[TowerTalk] Inverted Vees

[Grant Saviers]

On my way to try to find more low angle 80m gain than my Tornado loaded 
rotatable dipole at 100' (average EU arrival < 10deg  from 47.5N WWA) I 
explored (lot's of modeling) phased inverted V's hung off my 89' tower. 
The tower was always messing up the pattern.  Then I found that Greg 
Ordy (W8WWV) had written about this approach on his website and 
basically gave up on the idea after a very serious attempt.

So while a loaded vertical dipole is a useful antenna the tower 
interaction will likely be significant and modeling would be a very good 
idea.  The yagi top loading needs included since it will make the 
resonance not 90ft. OTOH maybe you have the resonance (or can make it) 
needed for a reflector and spacing the VD out on a catenary will yield a 
useful pattern.  I think that is described in ON4UN.  For an omni VD (or 
adjusting resonance for a yagi) probably detuning the tower into lower 
interacting segments will be needed, see the W8JI website for how this 
works.

It's a tough game to achieve low angles from horizontal antennas on 80m 
until over 1/2 wl high.

Safety is a concern since the voltage at QRO at the bottom end of any VD 
can be awesome.

Grant KZ1W

On 6/15/2020 07:49, Robert Harmon wrote:
> Interesting discussion on inverted V's.    I have probably a typical inverted V setup for 80M strung off of a tower.  I have the center of the V strung off my tower at 90 feet and the ends slope down to 35 feet to two poles on each side of my property.   Here's an idea I have been thinking about.  Hanging a vertical dipole from the tower with loading coils in each leg to compensate for the shorter length.  Better low angle radiation ?  I know I would have reduced bandwidth but that would be ok, I hang out in the very low end of 80 anyway chasing CW DX.  What do you think, improvement over the V ?
> 
> Bob
> K6UJ
> 
> 
> 
>> On Jun 15, 2020, at 7:10 AM, jimlux <jimlux at earthlink.net> wrote:
>>
>> On 6/14/20 8:23 PM, Jim Brown wrote:
>>> On 6/14/2020 7:03 PM, wesattaway wrote:
>>>> However,  as overall height is raised then best performance occurs when the wires are level.   I think Jim Briwn may have some data on this.
>>> Hi Wes,
>>> My study was on the effect of height on horizontal and vertical antennas, and I developed a figure of merit in dB for height of horizontal antennas. The executive summary is that for 30M and below, higher is better. :)
>> <snip>
>>
>>
>>> 3) Soil quality STRONGLY affects vertically polarized antennas -- the better the soil conductivity, the better they work.
>>> 4) HF verticals work better on the roof than on the ground.
>>>
>>
>> <snip>
>>
>> There's two separate factors at work in #3
>> a) a "near field" effect - for a monopole vertical, the ground (or radial field) is half the antenna. Hence the "120 radials" for FCC proof of performance exemption.  Not so much effect for a vertical dipole.
>>
>> b) a "far field" effect - H-pol is reflected well almost at any incidence angle and with any soil properties. Not so with V-pol which is strongly affected by soil properties and incidence angle.
>>
>>
>> The difference in these two effects (in broad strokes) is that (a) is a big deal close in (dimensions comparable to antenna height) and (b) is about the soil properties farther away.
>>
>> Consider a 50 foot tall monopole. You can think about the ray from the antenna hitting a spot at some distance and then reflecting. And each point on the antenna hits a different spot.
>>
>> For a low elevation angle, say, 10 degrees, the spot for the top of the antenna is 50/tan(elev) =  283 feet away.  And it gets way farther out very rapidly.  For 3 degree elevation, the "reflection spot" is 1000 ft away.  Of course, for a spot on the antenna that is 25 ft high, the "spot" is half as far away.
>>
>> So for really low angle radiation (like 3 degrees), everything within 20 times the height of the antenna contributes.
>>
>> Hence the popularity of verticals at the beach, or in the middle of the proverbial salt marsh.
>>
>>
>> As Jim points out in #4, raising the antenna is good (reduces losses from near field (a)) but does extend the far field issue. For a 50 foot elevated dipole at 100 ft the radiation at 3 degrees is reflecting from spots at 1500-2500 ft away.
>>
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