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Subject: Terminated Loops
Date: Sat, 4 Jul 1998 16:09:56 -0400 (EDT)
From: w a merriman <merriman@shore.intercom.net>
To: editor@noblepub.com, baconti@aol.com, chutton@stgmssmtp.nwest.mccaw.com,
crippel@exis.net, kiwa@wolfenet.com, k9rt@aol.com,
gatkins@seanet.com, w8jv@yahoo.com,
jburnell@plato.ucs.mun.ca, JimRenfrew@Delphi.com, MarkWA1ION@aol.com,
WA1ION@ix.netcom.com, neilkaz@interaccess.com,
mwdxer@webtv.net, plsBCBDXER@aol.com, steve.whitt@zoo.bt.co.uk,
tracey.gardner@rock.com,
nrclog@aol.com, werner@mail.on.rogers.wave.ca
Preliminary comments:
In the September 1997 QST on page 43 with a modification in the May
1998
QST on page 73 there is an article by Gary Breed, K9AY on the Terminated
Loop. These looked like they held great promise as Medium Wave
DX
antennas. In fact the termination resistance for these antennas
is
determined by using a BCB station off the end of the loop and adjusting
the resistance for minimum signal.
In a word, THESE THINGS WORK!!!!!!!!!
I have a single loop up at the moment oriented roughly N/S. This
antenna
is parallel to a pair of slopers that are approximately 135 feet long,
50
feet at the high end and sloping down to 10 feet at the bottom.
These
antennas run parallel to each other but are sloped in opposite directions.
They are fed at the low end with coax through 4:1 matching transformers.
This pair of slopers have a very good "front to back" ratio when compared
to each other. On many frequencies it is possible to swap dominate
stations just by switching from one sloper to the other. Up until
now I
have considered slopers, and I have a total of 4 oriented roughly N/S/E/W,
as being the best wire antennas a Medium Wave DXer could use unless
they
were fortunate enough to have the room to put up Beverages, rhombics,
etc.
That was before I tried a terminated loop!
The loop I have up is a delta, 37 feet on a side for a total of 117
feet.
It is hanging from a tree limb and the bottom is about 3 feet off the
ground. The remote relay box uses a 12 volt relay from Radio
Shack and
the termination at the moment is a 2K pot. The transformer I
used is
11 trifilar turns of #24 insulated solid telephone wire on a Amidon
FT82-75
core.
All performance comparisons are made to the N/S pair of slopers which
are
parallel to the loop.
SIGNAL LEVEL: Signal levels are down about 8-10db across
the entire MW
band compared to the slopers. However even with this signal loss
I am
still able to hear the two JFK Airport TIS stations on 1630 and 1700
kHz
during the day on the loop. This is not bad for 200 miles and
50 watts
or so max even if part of the path is over water. In addition
the loss
can easily be made up with a quiet amp.
FRONT TO BACK: In a word, impressive. It is no worse
than the pair of
slopers over the band from 600 kHz up and on many frequencies it is
better. Nulls vary from 5 to over 20 db in a couple of instances
and
this is during the day. On many frequencies it is possible to
swap
dominate stations just by reversing the loop feed.
Below 600 kHz the loop is almost completely ineffective. There
is absolutely no signal difference when you flip the loop termination/
feed. On this segment of the band the slopers outperform the
loop. I
have no idea why this is so unless it might have something to do with
the termination/ground. More about this later.
TERMINATION: At the moment my terminating resistor is a
2K pot. The
ground I am using is only a 3 foot Radio Shack ground rod. This
gives
a very effective ground when used with one of my slopers but might
not
be good enough for the loop. Termination resistance for best
nulls
varies across the MW band and unless this can be smoothed out with
a
better ground it is obvious that to get maximum performance a variable
resistance is going to be necessary. This of course brings to
mind the
Steve Byam system. Since I have a couple of the VTL3A17 Vactrols
that
Steve uses in his system I will be playing with this in the next few
weeks. Stay tuned!
These terminated loops look real interesting. While much more
playing
around is necessary they hold a lot of promise.
73/DX
Al-K 4 G L U
Chincoteague Island, VA
More comments:
First. Ignore my comments in the last posting about the antenna
not
working below 600 kHz. Wrong! It works very well all the
way down
through longwave. I'm going to blame this on noisy conditions
when I
was doing initial testing.
The two loop system is up and running. In a word, super!
There is no
question that in many cases the front to back on the loops is superior
to a pair of slopers and I've not run into any situation yet where
it
was worse. During the day on some frequencies I'm able to choose
between
three different stations just by switching antennas and adjusting the
termination.
Termination. As mentioned earlier to get full performance from
these
antennas a variable termination is required. The Steve Byan Vactrol
method works a treat! Thank you Steve! This is very easy
to implement.
All you need is the Vactrol installed in place of the terminating
resistor, a 1K pot in the control box to supply power and an additional
control line. For my unit I'm using 5 conductor flat rotator
cable.
