Many people have tried this DIY antenna project with great success in Australia, USA, Colombia, Uruguay and the Philippines. Thanks for the feedback.
Frequently Asked Questions
Q:...is it necessary to include a balun?
A:... NO it's NOT necessary for this antenna because you are generally Receiving and not Transmitting.
For those who wish to know... To make an ugly balun I wound the coax around a piece of 2" PVC... using small pieces 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 and you have 'ugly balun'. It's not a separate piece of coax.. you simply put some "rolls" in your long coax - up near the Driven Element end.
With my Amateur Radio antennas I am mostly Transmitting so I have the worry of matching my antenna very carefully and ensuring that any stray RF doesn't cause a problem... that's why I use baluns.
Q:...My USB dongle has a cable with a large plug on the other end.
I assume I need to also buy a large plug to connect the coax to this little lead?
A:... Yes. It sounds like you have a patch lead so use whatever fittings or adaptors YOU need to achieve a "join" with the least metal that you can. Each time you introduce another adapter you degrade your signal a little more - that's why I try to use the correct fitting when I can.
Here is a link to a supplier of patch leads etc. campadelectronics.com.au Disclaimer: I haven't used this company, the recommendation was on an RV/Camper site for leads and connectors for travellers with unusual needs.
In my case the coax has 1 end fixed into the antenna and on the other end I crimped an FME fitting which screwed into the Modem.
Q:...Can you clarify 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?
A:... Correct. Cut away about 25mm of black coax insulation and pull some braided shield mesh to form it into single thick wire. Then carefully remove the white plastic dielectric to expose the centre wires and twist them into a single wire. It's a fiddly process but now you have 2 separate tails to work with and each will get soldered to a lug.
I usually Tin both of my wires at this point so they're easier hold at the strange angles needed as I solder onto those tiny lugs. Also the lengths you need will vary depending on where you drilled your entry hole for the coax and the 'angle' you need to achieve.
You end up with 1 thick and 1 thinner wire which is 'unbalanced' and why I have to use Balun's with my Amateur Radio but as mentioned in this project thick and thin won't worry you.
Q:... 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?
A:... 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 of the Driven Element we need to have coax tails as close as possible to the centre.
In practical terms 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 but don't allow the two lugs to touch.
Q:... 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?
A:... 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.
Q:... You suggest 900mm length, yet the spacings of the elements from the reflector add up to 2,361mm. I must be missing something!
A:... Yep. You missed the keywords Element spacings: from Reflector. Those measurements are not ADDITIONS.
You take the centre of your 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.
A 900mm riser was a convenient length for me, with enough sticking out the back end to devise a way to mount it.
Q:... Coax Question - 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?
A:... RG213 is better than the "cheap" RG58 coax and good to see you researching.
RG213 is a THICK coax and difficult to work with as you have to finally connect to the tiny FME antenna fitting on the modem and the more adapters and patch leads you add will degrade your signal, so it's a trade off.
Working with a thinner coax gives more flexibility and there are high quality RG58's on the market but you have to search around for them. Dick Smith and Jaycar generally sell the cheap coax with markings like /R or /CU on them.
My Coax is Cellfoam Low Loss RG58 Type RFI CAT. No 9001 which is rated as good as RG213 and if you're serious about finding this quality look for the "Installer" in your town who puts radios in Ambulances, Fire Trucks etc... They should have high quality stuff as it's a required spec for emergency vehicles. Will they sell you 20 or 30metres? I dunno but it's worth a try.
Q:... Can the Driven Element have wood inside?
I realised that a standard wooden pencil fits perfectly inside the aluminium tube and makes the D.E. strong.
Another question; To change the polarity to vertical I only have to put the antenna with the directors in vertical position.
A:... A wooden pencil to keep the two halves apart and strengthen the whole thing is a brilliant idea as wood is also an insulator.
And, yes you are correct. If your nearest tower is Vertical you place your antenna so the aluminium cross pieces are pointing up and down. If your tower is Horizontal you place them crossways, just like looking at the horizon.
Q:... I'm asking about a Yagi antenna covering 850mhz to 2100mhz frequencies used in the Philippines.
Some telecoms here use 850/2100MHz. I made your Yagi design, its 100% success to my broadband connection, could you pls give me the design so I would try?
A:... I don't build 2100MHz antennas so I can't recommend anything but.. If you check this Whirlpool page there is a list of Yagi's for various frequencies.
In Australia whirlpool.net.au is a very popular site to seek technical advise but be careful as some people talk quite a lot in forums but don't really build anything so their advice might not be so practical.
