RE: NEC-LIST: Q: Effective Antenna Height

Ken
The effective height of a monopole is the physical height times (average
current/base current), so that for a short monopole without top loading, the
effective height is half the physical height. The open-circuit output
voltage is the incident E-field time the effective height. For a monopole
with plenty of top loading, so that the current in the vertical section is
constant, the effective height equals the physical height. The source
resistance of a receive antenna is equal to the radiation resistance.
For a short vertically polarised antenna over perfect ground the radiation
resistance is equal to
1578*(effective height/lambda)^2
so you can use the radiation resistance from NEC to estimate the effective
height from this formula.
Alan

-----Original Message-----
From: Carrigan, Ken [mailto:KCarrigan_at_anteon.com]
Sent: 03 March 2003 20:58
To: nec-list_at_gweep.ca
Subject: NEC-LIST: Q: Effective Antenna Height

Hi,
Is there a way to compute the effective height of a electrically small
antenna
(<<lambda/4) with Nec 2? Lets say that it is a monopole (with variable
conditions of ground plane), it has a 50cm height, and will receive 2-30MHz.
What I would like to be able to do is to compute the field strength at the
antenna based on "effective height" and voltage level of the monopole; or
compute the voltage at the antenna with a certain field strength times the
effective height. Can someone make a small NEC card which will compute the
effective height as an example? Thanks,

Ken Carrigan

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