoRa module.

To save power, the GPS is powered up every minute at the moment for testing.  A REG103 LDO regulator with shutdown is used for turning off the GPS receiver and RA-02 between transmissions.  The initial cold fix takes about 30 seconds inside the house.  Subsequent warm fixes are very fast at about 2 seconds.

With the Arduino sleeping between the 2 minute GPS reports, the cell should last about 15 days.  The idle Arduino Pro Mini sleep current @ 8 MHz is about 2 mA.  The GPS uses about 60 mA and the LoRa transmit, about 120 mA.   It should run for more than two weeks hours on a 2500 mAh cell (providing GPS signal available, if not it will spend longer searching).   After a warm start, the GPS only takes a couple of seconds to acquire.

With the LED removed and the regulator bypassed, the sleep current should be even lower.

Tracker packaging

For the moment, the tracker is packaged up in a section of PVC pressure pipe with the cell.  This is quite robust and water resistant although not very efficient in terms of space.

If I can source a robust enclosure of the right dimensions, it could be much more compact.

PVC Pipe Housing

The housing turned out to be far to big, so I found a standard ABS enclosure that was about the right size and rebuilt the board to fit.  Unfortunately the 2500 mAh cell was too big for the enclosure, so I had to settle for a 1000 mAh cell with a rectangular footprint.

This cell fits very well, but the run time is now reduced to about 1.5 weeks, assuming a report time of 3 minutes.  The idle current has dropped again by reducing the bleed current from the Arduino port pins to the LoRa module.  The port pins are now all set low before entering sleep mode.  The idle current is now sitting just over 1mA.

New smaller case

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NanoVNA and EFHW

The NanoVNA arrived the other week, these units are very good value and work remarkably well.  With small size and weight (63 grams)including battery, it can easily be taken out in the field, providing it is protected from the elements.  The NanoVNA is a PCB sandwich essentially, with open sides.

The first test was to sweep the filters in the compact 20 metre transceiver.  The filters came out pretty well spot on.

Next test was the 3 band SOTA portable end fed half wave antenna to see if it was still in resonance after many activations over the last few years.  It had been repaired a couple of times after tree snags, and maybe lost a cm or two.

The antenna was tested as a sloper in the back yard with one end supported by a 6 metre squid pole, and the feed end supported by a walking pole.  It was also tested in the same configuration but using an 8 metre squid pole.  The results only changed slightly, lowering the resonant frequency.
A short counterpoise was connected but this made very little difference to resonance.
The shots below have some light reflections, it would have been better to connect a PC, but convenience won.

40 metres using 6 metre pole

 

20190906_121349

20m using 6 metre pole

10 metres on 6 metre pole

 

40 metres using 8 metre pole

20 metres using 8 metre pole

10 metres using 8 metre pole

 

 

 

 

 

 

 

 

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20 metre SSB Compact Transceiver

This one follows the design of the DK7IH Cigarette Packet Micro Transceiver.  The changes made to the original design are:
– Plug in front end, transmit driver and PA low pass filters
– FET power amplifier (IRF510) rather than bipolar
– Toroid filters for front end, transmit driver and PA low pass filter
– Discrete crystal SSB filter
– Nokia type LCD display

The construction is mostly SMD on the bottom of the board, with leaded parts on the top side of the board.  I didn’t make a PCB for this one, it is built on pad per hole prototyping board.  Earthing could be a problem, so lots of earth run around the board underneath.  It does look  rather untidy compared to the previous compact transceivers where a PCB was made.  Maybe a PCB later on if it works out ok.
I like the idea of swapping the clock generator outputs to the mixers in software for receive to transmit switching.  It certainly simplifies re-use of the mixers for transmit and receive.

So far the receiver is working fine, with a 0.1 uV minimum discernible signal (MDS).  Still some work to do on software before the transmitter can be tested.  The SSB filter is slightly broader (~ 4kHz wide) than intended although the response shape is good.

The main transceiver and clock generator board is 50mm x 100mm.  With some luck it will fit into a 60mm x 120mm x 35mm enclosure.  It may end up being a hand held type HF radio if things work out.  Of course, it will need a trailing ground if used in this configuration.  There also needs to be some access to the plug in band modules on the enclosure.

