[Elecraft] Sloping Terrain vs Feedline Losses

[David Gilbert]

Hi, Brian.

I have no idea how or to what extent terrain affects a vertically 
polarized signal.  I am, however, pretty certain that if it does at all 
it would be worth more than 1 db.  That's just the nature of proximity 
effects in general.  I suspect that one possible effect of sloping 
ground for a vertical antenna might be to move the lossy environment to 
where it has less effect on the signal (i.e., lower), and that might be 
more significant with poor soil conductivity than with good 
conductivity.  It seems reasonable to me to imagine that the pattern for 
sloping ground would shift at least to some minor extent toward that of 
a free space pattern, but I'm pretty sure that ON4UN and others have far 
more insight into this than I do.

I've always wished we had a version of HFTA that handled vertically 
polarized antennas ... that would probably be enlightening.  I've also 
tried on occasion to use EZNEC+ for the same purpose since it allows you 
to specify at least two different zones around the antenna, but I didn't 
have much success with that.

I'm one of those who had quite good luck with roof mounted verticals, 
but it's hard to say whether any improvement (if there was one) was the 
result of distance from lossy ground or simply the ability to shoot over 
lossy surrounding structures like trees and houses.  I do think it is 
more than "folklore" that elevated radials have benefits over in-ground 
radials unless the in-ground radial system is reasonably extensive.  
There have been some pretty decent studies on that.

But again, it is important to keep separate the effect of radials on 
feedpoint return loss from the effect of ground on radiation pattern.  
Radials reduce feedpoint loss but have minimal effect on radiation 
pattern unless you are able to go out several wavelengths.  On the other 
hand, the conductivity of the ground has much less effect on return loss 
than a decent radial system, but it is the ONLY determinant of far field 
radiation pattern (other than whatever effect the terrain profile itself 
may have).

73,

Dave   AB7E



On 7/13/2016 3:46 AM, brian wrote:
> Hi Dave.
>
> Care to comment on how much benefit vertically polarized antennas 
> might gain from terrain sloping away from vertical?
>
> For horizontally polarized antennas, where ground reflection gain is 
> up to 6 dB, the sloping terrain can lower the effective take off angle 
> a lot- 10's of degrees.  There was a program called YTAD that 
> estimated this effect in one dimension.  It's results were quite 
> enlightening.
>
> Vertical antennas have no ground reflection gain.  Would one then 
> expect sloping terrain NOT to alter their already low take off angle 
> much?  On the other hand, folklore seems to indicate a benefit of roof 
> top verticals with their "elevated" radials over ground mounted 
> verticals with elevated radials/or in ground radials.
>
> 73 de Brian/K3KO
>
>
>
> On 7/13/2016 8:49 AM, David Gilbert wrote:
>>
>> Agree on the coax losses, but totally disagree on both of your other
>> comments:
>>
>> 1.  Elevated radials will ONLY help reduce near field ground losses ...
>> they will do nothing to help radiation pattern.  The effects of ground
>> conductivity determine far field pattern (given a particular profile) no
>> matter what kind of radials he uses.
>>
>> 2.  If there is any gain benefit from the terrain profile at all, it
>> will be much more than 1 db.
>>
>> Dave   AB7E
>>
>>
>> On 7/12/2016 3:49 PM, Craig Smith wrote:
>>> Ted …
>>>
>>> I think you are overstating the coax losses.   Even stock RG-11 should
>>> be perhaps 0.3 dB/100ft on 80 meters - around 1.5 dB for the 500 ft. 
>>> run.
>>>
>>> Even so, I would probably gravitate toward the closer location.  With
>>> the elevated radials, the effects of the ground conductivity should be
>>> minimal.   Not sure if ON4UNs data assume elevated radials or many
>>> on-ground radials.  It could be that his estimate of the sloping
>>> ground advantage is for the later.   With the closer location, you
>>> will have perhaps 1 dB stronger signal in all directions because of
>>> the lower feedline loss.
>>>
>>> 73    Craig   AC0DS
>>
>> _
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