Sunday, June 12, 2016

Antenna length thoughts

Antenna length for the WSPR tracker


So, there are a few factors that impact the ideal length of the antenna for the WSPR tracker.  The classic wavelength formula is:
wevelength = 984 feet / Frequency in MHZ
This is adjusted by the velocity factor of the wire, which is also impacted by whether or not the wire is insulated.  I found several resources discussing wire length.  Conventional wisdom seems to be to adjust by between 4-5%.  W7NAT likes 5%.  This would be for ground-mounted antennas.

However, we're using very thin wire,  and we're in free space.  I'm going to try a full 1/4 wave with no adjustment.

Antenna scenario Element length (inches)
20m 1/4 wave dipole for 14.0971.  No Adjustment.209.4
20m 1/4 wave dipole for 14.0971.  4% adjustment for insulation.201.0
20m 1/4 wave dipole for 14.0971.  5% adjustment for insulation.198.9

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