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## Re: Topband: circular polarization on 160m

 To: , Re: Topband: circular polarization on 160m "Tom W8JI" Tom W8JI Wed, 5 Feb 2014 12:38:06 -0500 mailto:topband@contesting.com>
 In producing a good satellite AMSAT antenna KLM uses the method of quarter wave stagger of two yagis. One is about a quarter wave ahead of the other and fed with a 1/4 wave delay line. ``` ```To be circular, one is either staggered 1/4 wave forward and they are fed in phase, or they are even without stagger and fed in quadrature. ``` ```Polar plots of this antenna suggest that they are not really producing a screw sense CP antenna but rather an Axial mode antenna that receives both vertical and horizontal components of the arriving space signal as they occur. ``` ```That cannot be done. If two antennas are combined without spatial 90 degree stagger **or** phase 90 degree stagger, they are simply a tilted linear polarization. ``` ```Many people tilt polarization and think it is both V and H, and think it somehow eliminates polarization rotation fading. All they do is tilt the polarization, and 90 degrees from that tilt is a new null. The confusion is because people and programs express polarization from only tow references, V and H. If I tilted a vertical the right amount it would look like a perfect mix of V and H, but it really would be a single polarization tilted at a 45 degree angle. 90 degrees tilt from that angle, say at -45 degrees, would be a null. With different waves and a "left" tilt we would have: ``` 1.) circular polarized = no improvement at all 2.) slow lazy fading rotation (this is NOT circular) = no improvement at all 3.) polarization tilted at left 45 = a peak response 4.) polarization tilted an -45 degrees = a deep null. ```To be circularly polarized the wave has to be rotating fast, at the frequency of the wave, so the wave makes one rotation every wave period. This would NOT be a slow fade anyone would hear, it would just be a few dB signal loss. ``` ```If the wave were slowly rotating, such as to produce a slow fade, the SENSE of the antennas would not matter one bit. You never get the 3 dB back. You would stop the fade from cross polarization, but would also pick up some significant amount of additional noise. ``` ```I'm not sure how well thought-out or properly conveyed any of this has been, so I'm enjoying the brain exercise. ``` ```A circularly polarized antenna on 1 MHz cycles through the entire polarization shift in 1uS. A circularly polarized antenna on 1 MHz cycles through one electrical rotation in 1 uS. ``` ```Anyone here having fading at a 0.5464481 uS rate? If so, the CP antenna will either make fading near infinite or near zero. :) ``` ```The way I see it is if the rate is not 0.546 uS or so, you do not have circular polarization.You have a slowly rotating wave, and the sense of the RX antenna would be meaningless unless you could time-sync rotation at that slow fading rate. ``` Someone correct me if I am wrong. ```73 Tom ```_________________ Topband Reflector Archives - http://www.contesting.com/_topband ```
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