I think today I received another  great lesson in why it’s “good to grow up in a Metric world”.

I dropped into our local rigging store A. Nobles and Sons to pick up a Collared eye bolt for my tower, however they were out of stock of M12 collared eye bolts.  Ok no problem there’s a 1/2″-UNC option that I can just substitute.  I would have needed to purchase a M12 nut regardless, no harm done.

So off to the local bolt and nut store United Fastners just around the corner and pick up a suitable 1/2″-UNC nyloc nut.  However sitting down at my desk at work I try to dry assemble the eye bolt and nut and they will turn 1-2 turns and then bind.

So out with the thread gauge, nut 12-tpi check, eye bolt 13-tpi, Umm hang on a second I smell a dirty rat.  Turn eye bolt over and read from the bottom…

*&^%$# that 1/2″ thread it’s a Whitworth (BSW) not UNC !!!

Anyway snot-a-gram sent to Nobles, we wait to see what fun that will create.  However once again I find that there are two thread pitches being used for the same imperial sized bolt which are not visually different enough to raise suspicion.   I’m sure that the old timers that grew up with this UNC/BSW thing would be having a good chuckle.

Serves me right for not dry fitting them in United Fastners and finding the obvious mistake… but this variation between tpi in imperial is quite simply at times unbelievable, this is the second time I’ve struck this issue this past year.  don’t get me started on 1/4 & 1/2 tapered pipe threads, you’ll see the fun I had there with the Hilux Turbo EGT sensor.

I’m lucky that I work for a business that has been around for more than 50 years… So at morning tea time I droped into visit the onsite Fitter and Turner, there I find we have surplus 1/2-BSW nuts that have been quickly turned down to half-nuts so I can lock them together and stop the collared eye bolt from undoing.

So now all I have to do is assemble everything, watch this space.

HAB Diplexer

This past week after work I’ve been working on a RF diplexer and filtering arrangement for a HAB Crossband repeater we’d like to fly on this coming weekend.  So after a bit of simulating and gnashing of teeth I came up with the following arrangement.

HAB Diplexer Circuit

The Crossband repeater will RX on 2m and TX on 70cm using a single HT 2m/70cm antenna suspended under the payload.  Being worried about interference from high power VHF services on the input to this repeater and high harmonic content on the transmitter I decided to use BPF arrangements.   We’re only using Dorji modules on the repeater to keep the weight down, so too much RF at their front end would cause them to freak out a little when suspected 35km above the earth with a radio horizon of 800km or more in all directions.  These modules are also known for having a fairly rich harmonic output on the TX.

In the past I’ve build a few of the filters designed by Tasa YU1LM, so I’ve borrowed his high performance 2m BPF design, you can find the original article on this page (click).  Tasa’s designs are excellent and easily reproducible, so many thanks to Tasa for sharing his knowledge !

The remaining circuits in the arrangement above are standard HPF, LPF and manufacturer reference designs which were optimised for various characteristics.

Having completed the theoretical part it was time to build it.

The board was quickly roughed out in a CAD package and thanks to Mark VK5QI a routed board produced as the first prototype.   Routed boards require you to pick off the large expose sections of copper on the board, so 30 minutes with a scalpel under the microscope and I had a board that was looking the business.

So then all that was left was to populate it, which is easier said than done.  The worst part was the ground plane stitching which was done with a combination of 0.7mm TCW and 0.35mm wire-wrap wire.  However I’m pleased with the result.

Now the inductance of the coils in the 2m filter were initially too high, so a turn was removed after this photo was taken.   The response of the 2m filter (with 5T coils) after a few minor tweaks pulling and pushing coils together can be seen below;

Not too shabby.  The Insertion loss is a little higher and the bandwidth a little wider than I had simulated, but all in all that is the beginnings of a quite reasonable 2m BPF.  The two frequencies you can see in the marker table are the RX and TX frequencies of the cross band repeater respectively.  So the filter is giving a isolation between ports of greater than 55dB which should keep things going well.

However looking at the 70cm port told a different story.

The TX harmonic filter had a terrible response with the cut off frequency below 400MHz, so that was killing any chance of the diplexer working satisfactorily.   So I temporarily bypassed the harmonic filter so I could see what the 70cm HPF was doing, the plot of that is below.

The insertion loss is still too high, but moving the cut off frequency 40MHz higher should restore the insertion loss figures I’m aiming for (<1.5dB), so I’ll pull out the simulations and see what i need to to change.   Looking at the response it’s quite apparent that parasitic capacitance and inductance has crept into the design via the PCB, so with luck we can tweak this back to where we need to.  I’m not lucky enough to have the tools that allow me to simulate the effect of the PCB design as well, sigh.

