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Old 7-Aug-2019, 5:36 PM   #13
GroundUrMast's Avatar
Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,773
Originally Posted by freetvplease View Post
On both my Y10 and Y5 antennas the connection with the balun is actually connected to the whole antenna because all the elements are connected through the square tubing as a whole. Does this make sense? I'm kinda thinking that If I replicated this with the 751 it may replicate the performance of the Y5 to a degree and being smaller. I understand this antenna is different from a VHF one but I'm curious if it's properties will lend itself to the VHF side.

I'll get back as soon as I can try this. Thanks
Re. Yagi style antennas in general (which the Y5-7-13 and ANT751 are examples of);

It's quite common to see antennas built with no insulator at the point the directors and reflector attach to the boom. Given that the center of a resonant dipole is a current maxima point one might assume that the boom then becomes a major circuit element... However, you need to consider that That same mid point of the element is a voltage minima point. Power = E*I so theoretically the power is zero because any value of current times zero = zero. An alternate way to examine this is to to simply add the current from the left and right. They are theoretically the same absolute value at any instant but with opposite signs from the perspective of the boom... If the same amount of current arrives from one side of the element as is going out the other half, then there is zero current available to flow into or out of the boom.

The bottom line is that the boom does not act as a transmission line or otherwise couple the antenna elements together at RF frequencies. Coupling between the director and reflector elements and the driven element(s) is largely through inductance though very small amounts of capacitance play a roll as well. To further complicate everything, spacing between elements plays a major roll in the way the antenna is tuned and develops gain.

If you modified and adjusted the ANT751 to perform similarly to the Y5-7-13 you would need to replace the UHF elements with longer elements and change their spacing... In the end it would bear a striking resemblance to antennas like the Y5-7-13.
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

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Last edited by GroundUrMast; 7-Aug-2019 at 5:41 PM.
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