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Author Topic: Question about skip  (Read 2444 times)
KE3WD
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Posts: 5694




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« Reply #15 on: April 07, 2013, 04:10:38 PM »

"Skip" signals were indeed originally an Amateur Radio term. 

CBers picked up on it and at one time both hams and cbers used the term. 

Origin is from early written explanations to imagine the Ionosphere as a water lake or pond, upside down, and the signal as a stone being skipped across that lake. 


73
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KE3WD
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Posts: 5694




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« Reply #16 on: April 07, 2013, 04:14:41 PM »

I thought that vertically polorized antennas were omni directional?

The vertical antenna is omnidirectional, but its signal is vertically polarized, which makes it difficult to communicate using the ground wave with horizontally polarized signals, no matter what direction they are received from. 

Omnidirectional refers to the pattern around feedpoint of the antenna. 

Polarization refers to whether the Electric portion of the electromagnetic wave is Vertical as referenced to the plane of the Earth, or horizontal. 

Two different terms that mean two entirely different things. 


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KF5PGT
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Posts: 38




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« Reply #17 on: April 07, 2013, 06:35:04 PM »

Ok, I see the difference now. So just because an antenna is omnidirectional doesn't mean it's vertically polorized.
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W8JX
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Posts: 5324




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« Reply #18 on: April 07, 2013, 07:08:32 PM »

The vertical antenna is omnidirectional, but its signal is vertically polarized, which makes it difficult to communicate using the ground wave with horizontally polarized signals, no matter what direction they are received from. 

I agree this can be quite noticeable on VHF and UHF at times but never seen it make much difference on HF 
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WB6BYU
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Posts: 12974




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« Reply #19 on: April 08, 2013, 01:55:38 PM »

There is a danger here of confusing ground wave and direct wave
propagation modes.

Groundwave is where the signal is propagated along the ground, and only
works for vertical polarization.  (That's why AM BC stations are all vertically
polarized, even when they use directional arrays.)  Attenuation increases with
frequency, and is relatively high compared to other modes, except over salt
water.  It is the primary mode for LF and local AM BC coverage, but by the time
you get up to 80m the maximum range is about 50 miles for a 1kw signal under
good conditions, and much less on the higher bands.  Because of the high
attenuation is isn't used much in ham operation above 160m.

Space wave, or direct wave, is the signal traveling directly from one
antenna to the other.  It is more associated with VHF/UHF, but is the most common
mode for local propagation on 10m and CB.  Unlike groundwave, raising the antenna
will increase coverage because the antenna can "see" further.  Vertical polarization
is commonly used on CB for compatibility with mobile stations using whip antennas,
but other polarizations work as well (or better) as long as matching polarization is
used at each end of the path.

Once you get into the ionospheric propagation modes (and some of the other special
cases) then the path changes the effective polarization of the wave, and matching
the antenna polarization at each end isn't important, because that doesn't guarantee
that the antenna actually matches the incoming wave.

In fact, polarization rotation is one cause for fading:  I ran some tests one day with
a KH6 station where we showed that the periodic fading (about every 5 minutes) was
due to polarization rotation along the path, and the optimum polarization for receiving
at my end was not always best for transmitting, as he couldn't change his antenna
polarization.
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