From: randall@informix.com (Randall Rhea)
Newsgroups: rec.radio.amateur.misc
Subject: Re: Iso-Loop info?
Date: 8 Sep 92 20:30:18 GMT
Organization: Informix Software, Inc.

price@cod.nosc.mil (James N. Price) writes:

>-------
>A friend is considering buying an AEA Iso-Loop to solve his age
>old problem of putting up an antenna in a no-antenna area.  But
>he'd like to get some first hand testimonials (not just the ones
>in the advertising literature) before plunking $300 on the counter
>to buy one.

>I think this has been discussed before on this newsgroup, but I
>didn't read it--sorry.


After reading the ARRL Antenna Book on loop antennas, I think that
I will try a small loop myself.  

Here is an excellent response I've received to the same question:


From uunet!MVS.OAC.UCLA.EDU!CSMSCST Sun Aug 30 13:36:49 1992
Status: OR

I'm a happy user and a big fan of the AEA Isoloop antenna.
Whenever I post a comment to the net about it, I get several
requests for more information.  Perhaps the following summary of
my experiences will be general interest.  If not, hit your KILL
key now, as this is a bit long.

AEA is Advanced Electronic Applications, in Lynnwood, WA.  AEA's
Isoloop antennas are small loop antennas which cover 14-30 Mhz
(original model) or 10-30 Mhz (new 10-30 model). You can find
their ad in most any issue of QST or CQ.  The concept behind this
type of antenna is well described in the ARRL Antenna Handbook,
Chapter 5, "Small High Efficiency Loop Antennas for
Transmitting".  That reference contains enough information to
build your own version, in any of several sizes and frequency
ranges.  A key point, stressed in the reference, is that a small
antenna, if constructed properly (efficiently), will couple RF
into the ether as well as a full-size omnidirectional antenna
such as a 1/4 wave vertical or half-wave dipole.  The inherent
losses in this type of antenna are quite low.  The antenna may be
mounted horizontal, which gives an omnidirectional pattern, or
vertical, which yields a figure-8 (possibly useful for nulling
interference.)  Big-gun DXer's will tell you nothing this small
can work.  They will continue to tell you this even after you
work a couple hundred countries with it.  Says something about
their mind set.  Ignore them.

AEA's original Isoloop consists of small diameter aluminum
tubing formed into a 30" (75cm) square loop.  Unfortunately, the
tubing is in segments held together with clamps; this mode of
construction tends to be lossey.  The 10-30 model consists of a
continuous 1.5" (4cm) wide heavy aluminum strap formed into a 38"
(1m) diameter circle; this is optimum (low loss) construction.
Both antennas are fed with 50 ohm coax through a simple coupling
loop, which may be slightly tweaked to minimize SWR on a favorite
band.  (I have no trouble getting 1.2:1 or better on all bands.)
The opposite side of the loop is open, and the ends are connected
to a motor-driven variable capacitor, which is manipulated from a
control box in the shack.  The antenna is a simple LC circuit,
operated at resonence (although I suppose that can be said of all
resonent antennas.)  LC circuits have high circulating currents
(depends on Q), hence the importance of no joints.

To tune the antenna, one simply runs the motor back and forth
listening for a noise peak in the receiver.  These antennas are
very, very narrowband compared to full-size antennas, and the
peak is very, very sharp.  The 10-30 model has a set of four
LEDs connected to form a simple audio voltmeter.  There is a
jack for plugging in receiver audio.  The manual, however,
neglects to mention this, leaving one to puzzle over how the
LEDs know when the antenna is tuned.  AEA provides a schmatic
of the control box which answers the question quickly - no magic.
I have no use for the LED voltmeter - the receiver noise peak is
extremely obvious and simple to use.

