Incredible Reception Story!

DW-77

DTVUSA Member
#21
Apparently so. I stated nothing about raw gain, or net gain, or any specific type of gain. I just passed along some numbers from multiple third parties, which reportedly came from Channel Master.
I understand now that you were referring to the raw vs. net gain aspect. I was referring to the availability of data (and that is why I re-quoted the "pulling teeth" part). Sorry about the confusion.


Just take a look at any simulated data. There are multiple examples of small variations like that. ...
Sure, let's do that! Here is the gain vs. Freq. chart for the Hacked 4221HD (simulation done by holl_ands):

4221HD-Sim.JPG

No "warts"; but it could be that applying the mods "cured the warts".

Here is a chart made by me, based on the data in the table (which was reportedly originated from the manufacturer), showing the 4 CM422x antennas (4221, 4228 and their HD replacements):

422x.JPG

The "old" and excellent 4221 and 4228 antennas show smooth gain variation across the usable band, while the newer ones have multiple peaks and valleys? For 4221HD, we are looking at 2.5dB gain difference from Ch.27 to Ch.43, and another good dB down and back up from Ch.43 to Ch.60. This should not happen (unless there is a problem, either with the HD antennas, or with the numbers). BTW, the gain for 4228HD also goes beyond "small variations", and the values shown in the table for 4228HD Beam Width (VHF section) look weird as well; which are more indications that this data should be looked at with caution; not taken for granted.


You should immediately adopt my definition and use it forthwith in all your posts. :thumb: You'll be more accurate. There's nothing in the dictionary about an obligation to publish repeatedly on demand.
To me, "publishing" means making something (reading material) available to the public (like putting data in a catalog or on a web-page, or providing it on demand). You are saying keeping data secret, refusing to share it when asked (with the exception of someone who had to "pull teeth" to obtain that data), can also be considered "publishing". I do not agree with your definition; yet I respect it; not saying you should adopt a different one.


I think there is overwhelming evidence that it works, yes. You have solid theory going in behind it. Then you have multiple reports from people on that site that it worked. Then you have rabbit73's hard data. Finally, there is this statement from well regarded simulation expert holl_ands...
I am not disputing whether the hacks work or not. I appreciate the work done by Rabbit, and I realize that he did the best he could have done given the circumstances. I also acknowledge the other evidence that the mods do improve the gain of the 4221HD. But, at this point nobody can tell "by how much". In a lab, with calibrated test equipment, technicians do 3 or more measurements and take the results through certain statistical filters before they call them "reliable". I hope you agree that a single test done with OTA signals as reference is not conclusive enough to be able to state that the mods bring xxdB gain improvement.


It's safe to assume holl_ands did simulations with and without the mods. He had no reason to put his reputation on the line without that simple check. It's just a few parameters to change.
I am aware of the simulation he did on the antenna with mods. If you know of a simulation for the antenna without the mods somewhere, that would be a good reference for getting an idea of how much the mods help.

We drifted away from the topic, though. This conversation was about the Sigma6HD antenna. Based on the numbers that are available, I stated that it is somewhat better than the 4221HD. You dismissed the initial comparison I did (using the data obtained by holl_ands' simulation); suggested we should use the higher values shown in the table (reportedly from CM), also bump those values up (by an unknown amount attributed to the mods), and declared: "4221HD wins". My next points were:
- Do the numbers in that table look realistic to you? I showed why I think they do not;
- Do we know how much of an improvement the mods bring? The answer seems to be "not really".

I also like the 4221HD. It is more compact, less expensive, available from more than one source, which are all important advantages. But this thread is about a very unusual application, that involves reception under extreme conditions, where any additional dB can make a difference; therefore all my posts were based on documented performance data (not on my assumptions or personal preference).
I am not trying to beat a dead horse, just trying to make sure I am not misunderstood. :)
 
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#22
zzzzzzzzzz... What was the subject again?

Oh yeah, sorry. You asked "How many other UHF antennas have you seen out there with a gain variation like this?" So I provided two links with a couple dozen antennas, several with gain variations like that. Then you pick out one antenna -- the same antenna -- and make a fancy graph with no variation. :huh:

To sum up, I have no reason to believe the smooth graph is closer to reality than the lumpy one, but you win. :bowdown: You make fancier graphs than I ever do (or care to -- I guess I trust graphs even less than raw data).

I can think of a simple reason physical measurements might take a dip like that, with a given length of coax. I'm sure you could too, if you put your mind to it.

On the difference between the 4221HD as shipped and the modified version, I read theory *somewhere* saying just pulling out the balun a half inch should add about 2 dB on average. Another guy named mugwai(sp?) said he reversed the balun mod and lost about 3 dB throughout on his spectrum analyser, or strength meter, or whatever it was.

I remember now -- holl_ands said he simulated the unhacked 4221HD, but didn't post the results, cause he knew they would be inaccurate. Putting the balun so close was really a stupendous goof -- probably done just to stuff the antenna into the box for shipping.

That's correct -- I read all 22 pages of that thread about two years ago. Mclapp(sp?) was another one who did some simulations, but I don't know if they're in that thread, or if you can even find them anymore on the net. There was another one ... name escapes me.

