Topband: Tides and SWR

Hugh Valentine hsvdds at juno.com
Tue Sep 16 15:58:05 EDT 2014


This is preliminary, but just for an experiment and to satisfy my curiosity,  I have made some basic measurements of the Bird Feeder's SWR and Resonant Frequency Changes as the tides move in and out.I am certainly not in possession of an Electrical Engineering degree.  They ain't got none of them at Emory University.  I was just lucky enough to learn a few tooth things. Maybe someone else has done this before. Bird Feeder=disguised Inverted "L" (35' Vertical, 95' Horizontal) on a seawall and the Feed point is at High Tide about 6" above salt water, and within a few inches horizontally from water.  Don't make fun, it is all I got. We have 6-9 foot Tidal fluctuations here on the GA coast.Approx 16 Radials of varying lengths, some lay on the Marsh floor at Low tide, hooked into 8' Ground Rods 3' apart in the marsh floor,  K9YC Balun at feed, but measurements were taken without the Balun.  Approx 90' of RG213 to shack. Measurements w/ MFJ259B.  At the FEED POINT of the Bird Feeder,   LOW TIDE:1800    1.6:1    R=29    X=71825    1.6:1    R=29    X=01850    1.8:1    R=30    X=171875    2.2:1    R=30    X=301900    2.2:1    R=29    X=44 High Tide1775    2.3:1    R=34    X=331800    1.9:1    R=33    X=231825    1.6:1    R=32    X=81850    1.4:1    R=33    X=01875    1.6:1    R=34    X=121900    1.9:1    R=34    X=27 Conclusion:  Hi-Tides raise the frequency of the minimum SWR point and raise the Radiation Resistance about 10%. In the shack, the Resonant Freq (Low SWR anyway) was around 1800khz  @ 1.6:1 at Low Tide and was 1.2:1  at 1850 @ High tide. Just to solve my curiosity,( I always noted some variance from time to time in using a Tuner to make the SWR Flat at the Linear....)  I now conclude the fluctuating water table changes Impedance and Resonance of the Antenna.  Why and How,  I will leave to those who know the basics and more. I just am sharing this observation, that is all.  What to do with this information, I don't know.  Maybe I now need a remote tuning device which is Tide Controlled. See you in the pileups with the lowest antenna on Top band this season.P.S.  The Birdfeeder now comes in a New and Improved version using an LC circuit and Vacuum Relay to make it switchable 1/2 wave on 80M.  The Tide also lowers SWR on 80M as well at high tides. ValN4RJ 
____________________________________________________________
The #1 Worst Carb Ever?
Click to Learn #1 Carb that Kills Your Blood Sugar (Don't Eat This!)
http://thirdpartyoffers.juno.com/TGL3141/541896bd67d2516bd3bddst04vuc


More information about the Topband mailing list