This is still sold by Radio Shack. I'm using the updated control
box,
with added 1K pot that was described in the May 98 QST on page 73.
This
gives seperate lines for each relay, variable termination and leaves
another unused for possible inclusion of a preamp later.
These antennas work very well as half of a 2 antenna phasing setup.
I've
tried them against my slopers and an MFJ-1024 Active Whip with a DL-2
Delay Line Phasing Unit and gotten excellent nulls. More testing
is
going to be done including building a control/relay box that uses
separate feedlines for each loop to see if these loops can't be phased
against each other. Since they are mounted at 90 degrees to each
other
this should work. We will see.
That's about it. If anyone has any questions or comments I would
be very
interested in hearing what you have to say. For Medium Wave DXers
this
is an excellent project and I think I can guarantee you will enjoy
it
very much when you have it up and running. SWL's - don't ignore
the
possibilities here. These antennas were originally designed for
use on
the 160 and 80 meter Ham Bands. You will have to make yours a
bit smaller
to cover the Tropical Bands.
My thanks go out to Gary Breed, K9AY for the original design and to
Steve
Byan for the variable termination. It's very nice to build a
project and
have it work as "advertised".
73/DX
Al - K 4 G L U
Chincoteague Island, VA
Additional Notes
Over the past few months Andy Ikin and myself have been experimenting
with these fantastic antennas. The original articles for these
appeared in the September 1997 QST on page 43 and in the May 1998 QST
on page 73.
Between myself and Andy Ikin of Wellbrook in the UK a number of changes
have been made. Most of these have been covered in my previous
postings
but here is a quick rundown:
1. Variable termination using a Vactrol or some other method.
This is
an absolute must - peak performance cannot be realized
with a fixed
resistor. This is very easy to do. All
that is needed is a Vactrol
or Andy's unit that was described recently in MWC
mounted in the
termination/relay box in place of the termination
resistor; an
additional control line running from the in shack
control box to the
termination/relay box at the antenna and a 1K pot mounted in the
control box to vary the voltage.
2. Use of a "magnetic" matching transformer in place of the one
used by
K9AY to reduce local noise pickup. Among other
designs the xfmr
designed by Nick Hall-Patch years ago works fine.
Both Andy and
myself came up with this at about the same time.
3. Ground. For a portable setup a 4 wire counterpoise system
with a
wire running under each leg of the antenna works
well. For fixed home
use a ground rod is the easiest way to go but the
counterpoise will
also work - in fact it is what I use. Suggested
by Andy.
4. Separate feedlines for each loop. This was done by me
so that I
could use the 2 loops in a phasing setup against
each other in the
the few instances where phasing is still necessary.
Although the
two loops can be successfully phased against each
other I'm not
totally satisfied. Am currently playing with
a active whip antenna
- MFJ1024 at the moment but a Dressler ARA60 is
ordered - mounted
at the top of the mast just above the loops.
Phasing one of the
loops against the whip is working extremely well
so far and will
probably be my final setup. I then may revert
to a single feedline
for the two loops per the original K9AY article.
Had concerns that
the active antenna feedline running down through
the middle of the
loops might mess up their patterns but so far that
does not seem
to be a problem.
5. Ground disconnect. Discovered by accident that in some
instances
nulls could be greatly improved by disconnecting
from ground so I
have added an additional relay to do this.
Have a difficult time
describing this as it is very random. Don't
know for sure why this
is but it seems to be caused by a interaction between
the two loops
when ground is removed. In some cases nulls
can be improved on
one loop by varying the termination resistance on
the other. Don't
ask me to explain it any further - I can't.
To get the full benefit
of this I'll have to continue using two feedlines
instead of going
back to one because with a single feedline a single
termination
resistance is used used for both loops.
6. Modified the control box so power could be fed to remotely
sited
amps. This is not needed if you don't use
remote amps. A 10db
or so amp is needed but in shack units - such as
the Kiwa work
very well.
7. Separate RF and DC grounds are used in the relay/termination
box.
This is to minimize the possibility of noise getting
into the
antennas from the power supply. Suggested
by Andy.
Think that's all. Of the above listed changes only number one
is
absolutely required for maximum performance.
My portable setup - a description.
The base is 30 inches square and is made out of 2x4. A piece of
2x4
is used across the middle in one direction as a brace and across the
top at a 90 degree angle I use a piece of 1x6. In the middle
a 2"
galvinized pipe flange is installed. A piece of 2" pipe, 2' long
is
used as a bottom support for the mast. To help hold the frame
down
2 screw eyes are installed on each side of the inside of the base
frame - total of 8. Tent stakes are used as holdowns. The
ones I
use came from Walmart - I don't remember the brand. They are
about 15" long, v shaped and at the top there is a L shaped hook.
