Re: [IRCA] IRCA Loop update

["Steve Ratzlaff" <steveratz@xxxxxxxx>]

Yesterday I built a 5-foot diameter square copper pipe loop, using 1/2 inch 
copper pipe (two 10 foot sections), and an FT-140A-J high-permeability 
toroid. Fortunately I took the toroid with me to the plumbing supply store, 
thinking I would buy 3/4 inch pipe. But this toroid just barely slipped over 
the 3/4 inch pipe with no room left to wind the secondary winding, so I had 
to go with the smaller 1/2 inch pipe. (Regarding the elbows--they are 
anything but a snug fit on the pipe ends, they just fit loosely and easily 
pull out with the slightest effort. I don't believe you could make a 
portable loop with loose pipes and elbows fitted together, without some 
additional securing method. You could wrap aluminum foil around the joints 
and tape them together--I think that would work, for a portable loop.)
It takes a LOT of heat to solder the elbows to the pipe ends. I started out 
with the standard propane torch, but my cylinder used up within 5 minutes--I 
hadn't used the torch in years. This was late in the day and no chance to 
drive to a store for a replacement (50 mile round trip). Then I remembered 
my oxyacetylene torch that also hadn't been used in years. But both bottles 
had gas, so that worked fine for soldering the connections, and I even 
remembered to slip the toroid transformer over one section!
My thinking on the toroid transformer was the pipe resistance was in the 
range of 0.1 ohms; a match to 50 ohms coax would be the square root of 
50/0.1 or 500, which rounded off gave a convenient 22 turns for the 
secondary winding on the toroid. I used #24 gauge enamel wire, with a BNC 
connector attached. I hung the loop outside between two trees (where my TA 
EWE ended) and used that coax cable for the loop cable.
(A 5 foot square loop is actually a pretty big loop, once I got the thing 
constructed and was carrying it outside.)
I have an antenna switch indoors next to the radios, so it's simple to 
switch between the various antennas to check the signal levels.
It was immediately obvious that the loop's output was very small compared to 
my other wire antennas--very, very small, on the order of 5-7 S units lower, 
on the MW BCB, with more output at the high end. Using my R75, with Preamp 1 
about +10dB gain and Preamp 2 about +20dB gain, use of Preamp 2 brought 
signals up quite a bit. Down at LF, I only have two beacons that give strong 
S9 to S9+20 on the longwires, with the loop using Preamp 2, they were 
audible but anything but strong. I could just barely hear 60kc WWVB (which 
is S9+40 on the wires). But the loop could be used on MW, even with no 
preamp.
So, on LF I would not want to use this if I had any other LF antenna, but at 
MW it would certainly work, with so much stronger signals.
I got strong QRM buzz on the loop, at the low end of the BCB that was barely 
heard on the longwires--apparently the noise was coming from the house. The 
loop was about 100 feet from the house.
I tried an external preamp, a +21dB ARR broadband preamp, but that didn't 
work any better than Preamp 2 of the R75.
This morning for my TP reception, I tried switching to the loop a number of 
times; there was never a trace of any TP heard on the loop.
So, for my initial experiment with a 5 foot copper loop, frankly, I am quite 
unimpressed--at least compared to what I can hear with my wire antennas. I 
bought enough extra pipe and elbows to make a 10 foot diameter loop, but 
based on this first test, I'm not sure I'll build it. It will be a very huge 
affair and won't be easy to suspend and rotate.
But if you're thinking about building a copper loop and trying it out, by 
all means do so, you may have much better results than I had, especially if 
you don't have decent outdoor wire antennas as a (perhaps unfair) comparison 
to test against.
Steve
NE Oregon

----- Original Message ----- 
From: "Russ Edmunds" <wb2bjh@xxxxxxxxx>
To: "Mailing list for the International Radio Club of America" 
<irca@xxxxxxxxxxxxxxxx>
Sent: Saturday, November 12, 2005 10:43 AM
Subject: Re: [IRCA] IRCA Loop update


>
>
> --- Bob Foxworth <rfoxwor1@xxxxxxxxxxxxxxx> wrote:
>
>>
>> Could the antenna be
>> made from 4 straight sections designed to be
>> attached at the corners, then made transportable
>> in some sort of oversized fishing-pole-type
>> carry bag? (That's probably over-kill, but an
>> interesting thought anyhow. You'd need a
>> really rigid corner attachment mechanism)
>>
>
>
> *** Let's think copper elbows with an inner diameter suitable for the
> pipe to fit snugly into. This could be snapped together and taken apart
> without a lot of difficulty. Seems to me as long as the fits are snug
> enough to not break the conductivity you'd have a knock-down portable
> model which would fit in a fishing pole ( or pool ) carrier.
>
> Russ Edmunds
> Blue Bell, PA  ( 360' ASL )
> [15 mi NNW of Philadelphia]
> 40:08:45N; 75:16:04W, Grid FN20ID
> <wb2bjh@xxxxxxxxx>
> FM: Yamaha T-80 & APS9B @15'
> AM: Hammarlund HQ-150 & 4' FET air core loop
>
>
>
> __________________________________
> Yahoo! FareChase: Search multiple travel sites in one click.
> http://farechase.yahoo.com
> _______________________________________________
> IRCA mailing list
> IRCA@xxxxxxxxxxxxxxxx
> http://arizona.hard-core-dx.com/mailman/listinfo/irca
>
> Opinions expressed in messages on this mailing list are those of the 
> original contributors and do not necessarily reflect the opinion of the 
> IRCA, its editors, publishing staff, or officers
>
> For more information: http://www.ircaonline.org
>
> To Post a message: irca@xxxxxxxxxxxxxxxx
> 

_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
http://arizona.hard-core-dx.com/mailman/listinfo/irca

Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers

For more information: http://www.ircaonline.org

To Post a message: irca@xxxxxxxxxxxxxxxx