[NLRS] 6m rover antennas

[Jon Platt]

Just playing around with EZNEC before the Vikings game and following up =
on a previous thread.  For the following analysis I used the "canned' =
2-ele quad and the 3-ele NBS yagi in EZNEC and rescaled them as needed, =
then compared their gains vs a dipole.  =20

Ignore the absolute numbers and look at the differences compared to the =
dipole.   Remember that "tropo" contacts are the result of RF that comes =
off the antenna at very low take off angle, say below 3 degrees =
(probably lower), while the E propagation is more in the 3 to 30 degree =
range with the lower angles providing the better "DX".

Dipole at 10' above ground :
  Max Gain =3D 7.30 dBi @ 28 degrees take off.
  Gain @ 3 degree take off angle =3D -7.20 dBi

Dipole at 20' above ground :
  Max Gain =3D 7.68 dBi @ 14 degees take off=20
  Gain @ 3 degrees take off =3D -1.5 dBi

6m Quad with boom at 10' above ground :
  Boom length =3D 4.2'
  Max Gain =3D 11.55 dBi at 24 degrees take off
  Gain @ 3 degree takeoff angle  =3D -1.95 dBi

6m 3-ele NBS yagi with boom at 10' above ground :
  Boom length =3D 7.8'
  Max Gain =3D 13.25 dBi at 23 degrees take off
  Gain @ 3 degree takeoff angle =3D 0.09 dBi.

Comments:    Regarding the low angle take off gain (at 3 degrees), =
raising the dipole from 10' above the ground to 20' above the ground =
provides about 6 dB of gain for "tropo" contacts.   At 20' high, the =
dipole compares favorably with the two mechanically larger gain antennas =
that are at 10'.   So, which is easier for the rover, mounting a small =
gain antenna at 10' or a dipole at 20' ?   My experience is that you can =
build a very light weight 6m dipole, perhaps out of whips, and mount it =
to a push up mast, or two 10' extension masts, for rover & portable =
work.   Obviously, this won't work while going down the road, but for =
6m, height above ground is important for rover work.  This same story is =
(50/144), or about 1/3 as true on 2m too.  =20

73, Jon
W0ZQ


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