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Building a Bigpond Next G Wireless Internet Antenna

Click on this frame and print it for a handy workshop reference

Construction process:

Photo shows elements in place with hole left vacant for the driven element

So you've drilled 8 holes in the boom just the right size for the aluminium elements and you've pressed 7 of them in... Do not fit the driven element yet.

I don't need to tell you how to drill a nice tight hole and get the elements fitted in the correct order, do I?

By making the elements press fit we didn't have to glue or screw them so do think about precision and accuracy to make it an easy construction.

The photo (at right) will give you a clue to how we will cut the main boom (cutting through the centre of the D.E. hole) and replace it with the plumbing white PVC Joiner.... later... later...

Note the detail of the driven element. It was cut as one piece 154mm long then cut in half and has a piece of plastic cut to fit the ID of both ends, with a ridge left in the middle to stop the two ends of the driven element from touching.

However you decide to join the two halves of the driven element, (stick a piece of dowel in... whatever) ensure your gap is only about 1mm. Remember we're dealing with high frequencies so millimetres make a difference.

We drilled and tapped two 3mm holes through the driven element quite close to the end. These will take the pig tail coax ends and also ensure the ends don't move and touch each other. If you can't Tap the hole, no problem but do be sure to pre-drill the holes so you can work with the coax ends in a confined space later.

Drill 3 holes in the white PVC joiner

This step is drilling the white PVC joiner.

One hole through the centre to take the Driven Element and another off-centre smaller hole to take the coax. We used RG58 CellFoam Low Loss highly flexible coax (see coax info later).

Drill a hole sized to suit your coax... and being off-centre will aid attaching the coax and facilitates Horizontal or Vertical polarisation.

Take a deep breath and cut the Riser through the centre of the hole you drilled for the Driven Element. There will be a little shaving of one cut end later to accommodate the coax.

The intention is to now work separately on the PVC Joiner affixing the tails of the coax and then inserting the cut ends of the Riser into either end of the PVC joiner.... making sure your centre-to-centre measurements are correct.

You're working with the critical dimensions between your Reflector and the Driven element when it's all back together that measurement must be 74mm. (see the table of specifications above)

Working in the PVC Joiner:

Remove about 20mm of black coax outer cover. Extract the outer braid, twist together to make a single thick tail/wire. Remove some inner coating to expose the inner wires. Twist them together to make a single thin tail/wire. Keep these unshielded tails as short as you can and Tin (with silver solder) both coax tails.

The small lugs had quite long tails so I nipped them off too then soldered the coax tails onto the remaining lug-tail.

Keep checking that they'll fit and be able to be screwed into place without touching (shorting). Adjust as necessary.

Use insulation tape to maintain the angles that you need to get a tight fit. You will have noticed one tail must be longer than the other due to the angle that your coax is coming into the PVC Joiner.

Now you'll be very pleased you pre drilled the holes in the Driven Element.

A long skinny screwdriver will get the 3mm stainless bolts with washers screwed down tight to the Driven Element... while at the same time you retract the coax back out the hole so it doesn't kink.

I also test the continuity quite often during this process to ensure I haven't shorted these fiddly pieces together somewhere. Better to find it now that when it's taped and joined back into the antenna.

Here is a photo of the rear of the PVC Joiner. Those 3mm stainless bolts were a bit long, but it was all we had.

The Riser is going to fit around them just fine when it butts right up to the aluminium element on this side.

Choosing your Coax:

Coax used was RG58 CellFoam low loss. It has properties similar to good quality RG213 but is so much more flexible.

Mine is a 20metre run from the top of the antenna into the roof cavity, through the trusses and down into the office.

Would better quality coax and shorter run give better performance? I would expect it would... but I live in the real world and I want my Wireless Modem in the office - not up on the outside eaves... just to shorten the coax run.

Buy what you can afford of course - just don't scrimp and use cheap RG58 - you'll get what you pay for.

The Balun is just an 'ugly balun' - 6 turns of the RG58 Cell Foam formed up and taped. You can see that the Cellfoam lends itself to this shape... imagine trying to do it with RG213 or heavier.

I put the BALUN in because of the short lengths of exposed/unshielded coax and this will mitigate any problems.

Here it is mounted approx 10m above the ground

Horizontal polarization, braced for the fat kookaburra's who insist on sitting on my beams!

Tested consistently at 2.75mbps download

Telstra's Bigpond Elite Gateway Modem

Updates:

Here are some questions I've received and answers in case anyone else is wondering.

Question:

... are the measurements exact distances in between the adjacent surfaces of the tube, or the centres of each tube. I would really like to build this correctly.

