Active and Proximate Antenna Evaluation
Active and Proximate Antenna Comparison
March 5 and 6, 2010
Shelton, CT USA
It was a cold winter night here in Southern New England. I live 10 miles North of Long Island Sound between the coastal cities of New Haven and Bridgeport at 300 feet
above sea level. My favorite, and long-time, low band antenna is an end-fed 160 meter wire that is a quasi inverted-ell and almost a Marconi – let’s just call it an end-fed
with a 24-foot vertical element, and a 120-foot length, South to North. I use this thing for all my 160 meter Ham work and a lot of SWLing.
Earlier this week, I had been experimenting with several 9:1 transformer designs in an effort to optimize the low band performance of this kind of high-impedance antenna.
My goal was to take measurements of the prototypes in the areas of 24 KHz to well above the AM (MF) broadcast band. I finally standardized on a newer design that
shows very little loss, even at 24 KHz! Until my next attack of the self-inflicted “malcontent-obsessive experimenter” syndrome, I’ll continue on my merry way and we’ll just
call this whole thing a “passion.” I scaled down the transmitting version of the 9:1 transformer and am now using an SWL model that works just as well. This is the coupling
device that I used to feed the reference antenna, which I described above, for this report.
Primary standardized test points were the Cutler Naval 24 KHz maritime signals, the 60 KHz WWVB time signals, LORAN at 100 KHz, and various familiar NDB,
navigational beacons above 190 KHz, I always check several known, standard reference stations on the AM broadcast band, which I have used for many years for various
R&D projects, like preselectors, multicouplers, tuners, RF field meters, homebrew receivers, repair testing, and yes, even crystal radios.
I have made this report a subjective analysis rather than loading up the reader with tabulated data, charts and graphs. I believe that in the real world of “actual usage,” it is
far better to exchange information in a conversational format, rather than ask the reader to analyze the offered data. (Techies should note that my reference points are;
50uV for S9; –6dB = S8 at 25uV; S9+10dB = ~150uV; using a Cushman 24A.)
Here in Southern New England, a cold winter night is usually viewed as an ideal DX opportunity, if not just an enjoyable high-signal/low noise, armchair pastime. The
following evaluation is an overall average of such a night (March 5th) and midday today (March 6th).
All test antennas were evaluated at about 8 feet above ground, in the same location of a wooden addition on the back of my home – no foil insulation, noisy wiring,
computers, light dimmers, etc.
Enough caveat. Here’s the report:
1. My homebrew 2-foot square loop constructed from PVC pipe and wound with ½-inch turns spacing has proved to be a reliable favorite www.bobsamerica.com/2-foot-
loop.html. I have a switchable capacitor (C) arrangement so that I can tune down into the NDB lowfer band. It’s efficiency (Q) suffers by doing it this way, and in time I will
build another one that has the switching executed properly with selectable (taped inductor) coil turns (L) and thereby bring the L/C ratio back up to more efficient levels.
This antenna showed a signal level loss of about 2:1 and 3:1 (about 1 to 2 S-units) over the reference end-fed. Some differences were even greater – as much as 3 S-
units, but that wasn’t the norm. It is very quiet and its nulls are extremely deep. You can actually make a local broadcaster disappear into the noise with “pan & tilt.” This box
loop is a bit too big for “family room” residency (depends on who’s opinion you value), but I’m sure a cosmetic adaptation as a deep picture frame or Hummel figurine shelf
could be fashioned to please even the most tenacious housekeepers – the problem would be rotation – oh well, we’ll have to work on that. This loop, like the others, must
be proximate, so that the operator can reach out and tune (re-resonate) the thing after each frequency change. I don’t mind doing that since I’m a twiddler, but I know that
many listeners are minimalists and tend to complain about anything that has more than tuning and volume knobs. But, that’s the trade-off for performance and the
convenience of not having a monster outdoor antenna. (Sidebar to builders: think about a 3:1 planetary reduction drive for the variable capacitor. It makes finding the top of
the signal’s hot spot much less tedious.) This loop is definitely a keeper and will be the baseline design for better generations of LF and MF reception.
2. One of my new sweethearts is the CCrane Twin Coil ™ which I have had all over the house and shop, in various roles, and tucked away in all kinds of stealthy places –
think behind curtains, Velcroed ™ to the back of the couch, and bungee corded to the back of a closet door. I liked the system so much that I have 4 of them! The nice
thing about this animal is that although the tuning head is proximate, the sensor unit (ferrite bar and circuitry) can be remoted. I haven’t taken advantage of its purported
outdoorability since it really doesn’t look like it wants to spend a lot of time in Connecticut’s environment. I guess a good plastic weatherproof enclosure would do, but I
haven’t gotten there yet. I have the 50-foot extension option, but didn’t use it for these tests, because I wanted to keep all the victims in the same area. There is no doubt
that Mr. Justice did his homework and probably a ton of R&D, as this little device is amazingly efficient. I’ve known the attributes of ferrite bar antennas for a very long time,
but confess to not really delving into a “super design.” I have not tweeked any of these units yet, and maybe I shouldn’t, but I did open one up and studied all the goodies.
Nice job. The Twin Coil is certainly worth consideration if it seems like it fits your installation and usage requirements.
