As I recall, this is the type of antenna my handheld GPSr has. I had a set of batteries bleed out in and had to disassemble it in order to do a good cleaning.
-Dave ----- Original Message ----- From: "Magnus Danielson" <[email protected]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Saturday, August 15, 2009 9:27:30 AM GMT -07:00 US/Canada Mountain Subject: Re: [time-nuts] Difference in GPS antennas Lux, Jim (337C) wrote: > > > On 8/15/09 7:58 AM, "Magnus Danielson" <[email protected]> wrote: > >>>> >>>> >>> Thats a quadrifilar helix antenna. >> A quite traditional antenna form. >> >> Not sure I have one of those around here. >> >> > > If you're near a harbor with fishing boats, you'll see plenty of quad > helices about a half a meter in overall height, used for VHF Weather > satellite reception. They're also used on spacecraft (Mars Science Lander, > Mars Reconnaissance Orbiter, and Phoenix all have UHF quad helix antennas, I > think, for about 400 MHz) Not used by the fishing vesels near me... I didn't mean helixantennas as such, I was just asking myself the question if any of my *GPS* antennas was infact of the quadra-helix design, a few of them have the sizes that they *could* be that. > The 4 helices need to be fed in the appropriate phase (0,90,180,270), > usually, they're fed in pairs (a differential signal feeds 0,180 and another > feeds 90/270) > > There are several ways to phase them, depending on the bandwidth > requirements. A quadrature hybrid is one way. The other is to make one helix > slightly longer than resonant and the other slightly shorter. A typical GPS sat has two rings of helix antennas, an inner and outer ring. These create a far-distance shape of lobes that i circularly fairly even but pushes more energy towards the edge of the earth, as seen from the satellite, such that the additional space loss from increased distance is being somewhat equalized by the GPS antenna. That's the trick being used to reduce the power variations from the GPS sats as experienced by the user. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
