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Antenna No 56

 

2m and 4m Yagis in 2-bay configuration

 

I had for some time planned an experiment with two Yagis in vertical polarisation in 2-bay configuration.  It would at the same time allow me to receive more distant fixed, mobile or portable [SOTA] stations and I was keen to try out the splitter/combiners I had made recently.

 

For a VHF setup in Ireland I had made a light version of a 2m 6 element and a 4m 4 element Yagi (DK7ZB design, 50 ohms feed point, 2m boom length) and I was pleased with the results.  For this experiment I opted again for the DK7ZB design (now using 10mm elements) and commenced on building a pair of each.

 

I ran a simulation using MMANA-GAL on a 2-bay configuration and decided on a 1/2 wavelength separation with both antennas in vertical polarisation.  This setup provides a deep null at 0 and 180 degrees and wastes very little energy upwards.  It narrows the front lobe by 3dB compared to a single Yagi.

 

 

Antenna simulation for "free space" using MMANA-GAL.


 

Some photographs from the antenna construction process:

 

 

I use Box G366 (82x80x55mm) for the open dipole construction.

Drilling the 20x20x2mm aluminium boom.

Marking where the support bracket will come.

I reclaimed this weathered aluminium for making support brackets.


 

Recently I assembled the antennas in the garden and started measuring each one on a 6m fiber mast, I was especially keen to compare the "batch built" antennas for 2m and 4m.

 

First the 2m 6 element Yagis:

 

 

The Yagi in test position in HP on a fiber mast.

Detail of the 2m Yagi, now with the metal support fitted.

A pair of 2m 6 element Yagis is ready to be installed.

SWR plot for both Yagis shows almost no in-band difference!


 

Followed by the 4m 4 element Yagis:

 

 

The Yagi fully assembled but with test mast support affixed (in PE).

A pair of 4m 4 element Yagis is ready to be installed.

SWR plot for both Yagis shows good convergence.


 

Finally I fitted a 35x35x2mm support arm to the rotary mast and mounted the 4m and 2m Yagi pairs.  I made up one wavellength patch cables with N-connectors and attached these to the band splitter/combiner which is strapped to the mast.

 

 

The splitter/combiner 'tube' can be seen in the middle.

All vertically polarised on this mast.  At the top are 4m and 6m vertical dipoles.


 

July 2014:  this is a long term experiment - results from observations will follow.

 

 

Work in progress for another pair of Yagi's.


 

 


 


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