[FoxHunt] antennas for harmonic sniffing
Kuon & Dale Hunt
[email protected]
Thu, 29 Jan 2004 17:57:47 -0800
>... I find that the quad is a near
>perfect antenna for vertical polarized hunting in that the lobe width is
> good in both planes. Long Yagi's are better than short ones. These
>little short Yagi's are near useless V-pol for anything other than 180
>degree homing. Most any thing has quite useable lobe width in the
>horizontal plane.
>
I prefer the quad for mobile hunting, but because it doesn't
stick up as far above the roof.
How useful an antenna is also depends on how sensitive your
signal strength indicator is: I've known a number of folks
who hunt with 2-element beams, even with vertical polarization.
The VK3YNG 2m sniffer can easily detect a 0.2dB difference
in signal strength using the audio S meter. The 2m mobile
rigs I have tested have around a 10dB range on their S meter
with at least 7 steps, so can indicate differences less than
2 dB. If you eyeball average between the edges you can still
get a reasonable bearing - certainly better than the 3dB
beamwidth of the antenna.
But that also explains why hunting the pattern null is
popular (when it is predictable enough) because it is easy
to get a 10dB variation over a small angular range.
>I have not done much harmonic hunting, but are the harmonics most always
>in the dame pol as the fundamental?
Not necessarily... it depends on the antenna pattern on that freq.
a quarter wave whip will act as a long wire on the higher harmonics,
so it may radiate more upwards. But in my measurements with
vertical whips the yagi always gave better response with vertical
polarization. With a tilted or horizontal antenna this may not
be the case, however, so I would recommend always checking both
and choosing the one that gives the strongest signal.
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