[amsat-bb] Re: QFHA for SO-50... polarization issue ???
Ing. Pavel, There are a whole series of QFH antennas. 1/4,turn, 1/4 wavelength through 1 turn 1 Wavelength. Gain at the horizon is determined by the ratio of the axial length in fractions of a wave length. The best performance I have obtained is a 1 wavelength per side, 1 turn, for good gain at the horizon with an axial length of .65 wavelengths. You need the least gain at the Zenith as the satellite is closest in range at that point. The best reference I found is "Resonant Quadrifilar Helix Design" by C.C. Kilgus, December 1970 Issue, of the Microwave Journal, Pgs 49-54. 73, Art KC6UQH -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Ing. Pavel Milanes Costa Sent: Saturday, February 16, 2013 8:22 PM To: amsat-bb@amsat.org Subject: [amsat-bb] QFHA for SO-50... polarization issue ??? This weekend I tested a Quadrifiliar Helicoidal Antenna for 70cm (LHCP) I designed it by the online calculations of jcoppens on the internet... It is a 1/2 turn and 1 lambda, about 5 meters of elevation with ~25 cm of RG-58U (a section of it is coiled to form a balum) and then ~15 meters of A.H. LDF4-50A down to the shack directly to the radio, of course BNC to N adapter on the antenna and N to PL259 on the radio side... It's at mast top. Results are good... In passes of over 20 degrees (almost the real horizon here) I have a good copy, until... TCA, in which I lost the signal completely... TCA = Time of Closest Approach. In northbound passes (I've not tested it in southbound) it work as I just said... I have been reading and investigating this strange issue and I think it is due to polarization... I had read that SO-50 is linear polarized on 2m AND 70cm with aprox 45 degrees each other... Then Linear to LHCP in the worst case is 3dB loss (half power) but consistent over the entire pass... or have SO-50 some circular/elliptical component in it's signals that renders useless the antenna after TCA? spin maybe? There is any chapter of the book I missed or other variable(s) that I have not taking into account here? Any comment, link or other kinds of help are welcomed.. 73 de CO7WT. ___ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
[amsat-bb] Re: QFHA for SO-50... polarization issue ???
Hi Pavel, The issue may not be the antenna - but SO-50. The antennas are linear - but the received signal strength can vary a lot if you have just RHCP or LHCP. During passes here in Copenhagen, Denmark I experience large differences in signal strength which can be counteracted by changing polarity from RHCP to LHCP during the pass. With large changes I mean from nothing to 59 signals. Hope that helps. 73 de OZ1MY/Ib -Oprindelig meddelelse- Fra: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] På vegne af Ing. Pavel Milanes Costa Sendt: 17 February 2013 05:22 Til: amsat-bb@amsat.org Emne: [amsat-bb] QFHA for SO-50... polarization issue ??? This weekend I tested a Quadrifiliar Helicoidal Antenna for 70cm (LHCP) I designed it by the online calculations of jcoppens on the internet... It is a 1/2 turn and 1 lambda, about 5 meters of elevation with ~25 cm of RG-58U (a section of it is coiled to form a balum) and then ~15 meters of A.H. LDF4-50A down to the shack directly to the radio, of course BNC to N adapter on the antenna and N to PL259 on the radio side... It's at mast top. Results are good... In passes of over 20 degrees (almost the real horizon here) I have a good copy, until... TCA, in which I lost the signal completely... TCA = Time of Closest Approach. In northbound passes (I've not tested it in southbound) it work as I just said... I have been reading and investigating this strange issue and I think it is due to polarization... I had read that SO-50 is linear polarized on 2m AND 70cm with aprox 45 degrees each other... Then Linear to LHCP in the worst case is 3dB loss (half power) but consistent over the entire pass... or have SO-50 some circular/elliptical component in it's signals that renders useless the antenna after TCA? spin maybe? There is any chapter of the book I missed or other variable(s) that I have not taking into account here? Any comment, link or other kinds of help are welcomed.. 73 de CO7WT. ___ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
[amsat-bb] Re: QFHA for SO-50... polarization issue ???
