[time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nut can answer

[Tom Knox]

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 at rubidium.dyndns.org
> To: time-nuts at 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
> 
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