Progress has been slow in the radio link side of things. Testing of the new RFD-900 modems has been painful for a number of reasons.

1. They chew up a lot of power and go through a lot of batteries and I have a feeling that when the RFD-900 demands a lot of power, the batteries just cannot supply it.

2. There seems to be packet loss, and some very strange things occuring. I’ve been in contact with the supplier regarding this.

3. I SUSPECT there is some interference between the wifi and rfd-900…but there is a lot more work to do there.

So in short, I’m a long way from doing some long range tests and I’m probably going to need to purchase more batteries.

I purchased myself some 18650 batteries from China – 8 in total. For those who are unfamiliar with 1860 batteries, they are 18mm in diameter and 65mm long. They are Lithium Ion batteries with a voltage of 3.7 volts.

These batteries fit in a battery box that fits VERY snugly in the main Electronics box. Alas…on the first test, the batteries failed after 30min of operation. It turned out that one of the batteries died – collapsed. This apparently happens if too much current is drained from these batteries, or they are charged with a charger in a ‘bad’ (over voltage?) way. That is apparently why most 18650 incorporate a circuit protector to stop this from happening. (When they have this circuit protector added…they are typically a few more mm longer).

I suspect I’ll need to invest in more expensive (non-China 18650 batteries).

I am continuing to make improvements to the web interface that we will use to get most recent information on the High Altitude Balloon journey. The latest is a TAB with a Google Map showing where HAB has flown. It has the co-ordinates superimposed on the map. There is one potential issue and this is with the fact the phone needs to be connected to the Internet (to connect to Google) and it needs to also be able to talk to the Beaglebone black – simultaneously. Initial suggestions are that this might be difficult. I will continue to investigate ways of setting routes on the phone. There must be a way.

An attempt was made to communicate approximately 15km recently with the xBee’s but unfortunately there was no signal at all. I then drove closer (approximately 9km) and was able to get a signal and was able to retrieve a picture. During the transmission of the picture, the module had to re-download packets, but the image came through successfully without any distortions. This means the corrections to the xmodem libraries and the receiving module xmodem code has fixed up the issues!

I’ve made the decision that I need greater range for the HAB, so I’ve decided to purchase RFD900 modems. I’ve also decided that lugging a laptop around with a virtual operating system installed and trying to use it in the terrible light, connected up to the antenna is not practical and have decided instead to use a different arrangement. I’ve started coding this and it is working extremely well. A diagram showing how the data is ‘moved’ from the High Altitude Balloon and ultimately to the user is shown below.

I still have to work on the physical setup of these systems (putting in boxes) and connecting together in a reliable manner. Once this is done, I will start conducting some range tests.

I’ve been in touch with CASA regarding authorisation of the Balloon flight. What I do know is:-

* I need to ensure that the craft, procedures, etc follow procedures outline in the appropriate legislation

* It can take several weeks for authorisation to be provided

* CASA charge for the process. An estimate is provided, the estimated fee is paid and then work is done. For one application it too 3 hours at a rate of $160/hr. This is probably more then the cost of the payload.

CASA were helpful on the phone but came to the realisation that I obviously need to commit a large amount of time to this component, but suspect it will be time well spent.

I downloaded the Legislation (Volume 3 of 4):-

Civil Aviation Safety Regulations 1998 Statutory Rules No. 237, 1998 as amended made under the Civil Aviation Act 1988

which was file F2013C00316VOL03.pdf and I am interested in sections 101.140 and onwards.

Interpreting the Legislation

Several things to note about the legislation and how this matches with the project.

• The balloon that I am making is classed as a ‘Medium’ sized balloon.This is because it is less then 6kg weight but the diameter of the balloon will exceed 2 metres. (It will probably get to about 7 metres just before it pops).
• The balloon is not a zero-pressure balloon and so requires two ways to bring down the payload and two ways to finish the flight. The balloon ‘popping’ on its own is considered to be one way to satisfy both requirements simultaneously. Another way needs to be added to allow bringing the balloon down – preferably manually.

Summary

I need to test the antennas to make sure they will function as reasonable as can be expected. I’m secretly hoping that it can comfortably transmit/receive at a distance of at-least 10 km. This is probably realistic, remembering that the range of these XBee transmitters is about 20 km (as per specs).

A picture of the test range is below.

Details of the testing is below.

