Did it look anything like this? This is a balun from a European UHF antenna.Check out the balun box photo in this post, from what appears to be a Triax (Danish brand) UHF corner reflector antenna:

http://www.digitalhome.ca/forum/showpost.php?p=668830&postcount=65

I think all we see in those photos is the other side of the PCB... or is it really a balun?

I'm just pointing out that the President of Antennas Direct, Richard Schneider (rschneider) (http://www.digitalhome.ca/forum/member.php?u=19890) has been a member at this site for almost 3 years although he hasn't posted in quite awhile. I don't know if he watches for PMs from this site but regarding technical discussions like in this thread it would be nice to hear from him again if he has time. :) I haven't PMed or emailed him but if someone does please invite him back.

I think all we see in those photos is the other side of the PCB... or is it really a balun?

It's the same kind of halfwave balun implemented as a printed circuit. Look closely at the board and you'll see the trace.

Brian

To me its suspicious because its not the same term used by other manufacturers, which means not an apples to apples comparison.

Not all manufacturers express antenna performance the same way. It's up to you to translate. Some manufacturers quote gain in dBi, some quote it in dBd, some quote gain with respect to a tuned dipole (which is not quite the same as dBd), and some quote directivity, which is gain in dBi for an efficient antenna. None that I know quote mismatched gain for receiving antennas, which reflects the performance a user actually observes. But some manufacturers, like Antennas Direct, provide SWR data from which you can calculate mismatch loss and derive your own curve. Although it's not usually done at VHF and above, antenna gain may be quoted in free space or over ground. The latter can boost the gain figure as much as 6 dB. The most inscrutable gain figures are those quoted in simple dB with no explicit reference antenna. As far as pattern, many manufacturers quote front-to-back ratio, which is customary and well defined but ignores lobes not directly to the rear, which may be significant. Better to spec the level of the worst backlobe in the rear half-plane. I think I've seen one or two companies that do that. Better still is to provide a pattern plot, although often the scale is in unspecified linear units (power or amplitude?) Worst of all are manufacturers that provide inflated performance figures regardless of the units they use to express them. This got so bad for ham radio antennas that for many years QST magazine prohibited gain claims in ads. They allow it these days only if substantiated by results from a trusted antenna modeling program. I have seen many FM receiving antennas with gain claims 2-3 dB higher than reality. But so far the figures I've come across for UHF-TV antennas seem reasonable.

. . . to me it suggests professional marketing and legal people defining the term . . .

Next time you're at the library check out some antenna textbooks. You may find directivity mentioned more often than gain. The use of the term suggests to me that whoever labeled the curve had a background in antenna theory, not marketing or law.

Brian

It's up to you to translate.
Thats the problem for the typical consumer. No need for the library, its right here http://en.wikipedia.org/wiki/Directivity

I know what directivity is, and so do the people at Winegard, Channel Master and others who plot "gain" on their marketing charts. Its typical in antenna books, but not on marketing claims on uhf antennas. So why are they being so different from the rest ? And I think (Ill have to check) some of their older literature used "gain", so why change now ? The other thing that strikes me odd about that term in relation to the C2, is that the C2 has such a wide pattern. Not the first thing you think of when you hear "directivity".
http://www.antennasdirect.com/ClearStream2HorizontalPlane.html
When I see something out of the ordinary, it throws up red flags to me, heh. But maybe its just me.

Worst of all are manufacturers that provide inflated performance figures regardless of the units they use to express them. This got so bad for ham radio antennas that for many years QST magazine prohibited gain claims in ads. They allow it these days only if substantiated by results from a trusted antenna modeling program. I have seen many FM receiving antennas with gain claims 2-3 dB higher than reality. But so far the figures I've come across for UHF-TV antennas seem reasonable.

Yep, thats it, there are no antenna police. I too would say most of the UHF gain claims are reasonable, exception being some of the ebay ones and the stuff on amplified "rabbit ears" (sure you get gain, noisy gain heh).

The other thing that strikes me odd about that term in relation to the C2, is that the C2 has such a wide pattern. Not the first thing you think of when you hear "directivity".

Directivity and gain are technical terms, not descriptive words. They convey objective numerical values, not subjective associations. One of my FM designs has -12.5 dB gain with respect to the reference antenna when installed as intended and operating normally. It performs better than other antennas of similar size similarly installed even though its gain value is a large negative number. To understand the information being conveyed, you have to approach these things numerically.

