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