[TowerTalk] Re: Can takeoff angle be too low?

[n4kg@juno.com]

My interpretation of the VERY HIGH (>5 WL) antenna
observation that there are NO observable nulls is as 
follows:

Since the peaks occur at approximately 5 degree intervals
and the earth is not perfectly flat, reflections from minor
slopes (1 to 3 degrees) in the foreground tend to "fill in"
the nulls.  At lower heights, these minor slopes may move
the upper or lower edge of a lobe 1 or 2 degrees, but that
is of little consequence when the lobes are >8 degrees wide.
This is only a guess.  Any other theories? 

de  Tom  N4KG


On Mon, 18 Dec 2000  "i4jmy@iol.it"<i4jmy@iol.it> writes:
> This is only a personal thought developed in 23 years of contesting, 
> but who has very peculiar installations generally opens and closes 
> the  band, is generally stronger at any time, and often is "the only 
> signal"  from his area .

> When the antenna is very high from ground, althought peaks and nulls 
> should be a number, it looks instead as every angle is well covered 
> and  nulls are not present. I attribute this to the fact that
ionosphere 
> layers and reflections are produced in rather wide 3D areas and not 
> in > discrete points, therefore the arrival of the angle rarely can be 
> exactly in a null, of course if the null amplitude of the antenna 
> system is actually very narrow.
> The "very high" antenna expression covers those peculiar 
> installations 
> where not the tower but an hill top or a tall cliff fall establish 
> waht's the real antenna height in terms of many WL from ground.
> In such conditions the signal mess in wide open conditions is huge 
> and 
> sometimes a very low antenna that can't benefit the geographical 
> situation helps in favouring higher angles and allows reception. 
> I suppose this fenomena to receive better with a lower antenna is 
> also 
> caused by other factors, including that a number of correspondants 
> do  not have antennas high enough to efficiently radiate at low angles 
> and  when one can receive them it's only because a multihop condition
is 
> also present.
> It's also perfectly possible to have a wide range of angles 
> available > using a stack, but if the useful angle to receive for a
stated 
> station 
> is very peculiar this kind of antenna, when no provision is made to 
> select the best antenna, the system may actually ruin S/N, like when 
> one has gain but fair or no F/B and QRM is big at the back.
> It's anyway a constant evidence in my records that low anglers open 
> and  closes propagation and that stations with system radiating at very

> low > angles are 90% stronger if received with low angle system, 
> independently if a propagation allowing more hops is present.
> Another evidence for me is that beyond 9000 Km paths (like W6 or JA 
> from here) antennas with medium high angles are totally uneffective 
> in > the very most of the cases.  
> 
> 73,
> Mauri I4JMY
> 

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