The useable bandwidth of the Isoloop depends on what you are
driving it with.  My Kenwood TS-940 was very pickey, and wanted
the loop exactly resonent.  My Yaseu FT-1000 is much more tolerant
of slight mistuning, and works a lot better with the Isoloop.
(Actually, there's no comparison between the 940 and the 1000 in
several other ways as well - the 1000 is a superior piece of
gear.)  On 20m, with the 940, bw was about 20 Khz.  With the
1000, bw is 50 Khz, assuming you are willing to hit the AT tune
on the xmtr at the ends of the range.  On 10m, bw is 150 Khz or
so.  You will generally find receiver sensitivity propmts you
to repeak the Isoloop before your transmitter refuses to load
into it.  Retuning is not a hassle for me since I usually work
in the DX CW segments, which are narrow.  If you work mostly
SSB and QSY a lot, it would be more of a bother.

The motor speed on the original is too slow, even at the fastest
setting.  The 10-30 has several speeds -- too fast, faster than
that, and warp speed, which will take you from DC to microwave in
a split second.  Both models have a lot of hysterisis
(engineeringese for play in the gears), so by toggling back and
forth, one can find the sweet spot.  There is no way to memorize
settings for quick QSYs.

My Isoloop is located on the balcony of the 4th and top floor
of a large apartment complex.  The building has a lot of steel in
it.  I have a clear shot ESE thru WNW - Africa, SA, and So.
Pacific.  Europe is back thru the building.  I work Europe, but
not as well as the clear directions. Also, there is a range of
tall hills/small mountains a couple of miles north of me, further
spoiling that direction.  JT (Mongolia) is in my worst possible
direction - that's probably why I haven't worked it.  I don't
even hear it when others are working it.  On the other hand, I've
worked 4S7 (Sri Lanka, used to be Ceylon) long path 3 times - LP
is SE, a good direction from here.  Moral: Location matters, but
you may be surprized.

My Isoloop is mounted on a self-supporting stand originally sold
with a children's mini basketball game.  It is abt 5 feet off the
floor.  (See warning below.)

The construction of the original model is best described as
somewhere between lightweight and flimsy.  The 10-30 is much
beefier.  However, it has its own set of problems.  First of all,
the 10-30 is at least twice as heavy.  If you plan to mount it in
a "lollypop" configuraton out at the end of a boom as in some of
AEA's pictures, be advised you will need a STRONG boom and mount.
Also, the large black plastic case is poorly engineered.  It is
held together by only a couple of bolts.  Mine is somewhat bowed,
and doesn't seal worth a darn.  There is no way to use the bolts
to tighten it.  Also, the Isoloop held to the mast by a single
U-bolt.  I have trouble with mine wanting to slide down the mast.
It should be 2 U-bolts.  Tightening the U-bolt tends to spring
the case even further.  I plan to run a bead of silicon seal
around it.  Another compliant is that the motor cable is
permanently attached to the case in the 10-30; the original one
had a plug.  This causes headaches if you want to run the wire
inside the mounting pipe, for example.  (Reason for the change
was that the plug on the original model wasn't waterproof, or
even water-resistant, and I suspect it was prone to leaking and
corroding.) Fixed with wire cutters, soldering iron, and an
inline plug and socket.  There is a UHF plug for the coax.

I had my 10-30 on backorder for several months, and got one
of the first ones when AEA finally started shipping.  I got a
call from AEA's CEO, wanting to make sure I was happy with it.
Now that is a class act.  Unfortunately, he talked with my
answering machine, not me, and didn't leave his number.  He
is a ham - if anyone has his call handy, I'd like to send him
a copy of this note.   He left AEA's tech support number, but
I don't need support - I understand how antennas work.  (You
put RF into the little round thingie and DX stations hear you
and send RF back.)

CAUTION - do NOT locate this antenna where people or pets might
come in contact with it.  If you have small children, be
especially careful.  If you touch this antenna while
transmitting, you will get a NASTY RF burn.  (The same is true of
verticals and dipoles, but they tend to have their high voltage
points at their tips, which are usually up in the air and away
from fingers, paws, and noses.)

