![]() The peak signal signal strength of the beam in both cases is along the runway centerline and on the center of the glideslope angle. The glideslope transmits in the UHF band (3rd harmonic of the localizer) with a similar modulation implementation to the localizer. The relative phase between the two modulation frequencies being linearly dependent on angular position to the extended centerline of the runway and the beam. The airport localizer transmits in the VHF band with a signal modulated with two low frequencies. Just so we are on the same page about ILS systems and aircraft antenna lets just confirm some fundamentals before getting into the details. I put eyeball protectors on my belly mounted comm antennas to protect my dog, and me when cleaning the plane's belly. Even if under the tail you (or some kid crawling around at a fly in) will find it. If you really must put a cat whisker antennas on your nice RV, please put eyeball protectors on them. My homebrew wingtip antenna picks up LOC and GS far beyond practical range, and VOR stations at 100+nmi. The Balance feed you most likely are referencing is applicable to half wave dipole antennas.Īssuming properly installed and tuned, radiation pattern is hardly an issue considering the relatively strong LOC and GS signal strength of ILS systems. A Gama match is an elequent LC circuit to match antenna impedance to feedline impedance. "Balanced" feedline input is not applicable to Gama matched antennas, like most use in the wingtip. Again, as long as there is sufficient signal strength, the antenna has no effect on left-right (or up-down) indications. BTW, the same is true for a simple dipole, if you approach in a crab, in a strong crosswind, you won’t be at the peak sensitivity angle for the antenna.Īs to approaching minimums: at that point the signal is so strong that a coat hangar will suffice for an antenna. The absolute sensitivity may vary with angle, but the relative sensitivity - which is all that counts- does not vary between the two signals. But the LOC antenna is essentially a ‘point source’ for both lobes, and so the aircraft antenna’s sensitivity to one lobe (one modulation frequency) is exactly the same as for the other lobe (other modulation frequency). Yes, there are two lobes coming out from the localizer and GS antenna. This post shows a fundamental misunderstanding of the way LOC and GS signals work. The archer antenna is perfectly good enough to provide reliable VOR signal and guidance for en - route situations but does it provide adequate ILS localizer and glideslope reception? The Archer antenna is unbalanced so by definition it will have significant boresight errors …. Not sure I would ever have enough trust in an Archer style antenna (gammi match) to fly in weather down to Cat 1 minimums. More limit condition work to do before having the confidence to fly in “real” weather. ![]() I have done limited testing to date on ILS sensitivity and accuracy doing mostly standard ILS capture in VFR conditions. I did put a coax disconnect at the base of the vertical stabilizer that was ground isolated. I haven't done any polar plots to determine the lack of rudder influence on sensitivity polars. I measured VSWR for the RAMI with full rudder deflection across the band and it was unaffected. If I had only wanted VOR functions I would probably have gone with the Archer. I chose to put a RAMI cats whisker antenna on top of the vertical stabilizer because I wanted a reliable ILS capability. The only issue is the rudder counterbalance may affect the polar plot at full rudder travel ( but putting in full rudder input during an ILS approach may be the least of your problems). Mounting a RAMI cats whisker antenna with a factory made matching cable on top of the vertical stabilizer will provide a symmetrical polar sensitivity plot for both the ILS glideslope and localizer. Without the benefit of appropriate test equipment and doing radiation pattern measurements you just wont know. This may or may not be an issue depending on the exact location of the installation you choose. The archer antenna is perfectly good enough to provide reliable VOR signal and guidance for en - route situations but does it provide adequate ILS localizer and glideslope reception? The Archer antenna is unbalanced so by definition it will have significant boresight errors (main lobe of antenna sensitivity is not directly forward of the antenna and or the main lobe may be lopsided).
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