Incidentally, the C2 azimuth pattern does provide some insight. It's hard to determine accurately from the plot, but the -3 dB beamwidth looks like 70-80 degrees. The beamwidth of a resonant dipole is 79 deg. The beamwidth of a longer dipole whose mismatched gain is maximized over the UHF-TV band is 50 deg. The longer element provides collinear gain. The C2 appears not to take advantage of this trick, which is a cheap and easy way to pick up 1-2 dB of gain. Maybe their loop geometry precludes it.

Brian

Maybe their loop geometry precludes it.

Yeah, I think thats the nature of the loop.

Anyone,
Do have some detailed dimensions ? From the Best Buy display, I got the exact reflector dimensions, 1 1/2 X 2 inch mesh, 12 X 19 1/2 inches with 45 degree bent 1 inch edges. From others I got the 8 inch outside diameter and 5 inch inside diameter of the loops. It looks like the reflector to element spacing is 4 1/2 inches. Is that correct ? Do you have some pictures and dimensions of whats under the round plastic cover ?

300ohm, since the C4 is just two C2's mounted side-by-side with flat aluminum phasing llines between them and an integrated balun, I'll bring it home this weekend and get the measurements from it, with pictures. Let me know exactly what measurements you need.

The reflector to driven element distance.
The distance separating the two 8 inch loops.
Pictures of how the two loops are connected together.
(If the two hoops are connected by phasing lines, the distance between them, center of wire to center of wire.)
The gap distance of each hoop.
The gauge of the metal in the hoops, or a good guess.
Plus
Confirmation of my above measurements.

300ohm: Do you think if the two crescents had 1/4 WL (100 mm) between them that it would reduce the SWR. I know this would not match the size that they are using.

It may, it doesnt take a whole lot to change the SWR. It would also probably change where the peak gain occurs.

Just some further reading on antenna directivity:

http://www.antenna-theory.com/basics/directivity.php

300ohm, the plastic covers are glued together and so I was not able to remove them without risk of destroying the covers, sorry. But other measuremnts are shown below. Your's are very close to what I measured.

"reflector dimensions, 1 1/2 X 2 inch mesh"
- measured 1 9/16 X 2 1/16

"12 X 19 1/2 inches with 45 degree bent 1 inch edges"
- measured 11 3/4 X 20, 45 degree w/ bent 1" edges

"From others I got the 8 inch outside diameter and 5 inch inside diameter of the loops."
- measured 9 1/4 OD (edge of plastic cover), didn't get an ID measurement

"It looks like the reflector to element spacing is 4 1/2 inches."
- measured 4" from front edge of reflector to center of element plastic cover

Hi,

I'm the engineer that developed the Clearstream geometries for Antennas Direct. I don't usually have time to post to forums but I do monitor some of them from time to time looking to see feed back from consumers on my designs. I saw this thread I thought I'd take a few minutes to try to clear some of the FUD (fear uncertainty & doubt).

First of all, you don't need to worry, Antennas Direct is not trying to hide anything by showing a plot of directivity. The curves are generated using state of the art computer simulation software (Remcom X-FDTD). We are not afraid to show curves. That should be encouraging to you since many consumer grade antennas don't come with any tech data whatsoever.

We also test antennas using network analyzers (e.g. HP 8510C) and do field testing using spectrum analyzers (HP 8569A and HP 8566B) and consumer grade receivers. Antennas Direct is really doing serious antenna engineering and is trying to innovate in a field that has not changed substantially in a long time. We're a small company and sometimes the science and marketing get out of sync but rest assured we're doing all we can to get you good products.

The Clearstreams are based on the classic idea of a full wave loop in front a reflector. This was known for years to produce about 9 dBi gain (infinite reflector) if you could properly feed it.

Note that there is nothing wrong with specifying gain in dBi as oppose to dBd. The manufacturer isn't just trying to inflate numbers. dBi is actually the most commonly used reference in most of the professional antenna literature (e.g. IEEE). It is also the figure provided by all the simulation packages. The dipole reference is fine if you're doing field or lab testing. Directivity equals gain dBi for an antenna with no loss (not including mismatch). The simulator was configured to assume perfect electric conductors hence the plot labeled with directivity instead of gain. I'll talk to the marketing folks and see if I can get a new one with gain on the label...

I applied computer simulations, optimization algorithms and lab testing to figure out how to size and taper the design with a small reflector so that it would perform well across the whole post 2009 UHF DTV band. UHF is targeted since that's where 75% of the stations are transmitting and since most consumers want smaller rather than than larger antennas.

