On 05/06/12 04:51, Dave Martindale wrote:
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.
Well, the traditional Block-II antennas had an inner and and outer ring,
at it was made so on purpose to create a antenna-lobe such that it would
direct more power towards the edge of the globe than straight down, such
that the distance difference and hence the damping is first degree
compensated such that the signal strength depending on azimuth is more even.
I could dig up the reference if I where at home, but I recall it since I
think it is kind of neat engineering.
Good that you guys set me straight on the orientation-stuff.
Cheers,
Magnus
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