This was gathered from the Internet WXSAT mailing list. The antenna mods might also apply to the APT antenna in the ver 3.x user manual. To: wxsat Subject: Zapper II antenna modifications From: rick (Rick Emerson) Message-ID: Date: Tue, 31 Mar 92 20:30:37 UTC The following was taken from Dr. Ralph Taggart's WSH BBS (517-676-0368): DATE: 06 Mar 91 SUBJECT: Errors in the first printing of the 4th Ed. of the Weather Satellite Handbook SOURCE: SYSOP A small number of errors/omissions have been noted in the first printing of the fourth edition of the WEATHER SATELLITE HANDBOOK. The ones that I have spotted are listed below. If you find any more possibilities, please leave a message and I will check them out and add to this listing as appropriate. All of these should be corrected in the second printing. Page 2-6, Dipole Housing, Par. 1, Line 8 - the 20 inch piece of PVC pipe should read 21 1/2 inch.... Page 2-6, Dipole Housing, Last paragraph - the phasing line should be 13 inches instead of the 15 specified (see Project bulletin #5). Page 6-3, Figure 6.2 - the unlabeled pin on U11C should be #11..... Page 6-6, Figure 6.4 - the collector resistor of Q2 is labeled 0 ohms (!) - it should be 10 ohms.... ==================== end of bulletin ================== DATE: 09 March 1991 SUBJECT: Zapper (and other) antenna phasing line SOURCE: SYSOP Bruce Lanning (W1GBS), in a recent letter, quite correctly pointed out that the offset between the driven elements of a circularly polarized antenna such as the Zapper (I or II) should be taken into consideration in the calculation of the proper length of the phasing line used to achieve circular polarization. He is absolutely correct since positional offset can, by itself, be used without a phase line delay, to produce circular polarization but the offset is rarely taken into account in most antenna projects and it certainly wasn't in the case of the Zapper. The Zapper uses a 2 inch offset between the two driven elements or approximately 5.1 cm. Given a wavelength of 219 cm (L) at 137 MHz: 5.1 / 219 = 0.023L phasing line = 0.25L 0.25L - 0.023L = 0.227L actual length 0.227 x 219 cm = 49.7 cm (free-space quarter-wave) 48.7 cm / 2.54 = 19.57 inches 19.57 inches x 0.66 (velocity factor) = 12.9 inches The phasing-line jumper should thus be about 13 inches long instead of the 15 inches specified on page 2-6 of the WSH (4th Edition). In your specific case, be sure that you are using a value for the velocity factor that is appropriate for the cable you are using Note that this works with regard to RHCP. If you wish to set the antenna up for LHCP, the length of the phasing line would have to be INCREASED by about 2 inches (17 inches total). After shortening his phasing line based on the spacing of his dipoles, Bruce noticed a significant improvement in signal levels down toward the horizon. ==================== end of bulletin =======================