On Sat, 5 Jul 1997 15:17:16 -0400 "\"Dick
Green\"."<dick.green@valley.net> writes:
>Does anyone know what gain references are used by Hy-Gain, KLM, and
>Force
>12 in their ads and literature? Both Hy-Gain and KLM use "dBd", which
>the
>ARRL antenna book defines as gain over a dipole in free space. The
>antenna
>book also says that a dipole over perfect ground (or salt water) has 6
>dBd
>of gain due to the sum of direct and reflected radiation.
>
>In the most recent catalogs, the gain claimed by Hy-Gain for the TH7DX
>is
>"6.57 dBd average" (it used to be "9.6 db" in a catalog I have from
>ten
>years ago), and the gain claimed by KLM for the KT-34XA ranges from
>8.5 to
>11.3 "dBd" (depending on the band.) Since a dipole over perfect ground
>has
>6 dBd of gain, is Hygain saying the TH7DX only has .57 dB more gain?
>Is KLM
>saying the KT-34XA has from 2 to 5 db gain over a TH7DX?
Although Hy-Gain and KLM both use dBd, neither one goes into
an explanation of whether the dipoles and beams are in free
space or over earth. If over earth, the antenna heights and
elevation angles at which the gains are measured are
unspecified. If both manufacturers are using the same
assumptions, then KLM is claiming more gain. Direct
comparison is further muddied, since Hy-Gain's quoted gain
is an average over the three bands, and KLM's is specified
by band, with a curve for each band. The XA works
well (I have one), and it has a 32' boom vs Hy-Gain's 24',
but I think XA gain figures are overstated by at least 2 dB,
judging by optimized monobander gain expectations, stated
in conventional measurement units.
Force 12 is quite specific, but you have to be smart enough
to skip over the "Gain" column, and read the "Net Gain"
column in their literature.
Probably the best comparison is to look at the effective boom
length on each band, depending on which elements are active.
Look in an antenna book at what gain you could expect from a
gain-optimized monobander of that boom length, and subtract
1.5 dB because it's a tribander and also is probably not optimized
solely for gain. I think you will come out a lot closer to a true
comparison, rather than looking at manufacturer's literature.
Dave Hachadorian, K6LL
k6ll@juno.com
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