Once you find the Yagi specifications you have my basic design/build ideas and should be able to make something just for the 2100mhz signal.
Just to be clear - Your question says "yagi antenna covering 850mhz to 2100mhz"... you cannot make ONE antenna to do both frequencies as they are too far apart - it must be two different antennas.
If you mean that your Telco uses "either" one or the other - then if you have a strong signal on 1 of the frequencies... you don't need to use their other option. e.g. Here in Australia Telstra send me a 4G phone signal... if my phone can't get 4G at that time, it tries 3G... if no go, it tries 2G. If I watch my mobile phone it jumps from one signal to the other depending on my location. I hope this makes sense to you.
Q:... I presume it doesn't matter where the mounting fixture is located if I use a non metal 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.
A:... Correct, mount it anywhere that you like to make it compact and 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.
Q:... Do you have to tweak the Elite Modem so it knows you have an external antenna.
A:... There was no option to tell the modem I was using an external antenna until I upgraded the firmware for the modem. WOW an option appeared asking if I was using an external antenna - talk about putting the cart before the horse
Frequently Asked Questions
Q:... The ‘telcoantennas’ website says a Yagi provides upwards of 12db gain.
What gain would you expect from this design?
A:... 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 - which we can't measure to prove anyone right or wrong)
Don't worry too much about it, there are some basic rules like; the more Directors you have out the front of your antenna increases Gain but it narrows the bandwidth of the antenna.... too technical for this project.
But for those who want some simple rules 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 he could harness all those outward radiating radio waves into one direction. The 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, the forward directors pick up a signal and effectively amplify it they pass 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.
Q:... I checked the ACMA site not all towers have 839.8 and 884.8MHz frequencies.
If these are the only pair of frequencies used then I have a better idea where the yagi will have to point.
A:... Telstra Bigpond NextG Wireless Internet use only THOSE uplink and downlink frequencies so confine your search to Telstra Towers which have those two frequencies.
Building a transmission tower costs megabucks and to offset the cost they "let space" on the tower to anyone who'll pay so there can be dozens of antenna on it. Every antenna on the tower has its allocated frequency and ACMA licence. A tower may have competing Telco's [mobile phone internet] Community organisations or even nursing home paging systems, etc. Each tower will have a lot of data when you begin your search, but don't be disheartened, just find Bigpond.
Q:... Would that NextG yagi antenna be suitable for mobile phone (next g 850 band) as well as NextG USB broadband?
Both my phone and the elite usb modem have external sockets and I'm able to order the patch cables for both so everything should work fine hopefully
A:... Yes, the frequency is the important thing and if your devices will accept an external antenna you can connect the Yagi to capture NextG/3G Frequency. USB dongle modems sometimes have external antenna ports but some do not.
Q:... looking at the photos of the Yagi it appears that the directional bars are the ones to be either horizontal or vertical. Is that correct?
A:... Yes, when we talk about the "plane" of the antenna being either horizontal or vertical we are talking about the cross pieces of aluminium - the elements.
TV antennas are a good example; Some have a section with horizontal elements [looks like a swordfish] and a section with longer vertical aluminium elements. That's because some channels broadcast a "horizontal" signal and some broadcast a "vertical" signal so one antenna can 'capture' both.
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 position their antenna to match the tower they are pointing at.
Q:... Does much needs to be done to the NextG Yagi to convert it to 3G?
I'm currently travelling using a Telstra Ultimate modem and I usually camp for a week or more so having a directional aerial wont' be a problem if I can find a tower.
A:... Telstra's NextG IS a their 3G service...... NextG is Telstra's name for their service. It just meant is was 3rd Generation of mobile technology and it runs on the frequencies stated for NextG Internet [it's sometimes called Telstra's 850MegaHertz range].
By the way Optus 3G runs on very different 2Gigahertz frequencies - yet they are both called 3G **argh**
I rely on this WHIRLPOOL.net.au article for Australian mobile phone/internet frequencies and if you're in doubt check your modem manual for the frequencies it uses.
Q:... Can you give me a bit more info on how to use the ACMA site for tower polarisation search?
A:...The ACMA searchable website provides some boxes if you already know the Site ID or Licence number etc.
If you're a beginner you won't know what to search for so they provide a link called "Other Radiocommunication Licence searches" [look around the screen]. From these links choose the Assignment/Frequency search range then enter YOUR postcode in both the Hi and Low postcode boxes. 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 will returns a list of Telstra 3G licences in your area. Use the left hand column "Assignment ID" & check each one.
If the physical location is within 20-30km write note the Site ID details and keep checking them all until you come up with a list of towers around you.
