Question: Stellar Labs HDTV/DTV/UHF Outdoor Television Antenna | 30-2155 (302155)

#21
I had been keeping an eye on the Stellar Labs line of antennas for long before they were mentioned on this forum. The 30-2440 is of particular interest to me because of it's dual band capabilities. I do feel the gain claims are inflated. I don't buy the 10 db VHF gain claim. The single dual band driven element could certainly result in reduced UHF gain. Designing a single dual band driven element antenna could certainly involve some compromises.
Steve
 

DW-77

DTVUSA Member
#22
Rick, "Ditto" on the inconsistency between the ad page and the pdf chart for the 30-2155. Maybe they realized that people were not buying it because of the "ridiculous 20dB claim" that looked too good to be true, so they dropped the number to a value that looks less ridiculous, but forgot to update the pdf chart? I emailed MCM two weeks ago and sent a reminder today. Will let you know if they answer.

Steve, in the 30-2440 picture I see two driven elements - a "bow-tie" (UHF) and a straight dipole (VHF).
 
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#23
I don't buy the 10 db VHF gain claim.
But that's for max gain. That doesn't seem high to me. holl_ands has simulated (and simulations are the accurate way to do it) a 13.2 dBi gain on channel 13 for a Winegard HD-7080P, and generally around 13 dBi for 8 element and 14 dBi for 12 element Yagis on either RF12 or 13. That means the 7080P peaks at over twice the signal strength of the Stellar Labs tri-boom hybrid. He also mentioned a 11.6 dBi Gain in Hi-VHF band "somewhere" for the Y10-7-13. I know the AntennaCraft chart says 6.9, but a) that's in dBd, and b) that doesn't say max -- it's probably an average.

You have to always, always distinguish max/maximum/average/min/minimum/no descriptor/dBd/dBi yadayadayada. Maximums really mean very little.

Which VHF-Hi ONLY antenna or other solution? - Canadian TV, Computing and Home Theatre Forums

Yagi Antennas - ImageEvent

R.
 
#24
Rick, "Ditto" on the inconsistency between the ad page and the pdf chart for the 30-2155. Maybe they realized that people were not buying it because of the "ridiculous 20dB claim" that looked too good to be true, so they dropped the number to a value that looks less ridiculous, but forgot to update the pdf chart?
Look, I share your skepticism, but I think the inconsistencies are largely due to incompetence and poor communications between engineering and the marketing department. Here's a simple cover story for MCM: They saw 17+ dB in the PDF chart -- which comes from the Chinese firm that did original research on this, BTW -- and thought it was dBd, so they added 2.15 to get the "industry standard" dBi number, got 19.55 and rounded it off to the nearest integer. All very much in line with the "puffery" which courts hold as lawful marketing. After I, and our expert from Australia, mentioned the 20 dB figure was implausible they decided the 17 was maybe dBi, so somebody else on staff subtracted 2.15 and rounded to get 15.

The people who sell this stuff are not the same people who design them, and they don't speak the same language even when they both speak English. In this case, the engineers are Chinese.

I emailed MCM two weeks ago and sent a reminder today. Will let you know if they answer.
They might answer, but I'll be very surprised if you get an answer! You already ate up all the potential profit they have in one antenna sale by forcing them to read your email. If you were a potential distributor, it might be a different story.

Tri-booms are common in Australia, and our Australian friend thought 15 to 17 dBi was "in line." A larger tri-boom from Televes(sp?) quotes a 19+ dBi gain. That, and all the positive reviews (which don't seem fake to me, for a couple reasons) are enough that I'm willing to recommend those models if the shoe fits.