Thanks to all for the reply to this thread... Conclusion is that I need RHCP & LHCP switchable antennas... And my antenna is working good... but I'm reading an article Art send me to improve my knowledge about QFHA... 73 and Thanks to all. El 16/02/13 23:21, Ing. Pavel Milanes Costa escribió: This weekend I tested a Quadrifiliar Helicoidal Antenna for 70cm (LHCP) I designed it by the online calculations of jcoppens on the internet... It is a 1/2 turn and 1 lambda, about 5 meters of elevation with ~25 cm of RG-58U (a section of it is coiled to form a balum) and then ~15 meters of A.H. LDF4-50A down to the shack directly to the radio, of course BNC to N adapter on the antenna and N to PL259 on the radio side... It's at mast top. Results are good... In passes of over 20 degrees (almost the real horizon here) I have a good copy, until... TCA, in which I lost the signal completely... TCA = Time of Closest Approach. In northbound passes (I've not tested it in southbound) it work as I just said... I have been reading and investigating this strange issue and I think it is due to polarization... I had read that SO-50 is linear polarized on 2m AND 70cm with aprox 45 degrees each other... Then Linear to LHCP in the worst case is 3dB loss (half power) but consistent over the entire pass... or have SO-50 some circular/elliptical component in it's signals that renders useless the antenna after TCA? spin maybe? There is any chapter of the book I missed or other variable(s) that I have not taking into account here? Any comment, link or other kinds of help are welcomed.. 73 de CO7WT. ___ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb ___ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
[amsat-bb] Re: QFHA for SO-50... polarization issue ???
- Original Message - From: "Ing. Pavel Milanes Costa" To: Sent: Monday, February 18, 2013 9:29 PM Subject: [amsat-bb] Re: QFHA for SO-50... polarization issue ??? > Thanks to all for the reply to this thread... > > Conclusion is that I need RHCP & LHCP switchable antennas... > > 73 and Thanks to all. > > 73 de CO7WT. Hi Pavel, CO7WT The QFHA is not a switchable antenna from RHCP to LHCP because RHCP is wound with turns conterclockwise and LHCP is wounded with turns clockwise just the reverse of the classic W8JK helical antenna. If you like RHCP and LHCP polarizations you need two separate antennas swichable with a coax relay. In a separate email I have sent to you the best original article on helix antennas written by Walter Maxell W2DU. More information on QFH antennas from W2DU are available here: http://w2du.com/ 73" de i8CVS Domenico ___ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
[amsat-bb] Re: QFHA for SO-50... polarization issue ???
Yes, thanks for the quote... And sorry, I'm a Spanish speaking OM... When I said: "...I need RHCP & LHCP switchable antennas..." I was referring to two separate QFHA, one with RHCP and the other LHCP, with a coaxial switch... just like you mention... I have to improve my grammar in English... hi hi hi.. BTW thanks for the articles of Maxwel and I'm viewing the site right now... 73 El 19/02/13 02:14, i8cvs escribió: - Original Message - From: "Ing. Pavel Milanes Costa" To: Sent: Monday, February 18, 2013 9:29 PM Subject: [amsat-bb] Re: QFHA for SO-50... polarization issue ??? Thanks to all for the reply to this thread... Conclusion is that I need RHCP & LHCP switchable antennas... 73 and Thanks to all. 73 de CO7WT. Hi Pavel, CO7WT The QFHA is not a switchable antenna from RHCP to LHCP because RHCP is wound with turns conterclockwise and LHCP is wounded with turns clockwise just the reverse of the classic W8JK helical antenna. If you like RHCP and LHCP polarizations you need two separate antennas swichable with a coax relay. In a separate email I have sent to you the best original article on helix antennas written by Walter Maxell W2DU. More information on QFH antennas from W2DU are available here: http://w2du.com/ 73" de i8CVS Domenico ___ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
