? gamma for a home-made 70cm 6-element yagi ? - RF Cafe Forums
Post subject: ? gamma for a home-made 70cm 6-element yagi ?
Posted: Mon May 30, 2005 8:09 pm
Joined: Mon May 30, 2005
hi, with a 35" wood stick and 6 pieces of 3/32 welding
rod a 70 cm yagi was made. using the AD8302 eval
bd to check the reflected energy the
was for 429 MHZ. the open end of the DE was trimmed
at Fin=433.9 M until the same peak Vg was gotten.
the new peak was
at F=433.4 this is close enough
to 433.9. the gamma was calculated by
at no input signals to the 8302 and Vg=1447 mV at
gamma = (1447-928) / 30 = 17.3 (it's
really a minus ). for a VSWR
1.22 and 1.43.
my question is for those of you
who have too made your own yagi
its gamma ... what did you get ?
and do you know
what is a ball-park gamma for commercial yagis.
previous tests of gamma with the 8302 used a
string of VAT's on one
input to make the Vg =
900 mV. but i was getting this funny compression
with each add'l VAT dBm unit. until i figured the
VAT's themself were
adding up a significant insertion
loss compared to the add'l return loss
trying to achieve. anyway, now i simply utilize
the beauty of this
8302 device by letting the
A & B inputs be un-equal and using the Vg
output as the experimental data. then divide whatever
it is by the slope of 30mV/dBm to get a number for
ret loss. easy as pie this way