Anyway we have the makings of a 2m/70cm HAB Crossband Repeater Diplexer, now if only i had another week in which to play with it and perfect the design (grin*), launch will be in two days time nothing like a bit of pressure.

Tower Project – Foundation

Now the entire reason for building a new shed was so I could plant a 10m tower by the front door.  It wasn’t just about getting some more space in which to store stuff you see.

I’d been without a HF beam for the past 3 months while the shed was being built, so having the tower go up at the same time was the cherry on the cake.

I’d purchased a second hand uninstalled NBS Antenna Tilt mast that should do the business of holding up my Hexbeam.  It has also been sitting languishing this past 15 months in a corner of my yard.

So during the shed construction, prior to the concrete floor being poured I had a local contractor come in and excavate the foundation.

The ground as I’ve explained previously is hard to dig.  The clay holds what look like river pebbles that are smooth, when you get clear of those you find layers of limestone.

This should not come as a surprise since the Torrens River is not that far away at the bottom of the hill over my rear boundary.

I’m thankful that we managed to achieve a depth of just over 1200mm.   That meant I had to modify my foundation design a little to ensure I got enough weight into the hole to overcome any uplift from the tower and antenna at a later date.

The hole is over 900mm wide at the top and ratchets down to 450mm at the bottom.  You can quite clearly see the soil profile.  This hole took just shy of 4 hours to excavate with a 40hp Bobcat with auger, I’m glad I didn’t have to dig this by hand.

With the hole not being quite deep enough I modified the base to include some addtional steel reinforcing.  This meant I could then grab hold of the concrete at a greater distance from the pole.

Additional steel was later added and wired to the horizontals before being encased in concrete.  To get the mast base in the right place I had to offset the steel to ensure nothing protruded from the concrete block above a depth of 600m.

After the concrete had been poured they even finished off the pad to make it look neat.  There was also a layer of mesh added in the top box to give it that little extra strength and a fall of 30mm from the centre to the edges to ensure water does not sit where it is not wanted.

From here I’ve got to wait 28 days for the concrete to harden to 80% strength before I put the tower up.  This is going to be murder.

Shed Project – Concrete

So with the shed basically installed it was time to call in the concrete contractors and let them do their thing.   I was thankful to find a local concrete company that gave me a fair price, turned up on time every time and was a pleasure to work with.

You know things are getting serious when your concrete truck is willing to drive overland to get to your job site fully laden, I’m glad he had a seriously low range box and diff lockers.

Meanwhile the boys were getting the interior of the shed prepared, you can see the first three feet of concrete is being wheelbarrow’d into place.

And by the end of the day it was flat and smooth.

Now the more observant reader might have spotted the steel work by the front door, I’ll explain a bit more about that in another post.  But for now I’ve got to wait for the concrete to harden and then start filling my new space with my stuff !  and finish the door and locks.

Rear Diff Repair

Well after a few months of driving the Hilux it was apparent that all was not well with the rear diff pinion bearing.  It was howling and making terrible noises at highway speeds, it was so loud that you couldn’t talk to people in the back seat.   One afternoon after a run out to Chris VK5CP’s shack at Younghusband I noticed oil coming out of the rear drivers side wheel, so it was now time to fix it.

Upon undoing the nuts on the rear drivers side wheel oil began weeping from the threads, this was not going to be good. Yep just as I feared the inner oil seal had gone and diff oil had run throughout the drum brakes, bugger that’s got to be fixed now.  So once I’d removed all of the brake gizzards the drums were sent off to be machined, over sized brake pads radius-ed and new master cylinders obtained from the local brake repair shop.

The tricky part of this diff rebuild was getting the axles out.  They are quite different from my old Land Cruisers and I again phoned a friend Gary VK5FGRY to help me get it apart.  After removing  the brake lines (oh yay!) and four nuts the axles, backing plate and wheel bearings simply slide out as one assembly.  The wheel bearings were also very growly, so off to the local mechanic with these since you need a press to do the job properly.  Don’t forget to do both sides.  Car stands and a trolley jack are mandatory to do this safely.

Then the fun bit of getting the diff centre out.  That is simply undo 12 nuts and then prepare your self for the heaviest close quarters bench press of your life.  I still cannot believe how heavy the diff centre of the old Hilux actually is.  Anyway once out the initial inspection suggested just bearings would be required, but alas no.   As with all diff rebuilds they tend to be like an onion, once you start peeling the layers back your eyes water more and more.  Anyway for the precision diff stuff I sent it to a local diff re-builder to be looked at.