Testing on 16-June-2013

I set up the payload on a stool up the road from where I lived and mum watched over it. It was aligned so that from Taylor point it would be roughly 45 degrees. i.e. minimal loss. Taylor point is 4.5 km away. I was able to get lots of data from the payload while sitting on the beach. I also got 1/4 of an image before it froze. I then waited a few minutes for the payload transmission to give-up…which it did. Then I was able to receive data. I then put the earth station into test mode…it requested test mode and the payload accepted and responded accordingly. This is good. This means that at 4.5 km the communication both ways seems to work relatively well. The next test is from Yorkey’s knob ~8km away.

Testing on 23-June-2013

I set up the payload on a stool up the road from where I lived again…this time left it all by itself. I drove to Yorkeys Yacht club and was able to get some packets from a few rocks, just up from the sand. I wasn’t able to get a picture transfer starting very well.

I then drive around the corner to the top and found a perfect area to test! It was a patch of grass with uninterrupted view back to the hill where the payload was. I was able to get through about one quarter of a line of dots (4 1/2 lines of dots = whole file). So…not able to get an image unfortunately, but a lot better.

When I got home, I found that about 24 minutes after I had set up the payload on the stall, the wind had blown it down. Fortunately the antenna was not damaged. Amazingly I was still able to receive the signal. This suggests a fairly resilient system.

I still need to make file transfers a bit more robust. currently it just stalls…no more dots. I had an idea just was I was leaving that I should enable debugging in the xmodem library. I think I’ll also examining the xmodem code to try and guess where things are playing up and see if there is some retry/timeouts that can be adjusted. Even though I have my sights on RFS900 modem, I think xmodem enhancements are a good thing to look at.

Discussion

Much thought was put into how to connect the Cloverleaf antenna to the payload….attachment of the antenna is more of an after thought unfortunately. I’m thinking I probably should have somehow ensured this could have been put inside the box.

Anyhow…needed to engineer a suitable method of connecting the antenna to the payload.

Requirements

I knew that I needed to be careful not to include metallic objects with the install of the antenna. I was wanted to keep the attachment light, but still secure. The cloverleaf is a fairly ‘fragile’ antenna. Any bending of the conductors will result in reduced performance. I always wanted the antenna to point down. The antenna can flop around a bit…remember the whole payload will move around a bit from winds.

The Solution

Eventually it was decided to create some fibreglass structure and attach it to the payload jacket using Velcro.

Construction

Steps are below:-

• I used blue A4 card to construct a former. This was folded and trimmed to suit.
• I then used kids glue to glue the fibre-glass mesh to the blue paper.
• Then I trimmed off excess  fibre-glass mesh.
• Then I applied the fibre-glass resin/hardener mix.
• The next day, I marked on the jacket where I wanted the structure to hand from. I then  sewed the Velcro on to the jacket. I was able to stick the complimentary Velcro on to the fibre-glass. This seems to be sticking ok.

Below are some pictures taken during construction and afterwards.

Notice the paddle sticks above? There were sticky tapped on the back as a temporary measure to give the wall some integrity.

Yes, it doesn’t look pretty, but it should work!

The Design

The SWR meter is one done by IBCrazy who has very kindly shared this! Thank-you! A link to this is here

The Parts

Here are some photos of the parts I purchased to make this SWR meter.

Construction

I followed the steps described in the link to a ‘tee’. Here are some photos.

Yes. Soldering of this is hard.

Another night, another picture.

Summary

The helix antenna will be what we use to communicate with the balloon during it’s ascent.

Materials

Materials are:-

Item	Quantity	Notes
100mm PVC Pipe	1 metre
A4 Paper	4 pieces
2mm solid Copper wire	3 metres
Aluminum sheet	1mm thick 50x50cm
Thin plywood	5mm sheet of wood
Pipe Diameter reducer	Created from wood, with a 1inch hole in centre for wooden rod
Wooden rod	1.2 metre 1inch
RG-227U cable	15cm
Male RP-SMA connector	1
Copper Sheet	3cm x 6cm
Hot-Glue Gun	1	Lots of glue sticks
Solder	20cm
3mm metal screws	4	Used to fasten ground plane on to plywood
Copper plate	100mm x 100mm x 0.5mm
Fibreglass Kit	Rougly 4 strips, 6cm wide – total area 0.1m^2
4mm metal screws	4	Used to fix wooden reducer to PVC pipe
Telescope Tripod	1	Used Skywatcher 150mm tripod
Screws – 60mm x 1/4 inch	2	Used to mount wooden rod to the tripod.
1/16 bolt and nut	2	Used to attach ground plane to the Antenna tube

