DIY Build NextG Yagi


Before we begin Download PDF

Free pdf download
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LINK to download a PDF document for this project. Size 480kb


The Frequency

This antenna was made for Telstra Bigpond Next G Wireless Internet which used two frequencies: uplink 839.8MHz and downlink 884.8MHz [Referred to in Australia as "Telstra 3G 850MHz"].
Researching transmission towers for Telstra frequencies in different areas... this is frequency to search for.

Finished antenna

Materials and making a start:

First the Boom I wanted light, rigid and preferably non-metal and found a thick-walled black plastic pipe (called a 'riser'), in the hardware story gardening section. Both ends are threaded as they're used for attaching taps. This riser is 900mm and the final antenna will be around 700mm - cost is about $6.
From the plumbing section I got a straight PVC joiner which fit over the riser - costs about $2.
Get 2 stainless 3mm bolts, long enough to go through your 10mm alum tubing, (excess length won't matter). 2 washers to suit, and 2 small lugs to solder to the coax tails.
Elements are 10mm aluminium tube - you need just under 1200mm of aluminium tubing.
Cut all 8 elements at the lengths shown - mark the D.E. and put it aside till later.

The Specifications & dimensions

Shows length of each element and the spacings

Reminder: You can download a PDF document for this project
To clarify some points:

  • Measurements are Centre to Centre
  • Measuring left side of one element to left side of the next will maintain the C to C relationship
  • Measurements begin from the Reflector (the Back element) and each hole placement measurement is taken from that point
  • Note the "Element Spacings from Reflector" measurements in the specs image above
  • 10mm Aluminium Tubing was used
  • 12mm can be used with the same measurements without altering antenna characteristics

Construction Process

Step By Step Build

8 holes in the boom at the specified distances
7 Elements fitted
Hole drilled ready for Driven Element

Drill all 8 holes in the black plastic boom at the correct distances, and fit SEVEN elements - Don't fit the D.E. Yet!
The last hole (Director #6) should be out near the end of the boom, leaving excess at the back, behind the Reflector.
This excess provides a mounting point for a brace onto a mast.
End of the boom was stuffed with lightweight styrene and a blob of silicone, as a seal against rain and bugs.
Do Not fit the Driven Element at this stage.
The elements should be a tight, secure fit or glue in place if necessary.

A visual clue about where Driven Element will Fit
Note 2 bolts sitting in the holes in the aluminium to assist your construction

Later you will cut the boom & place the White PVC joiner into the boom.
The Driven Element was cut at 154mm long, then cut in half.
There is short pencil inside the aluminium 'halves' to keep them about 1mm apart.
Pre-drill 2 small (3mm) holes through the Driven Element quite close to the ends - coax will attach here.

Drill 3 holes in white PVC

3 holes are drilled in the PVC.
1 hole thru centre, 10mm or diameter of D.E. material being used.
1 hole off-centre, the diameter of Coax. It's a tight space so drilling the coax hole off-centre will aid attaching coax.
Pull coax through so tails [ends], can be prepared.

Prepare Coax End by making tails

Make tails by removing 25mm of outer black plastic. Extract the outer mesh braid and twist into a single thick tail.
Remove some inner plastic dielectric, expose the centre wires. Twist into single thin tail.
Keep tails short as possible - tin & solder a ring terminal onto each tail end.
Images shows insulation tape covering to ensure 2 terminals can be screwed into the D.E. without touching.
1 tail must be longer than the other due to the angle of coax.

Secure ring terminals to D.E. using 3mm bolts

Bolt the ring terminals onto the D.E. (this is why pre-drilling holes earlier).
A long skinny screwdriver will be needed to fit 3mm stainless bolts & washers. To prevent the coax kinking, slowly withdraw the coax back out of the PVC joiner, while screwing the bolts down onto to the D.E.
Test the coax continuity to ensure no short circuit from all the pulling & twisting.

View of PVC Joiner from the rear

The 3mm stainless bolts could have been shorter but so long as the boom will fit around them, it's OK.

Almost finished

Cut the Boom

Cut through the centre of the hole that was drilled for the D.E. earlier

Cut through the boom and pre-fit the ends of the black riser into the PVC joiner.
Before gluing in place double check the dimensions! Ensure the D.E. is at the correct spacing now that it is contained in the PVC.
If measurements aren't correct shave small amounts off the ends of the black riser, try the fit again, repeat until you have the correct dimensions.
The dimensions are critical, so take the time to test at this point.
The distance between Reflector & D.E., when it's assembled, must be 74mm.

View with the front section of boom attached

The 'roll' in the image is an 'ugly balun' - 6 turns of coax taped together.
The BALUN avoids interference from short lengths of exposed/unshielded coax at the Driven Element.
I use flexible RG58 CellFoam low loss coax which suits my balun.
Buy what you can afford but understand that you get what you pay for.


When the rear section of the boom, which has the reflector, is glued into place the antenna is complete.
As mentioned above, be prepared to shave away small amounts of the boom so the ends fit inside the PVC and maintain those correct dimensions. An additional small piece will be 'nibbled' out until the coax can pass out of the PVC and exit the boom.
Repeating once more...Check specifications throughout the build to ensure your distances are accurate.

More Info...

Finish the Job

The final stage of mounting will vary with every assembly. The aim is to get it into the air, at a comfortable height for each build, stabilized and pointing towards the signal.
The material behind the Reflector can be any length, it has no bearing on the antenna design and provides mounting and bracing points.


This may take a leap of faith as all the experts will tell you that Next G technology is a vertically polarised medium and hence they say you should make vertical antennas.
Research YOUR nearest transmission tower & you will discover that some are Vertical and many are SLANT polarisation.
Research on is helpful as people build and test antennas and compare results... proving that if your Telcos transmission tower is SLANT polarisation - you will get better download speed from a Horizontally polarised yagi.
Conversly if your nearest 850MHz transmission tower is Vertical - then you stick with Vertical polarisation too.


What about the signal-strength lights and bars on your modem?
The number of bars is simply an indication of the noise in the air that the modem can see/hear. It is NOT a true indication of the directional gain you're achieving with your yagi. (I could prove this to you with lots of testing equipment but that would bore you).
A well-built antenna filters out all the noise and you'll only be seeing the signal you're looking for so 2 bars/lights might be great speed.
I'm not an expert by any means but I research propagation continually, and I can build an antenna to achieve the results I want - and at home handyman prices and that's good enough for me.
I hope this project has been of some help to you.

Important update 2020 Telstra Australia has published the following:

" Telstra will be switching off 3G in 2024. Before switch off, you can use handsets supporting 3G on 850MHz... After switch off you will still be able to access the Telstra Network on 700MHz." Find out more at: Telstra 3G is Closing

  • 3G telecommunications is being retired in Australia in 2024 but I will leave this page live on the internet
  • The 3G mode [and 850MHz frequency] is still used in other parts of the world
  • As you see in the FAQ/Gallery Page people from several countries sent feedback regarding their build and how they use this antenna for their local conditions.
  • With contacts from remote USA, Colombia & Philippines, people are building this antenna to suit local conditionss. So it is still a relevant resource.
  • I even had enquiries from Africa on how to use it to track lions (with their safety collar transmitters).
  • It is still a relevant resource

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To be sure..

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