A eureka moment. Understanding isn't knowing.

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KK4YWN, Nov 4, 2014.

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  1. K0RGR

    K0RGR XML Subscriber QRZ Page

    Yes, horizontal works better for DX, regardless of mode. Most FMers use vertical because mobiles are mostly vertical. I used to run SSB mobile years ago with a horizontal antenna, and the coverage was pretty amazing in mountainous central California. Those mountains almost seemed to disappear.

    Of course, there are exceptions. I just worked a guy in the Twin Cities on one of our local repeaters - he's a good 80+ miles away, using a vertical. But he's on a pretty good hill, and it's got to be one of those unusual situations. There are 'cracks' in the hills to our north, and vertically polarized signals do make it through there. But overall, horizontal works a lot better.

    Maybe we should all go circular. I've used circulars, and they are a great convenience.
     
  2. K8ERV

    K8ERV Ham Member QRZ Page

    Looks like an interesting site, but I don't see how to do an altitude plot between two points. Can you explain how to do this? You may want to send it to me at tlamb@westelk.com

    TOM K8ERV Montrose Colo
     
  3. KK4YWN

    KK4YWN Ham Member QRZ Page

    If you want to do it with google earth, there is a nice writeup on 4x4ham.com.
    http://www.4x4ham.com/showthread.php?1865-Elevation-Profiles-in-Google-Earth

    Regarding circular polarization: I'd like to know more about it. I found one interesting article that doesn't have any obvious holes: http://www.dielectric.com/inc/manuals/benifits_of_circular_polarization_for_mobile_services.pdf

    If I get time this weekend, I'll go googling for more.
     
  4. W0AAT

    W0AAT XML Subscriber QRZ Page

    Works quite well actually, with 160 watts and a pair of 17 element 31 foot long beams I could work ~350 miles almost anytime.

     
  5. KK4YWN

    KK4YWN Ham Member QRZ Page

    I started a new thead about tropo scatter as sort of a brain dump.

    Too many people are claiming its possible for me to not consider eating my words.

    I hope some of you would chime in and contribute so future readers will have a reference.
     
  6. KK4YWN

    KK4YWN Ham Member QRZ Page

    I have some new information about this that I think is worth sharing.

    I built a six element yagi yesterday and mounted it on a pole 16 ft above ground. It's slightly lower than my omni vertical. And I mounted it horizontal, so I'm purposely comparing apples to screwdrivers.

    My friend across town is difficult copy on the horizontal beam. His signal on the vertical omni is very slightly better. On either antenna he needs to turn on an amp in order for me to hear him.

    The beam easily hits all local repeaters with five watts. In many cases I don't have to point it toward the repeater.

    The beam easily hits remote repeaters. More power is needed and the beam must be pointed at the repeater.

    A new repeater 130 miles away is now reachable that I've never been able to reach. I've used a two element colinear, a two element moxon, and a four element cubical quad (both polarities tried on the beams). Vhf conditions were not conducive to ducting during testing.

    Other observations: distant mobiles are easily worked over hilly terrain at distances of 30miles (and possibly greater). The other bad stations with v-polarized antennas could not work the mobiles while I did so easily.

    There is another station across town who I can never copy on my omni. I get bits and pieces until he turns up an amp. As it happens, he has a crossed yagi antenna and almost exclusively uses the vertical portion.

    I received him at s4 and he received me at s4. He was impressed with the beam as I'm usually difficult to copy. What I neglected to tell him (on purpose) was: I normally transmit 50w. For testing I was using 5w.

    He made sure to remind me of the 20db of loss between h and v polarization before he switched to h polarization. It seems everyone needs to repeat this when discussing polarization.

    When he switched there was NO discernible difference in reception by either party. None. Zero. Nada zilch.

    By increasing power we were able to copy one another s9+.

    I'm not sure what 20db polarization loss means, but if it's a function of path loss, we might as well just chuck it out the window and stop worrying about it.

    H polarization is just plain better at vhf.

    All tests were done using fm simplex, except in the cases where repeaters were used.
     
  7. K4ISR

    K4ISR Ham Member QRZ Page

    This reminds me of the question on the Tech test:

    T3A03 What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands? Horizontal

    So for normal VHF use, you will not see much difference between vertical or horizontal... But switching to narrowband 2.5kHz with the directional or horizontal may net you some distance, even if it stays at S3 or S4, the incoming signal should be a bit clearer provided both have the same polarization.

    The polarization loss comes in when horizontal antenna is transmitting and picked up by a vertical, or vice-versa. Due to polarization differences, there is a "penalty" of a weaker sound, even if you get the same signal through.

    Think of it like a reversible 12VDC motor (hypothetical). Normal polarization gets you 1000rpm at 50 ft lbs torque. Reverse the polarization and it can only do 500 rpm but also gets 250 ft lbs torque. Still the same signal but slightly different results.
     
  8. KK4YWN

    KK4YWN Ham Member QRZ Page

    But what I'm trying to stress here is vertical polarization is inefficient at VHF/UHF.

    The horizon is very very close unless you're on a mountain or on the ocean (even on the ocean is only about 14 miles). Over real terrain vertical polarization falls flat on its face. And for whatever reason, this is universally accepted as a viable system among hams for no good reason.

    Last night I called CQ on 144.2 and got a really really weak station. After some fumbling around, we were able to beam each other. The copy was absolutely difficult until we found one another. He had 10w into a horizontal 19 element beam. I had 50watts into a 6 element beam. Both horizontal. Terrain is very hilly. Horizontal polarization on each end. S8 copy on both sides. Compare that to my friend across town: 25 watts into a 19 element vertical beam. Distance of around 26 miles. Practically no copy unless he cranks the power above 100 watts.

    New hams appear to be afraid of horizontal polarization because they're under the impression that they'll lose access to repeaters. This is false. I have observed the opposite: I can access repeaters that I couldn't access before using a modest sized beam mounted horizontally.

    I've also demonstrated that talking cross-polarization with mobiles is easily done. Because there exists this thing call ground gain, and it relies upon ground reflection, it would be fair to assume that mobile signals will reflect off the ground and change polarization. This happens with skywaves, so I don't see any reason why it wont happen when reflecting off ground.

    I also think that this is not ideal. I believe a h-polarized mobile will radiate further because there is less ground interaction.

    AM, SSB, FM, or CW does not matter for propagation.
     
  9. WA8ZYT

    WA8ZYT Ham Member QRZ Page

    I just did a simple test with the following set up; Icom 251A on FM with a power output of 10 watts, set up with a dipole up 16' (measured), fed with 88' of LMR400. The dipole is 20" away from the tower face on one leg facing the direction of the repeater. (Rohn 25)

    With the antenna set to vertical polarization, I am full quieting, into the repeater, and the received signal level of the repeater is 40DB over S9.

    With the antenna set to horizontal polarization, I cannot key up the repeater at all. If I use my Icom 2AT, I can key the repeater up and the received signal strength of the repeater is 20 DB over S9 on the 251A. The S meter is accurate and has been verified with a recently calibrated General Dynamics R-8000 service monitor.

    In this case there is indeed a 20 DB difference between horizontal and vertical polarization.
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'm impressed as hell you were able to calibrate an IC-251A "S" meter that well.

    I had a 251A, a 271A and a 275H and they were all good rigs, but the "S" meter indications were pretty meaningless on all three of them.

    Did you do something special to calibrate it? (I never really tried, frankly...just noticed that using my signal generator to "observe" the meter readings, they weren't accurate at all, straight from the factory.)
     
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