Hi Chris,
Thanks for your interest in the PVC-frame passive loop project, and
I'm
sure that you had lots of fun making your 4' altazimuth loop PVC
frame (and
discovered a few of the tricks I learned). Actually, my original
plan was to
make only two or three loops of modest size, but after settling on a
standard design (and discovering how these PVC loops work like
gangbusters for
DXing), I couldn't resist making seven of them, all the way up to
the 10 foot
diagonal size.
It's very important to choose the suitable PVC diameter to match the
size
of the loop being constructed, since tubing which is too small will
result
in a sagging loop (and sagging DX performance). One of the major
lessons I
discovered was to carefully test out a frame's ability to support
its own
weight (and the weight of the wire) before proceeding to glue it
up. My final
recommendations (and the tubing diameters actually used for the seven
loops) are as follows:
18" (side) Tabletop Model 3/4 inch PVC
24'" Tabletop/ Rotating Model 3/4 inch PVC
3' Rotating Model 1 inch PVC
4' Rotating Model 1 inch PVC
5' Rotating Model 1 inch PVC
6' Rotating Model 1 1/4 inch PVC
7.5' Rotating Model 1 1/4 inch PVC
The PVC fittings for all the above diameters (crosses, elbows, tees
and
caps) were all available at my local Lowe's store, along with precut
5'
sections of all the tubing I needed, in each diameter. The project
was like a
DXer's dream, with the antenna frames extremely easy to construct, and
providing a completely symmetrical mounting system for optimum
sensitivity and
nulling ability in each individual loop size.
Each of these PVC loops is easily rotated for nulling by placing the
loop
in a support frame, as pictured in the photos on Ultralightdx. The
diamond-configured frame rotates on an unglued "tee" fitting, which
is inserted
into the center pipe of the support structure. The support
structure's center
pipe is cut to be about one inch longer than the two side pipes,
making it
easy to tilt the entire loop for increased nulling simply by
shifting the
support frame's center pipe along the ground, in the desired
direction.
The DXing performance of each individual loop has certainly been all I
could have hoped for! I had several weak TIS stations down at the
noise level
that had escaped identification for weeks, but the 2' PVC loop
provided
positive identification of all of them within a couple of days
(with the $9
Tecsun R9012, no less). The 7.5 foot (side) PVC loop brings in the
notoriously
weak Yakima, WA TIS and eastern Oregon NOAA stations on 1610 kHz at
night
(frequently even near the overload level) on the R9012.
Thanks again for your comments, and it will be lots of fun to write
the
full PVC Loop article with construction details. Good luck also on
your 4'
altazimuth loop!
73, Gary DeBock
In a message dated 4/13/2009 10:16:39 A.M. Pacific Daylight Time,
chris@xxxxxxxxxxxxxxx writes:
Hi Gary,
Very nice PVC loop designs! What diameter of PVC did you use for
the frame?
Are these loops rotatable or tiltable?
I'm currently building a 4 foot altazimuth PVC loop. The PVC frame is
finished and the base (made of wood) is finished. The only major
things
left
to do are cut grooves in the PVC pieces for the wire, wire the
frame, and
interface to the base. You used PVC elbows to extend the wires out
away
from
the main frame. Several plumbing stores have saddle tees (looks like
half-pieces of PVC pipe) http://www.plumbingworld.com/pvcsaddletee.html
,
for example. This would mount directly on the PVC frame (on top of
the 4
arms of the loop frame). Then, one can attach a grooved PVC pipe
piece on
the saddle for the wire, probably using epoxy. There are other
options for
the saddle tee like threaded pieces combined with an adapter. I'll
send a
photo if you'd like.
Once the above loop is done, I plan on mounting an E100 (or another
portable/ultralight) on a piece of lexan that would be placed
inside the
loop frame somewhere, mounted with tie wraps. A 6' earphone
extension cable
would plug into the E100 and then earphones after that.
What sort of DX are you hearing with your PVC loop antennas? How
does the
DX
compare with your other antennas? I can't wait to read your article
(and
about the great DX these loops pull in...hi).
73,
Chris
-----Original Message-----
From: irca-bounces@xxxxxxxxxxxxxxxx
[mailto:irca-bounces@xxxxxxxxxxxxxxxx]On Behalf Of D1028Gary@xxxxxxx
Sent: Monday, April 13, 2009 10:24 AM
To: irca@xxxxxxxxxxxxxxxx; am@xxxxxxxxxxx
Subject: [IRCA] Monster PVC-Frame Passive Loops
Hello All,
The annual "March Madness" antenna project here this year was to
construct
a series of tuned passive loops, using ultra-cheap PVC tubing and
fittings.
Loops of 18", 2', 3', 4', 5', 6' and 7.5' (side dimensions) were
assembled, using PVC diameters suitable to support each size
without any
sagging.
One of the primary design considerations was to isolate the loops
from the
support structures as much as possible, to provide clean
electromagnetic
reception patterns. Perfect symmetry of the coils was also an
important
objective, with equally-spaced wire slots cut in each of four frame
tubes,
and
the tuning capacitor located exactly at the loop ends, with the far
end of
the loop routed through a short PVC tube to the capacitor. These
steps
seem
to have provided maximum sensitivity and nulling ability for each
loop
size.
Lightweight, rugged, waterproof PVC was found to be an ideal frame
material
for tuned passive loops, and of course, it is also ultra-cheap
(even in
the larger sizes). The 7.5 foot (side) monster loop frame cost all
of $35
to
build, and the cost of the "tabletop" 18-inch model frame was
about $7.
The 7.5 foot (10 foot diagonal) PVC loop does require some serious
real
estate for construction, however, and is certainly not recommended
if you
have a
shaky relationship with any of your neighbors :>)
Photos of the 18", 2' and 7.5' PVC loops have been uploaded to the
Ultralightdx Yahoo group site, and are available upon request. An
article
containing full construction details for these new PVC-frame loops
should
be
written shortly, which hopefully will provide a new, inexpensive
option for
boosting the DXing ability of any receiver.
73, Gary DeBock
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