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Antenna No 67

 

2 element Yagi for 4m

 

I built a few more 2 element 4m Yagi's based on the excellent model by DK7ZB, see Antenna No 63 for a recent build using 8mm aluminium tubing as well as Antenna No 45 for my early prototype. 

 

I decided to build one antenna for a friend.  Our QTH's are at opposite ends of a group of 4m enthousiasts about 50km apart.  Though we can copy each other using vertical dipoles the signal is often hissy and subject to fading.  A 2 element Yagi at both sides should improve reception.

 

The second Yagi is to take with me to Ireland where I shall be activating some rare locator squares on the West Coast [using a transverter for 4m SSB, Sporadic-E propagation].  The 2 element Yagi is very compact and easy to mount on a fiber mast for /P operation.

 

The following pictures are about the construction and testing of the 2 element Yagi's for 4m.

 

 

ABS project box (115 x 90 x 55 mm), PP saddle clamp, cable glands, 8mm aluminium tubing, N-chassis connector.

Preparing the impedance transformer: 2 quarter wave sections of RG-179 in parallel.

The completed impedance transformer for 28 to 50 Ohms.

The 2 Yagi's now fully assembled.

Extended boom (by 0.50m) with 50mm saddle clamp for before-the-mast mounting.

The holiday Yagi with polyethylene support for mounting on a fiber mast.

The SWR plot of both Yagi's is very similar.  They are aligned for centre-of-band around 70.200Mhz.


 

 

 

The 2 element 4m Yagi in VP in between other VHF horizontal Yagi's.


 

 

An initial 'on air' test showed the F/B ratio to be 18dB.  This is an improvement over the same antenna mounted on an insulated mast.  In an MMANA simulation the 50mm mast behaved as an untuned parasitic element, not actually contributing to any extra gain but improving the F/B ratio by "flattening" the rear lobe. 

 

The before-the-mast mounting technique also influences the feed point impedance, as a result the SWR is now 1.3 - 1.4.

 

 


 


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