Metal mast with vertically polarized 2m yagi

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Kenneth Meyer:
From a lightning protection standpoint, "Stacking" a pair of antennas is the way to go.  Plus, All that extra forward gain!!!!!!

An insulated mast could turn out to be a disaster with a direct lightning strike that would have otherwise been shunted safely to ground with a metal mast.

Philip Camera:
Everyone knows that a vertical yagi must be mounted on a non-conducting mast or end-mounted on a metal mast.

I've never heard that.  I have vertical VHF/UHF yagis mounted mid boom on a metal mast with no ill effects.

(although he was copying me when I was horizontal).

This is the key statement; see below.

 Not surprisingly, he did not hear me at all when I went vertical.

Correct, because your signal at the other end was horizontal and he may have been using a horizontal beam or your signal was inverting on the way over.  That does happen.

This suggests that a cross-polarized horizontal beam is more effective than a vertical beam with a metal mast in the middle.

No, it suggests that when the other op is copying you on a horizontal antenna, switching polarities may not work.  You proved that, that's all.

 Interestingly, the metal mast had no effect on the SWR, so apparently just the pattern was distorted.

Or maybe the signal path just needed to be horizontal and not vertical.  Don't be so quick to diss your setup.

Steve Katz:
A metal mast protruding through a vertically polarized Yagi *ALWAYS* has a detrimental effect on performance: Just how detrimental varies a lot, and might be pretty small.

It can also be enormous.  It depends on the Yagi design and where the mast is placed.  It also depends on the length of the mast, and the frequency band in question.

On an actual antenna range at CSVHF back in the late 1970s we tried a dozen different commercially made 2m Yagis, vertically polarized, with 1.5" metal (steel or aluminum) masts mounted "through" them, with the mast parallel to the elements and running through the approximate COG centers of the booms, and measured actual antenna gain.  Yagis by Cushcraft, Hy-Gain, KLM (predecessor to M2), Tonna, a few homebrew varieties, an 8 element Quagi, etc.

There wasn't *any* case where the metal mast did not degrade performance.  In one or two cases, degradation was several dB and F/B ratio impact was even worse.  But results certainly varied.

Horizontal polarization, with uniform polarization on both ends of the circuit (horizontal to horizontal, no cross-polarity) does work better for over the horizon tropospheric contacts, which represent *most* contacts on 144 MHz other than very local ones.  There's less signal loss scattering over the horizon with horizontal polarization.  If the two stations are LOS, it shouldn't really matter.


Well, it seems that changing this little antenna to vertical will be a more complicated project than I had hoped.  Will have to wait for a bit but I want to try it, not sure how.  I am in a restricted community and have the 2M9SSB on a push-up pole that I lower during the day and put up in the evening.  In the down position, the antenna is in a narrow alleyway, not wide enough for a 2x.

KB9CRY, it appears that, most of the time, a vertically polarized US station has a better chance of working a horizontally polarized EU station.  W5UN's Skymoon program shows you the spatial polarity of your signal at the other station's QTH, and there's often close to a 90 degree difference from the USA to the EU, due to the Earth's curvature.  Of course, spatial polarity is sometimes meaningless due to Faraday effect, but more often than not a US station needs to be cross-polarized from his European counterpart for EME.

In my case, I had just completed a qso with a German station with "X Polarity," the ability to manually change polarity to maximize the incoming signal.  He told me he had me on vertical.  Immediately thereafter, I tried with another similarly equipped German station, except that the second station was fixed horizontal.  I could not copy him; hence, the experiment in turning the antenna vertical, which he said caused my signal to drop out completely.  It is possible that the Faraday changed the polarity between the successful first qso and the unsuccessful second one.  But it seems more likely that my antenna pattern was distorted on vertical due to the metal mast.

By the way, a large number of the experienced EME guys are upgrading to X Polarity.  It is claimed that a single long XP yagi can outperform a 4-stack of horizontal-only antennas, due to the ability to eliminate the effects of spatial and Faraday polarity differences.

73, Bill NZ5N


Steve Katz:
Faraday rotation is very slow, and making an "instant switch" in polarity doesn't tell you much.

Stations using switchable polarity, circular polarity, and continuously rotating polarity for e.m.e. is not a new thing at all, and hams have been doing this since at least the 1960s.

Wayne Overbeck N6NB used to operate a lot of "mobile/portable e.m.e." in the 70s and 80s using an array of cubical quads (I think it was sixteen 4-element quads) from places where there was no local e.m.e. activity.  One of those places was Alaska; there wasn't a single local KL7 who was on moonbounce, so Wayne drove a moonbounce station up there and operated from AK to give this out as a new state for many -- it was all written up in QST and Ham Radio magazine with a lot of photos and descriptions.

Wayne used to "rotate" the entire 16-quad array not only for elevation and azimuth but also on its own axis so he could continuously change polarization from vertical to horizontal, and everything in between.  He discussed how that reduced Faraday fading and made more contacts possible in less time.

That was at least 25 years ago...



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