Home brewed 17M Moxon Beam up 30′ at KY6R
In Part 1 of this series, we discussed how DXA will be “your best friend” as far as working VK0EK goes:
And in the next installment of this series I will discuss the propagation tools – both Stu, K6TU’s fantastic propagation tool as well as VOACAP Online and the very important HFTA. But EVERYTHING in the DX space relies on your antenna, so lets spend a little time on antennas. If you are lucky, you have a tower and at least a 2 element 40M yagi and a 3 or more element 20M yagi – such as the N6BT DXU-32 that I have:
But not everyone can have such an antenna. In fact, I worked the first 300 DXCC toward Honor Roll entities using just wire antennas and 200 watts (or less) – using mostly doublets and extended double zepps – but also Bruce Arrays and the Moxon beam. I still use an Extended Double Zepp (3 dB gain) on 30M, but it is fixed perfectly for VP8STI – South Sandwich – 130 degrees from my QTH – but not oriented so well for Heard Island – at 215 degrees from my QTH. Therein lies the rub regarding Doublets, Dipoles, Extended Double Zepps and even Bruce arrays, Bobtail Curtains and other vertical arrays. Pattern – and directivity are important. You need to be able to beam your signal in the right direction.
So – enter the Moxon!
The Moxon antenna is probably the best “bang for the buck” antenna you can build – and do it for about $100 dollars US. In fact – you can build one for that price that either has one band (at 4 dB gain and > 25 dB F/B), or have a nested 2 band model that gives up 1 dB forward gain for the added band. It can be turned using an inexpensive TV rotator (such as the one Radio Shack has on sale now – for $30). If you can put up a dipole – you can put up a Moxon – and get two bands (non adjacent) out of it, and get gain, directivity and awesome front to back ratio!
Here is what VOACAP Online says about VK0EK for me:
and what K6TU’s propagation site says for me at KY6R:
The US West Coast is one of the more difficult areas to reach Heard Island – but overwhelmingly – all signs say that I better have serious antennas on 40, 30, 20 and 17M, and perhaps 15M.
My N6BT DXU-32 has 40 and 20M covered, and I have no worries there, but it looks like I need to pay more attention to 30M and 17M. VOACAP Online says 17M and K6TU says 30M. My Extended Double Zepp on 30M will have to do – its oriented more towards VP8STI, and I will just hope it does well for VK0EK. But on 17M – I have the chance to improve my antenna situation with maximum bang for the buck, so I decided to add a 17M Monoband Moxon to my antenna “arsenal”. Two elements on 17M will be perfect, and the Moxon fits the bill for the space I have out in the back yard . . .
So, lets build a Moxon for 17M. I’ll list the exact steps.
- Purchase 5 Cabela’s “Crappie” 17′ fiberglass fishing poles. I ordered 5 for $5 a piece on a special sale.
- Order a DX Engineering Boom to mast plate – BMP-2B and U bolts that they sell (see below)
- I also purchased 100 feet of the DX Engineering antenna wire – that is 14 gauge flex weave.
- I’ll assume you have coax – if not – check out DX Engineering’s Max line of low loss coax. I use DXE 400 Max – which is similar to the Davis LMR 400
- Here are the 4 Cabela’s Crappie Poles being sprayed with “Plasti-dip”. This is because fiberglass, when up in the UV for 2 years can be reduced to a splintered white powdered mess.
- Once dried, I insert 1″ aluminum sleeves to the ends of the fishing poles – and add them to the DX Engineering boom to mast plate. The U bolts on the plastic “collars” and bolts hold the poles tight:
By the way – the markings on the plate keep the elements leaving the plate at 40 degrees apart, and I used a simple school protractor to make those marks.
- Underneath, we have a “floor flange” that you can purchase at any hardware store:
The bolts will go through the aluminum sleeves, through the plate and through the 4 holes on the Floor Flange.
- Now we need to calculate the wire sizes of the elements. I use this web site:
I cut the wire to size and take in consideration that I will need to solder ring lugs to the spacers as well as the 1:1 current choke at the feedpoint
- Speaking of the feedpoint, I use a high power 1:1 current choke – and Balun Designs and DX Engineering both sell great 1:1 current chokes for running “full power”. I had to create some special “platform” to hold the choke onto the feed point fiberglass pole:
I had a spare “Carlon” box and I used it upside down on the fiberglass pole. This way, I could use nylon bolts and nuts to bolt the 1:1 current choke onto the pole:
I had sprayed this platform with the Plastidip as well. Here you see the nylon bolts and nuts holding the 1:1 current choke to this Carlon “platform”.
- The wire is attached while making sure that I keep true to the dimensions from the calculator:
And I use wire ties and electrical tape to hold the wire on the Cabela’s poles at the right place. The spacers between the driven element wire and reflector are extra pieces of fiberglass fishing poles – and with nylon bolts and nuts:
I used some “liquid electrical tape” to cover all of the nuts – so they would come loose (not shown here). Also note – the gap spacing of the wires is critical, but made easy by using wire lugs that are bolted through holes drilled at the right gap distance. Remember to measure the wire length for the antenna that takes in consideration that you are using wire lugs. Measure “hole to hole”.
- That’s pretty much it – I tested the antenna on the ground and it was “close enough”. Testing an antenna 3′ above ground will show the reasonant frequency to be higher than reality. Once I got the antenna up 30′ – the SWR was 1.1:1 and was flat for the entire 17M band.Success!
If you use VOACAP or the K6TU web site – you will find out which bands will be best for you. On the West Coast in the USA – 30, 20 and 17M will be the best – with 40, 15, 12 and 10M possible. Lower than 40M seems less possible.
A great resource on Moxon antennas is managed by our good friend and VK0EK Sponsor, Steve Hammer, K6SGH:
If you can’t put up anything large on 30M or 40M, you could phase two verticals using the Christman Method, and with a Stack Match II Switch by Array Solutions, get four directions for about $300 – $400 for all parts. See HTTP://ky6r.wordpress.com/2013/06/07/optimized-40m-vertical-array-built-tuned-and-tested/ it was an excellent low band vertical array, giving me years of great service.
I’m a DXCC Chaser and DX-er who will be home chasing VK0EK – just like you will. I hope to do everything I can to help you get into the VK0EK log, and hope you will ride along with the team on this most fantastic, rare and fun adventure.