On 10/21/21 11:30 AM, Randy Farmer wrote:
Sounds like they're specifying gain relative to isotropic, hence an
extra 2.1 dB.
73...
Randy, W8FN
SP7GXP is quoting dBd - but does not say "free space" or "ground reflection"
Frequency: 28, 21, 14 MHz
Number of elements per band:
28 MHz – 8 ele.
21 MHz – 4 ele.
14 MHz – 4 ele.
Gain [dBd]: 10,5 - 9,8 - 9,6
Front to back ratio [dB]: 26 – 22 – 20
Bandwidth for SWR 1,5:1:
- 28 MHz: 600 KHz
- 21 MHz: 300 KHz
- 14 MHz: 300 KHz
Maximal power SSB: 2000 W
Band change automatic
Boom lenght: 10,3m
Longest element: 11m
Radius of rotation: 7,35m
Optibeam
* = average gain over dipol in free-space / for comparison: 2 el
monobander 4 dBd, 3 el 5-6 dBd
** = average gain at 20m above ground (= dBd + 2.15 dB isotropic + about
5 dB ground reflection)
OB16-3 16 Element, 3 Band
Bands 20 / 15 / 10
Gain (dBd) * 7,1 / 7,5 / 8,5
Gain (dBi) ** 14,5 / 15,1 / 16,3
On 10/21/2021 10:38 AM, john@kk9a.com wrote:
I have modeled some OptiBeam antennas and the published specs seem
accurate.
Of course getting 2db more gain from the same boom length would
circumvent
the laws of physics. I recently installed a 4el 40m OptiBeam on my
tower,
the SP6GXP version is 37% lighter.
John KK9A
David Gilbert AB7E wrote:
His 16 element 20/15/10 tribander looks like an almost complete copy of
my Optibeam OB16-3, except that SP6GXP claims about 2 db more gain on
each band and uses lighter weight materials.
Dave AB7E
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