So a day later I get the dreaded call that tells me the surface hardening on the crown wheel and pinion was completely gone (worn away completely) and the spider gears were wearing on two faces instead of one.  That meant a complete diff rebuild, new crown wheel, pinion, bearings, spider gears etc.  Basically I’d given then a nice diff housing and carrier and well the rest was buggered.  I guess after 410000kms it had simply had enough.

“In for a penny in for a pound” was my Grandfathers favourite saying at times like this, I can still hear him saying it.

So after an eye watering $2300 in materials I was ready to rebuild the diff once and for all.

So the first job in rebuilding this diff was cleaning out the insides of the diff and to remove any previous traces of metal.   So armed with tins of degreaser, white rags and a broom handle we mopped and cleaned the inside of the diff housing until it was as clean as a whistle.

Then the fun job of wrestling the diff centre back into it’s position was tackled.  All nice and black and shiny this time.   I’ll admit installing cleaned parts that aren’t oily is always a nice change and a real turning point in any project.

The new pinion that was installed in the new diff came with a larger input shaft, it’s now 41mm instead of 39mm.  So that should be able to take the additional torque that the new motor puts out, so this diff rebuild is good in that respect.

Once the diff centre is in the axles can be reinstalled and the brakes put back together.  I really like the way in which Toyota prevent you from damaging the inner oil seals, hard to explain but the axles can’t hit the seal while your sliding the axle back in, it’s very ingenious and you’ll find out what I mean if you try it.

I spent a fair amount of effort cleaning up all of the brake components and they won’t look like this the next time I service the brakes.  However the proof that I’d done a good job of the cleaning was when we simply used the handbrake to adjust the drum clearance.  The winders when the handbrake is pulled will slowly wind the shoes out until they meet the drum.  The tension between the winder and springs keep things tight and the clearances small, meaning when you step on the brake pedal they actually work.

So from here it was get the other side done, reinstall the tail shaft and wheels, put oil in it and take it for a drive.  Don’t forget the oil, bad things happen.  Again I’d have been lost without the assistance of Gary VK5FGRY, there is no limit to the things that I learn each time we repair this Hilux in some way.  There’s not much of the insides of this old girl that I’ve not seen yet.

I still remember the first time we drove it out and onto the street.  About 100m down the road I say to Gary “do you hear anything” and the answer was “No”.  Cool job done.

So then the real fun of breaking in a new diff starts, being Mr Goody two shoes for the first 500kms, keep the speed down, don’t flog it up hills, no wide open throttle etc were obeyed.  After 1200kms the diff oil was then changed (yes I was 200kms late).  So far so good, there have been no subsequent leaks and the whole car has changed, it drives just like a new one.

Shed Project – The Main Event

With the retaining wall out of the way I could get the shed builders in.   This is the first time I’ve not assembled my own shed, I wanted this shed done fast, in total it took 4 days for the shed to be assembled including material delays and supplier issues.

The ground where I live is basically heavy clay that includes limestone balls.  You can hit this stuff when dry and it’s hard like concrete, when wet your tools bounce like they are on a trampoline.  It’s really tough to dig.  There were 8 holes required dug to a depth of 450mm, the poor builders are on a fixed price contract and required a full day just to dig the holes.

The back wall went up on the beginning of the second day.

It was about now that I realised a 3m high shed (at the eve’s) was large.  It doesn’t sound very big off the drawings, but when you stand in front of that wall of steel it hits you.  By the end of the second day we had two walls up.

Most of the second day, all of the morning in fact, was lost due to the shed manufacturer supplying the wrong columns, they were too short.  I’m glad it wasn’t me that had to unravel that mess.

So there’s all of the walls up just leaving the roof to complete maybe half a days work. The PA door can’t be fitted until the concrete is done, I’m changing the door to swing inwards which will require a bit of skull duggery to get right.

The shed dimensions are 7.2m long, 5.4m wide and 3m at the eve’s, can’t wait to have 39m^2 of additional storage space.

Anyway now on to the concrete

Shed Project – Retaining Wall

In late October last year I finally decided to pull the trigger on a new shed, every man needs a good shed.

So down to the local shed builders and select one off the plan, then send the plans to council and wait, and wait, and wait.  That has to be the worst part.  Thankfully the Council got the job done inside two months and approval granted.  Being close to Christmas meant the silly season festivities also put much on hold.  Oh well that gives me time to perhaps build a new retaining wall.