Answer:

The measurements are always meant to be read Centre to Centre.
Of course in practical terms... it's the same thing as measuring say... left side of element to the left side of the next element.. that still retains the C to C distance.
BUT... just ensure you're not measuring left side of one piece to the right side of the other.

Question:

.... the balun has been skipped over rather quickly and little to no detail.
... I noticed that the antenna built by a friend in a link from your site does not include a balun.....is it necessary or just a good thing to include ?

Answer:

I created an "ugly balun" which consists of about 6 to 10 rolls of the coax up near the PVC (driven element) to achieve matching and to inhibit any RF that's on the outside of the coax. I wound the coax around a piece of 2" pvc... putting little bits of electrical tape to hold it all side by side. Then I slid the pvc out keeping the coax flat and side-by-side and bound it up with electrical tape. That's all there is to an 'ugly balun'.

Balun's and their uses come under the heading of Theory of Propagation and can fill chapters in a text book. You can chose to fit one or not.

The balun isn't terribly important with this wireless internet antenna. Why? Because it's a 99% Receive antenna?

That means you're bringing signals IN most of the time (you're receiving) and you only Transmit when you hit enter/send/submit on your keyboard. Using a small, low powered modem/transmitter your web browser or email program sends a tiny packet of information as a request to your ISP. You're not really sending a transmission to the USA for that webpage.... Your ISP does all hard work of getting you the webpage and Transmitting it to you.

With my Amateur Radio antennas the reverse is true. I am talking directly with the USA or Europe so when I'm Transmitting any RF on my Coax (transmission lines) would be problem, so I build antennas with that in mind and add a variety of balun's to suit the frequencies I'm working with.

Question:

....I have a cable that plugs into a USB dongle - which has a larger plug on the other end (attaches to existing - poor - antenna). So I assume I need to also buy a large plug to connect the coax to this little lead? sound about right?

Answer:

I have a length of coax with one end fixed permanently into the antenna on the roof and the other end screwed directly to my Bigpond Elite modem which has an FME fitting. I took my modem into Dick Smith and found the correct screw on connector - as there are several small fittings of similar size. I 'crimped' the Dick Smith connector to the end of my coax.

It sounds like you currently have a patch lead so use whatever fittings YOU need to achieve the link.

Try to do it with the least metal that you can, meaning that every time you introduce another adapter etc you risk more signal degradation - that's why I try to use the correct fitting when I can.

Here is a link to a supplier of patch leads etc. www.campadelectronics.com.au

I haven't used this company but they were recommended on an RV/Camper site as knowing about leads and connectors for people with unusual needs.

Question:

....I am not real clear on where you put the lugs onto the end of the Coax RG58.
....I presume that one lug goes onto the single middle wire and the other onto the multiple shield wires. Am I correct?

Answer:

Absolutely correct-a-mundo. Open up about an inch of the black coax coating and extract some braided shield wire - pull it to form it into single thick wire. Then expose some of the centre wires and twist them into a single wire.

I usually Tin both of my wires at this point so they're easier hold at the strange angles you need when you solder onto those tiny lugs. It's a fiddly process extracting braid and centre wire and I can't give you exact lengths as one needs to be a little longer than the other and it depends on where you drilled your entry hole for the coax.

Yes, working with one thin wire and one thick wire seems odd and that's another reason we use baluns to sort out this unbalanced situation when we build Amateur Radio antennas but in this project thick and thin won't worry you.

Question:

.... I have come to the part where you suggest cutting the beam through the hole for the driven element.
.... Is there a reason that the cable ends need to be attached to the very inside ends of the driven element - could I attach the coax to either side of the driven element outside the riser?

Answer:

Where you attach the coax alters the electrical length of the Driven Element. (I know the physical length remains the same). To maintain the required electrical length and physical length of the Driven Element we need to have the thick and thin coax tails as close as possible to the centre.

In practical terms that means we try for a 1mm gap between the two halves of the driven element then put the two holes/lugs as close to the ends as practicable and so the two lugs don't touch each other.

Question:

.... I notice that you say 839.8 and 884.8 are the internet frequencies.
.... I have looked at the ACMA site and see that those freqs are not at every Next G site.
.... If these are the only pair of frequencies used then I have a better idea where the yagi will have to look.

Answer:

When a company goes to the capital cost of building a tower there are literally dozens of antenna placed on it.
Each of those the antenna (and corresponding ACMA licence) will be for a range of frequencies that your local community needs... some will be paging systems, telephone mobile frequencies, 2G, CDMA frequencies, etc. etc.

