Many people have tried this DIY antenna project with great success in Australia, USA, Colombia, Uruguay and the Philippines, and I thank them for the feedback.
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.
Want to know more... I did make a balun for this antenna by winding 6 rounds of coax around a 2" PVC pipe.
Held it with electrical tape and slid the PVC out. I bound this 'roll' with electrical tape to create my 'ugly balun'.
It's not a separate piece of coax! The "roll" is made from the longer transmission line coax and is placed close to the Driven Element.
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". Each time you introduce another adapter you degrade your signal a little more, so try to keep them to a minimum.
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
A:... Correct. Cut away about 25mm of the black coax outer plastic 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 tail is soldered to a lug.
The lengths you need will vary depending on where you drilled your Coax entry hole and the 'angle' you need to achieve.
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 connected as close to the centre as possible.
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
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
Your boom can be anywhere from about 700 mm onwards depending on how you're going to mount it. In my case a 900mm riser was a convenient length, with enough sticking out the back end 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 more 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. 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. They may sell you 20 or 30metres, 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.net.au page there is a list of Yagi's for various frequencies. 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.
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 then appeared asking if I was using an external antenna.. that was a surprise hahaha.
Q:... The 'telcoantennas' website says a Yagi provides
upwards of 12db gain. What gain would you expect from this
A:... Correct a Yagi = about 12dB gain (improvement) over a
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.
Want to know more... a simplistic explanation of how a Yagi works: Imagine a Vertical antenna, your signal is going out in all directions... a lot of your 'energy' is wasted if you didn't want it to go up, and out those other directions.
Professor Yagi & Shintaro Uda discovered they could harness all those outward radiating radio waves into one direction. The Yagi beam doesn't allow the signal to go out the back or to the sides but rather it goes in an elongated egg shaped 'lobe' 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:... 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.
Telstra/Bigpond mount their antennas either Vertical or SLANT on their towers..... you check your nearest tower (from the ACMA records) and position your antenna to match the tower they are pointing at.
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 vk4ion.au/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 are trained to believe 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 learn their craft and don't just take people's money. 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. Yes... there is no substitute for quality coax and it's annoying when a salesman says... "they're all the same mate" haha
When people take this leap of faith to build my antenna it's understandable they'll user cheaper coax to keep the cost down in case it doesn't work.
But if it does work replacing the coax will give that boost as you've outlined.
Ian was visiting a friend in central Qld who had printed off my
They scrounged some wire, 2-pack epoxy, timber & cut some coax off an old antenna and here it is - and IT WORKS.
A consistent 2bar signal in the day & three at night.
An extremely neat job using blue PVC which he could obtain there. He says he's had 100% improvement in his signal.
He's built several of them and this is his favourite.
He salvaged PVC water pipe to make the antenna and extend the flagpole. Had no internet before, now stable speeds at 1.5MB running on Solar with 12volt battery bank
David writes "My tower is about 4kms away but I only had a low
reading and used a Mobile antenna which gave a little boost.
I built the Yagi without the balun and I am rapt. Having never attempted a wireless antenna of any sort this thing went straight to the roof!"
An intrepid home builder, Andrew writes;
I didn't have a drill press and couldn't keep the elements millimetre perfect, it works a treat.
The family think this new internet speed is life changing too.
Wayne was frustrated with congested broadband so... a trip to
Bunnings and Jaycar & 2 hours later a quick test and a much
Remounted the Yagi now has best speeds ever - (3.67mbps)
Darcy emailed "I completed my first Yagi and it works! AMAZING,
Speedtest settled around 5.24mbps.
Mounted vertically rain could get into the alum tubing so I capped the ends with silicone. Total cost $18.68 including 8M of RG58 coax.
I now have FIVE Yagi's on the go for friends and family.
1km from a tower but with dense forest in between so very poor
My lucky day when I found your article and built one, with fantastic results.
The antenna looks sensational & is mounted inside, near the computer. Internet is now very fast. Imagine if I put the Antenna outside!
In a Hollow 1km from a Tower.
Before the yagi - 600kbps, now consistently over 5 Mbps.
It is my a test setup, yagi not yet mounted high! Will get more cable and move to my tv mast.
" 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
Each of these images will link to a dedicated webage where I share my Amateur Radio projects or travel pages.