After some rather strange questions from a potential builder of 50MHz Yagis, I was directed to DK7ZB's '50MHz Design Principles'. The information presented here is not wholly accurate and additionally, refers to statements of Lionel, VE7BQH in a way that the reader could be deviated from what really is important when designing Yagi antennas for low noise on any band.

These statements are common misconceptions relating to Yagis and beleived by many. Within the pages of DUBUS magazine, next issue (Q1, 2015) I will elaborate on why this is so and how these principles will not yield the best in 50MHz antenna performance.

A head of this article, I will give 2 examples of comparisons between antennas optimised for out-right gain, compared to my Low-Noise LFA Yagi. However, the comparison is not just on the 6m band, I have provided one on the 10m band too!

- 10m LFA comparison with TH6 by VK2GCC

- 6m comparison between 7el 50MHz WOS LFA and M2 7el JHV by VA3NCD - noise level change is significant. Lower gain LFA has Louder received signals due to reduced noise levels.

Subscribe to DUBUS and find out the facts!

Justin G0KSC

Low Noise LFA Yagis, there really is a difference!

Normally I like to write something of length but this time, I will let the real world results do the talking. Below is a link to a video created by Jarek, VA3NCD who compares his 7el 50MHz G0KSC LFA with a well-know, commonly used, US built equivalent. 

First Jarek simply switches between the antenna with just background noise only. Move forward 4 minutes in the video and Jarek points his beams at different beacons and conducts the A/B tests. Note how marked the audible difference is in noise this is 'many' DB's difference in noise floor and as you can see from the beacon tests, makes a difference between Q5 reception and not being able to copy a beacon at all.

Many antenna designers display antenna comparison plots against my antennas showing the similar patterns. However, the LFA is not a spot-frequency antenna and performance difference is not attributed to pattern alone. The LFA is a wide band antenna in terms of performance AND SWR. Many antenna vary greatly in side lobes, F/B and gain over a short frequency range and thus, the LFA has predictable performance everywhere. Next, the low noise characteristic is not a result of pattern alone, the closed loop driven element adds to this characteristic and reduces the noise floor and has a direct, 50Ohm feed point so any matching losses (whcih includes additional noise) are not added to the antenna after model.

Have a good look through this video and see the facts in the real world!