G3TXQ wrote: " My point is that, even if the propagation massively
favours the
very-low-angle path, the dipole will only ever be 6.62dB behind the
vertical. The fact that there may be other, much weaker, paths at higher
angles where the dipole response peaks is irrelevant.
W8AEF wrote: "Wrong. The dipole will be 8 dB MINIMUM weaker than the
vertical per F layer hop. 3 F layer hops will make the dipole 24 dB
minimum weaker, etc."
Paul, I suggest you sit down and rethink this. The propagation angle
does not change the gain of the dipole. If the dipole has X amount of
gain at at "Y" angle then the path does not change the fact it has X
amount of gain at "Y" angle.
And the propagation angle does not necessarily change if the gain of the
antenna changes.
Steve's statement is correct. Your's needs some re-thinking.
Jerry, K4SAV
Paul Playford wrote:
> ----- Original Message -----
> From: "Steve Hunt" <steve@karinya.net>
> To: "Paul Playford" <paul@w8aef.com>
> Sent: Monday, April 06, 2009 12:57 AM
> Subject: Re: [TowerTalk] EZNEC- needs improvement
>
>
>
>> Paul,
>>
>> I'm still struggling with your explanation. You seem to be claiming that
>> if the only propagation path which exists is at a lower angle than the
>> dipole's optimum take-off angle, the dipole wont hear anything.
>> Obviously that's not true.
>>
>
> That should be "Obviously that IS true". In practice you will find in the
> vicinity of 8 dB loss per F layer hop. And what you have not done is play
> with W6EL Prop and see what the differences in F layer hops are at different
> (try 1 degree where the vertical is still effective) elevation. When you
> get a difference of 5 to 10 F layer hops between the dipole and vertical you
> will see where 40 to 80 dB of signal is going - into the clouds to be
> absorbed and never to return to earth.
>
> When you have a vertical with a salt water ground plane you effectively have
> a rifle pointing at the horizon, whereas with the dipole at 1/2 wavelength
> you are pointing the rifle at the moon - and the moon keeps moving.
>
> This is by practical experience from DXpeditions to islands where we have
> excellent salt water ground planes. A vertical on the beach will outperform
> a yagi (at 1/2 wavelength above ground) for DX every time.
>
> You have got to play with W6EL Prop and change the numbers around a bit and
> you will see what I am talking about.
>
>
>> Let's take your figures for the dipole vs the vertical, and assume that
>> the only viable propagation path is at 5 degrees. Even though that's way
>> below the dipole's 30 degree optimum of 8.36dBi, it still has a
>> reasonable response at 5 degrees (-2.94dBi). At that angle the vertical
>> is 3.68dBi, so we'd expect the difference to be 6.62dB.
>>
>
> Propagation is not limited to only one viable propagation path. The signals
> will take all of the paths but only the strongest signal(s) will be heard.
> If the multiple signals arrive at the destination in phase they reinforce
> (add) each other and the signals out of phase cancel causing a fade. And
> the changing paths are - you guessed it - QSB!
>
>
>> My point is that, even if the propagation massively favours the
>> very-low-angle path, the dipole will only ever be 6.62dB behind the
>> vertical. The fact that there may be other, much weaker, paths at higher
>> angles where the dipole response peaks is irrelevant.
>>
>>
>
> Wrong. The dipole will be 8 dB MINIMUM weaker than the vertical per F layer
> hop. 3 F layer hops will make the dipole 24 dB minimum weaker, etc.
>
> And see my previous paragraph about higher angle paths - the ARE relevant.
>
>
>> What am I missing?
>>
>>
>
> Playing with W6EL Prop.
>
>
>> Steve
>>
>>
>
> And something else to think about. Higher is not always better. I have 4
> element monoband yagis on a 72 foot crank-up tower plus a Force 12 C3 (2
> elements on 20m) on a 37 foot tower. During Sweepstakes (a United States
> contest) I observed the C3 outperformed the monobanders, and by a big
> difference. Poking around in the dark with a flashlight I checked cable
> connections, SWR, front-to-back, etc. Nothing wrong. Finally I cranked the
> 72 footer down and the antennas became equal. For domestic QSO's (less than
> 2500 miles) The lower antenna works better but for DX it is still the high
> ones that work best.
>
> de Paul, W8AEF
>
> ZF2JI/ZF2TA FO8DX/FO8PLA 8Q7AA XZ0A VU7RG TX5C
>
>
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