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Re: [IRCA] Monster PVC-Frame Passive Loops
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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