[TowerTalk] SP7GXP antennas?

[Lux, Jim]

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 at 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
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>