[time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nutcan answer

Dave Martindale dave.martindale at gmail.com
Tue Jun 5 02:51:31 UTC 2012


Well, they could be consistent.

Most of those photos show only two sizes of helix-type antennas.  The
larger diameter (probably lower frequency) are quadrifilar helix designs,
and they are uniformly "left hand thread" helixes.  (I assume that everyone
agrees on what a left-hand thread looks like, no matter how they label
circular polarization).  The more numerous smaller diameter antennas are
multi-turn one-element helixes, and they always seem to be "right hand
thread" in all of the photos.  The smaller antennas are almost certainly
for L1.

The complication is the "Block-IIR-M-SV-2S" photo.  But it has *three*
sizes of antennas visible.  The largest are left-hand-thread quadhelix as
before, and thus likely close to the same physical dimensions as the large
antennas in the other photos.  The mid-size ones are multi-element
multi-turn helixes that look a lot like the quadhelixes in design except
that the ends are left open.  And they are about 2/3 the diameter of the
quadhelixes, much larger than the simple helix antennas in the previous
group, so probably for a different frequency.  Then there are the smallest
antennas, which appear to be a single-element helix with many many turns -
but these are about 1/3 the diameter of the large quadhelixes, and thus
*these* are likely the L1 antennas.  And, if I look closely, these small
helixes do appear to be right-hand-thread wound.

     Dave

On Mon, Jun 4, 2012 at 8:24 PM, Tom Van Baak <tvb at leapsecond.com> wrote:

> David,
>
> One of these two photos is correct (odd isn't it)...
> http://www.ausairpower.net/Block-IIR-M-SV-1S.jpg
> http://www.ausairpower.net/Block-IIR-M-SV-2S.jpg
>
> Maybe these break the tie:
> http://www.spacemankind.com/images/ms/20090817-lockheed-gps-iir-lr.jpg
> https://share.sandia.gov/news/resources/releases/2008/images/GPS1.jpg
>
> http://www.lockheedmartin.com/content/dam/lockheed/data/space/photo/pressrelease/GPS_4A_pr.jpg
> http://www.insidegnss.com/auto/popupimage/GPSIIF_photo_lo.jpg
> http://www.freepatentsonline.com/6653987-0-large.jpg
>
> /tvb
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