5 el. 6m + 5 el. 4m Duo band yagi antenna 

This design was originally published in “DUBUS” 2/2007 

This antenna is very good compromise for many of those suffering with a limited space for towers and antennas and still want to be QRV on as many bands as possible. Big advantage of this design is single feed line for both bands. The 4m antenna is actually sleeve fed by inductive coupling with 6m driven element. 

It is highly recommended to build this antenna with elements fully insulated from the boom since mutual coupling between elements is very strong and adding boom correction might have some unexpected influence. Eventually, element holders such as ones used by Nige G7CNF, who successfully has built and tested this antenna, can be used and in that case boom correction is not required. 

For this antenna it is essential to pay special attention to the perfect spacing of the elements since impedances are critical and there is very small margin for errors if correct result is expected. 

Measured SWR plots were generated by G7CNF who used an “Mini-VNA” HF/VHF analyzer and AC6LA “Zplot“ software. It is obvious that practical results perfectly match calculated specifications and SWR is even better than computer plots.

Just as with my other designs, feed impedance is 50 Ohm so only an RFC is required, consisting of 9 turns of cable close wound on a 60 – 80 mm form.

For more details, and complete story about practical experience and comments please go to G7CNF web pages 

 http://g7cnf.me.uk/EF_Duo.htm     

Several other DUO BAND designs were made, such as 6+7 and 7+8 elements but those will not be posted on the web.

Anyone interested to build other designs please send me mail for available versions and construction details