[AMRadio] Inverted V antenna


Geoff ars.w5omr at gmail.com
Thu Jan 28 23:22:40 EST 2016



On 01/25/2016 12:15 PM, Donald Chester wrote:
> The “cone of silence” of the null off the ends of a  horizontal half-wave dipole is very  narrow (or maybe “skinny” would be a better word), meaning it is limited to a very small range of vertical take-off angles, as well as horizontal coverage.  For all practical purposes, a dipole, whether truly horizontal or inverted-vee, can be considered omni-directional, particularly on the 160m, 80m and 40m bands.  The broadside advantage and end nulls are something blown way out of proportion in amateur radio lore, just like SWR. 
>
>  
>
> “One frequently sees a dipole azimuth pattern depicting a very sharp null off of the ends of a dipole. While technically accurate, this can be very misleading ... and is a result of trying to depict a 3 dimensional pattern in 2 dimensions. **This often seen null is only evident at the same launch angle as the maximum broadside gain**. Of major significance is the large amount of gain off the ends at higher launch angles. Due to multiple lobes forming above ½ wavelength, this is not easily shown in tabular form.”

Say what you will, but my experience was similar to Jim's.

My first antenna, a 75m Inverted V in San Antonio, TX, was broad-side
WNW by ESE. (city lot - 120'd x 60'w, long North and South).

Working stations in Austin and Dallas, like WD5JKO and WA5CMI vs the
likes of K5SWK and W5PYT, Otis and Bob were rock-solid 40db+ signals,
90% of the time, whereas comparable stations North and South were never
quite as strong.

2 things happened to change that original Inverted V into a more
omni-directional pattern;
1) adding open-wire line as feedline in place of RG-8
2) Closing in the bottom of the 'V', and making a full-wave delta loop,
fed at the original apex of the 'V',  in the vertical plane.

I never lost anything East and West, but North and South stations were
very similar in strength.

Bonus: My typical S-7~9 noise-level dropped down to S-2, typical.

I remember the day I closed in the bottom of the V and made it a loop, I
worked K5SWK and K5BAI and received higher-than-normal reports from
them, while they, for the first time, were equal (pretty much) in
strength.  Jim/BAI, in Dallas, was probably about 50 miles further away
than Otis was in Grangerland.

I've been sold on loops, ever since.  Of course, open-wire for feed-line
was decided on after lengthy discussions on the subject with John/WA5BXO.

I've lived in 3 places in the Houston area now, in the last nearly 8
years, the first being an apartment for 3 year (no antennas) and two
houses. 
First house had a 4-sided, square, horizontal loop, fed in the middle of
one leg.  Results were mediocre, I guess ... nothing spectacular to talk
of.  I mean, the rigs loaded fine into it, and signals were 'ok', but
there was always a local 'noise' at that location that ... just didn't
seem to make radioing 'fun' ...

At this house in Splendora, TX (about 10 miles East of where K5SWK's
xmtr was located)  another horizontal, square loop, instead fed with the
same home-brewed open-wire line, but this time fed on a corner of the
loop, and *BAM*, it's like hitting a nail on it's head from 200 miles
away.  Noise is gone, Signals are -HIGH- and signal reports are
astonishing! 

So, my experience tells me, that If you've got room enough for an
inverted V on 75m, you've got room for a Delta Loop.  Just get the apex
up ~1/4w above ground.

Hmmm ... I strayed, didn't I?  ;-)


The point is, go ahead and run the math, do the calculations, get the
'free-space' answers, but you're not going to be able to accurately
predict what's going to happen in any given practical "real-world"
application.

What 'should be' and 'what is' are very often two different things.

73 = Best Regards,
-Geoff/W5OMR



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