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? Gamma for a Home-Made 70cm 6-Element Yagi ? - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


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 Post subject: ? gamma for a home-made 70cm 6-element yagi ?
Posted: Mon May 30, 2005 8:09 pm 
 
Lieutenant

Joined: Mon May 30, 2005 7:51 pm
Posts: 1
Location: colorado
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
peak Vg 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
Vg=928 at no input signals to the 8302 and Vg=1447 mV at its peak.
gamma = (1447-928) / 30 = 17.3 (it's really a minus ). for a VSWR
somewhere between 1.22 and 1.43.
my question is for those of you who have too made your own yagi
and measured 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
i was 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



Posted  11/12/2012

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