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Old 13-Feb-2018, 2:40 PM   #119
davodavo
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Join Date: Dec 2016
Posts: 10
Quote:
Originally Posted by rabbit73 View Post
Thanks for the interesting photos of your dish.

Bowties are full wave dipoles. Since they are a collinear pair of dipoles spaced very close together, they don't have a lot of gain over a halfwave dipole. I suggest you use a stacked pair of halfwave dipoles, one above the other, fed in phase, for smaller size and greater efficiency at the focal point. A vertical spacing of 5/8 wave at the design frequency would give max gain. Adding a reflector behind the dipoles would give additional gain.

http://www.w1ghz.org/antbook/chap6-2.pdf
Thanks for the tips, and the reference to the antenna book! Seems like all of its characterizations are for transmission...but they should apply reflexively to reception.

I'll give the stacked dipoles a shot. In the "duh" department: won't I have an impedance mismatch when using stacked dipoles (I'm feeding a 300 ohm balun)?

Bowties are actually "supposed" to be solid (rather than "whiskers") for maximum gain...I'm going to be giving that a shot and will tell you the results.

However, given the special case of bowtie in the focus of a parabolic reflector I doubt that a reflector behind the bowtie (or dipoles) would help much: at that point, the waves are out of focus and bouncing off at a range of angles from 0 to about 120 degrees, causing a bunch of phase cancellations. Given I'm trying to use this from 170 to 700 MHz, I'm doubtful there's an optimum at all ;-) I don't have any issues with front/back ratio as there are no signal sources within 30 miles of me, and the landscape around me shields unwanted strays.

I'll give it a try and report back here.

Last edited by davodavo; 13-Feb-2018 at 3:18 PM.
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