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Articles

A Low-Noise 'Urban' 5 element LFA Yagi for 50MHz

If you suffer with noise from living in the city, this is an antenna for you.

The LFA design has a patent pending and all G0KSC designs are copyright. Any ham can build for their own use or those of a friend. Where profit or commerical gain exists, express permission of G0KSC must be sought.

NOTE: This is a concept antenna, I would recommend the wide-bandwith 6 element LFA's over this one.

This antenna has been designed in order to minimise the upward and downward lobes typically seen the the EL plane on Yagi antennas. By doing this, a drastic reduction in pick up of unwanted noise in City locations is the result. The double bonus is the likelihood  of reducing transmitted interference too.

Performance

Gain: 11.49dBi @ 50.150MHz

F/B: 28.5dB @ 50.150MHz

SWR: 1.0.1 @ 50.150MHz - bandwidth 300KHz 1.5.1

Take a look at the following AZ and EL patterns for proof.

Az pattern is very good with very high Front ot Back ratio and good forward gain for a 5 element design. However, it is the El plane where the difference really shows.

 

 

Huge suppression of the upward/downward lobes leads to much less man-made noise appearing on the receiver with less transmitted inteferance too.

 

 

The trade off is narrow bandwdith which is why I have built the model to prove it first. The tuning has been centred around the main DX SSB/CW and Digital activity

 

 

The dimensions for this antenna are above. While the tube sizing is quoted in mm, these do translate to imperial sizes available in teh US, UK and Ausralia. The EZNEC design file is available on the dowload page of this site which will allow you to alter the design to your own requirements.

Pictures of the completed LFA Yagi

 

The completed antenna above with additional support boom bolted beneath the main boom.

 

The feepoint of the loop. I don't have an insulator big enough for the 7/8 inch tubing of the loop!

 

One of the insulators holding the other side of the loop to the boom.

 

The completed loop sitting on the boom ready for feeding.

 

A close up shot of the end of one of the loop joints. Fastening can be done with bolts, hose clips or the prefered which is welding once you know the ideal size the loop should be.

 

A side shot of the long-boom 5el LFA with secondary support boom. That is my Wife's car in the back ground and no, I don't drive it.

 

I made a heavy duty clamp for the antenna to bolt to the mast with a recess for the mast to sit within. This baby ain't going no where!

 

Please note: There is a patent pending on the LFA design for commerical use. If you wish to sell LFA designs commercially, please contact G0KSC.