A Low-Noise 'Urban' 3 element LFA Yagi for 70MHz

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.

EZNEC files for this antenna are on the download page.

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

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. Note there are no lobes striaght up and down in the Elevation plane.

Note: The loop feedpoint as per the photo, at the front of the loop nearest the reflector

3el 4m LFA built by M0KSJ

'Thought you might like to see a picture of my completed 3 ele LFA Yagi 
- I ran some more tests today using a temporary tripod mast at about 5m 
and was very impressed at being able to work G4ASR in Hereford plus
heard a very loud G4RFR in Dorset (didn't work as I went out into the
garden to manually adjust the beam heading and he'd vanished by the time
I got back).   Next step is to get it up on the rotatable mast on the
house at about 10m.'

Kevin, M0KSJ

Performance UK/US version

Gain: 8.66dBi @ 70.20MHz

F/B: 22.44dB @ 70.20MHz

SWR: bandwidth 500KHz 1.3.1

Antenna Dimensions

Spacing                      Half Element Size  in Metres              Element Diameter

Reflector                0                              1.058                                             1/2 inch

DE1                      .347                          .886                 FEEDPOINT              1/2 inch

DE2                      .678                          .886                                               1/2 inch

D1                        1.388                       .9425                                              1/2 inch

Performance EU version

Gain: 8.63dBi @ 70.20MHz

F/B: 23.41dB @ 70.20MHz

SWR: bandwidth 500KHz 1.3.1

Antenna Dimensions

Spacing                      Half Element Size  in Metres              Element Diameter

Reflector                0                              1.058                                            13mm

DE1                      .347                          .885                   FEEDPOINT           13mm

DE2                      .678                          .885                                              13mm

D1                        1.388                       .9425                                             13mm

Notes:

The loop ends are joined using 3/8 or 10mm tube.

Azimuth pattern of the UK/US version

Elevation plot of the UK/US version

SWR Plot of the UK/US version

As always, ask if you have any questions and I look forward to working you at field day!

Justin G0KSC

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.