[VHFcontesting] A question of altitude

[jcplatt1 at mmm.com]

Hi Steve.   Good question, one that we rovers ask a lot.  6m is different
than the higher bands because is almost HF and because most 6m rover
antennas are within a wavelength (or closer) to ground, this impacts their
take-off angle.   I fired up EZNEC and using just a simple 6m dipole moved
it from 13' to 17' to 21' looking at the change in gain at low take-off
angles (three to five degrees) compared to the model at 13'.   At low
take-off angles, moving the 6m antenna from 13' to 17', all other things
being equal, equates to a gain increase of about 1.5 dB.   Moving the
dipole from 13' to 21' equates to a gain increase of about 3.7 dB. This is
solely due to a lowering of the take off angle of the main lobe.   My
thought is that if you can get your 6m rover antenna moved from 13' to 21'
that you would see some performance improvement, but that the move from 13'
to 17' would not produce much help.    Another thing to think about is a
"high" dipole, maybe one at 25', in that it may be equal to or better than
a simple gain antenna mounted at 13' or lower.   Mechanically speaking,
when stopped, it might be easier getting a simple lightweight 6m dipole
"high" rather than getting a physically bigger gain antenna to 17'.

As a rover, its all a compromise which makes designing rover stations so
much fun !     On 2m and up its more difficult to say if the slight
increase in height would be noticable .... higher is always better but the
improvement may not be as significant as it is on 6m.

Here in MN, the challenge is to get above the July/August corn - with
ethanol sales way up corn production is way up which is good for farms but
bad for rovers !

73, Jon
W0ZQ/R