So grab a few mates, throw on a barbie, find the sledge hammers and lets get busy getting that wall down.

One thing we did learn is that 65 year old hand mixed concrete is rather hard.  This required a much larger hammer.  A big thanks to Peter VK5KX for bringing the beast !


At the end of two full weekends we had finally finished the demolition and it was time to start building.  Yaaay !

Concrete retaining walls are easy to build, just cement in steel posts to the right depth and spacing, then load with concrete blocks.   This wall was simply adjusted in height to slope with the existing land profile.  Make sure you don’t hurt yourself loading the blocks, they are heavy !   Then it’s just a matter of getting in the bobcat to clean up the site remove any vegetation and rubbish ready for installation.

I’m kind of glad that the shed was delayed over Christmas a bit since the site prep took a little over 6 weeks to complete.  A big thanks to all of my fellow Radio Club members and friends that came to assist.

Ok now for the shed.

Cellular Modem & GPS

Well it turns out that the HP un2420 cellular modem has an inbuilt GPS that can be turned on and off..   So a bit more google foo and I found all that was necessary is to echo a command into the third enumerated serial port like so;

#$ echo "\$GPS_START" > /dev/ttyUSB2

Then we can just point our favorite GPS monitor program at /dev/ttyUSB2 and we should see NMEA data.  I used gpsmon to test mine.  I was amazed to watch this working on my bench inside the shack.

Now my Wenet ground station can easily go portable with Cellular data and GPS position information and no USB 3G dongles required.

HP Cellular Modem for HP 5320m

After pulling the bottom cover off my second-hand HP Probook 5320m a couple of times I was pleased to discover a PCI-E slot for a HP un2420 mobile broadband modem.  It appears that the Cellular antennas are already built within the lid (or screen) of the laptop.   A light bit of reading also suggested that these modules were capable of decoding GPS signals too.

I just had to try one.

So for the princely sum of $35 I procured a HP un2420 Gobi 2000 module from a local eBay seller.  There are suppliers on eBay that are selling these HP Gobi 2000 modems out of China for $11, which is an absolute bargain. YMMV.  I didn’t want to wait until after Christmas to try one so I purchased one at the higher price.

Now of course I want this to work in my shiny new Ubuntu 16.04 LTS laptop.  Oh well I’ve always welcomed a challenge.   I’ll detail the steps I took to get to a working solution.

First we should check we can see the module;

#$ lsusb
Bus 002 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 004: ID 05c8:0403 Cheng Uei Precision Industry Co., Ltd Webcam
Bus 001 Device 003: ID 03f0:241d Hewlett-Packard Gobi 2000 Wireless Modem
Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

I’ve highlight what we’re looking for (in blue) which is the “HP Gobi 2000 wireless modem”.  You can tell that this device is currently un-programmed as the product ID is “241d” and changes to “251d” once the firmware is loaded.   You also need to check that /dev/ttyUSB0 exists and that your user that starts the 3G cellular modem is in group dialout.  This isn’t necessary right now but does simplifies things later.

Now you’re going to require a Microsoft Windows machine, sorry there is no other easy way around this.  Some have managed to pull apart MSI files in wine, I didn’t get that lucky.  The Qualcomm Gobi modems down load the firmware into the modem at power on, once the firmware has been download the modems will work.   I was lucky to have the same laptop with Windows 10 installed, so I simply installed the driver on this second machine and then stole the files I needed on a USB stick.  I had to install the un2420 module in the Windows machine to get the drivers to load.

From within the Windows driver there are two directories from which we need three files;

  • ….\Qualcomm\Images\HP\UMTS\amss.mbn
  • ….\Qualcomm\Images\HP\UMTS\apps.mbn
  • ….\Qualcomm\Images\HP\6\uqcn.mbn

You’ll need to work out where the drivers get placed depending on your version of windows, it will be installed in the program directories there somewhere.  I found them in the Program Files (x86) directory on Windows 10.   The files above are what you require for a Generic UMTS modem (6) that is not vendor network specific or locked.  This worked nicely for my unlocked module and Telstra pre-paid SIM. YMMV.

Now once you have these files on a USB stick you can start work on the Linux machine.

