[time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nutcan answer
magnus at rubidium.dyndns.org
Tue Jun 5 04:49:34 UTC 2012
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.
More information about the time-nuts