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Re: [TowerTalk] Half Wave?

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Half Wave?
From: jimlux <jimlux@earthlink.net>
Date: Thu, 17 Jan 2019 13:49:46 -0800
List-post: <mailto:towertalk@contesting.com>
Are we talking a Yagi or a dipole?

We're also talking about a 4 foot difference - I would think you would have a hard time measuring the difference in the radiated far field.
(that's about 6% or 11 degrees of phase)
You *might* be able to measure the difference with a TDR or careful reflected power measurement on the feedline, because the feedpoint Z is slightly different. But he says "rocky soil" - which means it's probably not a salt water marsh acting as a perfect mirror.

But in terms of the radiated signal...
Let's say the return loss of the soil is 10dB - you're looking at combining a reflected signal at 31% amplitude with a slightly different phase - it's the difference between .31 or .31*cos(11 deg)
Cosine(11 deg) is 0.98 so the difference between .31 or .304
So the "voltage gain straight up" is 1.31 or 1.304

I will buy a cold frosty beverage of choice if you can repeatably measure the 0.04 dB change in any one hour period. (because over many days, and many temperatures, you could probably get that kind of precision, and I don't want to buy unlimited beverages... I might buy you one anyway if you attempt the measurement...<grin>)





On 1/17/19 12:37 PM, Peter Voelpel wrote:
A 1/4 wave length height IS exactly a cloud warmer.
At least 3/8 wave length height is necessary for a lower take off angle.

From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Keith
Dutson

My experience is that 1/4 wavelength is okay to avoid a cloud warmer.
However, higher is always better for DX, aka lower take-off angle.





-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Warren Wolff
via TowerTalk
Sent: Thursday, January 17, 2019 11:47 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Half Wave?

Greetings:   My understanding is that a yagi should be at least 1/2wave
above ground to avoid warming the clouds.   So, considering that thought,
how much does an antennasuffer if such antenna is 63 feet up instead of 67
feetfor 40 meters over VERY rocky "soil"?   Thanks, Warren; W7WY
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