Rick
 
#25
DW take a look at the PDF assembly instructions for the 30-2240 I could be wrong, but what I see is a dipole with bow ties attached. That alone would be a trick to make work correctly. Possibly by not using a standard 4 to 1 balun? I could have this all wrong. What it looks like to me is a single dual band driven element, a UHF corner reflector, behind that a pair of VHF reflectors, and out front a tri-boom set of UHF directors.
Rick when looking at antenna simulations the dbi gain is raw gain with no correction for impedance mismatch to show net gain.
Formulae for calculation of Net Gain - Canadian TV, Computing and Home Theatre Forums
High SWR has a far bigger impact on reception of ATSC signals then it ever did on NTSC. Reflections on a feed line can cause some strange problems with ATSC signals.
DW It's good that you are looking studying, and doing your homework.
 

DW-77

DTVUSA Member
#26
Rick, thank you for bringing that up. If we look at the numbers from that perspective (confusion created by the dBd/dBi gap + rounding to the "nearest half"), then 15.5dBd / 17.5dBi is OK. Another element that made me be a little skeptical is the title on the chart: "Horizontal polar plot" instead of "Gain Variation"? If we attribute that to the language barrier, then the claims for the 30-2155 may be legit.

As for the 1.5dB difference in gain between the 30-2155 and the UHF side of the 30-2440 (although the booms and UHF reflectors look the same), the explanation could be in the design of the actual radiating element:
folded dipole (2155) 2155.JPG vs UHF bow tie + VHF dipole (2440) 2440.JPG

Maybe, as Steve said, the addition of the VHF rods "dampens" the signal captured by the bow-tie?

Steve, thank you for pointing out the installation instructions. I usually treat those as "approximate drawings for assembly purposes only", but now I zoomed in and noticed that they are pretty detailed and yes, the UHF "bow-tie" and the VHF dipole look like they are joined.

I also agree with you that a "raw gain" simulation, should be adjusted accordingly, anytime the VSWR exceeds 2. Some marketing people are trying to claim that "VSWR is no longer important in ATSC, because DTV tuners are built to deal with multi-path interference, and hence they can also handle reflections", but I don't buy that. If the signal gets reflected back into the antenna, instead of going down the cable, it will never make it to the tuner.
 
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DW-77

DTVUSA Member
#27
A larger tri-boom from Televes(sp?) quotes a 19+ dBi gain.
Televes also makes models that are similar in size to the 30-2155. They also have what seems to be UHF only and VHF/UHF versions of the same booms assembly. Making a comparison between those models and the Stellar labs 30-2155 / 30-2440, it looks like:

1. The gain claims made by Stellar Labs for the seem to fit within a realistic range. Whether they are real or not / accurate or not, that is a different question.
2. Adding VHF elements to an UHF antenna causes a drop in UHF gain of about 0.5 ... 1.5dB, and that seems to be somewhat consistent between manufacturers and models.
 
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#28
Rick when looking at antenna simulations the dbi gain is raw gain with no correction for impedance mismatch to show net gain.
Formulae for calculation of Net Gain - Canadian TV, Computing and Home Theatre Forums
Well, that's certainly the case for the 4NEC2 simulator output usually found on the internet. I doubt it's true for all commercial simulators that an engineer would use. (It's very simple to calculate net gain if you have the raw gain and VSWR output from 4NEC2, so I imagine a good commercial simulator would just do that.) I definitely have no idea whether the charts from China show raw gain or net gain -- or even actual measured gains, as on an antenna range.

That thread you linked was really funny -- poor guy never got an answer to his question! He did get a lot of people posting fancy formulas with no understanding. :rolleyes:

[Edit:] Just to be clear, you do want the simulator to output raw gain, more so than net gain. You want them both, really. Raw gain applies to the antenna itself. Net gain is an atypical minimum that applies only at certain coax lengths. Raw gain is closer to what a user is likely to experience.

Rick
 
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DW-77

DTVUSA Member
#29
Going back to the Stellar Labs 30-2155 - here is one more aspect I noticed:

Putting the data in the table and the gain chart side by side:

2155T.JPG 2155G.JPG

The gain chart starts at 8dB/470MHz and ends at about 13.5dB/860MHz. If that is true, and if the data in the table is also mentioning just the two ends of the band, it could mean that the table shows dBi and the chart shows dBd. Yet, I find it unusual to see a manufacturer advertise gain as "10 to 15.5dB(i)", omitting to mention that, somewhere within that frequency range, gain peaks at 19dB(i).

