On Saturday, July 14, 2012 8:57:07 AM UTC-7, Peter Higgs wrote:
At 15:03 14 July 2012, Richard wrote:
>On Saturday, July 14, 2012 7:19:34 AM UTC-7, Peter Higgs wrote:
>> At 13:43 14 July 2012, Richard wrote:
>> >On Friday, July 13, 2012 12:11:03 AM UTC-7, Ramy wrote:
>> >> On Wednesday, July 11, 2012 2:02:33 PM UTC-7, noel.wade wrote:
>> >> > On Jul 9, 10:34=3DA0pm, "Matt Herron Jr.."=
> <m.=3D
>> > wrote:
>> >> > > I won't be buying powerFlarm until the antenna=
> inst=3D
>> >allation is as unobtrusive as my Transponder.
>> >> >=3D20
>> >> > Please see the latest response from the FLARM folks. BUT, =
>please
>> >> > remember that:
>> >> >=3D20
>> >> > 1) The PowerFLARM runs at a *much* lower power level than
>> >> > Transponders. That means that antenna placement and visibi=
>lity is
>> >> > always going to be a slightly touchier issue than with tran=
>sponders.
>> >> >=3D20
>> >> > 2) The Dipole is only 3 inches long (tip to tip) and very
>> >> > unobtrusive.
>> >> > I again refer you to the in-flight photo of my installation=
>:
>> >> > http://www.flickr.com/photos/noel_wade/7518094912/
>> >> > And again, here's Tim Taylor's installation=
>:
>> >> > https://plus.google.com/photos/10893...330632/albums=
>/57617222=3D
>> >49435143009/5761722263754238914
>> >> >=3D20
>> >> > So...
>> >> > Is the FLARM antenna situation annoying? Yes.
>> >> > Are there a few details about the PowerFLARM that I wish we=
>re
>> >> > different? Yes.
>> >> > Is it OK to grumble about this stuff? Sure.
>> >> > Are people blowing the issues up larger than they need to b=
>e (on bot=3D
>> >h
>> >> > sides)? Yes.
>> >> > Is the antenna situation a good reason to avoid buying it? =
>Hell No!
>> >> >=3D20
>> >> > I challenge anyone to find a PowerFLARM user who has instal=
>led the
>> >> > system (after the initial range issues were sorted), and do=
>esn&#=3D
>> >39;t want
>> >> > it or doesn't like using it.
>> >> >=3D20
>> >> > --Noel
>> >>=3D20
>> >> Noel, both your's and Tim's instalation looks great from=
> an
>> >obvio=3D
>> >us reason: the antenna is installed behind the compass! But many of u=
>s
>> >don&=3D
>> >#39;t have compass on top of the glare shield, which makes a big
>> >difference=3D
>> >..
>> >>=3D20
>> >> However I suspected that the claim that the whole dipole antenna=
> must
>> be
>> >=3D
>> >above the glare shield is exaggerated, and this seem to be confirmed =
>by
>> >the=3D
>> > Flarm folks. I would like Flarm to clarify if in their opinion it is
>> >suffi=3D
>> >cient for collision avoidance to have the whole antenna below the gla=
>re
>> >shi=3D
>> >eld.
>> >>=3D20
>> >> Ramy
>> >
>> >Ramy,
>> >
>> >The antenna you may have been waiting for:
>> >
>> >http://www.craggyaero.com/cables_&_antennas.htm
>> >
>> >Approx 3" with a 6" ground plane bulkhead mount. I will in=
>stall in my
>> >Vent=3D
>> >us b and test today and tomorrow. I plan to put the ground on the
>> >undersid=3D
>> >e of the panel cover.
>> >
>> >Richard
>> >www.craggyaero.com
>>=20
>> Hi Richard, unfortunately because of the brewster angle, the
groundplane
>> type of antenna will not receive much from directly ahead, at the same
>> altitude, and even less beneath the groundplane.
>> The Dipole has a maximum response directly forward, but with a null
>> above... something like a ring doughnut.
>>=20
>> Pete
>
>Pete,
>
>I understand all this. I have tested with a spectrum analyzer and did
>not=
> see a significant difference. Also PowerFlarm has recommend this
antenna
>=
>although they said a dipole may be slightly better. If you dipole is
>above=
> the instrument panel I would suspect it is greately degraded by all the
>in=
>struments carbon fiber etc underneath.
>I will do some flight testing today and will post the results.
>
>Richard
>www.craggyaero.com
>
Hi Richard, there are several types of groundplane antennas, including the
one with three counterpoises at 45 deg to the horizontal. All tested by
ground stations, so not really in 'free space'. Also one with the
grondplane in the form of a sharp cone.
However there is one variation, called the 'Sleeved Balun' which uses a
sleeve of second co-ax outer, doubled back along the co-ax. It has to be
at least a quarter wave (taking into account the dielectric constant.) but
I should think 3 inches would be sufficient.
Whatever you use there is bound to be a Null somewhere, and overhead and
underneath with the dipole is probably best in this application.
A proper match of the grondplane (or counterpoise.) is mostly needed to
reduce any SWR on the co-ax, which would otherwise become a radiating part
of the system.

Pete

Pete,

After flying with the Antenna with the 6" ground plane today, I can say it isn't significantly different than the dipole antenna. I still recommend that all use both antennas. I have the 6" ground plane one on my instrument panel cover and a dipole attached vertily to the vent in the nose of my ventus b.

The arch enenmy of perfect is just good enough.

Richard
www.craggyaero.com