My simulations and tests have shown the C1 generally offers performance as good as a two element bow tie in about half the volume. The C2 is comparable to DB4 across UHF but smaller and better on VHF.

If you look at properly executed simulations you will find that the bow-ties don't reach peak performance until the frequency is above 700 MHz. This is because they were engineered for the old band allocations. The Clearstreams achieve even balanced performance across the new band allocation. The C1 and C2 offer a horizontal plane 1/2 power beam width of about 70 degrees. Unlike many antennas (e.g. bow-ties) whose beams get narrower as the frequency is increased, the beam width of the Clearstreams is almost constant across the band. This makes pointing and installation easier for most consumers.

The Clearstreams also generally work better on VHF. This is a characteristic of the loop geometry and the fact that there is a phase cancellation effect for frequencies below design passband on the four element bow-tie arrays.

We do not specify VHF performance on the C1, C2 and C4 because it is below the design passband and the PCB baluns do not produce a balanced antennas at low frequencies. The latter however enables reception from what is known as feedline radiation. While this is usually avoided for transmitting antennas, on receive it can in fact enhance reception on the out-of-band (i.e. not in design window) frequencies. The effect is quite dependent on installation specifics so your "mileage may vary" but this is still sufficient for many consumers near the VHF stations.

For those wanting to receive weaker VHF stations a separate VHF only antenna with a diplexer should solve the problem. Antennas Direct C5 is a derivative of the C1 for high VHF and should be on the market in a few months.

I know this is a bit long for a first time post but I hope that you find it helpful.

I'll try to check in again from time to time.

Best Wishes,

John Ross, Ph.D., P.E.

First off, many thanks JER3 for posting.

I'll talk to the marketing folks and see if I can get a new one with gain on the label...
Thanks, wouldnt the term "Directive Gain" be more descriptive to most ?

Also, holl_ands pointed out "BTW: In C2 & C4 Gain/VSWR Charts, Y-axis is trying to do double duty.
But VSWR should be labeled as a scalar number---NOT dB like Gain:"

I think you can see why picky people like us, who have wasted many useless hours reading antenna marketing literature in the past, kind of like to pick them apart, heh.


Unlike many antennas (e.g. bow-ties) whose beams get narrower as the frequency is increased, the beam width of the Clearstreams is almost constant across the band. This makes pointing and installation easier for most consumers.
Exactly, and what you just said should be used in the marketing literature. Its a good selling point. But reading over some of the literature on it now, almost implies the reverse, until I look at the pattern.

I know this is a bit long for a first time post but I hope that you find it helpful.

I'll try to check in again from time to time.

Best Wishes,

John Ross, Ph.D., P.E.John, you are more than welcome to post here as you see fit, and it is a pleasure for all of our antenna enthusiasts to "talk shop" with a professional antenna designer. I hope Richard can come back to this site too for some Q&A sessions if he might have time.

cheers :)

JER3: Fol. are the principal problems with information provided on A-D's website.
Perhaps you can get someone to correct them:

1. ClearStream summary brochure and webpage claim 14.8 dBi Gain for C4,
which is (improbably) 4.6 dB more than the C2:
http://www.antennasdirect.com/pdf/ClearStream.pdf
http://www.antennasdirect.com/C4-Clearstream-DTV-antenna.html

BUT, plot in fol C4 brochure shows 12 dBi (+/- 0.25 dB) Gain on second page,
which is repeated on first page, but called "Directivity":
http://www.antennasdirect.com/pdf/C4-sellsheet.pdf
That is nearly a 3 dB discrepancy that needs to be resolved.
[And certainly represents a major hole in A-D's credibility.]

2. The azimuthal pattern plots are nearly illegible, making it impossible to see
if the concentric circles represent 1 dB, 5 dB, 10 dB or whatever step size...
[Why hide the REAL performance????]

ClearStream C2 and C1 Brochures have same azimuthal plot legibility problems,
and difficult to read legend for three freqs in the big C2 azimuthal plot, although
I can barely make out the freqs are 500 (blue), 600 (green) and 700 (red) MHz
with 5 dB per circle step in fol. chart:
http://www.antennasdirect.com/C2-Clearstream-DTV-antenna.html
http://www.antennasdirect.com/pdf/C2-sellsheet.pdf
http://www.antennasdirect.com/pdf/C1-sellsheet.pdf

3. Front-to-Back Ratios are measured in dB, not "dBi".
Y-axis for VSWR plot should be a scalar label, not "dB".

4. Even if numbers are negative, it would help to know VHF performance,
esp. given A-D's published claims of some sort of VHF performance, even
if you are relying on common mode pickup and/or cable leakage (really???).

