[TowerTalk] Inverted Vees

[Robert Harmon]

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>
> 
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>> 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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