[TowerTalk] SP7GXP antennas?

[Pete Smith N4ZR]

 From another angle, I note that Remote Ham Radio and W2RE uses (used?) 
these antennas at the Eastport, Maine station.  An after-action report 
on how they performed and particularly how they stood up in a very 
exposed location could be informative.

Two things also puzzle me - I can't find any pricing information on the 
website (that may just be me), and while GXP is proud of his association 
with W2RE  and RHR, the link to W2RE on the GXP website has expired.

73, Pete N4ZR
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web server at<http://beta.reversebeacon.net>.
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On 10/21/2021 4:00 PM, Larry Banks via TowerTalk wrote:
> Are they mixing up dBi and dBd?
>
> 73 -- Larry -- W1DYJ
>
>
> -----Original Message----- From: David Gilbert
> Sent: Thursday, October 21, 2021 14:48
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] SP7GXP antennas?
>
>
> I own an Optibeam OB16-3 tribander as well as an Optibeam OB2-40 shorty
> 40.  I modeled both antennas in EZNEC+ using the published dimensions,
> as well calculating the impedance of the short square tube transmission
> line that connects all three driven elements on the OB16-3 and
> calculating the inductance of the "hairpin" matching coil used on the
> OB2-40.  My modeled patterns matched very closely the patterns that
> DF2BO had sent me.
>
> With the help on K9RX, who at the time lived about 30 miles line of
> sight distant from me (we both lived on elevated ground), I then
> measured the horizontal pattern by rotating my antenna while he took
> signal strength readings.  With him transmitting, I again rotated my
> antennas and took direct voltage readings using the microvolt mode (no
> AGC or other compression) on my K3.  In all cases the measured patterns
> closely matched the Optibeam specified patterns.
>
> It is a fact that you can't get additional gain without changing the
> pattern, and 2 db would require a pretty significant narrowing of the
> pattern.  It is also a fact that the vertical pattern is predominantly
> determined by height above ground for similar antennas.  My conclusion
> is therefore that either DF2BO has understated the gain ratings for his
> antennas, or that SP7GXP has overstated the gain ratings for his 
> antennas.
>
> 73,
> Dave   AB7E
>
>
>
> On 10/21/2021 7:38 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
>>
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