Bigpond Wireless Internet use only THOSE  uplink and downlink frequencies.
So yes, confine your search to Telstra Towers which have those two frequencies and then check to see if they show, Vertical, Horizontal or Slant polarization - so you get the next Tip for the final installation at your house.

Question:

.... I could only get 12mm Aluminium tubing not the 10mm mentioned.
.... Do I need to adjust the spacing to allow for the extra 2mm in width of each element.

Answer:

The technical answer is Yes... when you alter the diameter of the material it will change the specs but the alteration would be fraction of a millimetre. Most people wont be anywhere near that accurate in their building to begin with so I personally wouldn't worry about it. Just go with the measurements above.

Question:

.... would that next g yagi antenna be suitable for mobile phone (next g 850 band) as well as next g usb pre paid broadband?
.... both phone and the elite usb pre paid modem have external sockets and I'm able to order the patch cables for both so everything should work fine hopefully

Answer:

Yes... the frequency was the important thing in our considerations and as long as your device has provision for external antenna you can connect the Yagi if you're trying to capture the Next G frequencies.

The early USB dongle modems didn't have external antenna port but luckily they've evolved....My mobile phone doesn't have an external antenna port, I'd have to use a passive pad with it... I may have to give this some thought now you've piqued my interest.

Question(s):

.... Does it matter what the elements are made of eg how about Steel bar/wire or copper tube/wire?
.... If I can find/use thin elements how much does it affect the design
..... I saw on the ‘telcoantennas’ website that yagi provide upwards of 12db gain. What gain would you expect from this design?
...... I presume it doesn't matter where the mounting fixture is located if I use a non-metallic mount. I was thinking of using a T piece at the dipole junction and using a plastic pipe as a stand fitted into the bottom of the T.

Answer(s):

To answer your questions one by one
Material - "metal"  wire or copper works for antennas as long as you're insulating from your boom.

Thickness - yes is matters BUT... by millimetres and once again most people can't cut that accurately anyway.

Gain - yagi = about 12dB. Gain is quoted by commercial people to impress the buyer. It's a theoretical improvement over an antenna in free space (in a vacuum).... can we really measure it?
Don't worry too much about it. (some quote dBI or just dB and there is a difference - they tend to show you the highest as it looks more impressive)

Basic rule of antennas is - if it's a Vertical your signal is going out in all directions... a lot of your 'energy' is wasted as you didn't want it to go up, and out those other directions.
(Amateurs use this type of antenna as we are looking for contacts in all directions at times)

Mr Yagi found that when he looked at all those outward radiating radio waves, he could direct them.
The directional Yagi beam doesn't allow much of the signal to go out the back or to the sides but rather it goes in an elongated egg shaped 'glob' in the direction that the beam is pointed.
And it works in reverse, when the most forward directors pick up a signal it's effectively amplifying it as it passes it backwards from director to director until it strikes the driven element and it becomes of use to us.
The reflector at the back simply halts the process and bounces anything that hits it back to the driven element as well.

Mounting - you're right, mount it anywhere that you like and to make it compact consider making it collapsible for your travels.

I make a fox hunting antenna where the cross pieces are mounted with wingnuts.
We loosen them off and the elements fold back along the boom and with a couple of velcro strips around the 'bundle' it can be stowed.

A good source of antenna material are the welding/soldering rods from industrial supply places. I use the aluminium ones sold for TIG welding - they make nice high frequency antennas.
 
Feel free to be inventive - try out some of your own ideas. Between lightweight material and making them collapsible you might invent a great antenna for a few dollars. There just won't be any guarantees until you plug it in and get a speedtest on the screen.

And P.S. would love some photos of what you eventually make for your wandering lifestyle

Question:

.... At first I thought that the antenna was to be in either horizontal or vertical position. After looking at the photos it appears that the directional bars are the ones to be either horizontal or vertical. Is that correct?

Answer:

Yes, when we talk about the "plane" as being either horizontal or vertical we are talking about the cross pieces of aluminium - the elements (called the Directors if they are in front of the Driven Elements or Reflector if it is behind the Driven Element).
If you look at most TV antennas they have a horizontal section out the front... looks like a swordfish and the elements are horizontal... behind that is usually a section with the longer aluminium elements vertical (going up and down). That's because some stations like SBS TV sends a "horizontal" signal and most other channels send a "vertical" signal... and some smarty created a combined TV antenna to capture both for you.

With the Internet Telstra/Bigpond put their antennas either Vertical or SLANT on their towers..... each person has to check their own nearest tower (from the ACMA records) and put their antenna to match the tower they are pointing at.