Towers near populated areas will have multiple antennas for the same frequency but each one will be pointing in a different direction [that's the Azimuth mentioned in the ACMA licence details]. Keep in mind that if Telstra's antenna is pointing AWAY from you then it won't do you much good pointing towards that one.
Some towers near to highways are Vertical to give coverage in all directions for passing vehicles.
Find the closest one with antennas pointing in your direction, so they're beaming their signal at YOU, then you set up your antenna to point back at them.
Once you've selected your nearest tower, check how the antennas are Polarization? [are they vertical or horizontal polarisation or slant?].
The Latitude and Longitude of the tower is also recorded in the Site ID and there are Google Map tools to help you find the direction and distance so you can get the direction right once you climb onto your roof.
If you have a choice of Towers pick the one from a less populated area, 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. Lastly, do keep your notes on the other nearby towers and if you think your first choice is marginal, spin the antenna around and try another.
Remark: This is an email from "M" regarding his search for NextG Antennas... made me smile
Below is a reply that I sent to a Retail outlet this morning after inquiring how much for their 16.5Db Yagi & good cable, delivered to Mullaley NSW. Answer $194.70
Thank you for the speedy reply. While I was looking on the net for antennas I came across www.tigereye.net.au/vk4ion/nextg_yagi.html which details a home made yagi antenna with instructions. I had nothing to loose so in under an hour I was replacing my store bought 12Db with this PVC & aluminium tubing nightmare. Previously I was getting low signal strength @ 0.36 to 0.640KbS linespeed, and now 2.34MbS. Well I couldn't be happier. Total Cost about $6. But once again thanks for the reply. Your faithfully M.
In all fairness I must admit that my effort looks like a shower of s#*t but it works a treat for the 76Km straight line. I didn't have 10mm tubing for the elements, I used 12mm and the riser was 3x offcuts of 50mm PVC. The cable was supposed the be the best (Industry Standard) I was told, thin RG58. All I did was take the U-Beaut shop Yagi antenna down and put up the hours labour. I think I will go back to the drawing board and this time do a professional job on it, including replacing the RG58.
Reply:... Hello M. Thanks for the contact which made me smile. Yes, we've all been raised to think that Retailers know best and we do need them to help those who can't clamber on the roof. But having said that, I want the Commercial guys to really learn their craft and don't just take people for a ride. Your funny anecdote may inspire others and btw GREAT speedtest results too, thanks again for sharing.
Msg from James: I've now built a few of them!
My biggest advice to those building it would be to get good coax, I ended up using RG213 as I was having trouble sourcing good quality low loss RG58 coax, this was a great improvement over the cheap RG58 that I originally got from jaycar although it is tricky to work with such large cable. James, Stanthorpe Qld
Reply:... Hi James, Thanks for feedback and photo. Yes... there is no substitute for quality coax. I know how persuasive that Jaycar salesman is when he says... "they're all the same mate" haha. When people take this leap of faith to build this antenna they're understandably nervous about the cost and will try the cheaper RG58, when it works they might not bother replacing it with better coax.
Here are photos we've received from happy DIY NextG Yagi builders:
Now DON'T laugh at this one, there is a funny story!
Ian returned home to his station near Cunumulla and built a much better one but he wanted us to see that even with WIRE elements this antenna worked. They pointed it to Yowah and had consistent 2bar signal during the day and three at night
So it goes to show you... never be afraid to experiment. Well done Ian and friends. Good to see Queensland bush ingenuity at work. I feel like such a proud parent each time one of these photos and testimonials hit my inbox.
From the Philippines, Airrion sent this photo.
This Yagi is from James @ Stanthorpe's, he's built several of them and this is his favourite.
Here is the photo from David on the Coastal Plain, in Gippsland Victoria
And another intrepid home builder from Karabeal Victoria.
From the Gold Coast Wayne emailed...
>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.
From Condobolin in NSW Darcy sent this....
And from Caboolture Ron sent...
YAY RON! I never thought of putting it inside... hahaha see, you learn something every day!
And here's another variation.
Robert sent this photo........ Glad to see people using whatever they can lay their hands on.
Jim from WA photo
Web based research which assisted this project & commercial dealers for patch leads and connectors;
Telcoantennas a Queenslland company 100% Aussie owned might be able to help you with patch cables etc
campadelectronics.com.au the site recommended by RV Travelling group
ACMA search facility: locate Telstra/Bigpond transmission towers, check frequencies and polarization
VK7JJ - Phil's modeling of 800 mhz yagi's
VK4UD's Wireless internet - temporary fixes when you're going bush