5. The above brochures are not accessible directly from corresponding webpages.
[Is A-D intentionally hiding information????]

6. There can be differences between gain (directivity?) calculated in 3 dimensions
(which includes gain due to reduced overhead response) versus directivity (gain?)
calculated in only the azimuthal plane. There is also a difference in gain
calculated with horizontal, vertical and circularly polarized signals.

It would help if we knew which A-D was calculating....
Esp. for those of us who grew up using "directivity" to mean gain in azimuthal
plane and "gain" in 3D volume, knowing full well text book definitions would
require specifying which was intended.

PS: You probably get them from overseas, but note 91XG gain spec doesn't say
whether dBi or dBd:
http://www.antennasdirect.com/91XG_HDTV_Antenna.html
At least it says "Max Gain", so all we now need to know is "Min" and "Typical"
and preferably some Gain/VSWR/Azimuthal charts to achieve some credibility.

Any guesses on when A-D's Smart Antenna will be released????
And how well it will or will not perform for Hi-VHF???

Thanks for the feedback. I'll look into the issues you've listed. We're not trying to hide anything but its obvious that we're not communicating as well as, and consistently as we could.

I did not develop the 91XG, but I do have X-FDTD simulations for this model. I will see if we can get that data out there.

Its helpful to remember that antenna simulations and range measurements have a degree of uncertainty. In the case of simulation data, patterns are generally more accurate because they result from an integration of current. The integration smooths out errors. Input impedance is subject to more variation since its is computed from current and voltage at a single point so errors aren't averaged out.

Range time is very expensive so we use calculations for patterns and then verify that measured VSWR is within acceptable limits. This gives us confidence that our computer models are reasonable. Patterns are computed in free-space. Patterns in the installed environment will of course vary from this fiction. We do comparative field testing among antennas to convince ourselves we've got things right.

Real world performance and simulation / lab testing usually correlate well but not in every situation. Ultimately, the signal delivered to the tuner is a complicated integration of signals arriving from all directions, polarizations, and frequencies weighted by receive antenna pattern, passband and polarization functions all of which are aspect dependent and phase /time sensitive. Parameters such as gain, VSWR, etc only hint at what an antenna does or doesn't do to the incoming signals. Given this and the fact that the signals have been convoluted by a complicated propagation path, and polluted with both in band and out of band noise and interference, I'm constantly amazed that things work as well and as reliably as they actually do.

In the end, probably the best measure of an antenna is how consistently it works for most people. Our return rates are some of the lowest in the industry, often vastly lower than our competitors, so I believe we are doing some things right. Of course we are always working to improve our products and process and have a goal of regularly obsoleting our own products rather than waiting for someone else to do it for us. This is an ambitious goal for a small company especially given the the current economic environment.

All antennas are a design compromise of one sort or another. From the business perspective, we must target development efforts at solutions that work well for most consumers with lesser efforts and resources directed toward niche solutions. Realize that for the vast majority of consumers the key selling point has little or nothing to do with esoteric things like gain, VSWR, etc. Instead, they are more interested in size, aesthetics (i.e. wife-acceptance factor) and ease of selection and installation. Of course it still must work or the return rates would kill the product, if not the company. Cost also is a huge factor. Consider that large retailers want to buy at 70% or more off list for accessory items (the things that actually keep them afloat - flat panel TV's don't!) and then you realize that the technical issues about an antenna are actually sometimes the easier problems to solve!

I have been working on smart / reconfigurable antennas for over a decade and I'm guessing that we may have another 5 to 10 years before there is widespread adoption of the technology. That said, we now have demonstrable prototypes of a very sophisticated indoor smart antenna that employs tunable microstrip disc elements. Unfortunately, our ability to launch any smart antenna product is uncertain due to compatibility and implementation issues within the installed base of enabled receivers (mostly coupon boxes) and lack of commitment from the major television manufacturers to include well executed CEA909 / 909A interfaces and firmware in their flat panel televisions. Suffice it to say that there are substantial risks in rolling out a new product in a nascent market, which may or may not be ready from both technical and consumer acceptance points of view. We are capable of, and interested in, taking smart antenna solutions to market, but for now we are still cautiously assessing the situation. That is about all I can say for now.

Again, I hope you find my information and insights helpful.

John

That is about all I can say for now.

JER3 has a good article about it here : http://www.spectrum.ieee.org/feb09/7328/4