Design Parameters

We obtained details on the design from a number of sites. We ultimately arrived at the following dimensions:-

Parameter	Value	Notes
Gain	12.82	Theoretical gain
Wavelength Reflector	33.236mm
Circumference	357.29mm	Equiv diameter of ~113.73mm
Spacing between turns	81.17mm
Length of each turn	366.39mm
Length of wire needed	2931.15mm
Antenna Length	649.39mm
Spray adhesive	1 can

NOTE: some calculators said 106cm diameter was the correct value. I think that there is a lot of margin for error in the Helix antenna…i.e. wide bandwidth, so I’m trying not to get too concerned about getting it ‘exactly’ right.

Below is a picture shows the antenna part way through construction.

Construction

The constructions is broken into 5 stages. These stages are listed as follows:-

• Creation of helix coil on former
• Creation of ground plane
• Mount for Tripod
• Attachment of ground plane
• Electronics
• Tuning

Creation of Helix coil on former

We needed to mark on the PVC pipe where the copper wire should follow. We did this by getting some A4 paper and drawing diagonal lines. The design parameters above dictated the gradient of the lines and the spacing. Special care was taken to ensure right hand ‘coil’ was created. The four A4 sheets were then very carefully stuck on to the PVC tube.  I then used a hot glue gun to hold the copper wire in place as I wrapped it around the tube. This was quite difficult and I found it best to move myself around the tube as I coiled the copper wire on, rather than trying to move the PVC former. (If I turned the PVC tube around, the wire got harder to coil it).

Look closely at the picture above and you will see the hot glue.

Then we fibreglassed the copper wiring in place using 4 strips of fibreglass. We figured we didn’t need to fiberglass the whole tube because:-

• It is expensive
• It might change frequency more if we use more
• It will increase weight of the antenna, putting more strain on the tripod.

Here are a few pictures of the fibreglassing process.

We needed to solder a copper strip in the first 1/4 wavelength of copper wire. This is done to reduce the impedance of the antenna…bringing from about 130 ohms to approximately 50 ohms. A copper strip 1/16 lambda x 1/4 lambda was cut out. Here, lambda is the wavelength  – c/f = c/902 x e^6 – 33.33cm. A picture of how this was mounted is shown below.

Creation of Ground plane reflector

We need a ground plane reflector and we make one using some Aluminum sheet. A square with sides 333mm was cut out. Then the corners were trimmed off. This sheet was then mounted to some plywood of slightly larger dimensions. This provides safety as the Al sheet is quite sharp. We then needed to drill a whole allow the mount rod to pass through. This component is attached to the mounting rod using glue.

A picture of this is provided below.

Tripod Mount

I have a telescope (a 150mm Skywatcher). I noted that I should be able to attach a rod of some description to this, instead of the clamps used to hold the telescope tube. This rod I decided can be attached to the main tube using tube reducers…which are inserted inside the main tube. A picture of these reducers is below.

There is a reducer at each end of the PVC tube. Inside the PVC tube is a 1.2 metre length of 25.4mm diameter rod. The rod can wedged into place by rotating the end reducer slightly and tightening up the fixing screws.

The rod is attached to the black bracket on the telescope. This is done using two 60mm bolt/nuts (1/4 inch diameter). A picture of this is shown below.

Attachment of Ground plane

We wanted to attach the ground plane to the 25.4mm wooden tubing. We did this by bringing the wooden reducer right down to the bottom, securing with two screws. Then we put two small 1/16 inch holes in this, dropped two screws down and put these through the ground plane and secured with two nuts. See picture below:-

Below is a picture of antenna with ground plane attached to the tripod. Also notice the metal pole with counter-weight.

As one can imagine, this makes aiming of the antenna a lot easier. (The antennas does weight a lot!)

Electronics

We need to connect the antenna back to the xbee module which is mounted inside a poly- carbonate box. This box is mounted on to the back of the ground plane. This ensures minimal amount of cable between antenna and xBee module….reduced attenuation of signal.

This was accomplished by:-

• Drilling hole through found plane for cable
• Attachment of Male RP-SMA connector to end of RG-227U cable
• Attachment of Xbee module to the ground plane

Pictures will be added later.

Tuning

We are making a SWR meter using a Directional coupler, a microwave diode and few other components. We hope to confirm a perfectly operating antenna!

Testing

A lot of thought is being put into how best to test the antenna. Essentially, we need to find out the range. We will need help from others to do this.