20m Compact Transceiver

 

 

 

 

 

Mechanics test fit:

Hand Held Layout

Hand Held Layout

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New Case for the QRPLabs QCX CW Transceiver

The QCX transceiver was previously packaged in a standard plastic enclosure from Altronics.  The fit was good and the extra space allowed for a battery pack but metal is a better choice for RF.
I was not satisfied with the ergonomics of the controls so I decided to repackage it in an aluminium case.  The HB metal bender was used to make a simple two part case from 1.2mm aluminium sheet.

The case turned out quite well although I elected not to make space for a battery pack this time, and rely on external power.

Finished Case

This layout makes a bit more sense than the original one.

The most used control, the VFO is in the clear and the others further back.  I also turned up new knob for the VFO.

The switches will be set lower into the panel later as the RH one is close to a  trimpot inside the case .

Lid off the case

Here the lid is off the case.  To secure the lid to the base, four 3mm aluminium right angle brackets are fitted to the base and also serve as mounting studs for the board.  The brackets are threaded to accept the 3mm screws for the lid.

A brass shaft extension is added to the rotary encoder.  I may put a bearing in the lid from an old pot later on if play is an issue.

Left side with audio out

Right side with key socket

There is provision on the RHS for a switch to add a cap for operation on 30 metres (the unit is 20 metre).   This works fine for receive and probably needs something added to the LPF on transmit.

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Three Summits around Falls Creek

With nice weather forecast and a day off on Monday, it was an ideal opportunity to do a couple of new summits in the Falls Creek area.  I left home in Melbourne’s South East at 7am on Sunday and took the more scenic route via the Princes Freeway to Bairnsdale and then North through Omeo.
Once past Omeo I took the Bogong High Plains Rd., which was new for me.  This road is sealed and in very good condition although there are many twisting turns so progress is quite slow.

I arrived at the Mt Cope car park at about 1pm., from here, the walk is short (about 1.5km each way) and starts at the Bogong High Plains Rd.  Apart from a ranger posting a sign about upcoming deer shooting at the car park, I didn’t see anyone else.  Mt Cope, VK3/VG-001 at 1837 metres is a 10 point summit.

At the summits, contacts were made on 20m and 40m including a summit to summit with Brian, VK3MCD on Mt. Granya.  ZL, VK1, 2 and 5 call areas were worked.  Cell coverage was good and there were plenty of trees to bungy the squidpole to.
After about 11 contacts, I headed back to the car.

There wasn’t a lot of time left in the day, so I went to Mt. McKay as it is a drive up summit and should not take too long.   Mt McKay, VK3/VE-007 at 1849 metres is a 10 point summit.  Just before the car park on the summit, there was a short pipe sticking out of a rock.  This was ideal to fix the squid pole to, the antenna was unrolled and I set up on the top of another rock.


Two ladies came over and asked what I was doing with the fishing rod and were suprised to hear me talking to ZL1TM.  A summit to summit was made with Peter, VK3ZPF on Mt. Donna Buang.  Most contacts were made on 40m.  ZL, VK2,3 and 5 call areas were worked with some very strong signals.

As it was 4pm, I went south back down the Bogong High Plains Rd. looking for a campsite.  The Raspberry Hill campsite looked ok and it was empty, so I set up there for the night.  As the campsite was at 1600 metres altitude, the temperature dropped sharply at sunset and before long it was hovering at 2 degrees.

In the morning I left the campsite at 8am and drove back up the High Plains Rd. towards Falls Creek for the walk to Mt. Nelse.  The car park for the Big River Firetrail is just short of Falls Creek.  Mt Nelse, VK3/VE-004 at 1882 metres is a 10 point summit.

The walk to Mt. Nelse is about 12 km return.  Most of the walk is along a 4wd track in open plains.  The track goes past the closest point to the summit and then a walking track doubles back to the top.

At the summit, there are the remains of a trig point consisting of a vertical pipe a metre or so long. This makes a good fixture to attach the squid pole.

All contacts were made on 40m within VK2,4, 5, 6 call areas.  By now the wind was  getting up and the chill factor biting, so the kit was packed up and I returned to the car.