#$ sudo apt-get install gobi-loader

This will get the udev helper we need to load the firmware into the modem.  Once this is installed copy the files from the windows machine into this directory, watching file permissions of course;

#$ sudo cp /mnt/usbstick/* /lib/firmware/gobi

As mentioned we want all three “mbn” files above in that directory.  Now you might like to check that the udev rules for QDL modems are correct in the following file;

#$ less /lib/udev/rules.d/77-mm-qdl-device-blacklist.rules

Your looking to check that the following two lines exist;

#HP un2420 Gobi QDL Device
ATTRS{idVendor}=="03f0", ATTRS{idProduct}=='241d", \ ENV{ID_MM_DEVICE_IGNORE}="1"

These lines will prevent ModemManager in Ubuntu from trying to take control of this device at boot up before the udev helper gobi_loader gets a change to load the firmware.   Now if all is going well reboot the machine and then check the following in a terminal;

#$ lsusb
Bus 002 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 004: ID 05c8:0403 Cheng Uei Precision Industry Co., Ltd Webcam
Bus 001 Device 003: ID 03f0:251d Hewlett-Packard Gobi 2000 Wireless Modem
Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

You should notice that the product ID has changed from 241d to 251d, meaning that firmware is now loaded in the 3G modem.  I tried not rebooting this machine which turned out to be a mistake.  ModemManager is a pernickety piece of software that won’t do anything unless everything is 100% right.  I wasted a number of hours chasing my tail trying to get services shutdown and restarting stuff.

You should also see that there are now three tty USB devices attached to the system;

#$ ls /dev/ttyUSB*
/dev/ttyUSB0 /dev/ttyUSB1 /dev/ttyUSB2

If you don’t see these three devices then there is something wrong.  I’d suggest you start with dmesg and searching your way through syslog to find out why what’s gone wrong.  It can take a while.  When you do get things right about 13-15 seconds after the kernel loads you should see the firmware loaded into the modem and the additional USB serial ports being created.   If the firmware doesn’t load you will find error messages in syslog.

Now you should be able to configure the NetworkManager to actually use the Modem.  I simply went into NetworkManager -> Edit Connections and created a mobile broadband connection from scratch.   The APN we want to use for Telstra is “telstra.internet” and the rest is pretty much a vanilla install.

Once you’ve got the connection, done you should be able to connect to the internet via the cellular modem.

Oh and don’t forget to plug your SIM into the slot in the battery case.   Now you can sit back and enjoy Cellular Mobile data without any external USB dongle to snap off, or get left behind.

Yay !

SSDV equals Laptop Mania

I’ve been recently hunting for a laptop or computer I can run Linux on to allow me to participate in a Slow Scan Digital Video SSDV experiment from a High Altitude Balloon.   Some of our AREG club members are developing a high speed FSK modem that is capable of 100kbits or more on 70cm.  Over this high speed link digital images are sent throughout the high altitude balloon flight, the combination of SSDV and high speed FSK has been named Wenet.  These SSDV images are reconstructed on a server in the UK from multiple ground stations streaming their data (click).   Recent testing has shown that the on-air performance is less than 1dB away from the theoretical maximum, David has written an excellent article on it here (click).  However if I wanted to join the fun I need something to run Linux on.. Hmm what to buy.

So when one of my AREG club members emailed our club mailing list with details of a local computer recycling shop selling refurbished HP Probook 5320m’s for $100.  How could we go wrong.

The Intel i3-370M processor is relatively old and puts this machine at the low end of the performance curve, but with 4GB or RAM and 250GB 7200rpm drives these laptops still offered good performance and excellent bang for buck.

So once I’d visited the computer recycler and purchased a laptop it was installed with Ubuntu 16.04 LTS and the usual upgrades and massaging applied to make it all work.  This was the first time I’d experimented with Debian Jessie but the end result was a working machine.   By working I mean working, so the Wifi, Bluetooth, battery monitor, webcam, touch pad, buttons, keyboard, USB, Display port all just simply worked.  There is something to be said for sticking with non-bleeding edge hardware.

The Wenet installation is relatively painless if you’ve ever compiled things from source.  This was then married with a RTL-SDR and 70cm preamp.   The big test was then Horus Flight 39 in which said laptop and system were put through there paces by my eldest son Daniel, you can follow the write up here (click).   The entire team in the tracking car were amazed to watch the pictures “live” from the balloon on this flight.  I had to concentrate on the road a lot of the time with people making oooh and ahhh sounds around me.

I’m told the processor was loaded about 30% the majority of the time and the machine remain responsive under load.   This will certainly do very nicely for this experiment going forward.  What is also strange is I now find myself sitting on the sofa of a night time using this laptop in anger surfing the web.  It boots fast and is great for “looking things up”, so far it’s run for 5-6 days without needed to be charged.

Now to work out what else we can do with it !