On 07/ 7/12 05:43 PM, Magnus Danielson wrote: > On 07/07/2012 06:21 PM, Dr. David Kirkby wrote: >> I can confirm that I'm 100% sure that the polarization of the two >> antennas needs to be the same - i.e. both RHCP or both LHCP. I built two >> of them for RHCP, and got appreciate gain. >> >> Despite what other may say, there does seem to be a lot of confusion >> about this issue, but I've satisfied myself by building them and testing >> the gain using a VNA as the signal source and detector. > > We had this straighten out about a month ago, and me posting more or > less as I landed from a transatlantic flight wasn't optimum (tired and > waving hands didn't help, as I got it wrong). > > RHCP should match RHCP and LHCP should match LHCP. > > Cheers, > Magnus I must admit, I was pretty convinced a month ago they should match, but there is nothing like actually verifying something experimentally. Dave

On 7/7/12 9:21 AM, Dr. David Kirkby wrote: > > I can confirm that I'm 100% sure that the polarization of the two > antennas needs to be the same - i.e. both RHCP or both LHCP. I built two > of them for RHCP, and got appreciate gain. > > Despite what other may say, there does seem to be a lot of confusion > about this issue, but I've satisfied myself by building them and testing > the gain using a VNA as the signal source and detector. > Nothing like an actual test to clarify things, eh? wind one for LHCP and you can play with the reversal after a reflection.. In the latest Ant and Prop Magazine there's an article about a antenna lab with demos from Cal Poly SLO. Very cool.. all at 900 MHz, so things are small, but not so small that skin depth and precision measurements come into place. Lots of different kinds of antennas, and they built a nice little LED bargraph signal strength display. Reminiscent of a video taped lecture from Kraus that I saw.

Thanks for clearing up any confusion Magnus, one more question, are the any conditions such as reflected signals that can reverse polarization? Thomas Knox > Date: Sat, 7 Jul 2012 18:43:10 +0200 > From: magnus@rubidium.dyndns.org > To: time-nuts@febo.com > Subject: Re: [time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nut can answer > > On 07/07/2012 06:21 PM, Dr. David Kirkby wrote: > > On 06/ 5/12 12:26 AM, Magnus Danielson wrote: > >> On 05/06/12 00:30, Dr. David Kirkby wrote: > >>> This is not exactly a time related question, but I'm sure the subject > >>> must be of interest to time-nuts using GPS. > >>> > >>> If one transmits from an antenna such as a helical one, RHCP, can the > >>> same antenna be used for reception, or does the helix need to be wound > >>> the other way? > >>> > >>> If you google this topic, there seems to be a lot of confusion about > >>> whether the TX antenna and RX antenna need to both have RHCP or whether > >>> one needs to be LHCP and the other RHCP. > >>> > >>> Given GPS uses circular polarization, I'm hoping someone here will know. > >>> > >>> It would appear there are different definitions of "circular > >>> polarization", with one considering it from the point of view of the > >>> source, and the other considering it from the point of view of the > >>> receiver. The IEEE apparently uses the former, and others (especially > >>> optics) use the opposite. > >>> > >>> http://en.wikipedia.org/wiki/Circular_polarization > >>> > >>> My aim was to make a gain measurement of two circular polarized > >>> antennas. I have two identical antennas, but are unsure if the signals > >>> should be received strongly, or whether theoretically no signal would be > >>> received. (Of course in practice, one never achieves perfect > >>> polarization, so there will always be a signal detected, even if > >>> cross-polarized. > >> > >> They would have to have opposite rotation. > >> > >> The waveform rotation will follow the transmitter antenna into the > >> receiver antenna. The receiver antenna follows the same rotation that > >> the transmitter antenna has, it's just that the face each other, so when > >> you turn one of the 180 degrees such that they face the same direction > >> you would see that they are in fact rotated in opposite directions. > >> > >> I'm sure the sat folks can confirm this. > >> > >> Cheers, > >> Magnus > > > > I can confirm that I'm 100% sure that the polarization of the two > > antennas needs to be the same - i.e. both RHCP or both LHCP. I built two > > of them for RHCP, and got appreciate gain. > > > > Despite what other may say, there does seem to be a lot of confusion > > about this issue, but I've satisfied myself by building them and testing > > the gain using a VNA as the signal source and detector. > > We had this straighten out about a month ago, and me posting more or > less as I landed from a transatlantic flight wasn't optimum (tired and > waving hands didn't help, as I got it wrong). > > RHCP should match RHCP and LHCP should match LHCP. > > Cheers, > Magnus > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

Exactly. Reflections reverse the cp sense On Jul 7, 2012, at 11:40, Tom Knox <actast@hotmail.com> wrote: > > Thanks for clearing up any confusion Magnus, one more question, are the any conditions such as reflected signals that can reverse polarization? > > Thomas Knox >

On 07/07/2012 08:49 PM, Jim Lux wrote: > Exactly. Reflections reverse the cp sense > > > > On Jul 7, 2012, at 11:40, Tom Knox<actast@hotmail.com> wrote: > >> >> Thanks for clearing up any confusion Magnus, one more question, are the any conditions such as reflected signals that can reverse polarization? >> >> Thomas Knox This allows a first degree surpression of multipath signals for GPS. Choke ring and then damping material on the backside also helps. Cheers, Magnus