Throughout the area, 2m APRS worked very well via Mt. Hotham digipeater.

The trip home was by the same route via Omeo and Bairnsdale, taking about 6 hours including a fuel stop.

Posted in Hiking, SOTA | Tagged , , | 2 Comments

144 MHz for the KX2 Transceiver

Many times I have thought it would be nice to have 2 metres on the KX2, I do miss it from the FT817 days.

This bare board transverter was on Ebay from a Ukraine seller, the feedback was very good and it looked quite compact so for about $35, I ordered one.

Bare Board Transverter

It took about 4 weeks to arrive, but it was over the Christmas break, so probably not too bad.

Internals

It measures about 80 x 45 mm, a very suitable size for portable operation.  The power output is stated as 10 to 15 Watts, so not too shabby.

A metal case was then bent up using my home brew metal bender.
A relay switched attenuator

Boxed up

was grafted between the PCB and the transceiver side BNC socket.  I was satisfied that the leads were short enough not to cause a problem.

A 10dB attenuator is fitted to a stand off post to make it level with the relay.  The T configuration attenuator is made from paralleled 0805 SMD resistors so that the power rating is 1 watt.
The KX2 will be set up for about 500mW out so that the maximum drive level of the transverter is easily met.

The KX2 has some nice configuration options to suit transverters.  Parameters such transverter number (you can have several), power output, frequency offset etc. are easily configurable.  In fact, the default configuration was fine.
When powered up, the transverter worked straight off.  Power out was around 10 watts, more should be possible, but will wait until the linearity can be monitored.  Sensitivity seems ample as well.

Connected up

 

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Mt McLeod VK3/VE-034 SOTA

Mt McLeod was on the unfinished business list after we ran out of day light a couple of years ago when it was summit 3 for the day and decided to turn back.
Kevin, VK3KAB and I decided to have another go, this time as an overnighter rather than a day trip.  We left Melbourne on Boxing day with a leisurely start of 11am and arrived at the fire trail gate on Crystal Brook Rd., off the Mt Buffalo Rd. about 4pm.   This would avoid the heat of the day.
There is very little space to park the car near the gate to the Mt. McLeod Firetrail and thankfully there were no other cars.

The walk took about 2 hrs 30 minutes to the Mt McLeod bush campground.  We had pre booked a campsite there for the princely sum of $13.60 from the Parks website.

The walk is about 8km to the Mt McLeod campground and about 1km further to the Mt McLeod summit (one way).  My pack weighed 19kg, including 5kg of water as we were not sure of water availability.

on the way

There is a signed alternative route to Mt McLeod that avoids a partial section of the firetrail.  This route roughly follows a contour line and avoids a small climb on the firetrail, although I am not sure it was worth it.  The track was a bit overgrown and there were fallen trees in several places.  The alternative route is incorrect on the maps that we had with us, see the plot from the GPS later.

The hike has a lot of ups and downs and with the higher temperatures we had on Boxing day, going was a bit slower than normal.  The campground is just a cleared area near a creek and marshy area with a pit toilet up the hill a bit.  There was ample water supply from the creek, so we could done without carrying 5 litres or so each.  We were the only hikers there and we did not see anyone else during the two days.

campsite

Mt McLeod from the campsite

The next morning we arose about 6am and took the radios to the summit.  As the day was predicted to be hot, we thought it best to get an early start and return to the car as early as possible.  Kevin set up a linked dipole from a squid pole on the summit, an I set up the loaded end fed on a mini squidpole tied to a tree.  I qualified on 20m and Kevin on 40m.  Conditions were fairly average.

The walk out was uneventful and took about 2 hrs 15 minutes with temperatures around 30 degrees towards the end.

I must have had my laces loose as my toes took a beating on the many downhill bits with them ending up rather bruised and painful!

After we returned to the car, we drove to The Horn and did a quick activation hand held using the KX2 and the Diamond RHMB2 loaded whip.  There where tourists everywhere so we activated just in the activation zone where the railing starts.

 

Summit views

Summit views

 

 

 

 

 

Trig

KX2

GPS track

Elevation Profile

Posted in Hiking, SOTA | 4 Comments