Topband: Fresnel Zone

[donovanf at starpower.net]

Hi Ray, 


The classic source for Fresnel zones as they apply to HF site selection 
is NBS Technical Note 139: 


https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote139.pdf 


While Technical Note 139 applies primarily to horizontally polarized 
antennas mounted above the ground, its general conclusions apply to 
1/4 wavelength 160 and 80 verticals mounted on the ground. 


The outer edge of the Fresnel Zone is several kilometers for low angle 
radiation from 1/4 wavelength 160 and 80 meter verticals, especially 
when the verticals are installed on a highly conductive surface 
( e.g., sea water, salt marsh or wet marshy soil ). 


The outer edge of the Fresnel zone is much closer when 160 and 80 meter 
1/4 wavelength verticals are installed over a low conductivity surface 
(e.g., dry, chalky or sandy soil). 


73 
Frank 
W3LPL 




----- Original Message -----

From: "Ray Higgins" <ray.w2re at gmail.com> 
To: topband at contesting.com 
Sent: Thursday, April 18, 2019 2:48:57 PM 
Subject: Topband: Fresnel Zone 

I have two questions about fresnel zone. 

I just purchased 22.5/ac near the ocean near Machiasport, ME. This is in the Northeast corner of Maine about 30 miles south of Eastport and a Lubec. This is going to be my personal Remote Contest station! I plan to be contesting from this new qth starting in 2020 but will be QRV by mid 2019 for testing. 
This qth is anywhere between 1-3 miles from the ocean or the bay, it sits on a high plateau 150’ asl thats slopes in all directions to saltwater (peninsula) except N/NW. The property has a saltwater river and marsh that runs the perimeter from south to north favoring the NE direction, the marsh is only 50-100' wide and 1500-2000’ away from the property. The land has a gradual slope to the marsh. 

My questions: 

1.) Is the saltwater river bed/marsh wide enough to be an effective field in the Fresnal Zone? 
2.) What is the wavelengths needed to be within the Fresnal zone of a river/marsh compared to an ocean? 

In this photo album (last pic) I have outlined the river saltwater marsh and property boundry from a google earth shot. https://photos.app.goo.gl/ui79t2jFo95b29et6 

I’m only concerned about 80 and 160m in the Fresnal Zone. 

Any input would be welcomed. 

Thanks, 

Ray W2RE 


Sent from my iPhone 
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