I made one big assumption, and I didn't realize it until now, reading "if the
bend is roughly half-way". I personally have a 60 ft antenna support, and if I
increase my length to 5/16, or 3/8 wl, I end up with alot more horizontal wire
than vertical, whereas at 1/4 wl they are about equal. I considered all these
things before putting mine up, but I didn't think of a different vertical
length. The argument I made for a 1/4 wl inverted L was assuming a 60 foot
support.
Guy,
Would you model an inverted L with a 60 foot vertical length, various
horizontal
length (totaling 1/4 to 3/8 wl), and include 30 deg. elev as well as 15 deg,
and
with a 15 ohm ground?
73,
Trey KJ4FDV
---------------------------------------------------------------------------
No flames at all.
If you look at the table in my prior post on this thread, you will see that the
range between 5/16 and 3/8 is a very good one, DX or local, if the bend is
roughly half-way.
A 3/8 wave equal up, equal out L can be tuned with a bifilar 2:1 transformer
with a series capacitor to get a pretty decent match to 50 ohms. A friend has
a
57 up, 57 out version for 80 meters tuned that way that is a real killer
antenna. At my place, if I COULD do 110 up and 110 out for 160 I would. The
losses that can be attributed to ground loss diminish with the 100 ohms R feed,
and make the whole system a little more forgiving of issues in the
ground/radials/counterpoise area.
73, Guy
On Fri, Sep 24, 2010 at 7:15 AM, Edward Swynar <gswynar@durham.net> wrote:
On 23rd September, Trey wrote:
>
>"...By increasing the length of the inverted L to 5/16 wl, you move the
>
>current maxima up the antenna. If you kept lengthening the antenna, you
>would eventually get the current maxima to the junction of the vertical and
>horizontal parts. In this case the horizontal part would have as much
>current and radiate as much as the vertical part. So by lengthening the
>antenna over 1/4 wl, you decrease the percentage of
>the total antenna current that is flowing in the vertical portion from the
>1/4 wl case. This isn't what we want..."
>
>*************************************
>
>Hi Trey et al,
>
>Most interesting to me personally, because my system here uses three
>inverted "L" elements, each 3/8-wave long & tuned at the respective bases by
>large air variable capacitors...
>
>I like that latter feature because it greatly facilitates the resonating of
>each "L": you simply adjust the cap, check the SWR in the shack relative to
>the design frequency, then repeat as necessary(!)---no pruning, trimming, or
>lengthening of wires required...
>
>On the other hand, I would like to maximize the low-angle take-off radiation
>of each "L", in order to facilitate the working of DX.
>
>So allow me to run this by the group for comments & criiques, i.e., what if
>I was to shorten each "L" from the existing 3/8-wave length, to something
>approaching, say, "...one-quater-wave-plus-ten-feet"...? And what if I left
>the tuning capacitor at the base of each "L"...?
>
>I believe that by doing so I'd accomplish two things:
>
>(1) The current node of each "L" would be more concentrated in the vertical
>portion of the wire away from the horizontal, thus aiding & abetting the
>pursuit of DX, and,
>
>(2) I could still benefit from resonating each "L" with base-mounted
>variable capacitors (albeit with much SMALLER "C").
>
>Let the flaming & the sniping begin...! Hi Hi
>
>~73~ de Eddy VE3CUI - VE3XZ
>
>
>
>_______________________________________________
>UR RST IS ... ... ..9 QSB QSB - hw? BK
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|