The narrow bandwidth charactersitic of this antenna makes it a
effective harmonic filter, unlike a dipole which will efficiently
radiate your 3rd and 5th harmonics right into nearby TV's.
However, much RFI is due to fundamental overload, not harmonics,
and operating with this antenna low and much closer to your
neighbors' electronics than would be the case with a big beam
high atop a tower, may well give you worse RFI problems.

My FT-1000 puts out 220 watts.  The Isoloop is rated 150.  This
is presumably limited by the voltage breakdown point of the
variable cap.  I usually back the drive off a touch, but from
time to time operate with full output.  I have never had a
problem and have never identified an arc over.  I realize
that this invalidates the warantee, and if I burn the cap,
I wouldn't expect AEA to fix it.  But it seems conservatively
rated.

Now for some results.  I am one of those wierd people who gets a
kick of picturing some fellow ham half way around the world bent
over his/her rig, picking my signal out of the air.  I operate
largly CW.  I obtained my original Isoloop in October of 1990.  I
replaced it with the new 10-30 in January.  In 20 months, I have
worked 211 countries and confirmed 195.  Of these 211, I have
149/129 on CW, and 162/146 on SSB.  (Well, a lot of DXers operate
only phone these days.)  I have worked 38 zones, 35 each on phone
and CW.  Broken down by band, I have 137 countries on 10m, 100 on
15m, 116 on 20m, and since January, 21 countries on 30m.  I just
worked YX0AI (Aves Is.) Dxpedition on 15 CW, amidst a monster
pileup.

My point here isn't to brag - others on the net have more im-
pressive stats running QRP.  The point is that given no space to
erect a monster beam, or even a dipole or vertical, one can still
have a tremendous amount of fun.  The Isoloop has made it
possible for me to enjoy ham radio in an otherwise impossible
situation, and was worth every penny I spent on it (them.)

The Isoloop is not a miracle antenna.  It is roughtly equivalent
to other omni antennas, such as dipoles.  It may have a little
lower radiation angle, etc etc, but given that it is generally
used in very space-restricted locations, its pattern is greatly
distorted by the surrounding building anyway.  My DXCC stats show
mine works.  However, do not assume this antenna (or any other
similar antenna) will compete with a large monobander mounted 30m
(100') in the air and driven by enough RF to make it glow dull
red (2KW or whatever those guys run).  That setup will have a
25-30 DB advantage (10db antenna gain, 13db power, 6DB+/-  for
height) over you, and that's like the difference between 2KW and 2
watts (to the same antenna).  The DX will hear you when the big
boys go away, or when you outsmart them.  These are basic skills
familiar to any QRPer.  Running QRP (or more accurately QRP ERP)
is character building, and will really hone your operating skills
(if it doesn't drive you crazy first.)  Would I trade for one of
those big gun stations?  In an minute...  But I bet I'd get less
enjoyment and many fewer thrills that way.  I about fell out of
my chair when Aves Island answered, or Jacky (3B8CF, Mauritius
Is, off east Africa) gave me a 569 on 30m the other evening.

I found that my Isoloop significantly outperformed a tuned dipole
fed with open wire which it replaced. (The dipole was about 20'
long overall.)  It also was much better than my attempts to use a
mobile whip.  The Isoloop has very, very much less unbalanced RF
flowing on the coax - I used to get RF burns when my nose touched
the mike using the dipole.  The difference in noise pickup using
the Isoloop is amazing.

Keep the limitations in mind and you can have a ball with this
antenna.

  -- 73 de Chris Thomas, AA6SQ (ex-WA6HTJ) (CSMSCST@MVS.OAC.UCLA.EDU)

-- 

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Randall Rhea                                        Informix Software, Inc. 
Project Manager, MIS Sales/Marketing Systems    uunet!pyramid!infmx!randall
Newsgroups: rec.radio.amateur.misc,rec.radio.cb,news.answers