Question:

.... You suggest a riser of 900mm length for the next g antenna, yet the spacings of the elements from the reflector add up to 2,361mm - I must be missing something!

Answer:

Yep. You missed the words Element spacings:  from Reflector. Those measurements are not ADDITIONS.

You take your centre of the Reflector and each one is measured from that point.

So Driven Element is 74mmm out from the Reflector
Director #1 is 124mm out from the Reflector and so on...

Until finally Director #6 is 670mm out from the Reflector

That's why your boom can be anywhere from about 700 mm onwards depending on how you're going to mount it.
The 900mm riser was just a convenient length for me to buy and have enough sticking out the back end to devise a way to mount it.

Question:

...Just a quick question about which is the better cable to use.
Is RG213 better than the RG58. I read that it has a lower loss per metre. Even better than that is the LMR400 which has roughly half the loss of RG58?

Answer:

Absolutely RG213 is better than the "cheap" RG58 coax and looking up the tables that you've found is a good start... the Coax I used is Cellfoam Low Loss RG58 Type RFI CAT. No 9001 which is rated as good as RG213.

RG213 is a THICK coax and quite hard to work with and you have to get down from the thick RG213 size to the tiny antenna fitting on the rear of your modem and the more adapters and fly leads you introduce will degrade your signal - besides working with a thinner coax that's more flexible is soooo much easier.

There are very high quality RG58's on the market but you have to search around for them and it's like that old ad campaign.... oils aint oils Sol.
Domestic suppliers like Dick Smith and Jaycar generally only sell the cheap coax with markings like /R or /CU on them (although many DSE they are now franchises so may carry better stuff if their clientele require it).

Question:

...The aerial you made for Next G, does much need to be done to convert it to 3G?
... Currently travelling using a Telstra Ultimate modem and a Laser 7dBi aerial I get one bar if I am lucky. Even using an extendable pool handle and reaching 5m high hasn't helped.
...When I camp up it is usually for a week or more so having a directional aerial might not be a problem if I can find a tower. This is driving me and the wife nuts and local shops aren't able to help.

Answer:

Telstra's NextG IS a 3G service...... NextG was just Telstra's name for their service [which sounds pretty silly now that they're launched their next newest service called 4G LTE operating on 1800MHz]
The critical thing is.... Telstra's NextG/3G  (3rd Generation of mobile technology) runs on the frequencies that I mention in the article [in what they/Telstra refer to as their 850MegaHertz range].

By the way Optus 3G runs on very different 2Gigahertz frequencies - yet they are both 3G **argh**

If in doubt, check your manual to make sure of the frequency your modem/service is utilizing and point an antenna towards one of their towers that has that same frequency listed. [and remember to read the Polarisation notes above]

Also check your modem settings to ensure you've told the modem that you're using an external antenna!!! [that's a trap for new players as that option wasn't in my old firmware - once I upgraded the firmware for the modem I got that option to optimise the modem - talk about putting the cart before the horse]

Question:

Can you give me a bit more info on how best to use this site for tower polarisation search?

Answer:

The ACMA searchable website provides some boxes if you already know the Site ID or Licence number etc. But when starting out you won't know what to ask for... they do provide "Other Radiocommunication Licence searches"... from these links choose the Assignment/Frequency search range.

Enter YOUR postcode in both the Hi and Low postcode boxes and for the Frequency use Telstra's NextG Transmit Frequency 885MHz in both Hi and Low boxes [be sure to change the option to MHz - it's not kHz].

The search returns a list of Telstra 3G licences in your area. Use the left hand column "Assignment ID" & check each one. Is the physical location of the tower near YOU? If it's within 20-30km write down the details... and check the next one.

Your checked list should be a group of Telstra towers around you [and you noted their Polarization as you checked each one] and each site showed the latitude and longitude of the tower so you know the direction to point your antenna. [there are google tools to help with that if you don't do the old Map and Compass trick]

If you're lucky enough to have several viable options of towers, I suggest pointing to the least populated one... meaning don't point to the Post Office in town... point to the one out on the highway, it's likely to be less congested. Do keep your notes on the other locations and if you think your first choice is marginal, spin the antenna around and try another.

Question:

Hi. Im from Uruguay so first of all sorry my english.
I wanted to thank you for the guide to make the 850mhz yagi antenna, is one of the most complete and clear in internet.
I am building it and i have a (maybe silly) question. Can de driver element have wood inside? I realised that a standar wood pencil fit perfect inside the aluminum tube and with a pencil inside is easy to make de driver strong and accurate.

Another question i have is that if to change the polarity to vertical I only have to put the antenna with the directors in vertical position.