If, on the other hand, the table shows minimum and maximum gain values (in dBd) and the chart shows dBi, there must be a mistake in the table: it should show 6dB(d) at the low end of the band (instead of 10). That's more believable, but far less attractive due to the low gain at the low end of the band. It may be good for some users, not for me.

Clearly, something is NOT "for real" here. Don't know what; the only way to find out seems to be "buying and trying", unless MCM replies to Rick's email (they did not reply to mine).
 
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#30
Clearly, something is NOT "for real" here. Don't know what; the only way to find out seems to be "buying and trying", unless MCM replies to Rick's email (they did not reply to mine).
Holy smokers, you won't let go, will you! I think you're confused. I sent them no email recently. I sent one to Channel Master, maybe that's what you're thinking of.

Why would you expect their numbers to add up? What if two different simulators came out with two different results? What if the numbers came out different on range A compared to range B? Prove that didn't happen!! It's not like there's any kind of legal definition of the word "gain," you know?

Shoot, the FDA closely monitors food labels. Yet they explicitly allow food manufacturers to lie in the ingredients. One example: they can claim zero trans fat in a product, when in fact there's just a small amount. So what they do is cut portion size down to an absurdly small size, so there's less than 0.5 whatever-it-is (mg, I think) trans fat per portion. Then they advertise "trans fat free!" Nobody can touch them. The FDA regs actually protect the mfrs.

Are you just waking up to the American Way of doing business? Tell the truth now, did you believe "If you like your plan, you can keep your plan"??? :becky:

Rick
 
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DW-77

DTVUSA Member
#31
I was actually referring to your post #13,

I'll email MCM asking for clarification on the pdf figures.
Rick
trying to be a little sarcastic with respect to MCM and how good they are when it comes to getting back to their customers.

It is a good thing there is no "legal definition of gain" ('cause wherever there is anything "legal", there are loopholes, too)! I know the technical definition of gain though and, in the technical world, numbers should add up. If they don't, something's fishy, and that's when the FDA comes in. :(
 
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#32
I was actually referring to your post #13,
You know, I honestly don't remember if I ever sent that email. Whatever their reply, I probably wouldn't believe it anyhow. But the same thing goes for every antenna manufacturer I've aware of. They all do the amplified indoor antenna scam -- you know, where the amplifier chokes off the signal if it's turned off, causing people to think amplifiers are critical components?

Solid Signal came out with the HD-Blade flat antenna with much ballyhoo about the folly of amplifying indoor antennas. Three months later they took down all that idealistic rhetoric and added the amplified HD-Blade to their line. Apparently, there's not a single antenna mfr that can afford not to scam their customers.

And they all add antenna gain to amplifier gain to get total gain -- unless the antenna gain is negative, in which case they just advertise the amplifier gain. If they'll do that, they'll do anything, including faking a few test results here and there.

in the technical world, numbers should add up. If they don't, something's fishy, and that's when the FDA comes in. :(
Yeah, got to make sure those mercury levels are up high enough so's the public will swallow ObamaCareless ... :hungry:

R.
 

DW-77

DTVUSA Member
#33
I agree to every statement you made above. I don't know who started this scamming, but it spiraled its way up and became standard practice, as part of what you called earlier "the American way of doing business".

In a certain way, this is where such a Forum can help. While it is not possible to curb the "creativity of marketing experts", we do get a chance to learn from each other's experiences, and especially from people who know what they are talking about (like You, Steve, and many others).
 
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G

Guest

Guest
#34
mcm antenna

i have one of their quad bay bowtie antennas. it is mounted on a simple mast only about 10 feet off the ground and picks up about 40 stations within 65 miles. but nothing beyond that. i bought a dual quad and plan to mount it about 30 feet up with a rotor and we will see how that does. for the money, its the best antenna i have used in that freq range
 
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