This antenna also gave me a 1 to 3 S-unit loss of signal strength, but its noise-ignoring character more than makes up for that. It consistently grabs less signal than the box
loop, but unless you have the test equipment, you’ll never know it. It nulled stations very well, maybe not as sharp a pattern as the box loop, but certainly quite deep, and
that characteristic utility is of immense value when needed. The knob twisting on this one is not at all touchy, primarily due to its fine and coarse knobs. These antennas are
a great value for “plug ‘n’ play” applications.
3. The North Country antenna kit is another little gem that I’ve kind of latched onto as a favorable standby.
I have a review of it here: http://www.bobsamerica.com/Northcountry.html
Let me begin by saying that I am not a huge fan of “E-field” active antennas. I have used a number of commercially available ones, including the Ramsey offering, the old
Yaesu FRT-7700, and a few of my own design. Do they work? Yes. Do they do what is claimed? Yes. Then why am I not professing their great utility? Hey, don’t shoot the
messenger – it’s not the antenna’s fault that there is neighborhood noise. The NC active antenna is a great performer and not at all expensive for what it is and what it
does. If your area is light on E-field QRM, then go for it. But if you have neighbors with touch lamps, lamp dimmers, bug zappers, noisy computers and switching power
supplies, and the all-discouraging leaky cable TV and Internet lines, then you’ll have to do your do-diligence in finding a “quiet” location somewhere around your property.
We have some noise here, but I thank the RF angels every night for its mediocrity. Of all the E-type probe antennas, I kind of sided up to the North Country. Its signal feed
to the radio is down from the end-fed by a couple, to a few S-units, but in a quiet location, the receiver’s AGC circuits will never let you know that. The real advantage of this
guy is that you can find a nice spot for it and lock it down there … permanently. There’s no knobs to turn. Additionally, you are not limited to the AM broadcast band. After a
while, you’ll probably forget that you have an active antenna out there on the patio and just view the coax that enters your house as “just another antenna.” I turned on the TV
while playing with this one and immediately all bet were off. I just cannot have it near any appliance that is in use. If you have a computer nearby, you’ll undoubtedly begin to
think about where in the back yard you can stick this thing. Once you do, you’ll be a happy listener.
4. TERK Advantage ™. I included this one because both of the units I have are like old friends. I had one at my office at work sitting on the windowsill. It was set for a New
York station, about 65 miles to the Southwest, and coax’d back to my radio via its mini-phone jack. Very utilitarian, and very effective. It’s like having a friend who’s always
there – just assumed and seldom appreciated. My second TERK was placed just outside my basement shop window, on the ground under a raised room. It was sort of out
of the direct weather, but I wouldn’t recommend leaving it in that environment. It was also pre-tuned for a specific AM station and used for background listening during my
day-long adventures at the workbench. During this evaluation, the little bugger performed better than I would have guessed. It provided the lowest signal feed to the radio
and its nulling pattern is softer than the CCrane and box loop. But what the heck, it’s a bantamweight warrior that performs admirably for its cost and size. It is a bit touchy
to tune and the knob arrangement, although cosmetically pleasing, is placed in a kind of awkward place. I did not try to test this as an inductively coupled antenna, but
rather connected the coax to it as with the other antennas. This allows much more freedom of rotation and tilt, without any concern for magnetic coupling Q to the radio’s
internal ferrite rod. It will serve the casual AM listener well, but I can’t imagine any situation where a condo or apartment dweller would stop at this when other options could
do better, even within the confines of residency or spousal restrictions – think picture frame loop, or some other creative stealth design.
I did a short comparison test with a night table radio (Sangean 803A) using the TERK and the CCrane. The CC wins, almost every time … sometimes a draw; sometimes
by a lot, but even at twice the price, that difference is worth it. But life is full of compromises. With the CC you’ll have several cables and a wall wart to hide from your
keeper, the cat and the vacuum cleaner, whereas the TERK just kind of sit there. My solution: buy them all. All the CCrane and TERK antennas I have came from that e-pay
place where I paid less than half the retail price. They were all used, and to some degree, scratched, scuffed and scraped – some incomplete regarding cables, instruction
books, etc. You always take some chance as to the seller’s integrity and condition of the device. If you want a nice new one, and are not a “take-apart-er” like I am, then go
directly to CCrane and/or TERK and get a factory fresh one.
Some day I will add a Wellbrook antenna to this list. I have been in touch with
Andy Ikin concerning one of my customer’s needs and will buy myself one of his fine offerings at the same time. But somehow, from the reports I’ve read so far, I have a
feeling that Andy’s loops are going to dominate all the above evaluations – well, maybe not for the bedside radio. We’ll get to that when it happens.
Anyhow, I hope some of this has been of some assistance to at least some people. My testing and evaluation are done at my location, with my equipment, under ever-
changing propagation conditions. My evaluations are mostly subjective and hands-on, real world impressions –
yours may differ. Dad said to never discuss religion and politics in public. I’ll add ‘antenna opinions’ to Dad’s list. Well, to some of us, antennas are almost a religion.
Good signals and happy listening,
|Here's how I see it. Your opinions, applications, needs and wants will probably differ to some degree, but I hope that
this data and evaluation is of some help to those who are searching and researching an alternative to a large outdoor
antenna, or who live with residential restrictions. This evaluation is presented as the subjective results
of tests conducted at my location in Southern New England, USA.