These are driven in right next to the screw eye so that the L hook
goes inside the eye. The same tent stakes are used to support
the
corners of each loop. To secure the ends of the loops at the
base
of the mast I used 4 pieces of 1x3 about 10" long and put them
together so that they formed a square block that slides down over
the 2" base support pipe. On each side of the top of this block
I
use a screw eye to support each end insulator. On each side at
the
bottom of the block there is another screw eye - all of which are
tied together with a piece of wire. This is used as the common
point
for connecting the 4 conterpoise wires. Before I forget the base
is
put together using 1/4 x 3" lag screws.
A note. All base dimensions were simply pulled out of a hat -
there
is nothing scientific about them. From observations so far the
base
could probably be made smaller and lighter and still work well.
The mast I use is called a "Portaple". This is a seven section
collapsable mast made from aircraft aluminum and extends from just
under 6 feet to about 26. The only source for this that I know
of
is Amateur Electronic Supply and at $150.00 plus shipping it is
the most expensive part of the setup - but in my opinion its ease of
use more than makes up for the expense. When using a metal support
you have to be sure it is not grounded or the loop patterns will be
affected. A mast using wood, pvc pipe, etc could probably be
devised
but I'll leave that to others.
The antenna. Just about any type of wire can be used but I would
advise
something fairly heavy as the antenna doubles as the mast guys.
I used
some number 14 teflon insulated wire that I happened to have on hand.
As a top common insulator for both loops I use a 15" or so piece of
1 1/4" pvc pipe. Near the top two holes about 1" apart and at
right
angles to each other were drilled and are used to secure the middle
of
the loops in place. This pvc pipe fits nicely over the top of
the metal
mast. About 6 inches from the bottom I put in several sheet metal
screws
to keep the pvc pipe from sliding too far down the mast. A pvc
end cap
is used on the top. The corner loop insulators are slipped over
the wires
and left to float - don't lock these in place - they automatically
adjust
when the corners of the loops are tied off. At the end of each
loop
segment I use a plastic insulator - the wire is attached to one end
and in
the other I drilled a hole into the body of the insulator and installed
a metal hook which is used with the screw eye in the bottom support
at
the mast to make a "quick disconnect" tiepoint for the loop ends.
Total
length of each of my loops is just over 90 feet - 30 feet on each side
plus whatever extra is needed at the base to make the connections to
the relay/termination box.
The counterpoise. 4 pieces of number 14 bare wire are used.
At one end
of each wire I installed a heavy clip which is used to attach each
wire
to the common point at the mast base. One of these wires is then
run
directly under each of the loop segments and is wrapped several
times around the tent stake that is used to secure the loop corners.
That's it. This setup takes 30-45 minutes to have up and running
so
it makes for an excellent portable antenna. It is also DXpedition
proven - mine was taken to Newfoundland this year and was a huge hit.
If anyone is confused at some point in the future I plan to make a set
of photos available. Please don't write asking for these until
I let
you know they are available and the cost.
73/DX
Al-K 4 G L U
Chincoteague Island, VA
My own experience with K9AY Terminated Loops
I had almost given up on DXing from my high noise location in Guelph,
even with my venerable Kiwa, and various phasing units with other
antennas. In fact, I was using the phasing units for noise reduction,
rather than to steer nulls. In December 1998, Al Merriman built me
the control units of my K9AY loops system. As Al wrote above, his
K9AY system was a huge hit on the Newfoundland Dxpedition in
October 1998. I saw first hand what the system was capable of.
Since then, I have had good DX successes in a highly noisy environment,
including regular reception of TAs in the longwave band, most recently,
July 11, 1999. Given the right conditions, regular summertime reception
of the more common Cubans, Venezuelan, Mexicans and Colombians is
possible. Since 690 kHz was vacated by CBM, I have heard CBU a
number of times with this system.
The antenna is highly directional in its various elements which are
aimed
NE, NW, SW, SE. I hear CBA on the NE element, while killing CHOK,
which appears best along on the SW leg. Since CBL left 740, I regularly
hear CHCM. Prior to that, a usual easterner was CHTN, despite WGN.
I use a Dressler ARA 30 with an MFJ 1025 for phasing, but find that
it
is only infrequently necessary.
I use my system without amplification, relying the internal pre-amps
of my
Drake R8B or my Icom R71A. On MW, I generally operate without the
preamp. In fact, many times I will attenuate the signal. Longwave is
another
matter. There, the preamp is engaged, and AGC is generally set in the
"off"
position.
Real Audio examples of the front to back performance in this antenna
can be heard in reception of CKLW vs. CJBQ. I am roughly midway
between these two stations. The listener can hear the reduction of
CKLW's
QRM as I switch from the SW to NE element and ajust for maximum
CJBQ signal. Another example shows the almost in-the-clear signal of
CHTN, then a sports stadium speech over WGN. Sorry about the poor
sound of the first example. The CKLW example was recorded during
the day, the CHTN example, at night.
Werner Funkenhauser, Guelph ON, July 12, 1999
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