Building a 4m & 6m dual band Yagi.

New 2m, and dual 4 & 6m yagi installation

The following notes will hopefully help anyone thinking of building this or something similar.

All design information and credit goes to Justin, G0KSC and as I’m sure many of you will have  already discovered Justin has a lot of useful build tips on his web site. The actual design I used was the SC6-4-8D

The SC6-4-8D uses stock material so I would expect the element and boom material to be available from most aluminium stockists. I’ve used Aluminium Warehouse before for material to build 2 x 9 element DK7ZB antennas for EME. I now use Aerial-parts of Colchester for most of my antenna parts, fortunately they are located fairly close to me so I can collect (by arrangement). The delivery costs for long lengths of tubing add a significant amount to the overall build costs… it helps if you have another local amateur or some club members who also have an interest in building antennas and can share the cost.  🙂

The all-important element clamps can also be sourced from Aerial-parts of Colchester, as can the mast to boom clamp which needs to be specially ordered for this yagi as there’s not a lot of space between the D1 and DE elements.

Fasteners are all stainless steel and I sourced them all from eBay – again volume buy helps keep costs down.

The actual antenna build was very straight forward, I invested some time in making a small jig (from a scrap piece of aluminium) to help mark the positions of the holes for the element clamps. A pillar drill makes the drilling of the boom quicker but with the jig and careful measurements the boom can be drilled from both sides – measure twice, cut once 🙂

The plate for mounting the DE was made from some scrap 3mm aluminium sheet I had available.

I used a plumber’s copper pipe tube-cutter to cut the round aluminium tube. I find it more accurate and better than using a hack saw.

I chose to mount the yagi with the elements hung below the boom, this then allows the balun to also hang below and you then do not need to drill a hole in the boom to allow the coax to pass through – it’s also easier in the future to dismantle the antenna / change the cable.

A tip given to me by another local was to use spacers on the back 6 elements. Due to the different element lengths and the way the interlaced yagi works people have noticed that the SWR can vary due to the element spacing changing in strong winds. I looked at many different things to find something suitable in the end I found the snap-on cover used on small rectangular cable conduit was ideal in size and weight so I used this to produce four spacers which can be seen in the photo below. I should add I have no idea of the UV properties or longevity of this solution.

4&6m yagi - spacer for reflectors 2014-06-08 15.29.484&6m yagi - spacer for 2 x D1 & 2 x DE  2014-06-08 15.12.59

 

 

 

 

In summary the construction was very easy and can be done with what I would consider to be the average  DIY tool kit. The hardest part was making the choke balun – I am not kidding… I used RG-214 and trying to wind five turns of that while keeping the cable-ties in place and then cable-tying it all together single handed is not easy.

 

Choke Balun 4m-6m yagi 2014-05-01 13.10.56Once again Justin has some good instructions on his web site on how to wind a choke balun.

 

 

 

 

I hope to publish some SWR graphs of the antenna in the future….

Update:  I have had an opportunity to use an MFJ-259 SWR Analyser to run a few very quick tests on the antenna. The results showed a good match on 6m, on 4m resonance was right at the bottom of the band (ideal for DL band plan  🙂  )  and on 70.200 MHz the SWR was measured at 1.5:1  I believe this “shift” is due to adding the PVC strips. More time is needed for further investigation…  and for me to invest in some new test gear!

4m & 6m dualband yagi SWR

I should also add that I have no business association with any of the  companies listed other than being a  satisfied customer.

Acknowledgements:

Justin, G0KSC for the antenna design

 

 

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