Thanks for reading!, Regards from Uruguay

Answer:

*WOW* Uruguay, I thought it was fun getting questions from Americans, and don't worry about the English... you should hear my Uruguayan . To answer your first question, Brilliant idea! A wooden pencil to keep the two halves apart and strengthen the whole thing is fine as wood is an insulator and wont conduct any of your current/energy/signal.

And secondly, yes you are correct. If your nearest tower is Vertical you place your antenna so that your aluminium cross pieces are pointing up and down. If your tower is Horizontal you place them crossways, just like looking at the horizon.

Hope these FAQ's help.
 

Next ?

Feedback:

I am pleased to say that some people have tried this antenna project with great success both in Australia and rural USA.

It was nice to get some feedback and pleasing to see people wanting to try something themselves before resorting to commercially made (and expensive) options.

Thanks to those who emailed and gave positive responses.

I'll place any photos I receive from other happy Next G Yagi builders in a gallery below.

Gallery

Here is the photo from David who lives in Yarram on the Coastal Plain, in Gippsland, just a bit East of Wilson's Promontory; Dairy farming and timber growing territory in victoria.

David comments: I was very disappointed when I first set up my Gateway and found that I only had a low reading.
The tower is about 4kms away and line of sight. I purchased a Mobile antenna and got to Stage 2.

Still not satisfied, I built the Yagi as instructed but without the balun and damn me, straight to the top of the tree.
I am rapt. Having never attempted a wireless antenna of any sort, long-wire, beam or dipole,(See, I have a lightweight knowledge, ha ha.), I was absolutely busted when this thing went straight to the roof !

And another intrepid home builder from Karabeal Victoria.

Andrew sent a snapshot of his download speeds (3.02Mbps) after installing his Yagi. He says that although he didn't have a drill press and couldn't keep the elements millimetre perfect, it works a treat. His family think this new internet speed is life changing too. Here's his photo.

From the Gold Coast Wayne emailed...

I live at Upper Coomera Qld, the fastest growing area in Qld with the most congested wired broadband in Oz, very frustrating.
After reading your pages it was off to Bunning's and Jaycar and with the help of a drop saw, 2 hours later a quick test and a much better signal.
The Yagi's mounted better now and I am getting the best speeds I have ever had since I have lived here.(3.67mbps)
To join the driven element together I used a blue Raw plug (used to hammer into concrete) it was a good fit and cut a small plastic washer to keep them separated the black cable ties are to keep the birds away.

And here are the photos of Wayne's project.

Using a 'T' in the beam and cutting another 'T' in half to secure it to the mast and used PVC caps to seal the ends.

Now we cross to a farm property near Condobolin in NSW and Darcy writes....

I completed my first Yagi and it works! AMAZING. Using Speedtest.net it yielded a massive 7.7mbps some times but has settled generally around 5.24mbps.
Some things you might like to note - as I had to mount for vertical polarisation and the driven element was joined by a wooden dowel. This meant it was going to be exposed and could fill with water that would sit on the dowel so I capped the end of that tube with silicone to stop this from happening.
Another thing I found useful was using the ruler in Google Earth to see exactly the line I needed to set the antenna to the Telstra Tower. The ruler is marked as a line on the map so you can see in the back yard how close to this tree or that you need to point the antenna. It also gives the exact distance for interest sake.
Total cost $18.68 and that included 8.5M of RG58 coax. I now have FIVE Yagi's on the go for friends and family.

Here is Darcy's photo

Ron from Caboolture says,

I live 1km from a mobile phone cell tower but I suppose because there is a dense forest between me and the cell I got very poor signal (1 to 2 bars). It was my lucky day when I found your article so I built one, with fantastic results.
I get an extremely strong signal now, 4 to 5 bars!
I used a black joiner, which is made for that particular piping, at the Driven Element where the cable comes out, so that after I screwed the Coax on to the Element, all I had to do was screw the two parts of the boom in to the socket.The antenna looks sensational.
As you can see from the photos below, I have it mounted inside, near the computer.
Internet is now very fast. Imagine if I put the Antenna outside!!

YAY RON! I never thought of putting it inside... hahaha see, you learn something every day!

References

Web based research which assisted this project;

VK4UD's Wireless internet - temporary fixes when you're going bush

VK7JJ - Phil's modeling of 800 mhz yagi's

ACMA search facility: locate Telstra/Bigpond transmission towers, check frequencies and polarization

Telcoantennas a Queenslalnd company 100% Aussie owned might be able to help you with patch cables etc

Contact VK4ION

If you have any feedback on these pages or would like to contact me please email

Goodbye and thanks for calling