I thought you summarized it well when you said:
DW said:
"A fair comparison "on paper" becomes pretty difficult, because confusion dominates when it comes to antenna documentation in general..."
But you seem to trust people MORE when they spit out gobs of data on request. My experience is exactly the opposite. The gabbiest, most encyclopedic president in my lifetime was Bill Clinton. Man couldn't stop talking... breath taking knowledge on practically any subject. Problem is, he made it up as he went along!! Still an impressive talent though. :becky:

Rick
 

rt1

DTVUSA Member
#23
where can i go to read on the basic knowledge of how tv antennae's work.....
I read on here about gains and all this other tv antenna lingo...and have not much idea what it all means.
 
#24
where can i go to read on the basic knowledge of how tv antennae's work.....
Excellent question! Here are some sources on the internet, in order from simple to a little more detailed:
Antenna (radio) - Wikipedia, the free encyclopedia
Antenna Basics
The Antenna Theory Website

The glossary on hdtvprimer is also very useful:
Glossary A to F
Glossary G to Q
Glossary R to Z

Finally, the inventor of the Kosmic Quad antenna, Escape Velocity, lists his favorite text books here:
EscapeVelocity Blog: EV's Best Television Antenna Books

Some of those texts can be found on the internet in PDF form (watch out for the copyright police :rolleyes:). The google search term filetype:pDF is useful.

Any other suggestions?

Rick
 

rt1

DTVUSA Member
#25
Excellent question! Here are some sources on the internet, in order from simple to a little more detailed:
Antenna (radio) - Wikipedia, the free encyclopedia
Antenna Basics
The Antenna Theory Website

The glossary on hdtvprimer is also very useful:
Glossary A to F
Glossary G to Q
Glossary R to Z

Finally, the inventor of the Kosmic Quad antenna, Escape Velocity, lists his favorite text books here:
EscapeVelocity Blog: EV's Best Television Antenna Books

Some of those texts can be found on the internet in PDF form (watch out for the copyright police :rolleyes:). The google search term filetype:pDF is useful.

Any other suggestions?

Rick
Thanks for the info...i will be sure to read.
 

DW-77

DTVUSA Member
#26
... I have no reason to believe the smooth graph is closer to reality than the lumpy one...
According to the Resonant Circuits' Theory (antennas are resonant circuits, too); sharp gain variations induce signal distortion. Nobody wants that in a TV antenna, therefore a properly designed one shows smooth gain variation. BTW, in the comments that come with the simulation plots you referenced, the authors mention that those glitches you used as examples are probably caused by errors in the simulation software.

... I can think of a simple reason physical measurements might take a dip like that, with a given length of coax. I'm sure you could too, if you put your mind to it....
You are absolutely right, and people who are familiar with working in an RF lab know that, when such a cable induced resonance (or impedance mismatch) happens, the entire set of measurements made with that setup is fundamentally flawed + totally irrelevant. At that point, a competent engineer would work to identify the cause of the erroneous results, fix it and re-run the measurements so that they are accurate.

... I remember now -- holl_ands said he simulated the unhacked 4221HD, but didn't post the results, cause he knew they would be inaccurate.
I remember reading that, too.

... But you seem to trust people MORE when they spit out gobs of data on request...
Not "gobs of data", my friend; relevant data is what I am looking for. Of course the numbers can be "doctored" to look better than they really are, and that is why I tend to rely on my "technical common sense", to sort the values that look realistic from the ones that are clearly flawed. I do not expect to be always right, because first I'm human, and then I'm an engineer, not a lawyer :)
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#27
Okay kids -- I have been enjoying your numerical 'Chess game' ... but has it crossed your minds that your 'theoretical' results have very little to do with reality?

I am not an Engineer, I am an Imagineer so I am not locked into your assumptions. You may promote and argue reasons why something will not work or something else will or must work better but I call BS.

Antenna height NOT GAIN usually wins. My (enormous) 16-Bay Hoverman proved to be a crap antenna compared to my (tiny) DB-2 because it was too large to be raised high enough to capture signals AND because it captured too much multipath. Plus, the Hoverman's tremendous gain could not overcome the lack of signals at the lower height. Screw 'assumed' dB gain numbers. I can receive a translator 86 miles away on a tiny DB-2 elevated to a crazy height which proves my point.

Jim
 
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#28
Okay kids -- I have been enjoying your numerical 'Chess game' ... but has it crossed your minds that your 'theoretical' results have very little to do with reality?
Nope. I've been trying to convince this guy he should have less faith in numbers, but I can't go as far as that.

I am not an Engineer, I am an Imagineer so I am not locked into your assumptions. You may promote and argue reasons why something will not work or something else will or must work better but I call BS.
But nobody said that. At least I know *I* didn't say that! Here's what I said: "you could put together a setup that theoretically should work as well as his "Super Yooper" for $300 - $380" [emphasis in the original].

This is the theory page. Does our super moderator feel we should shut it down!?

Antenna height NOT GAIN usually wins.
When trying to commit suicide by jumping off a tall building, skyscraper height NOT GRAVITY usually wins. Really struggling to see your point here, Jim. :behindsofa:

Hey but you gave me an inspiration! I now have a theory on why the Super-Yooper might work in da U.P. It's related to SNR, height and location. Highly theoretical. Jim won't like it. :evil:

Rick
 
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#29
So DW, now we know you are an engineer. Glad to have you aboard! Are you also saying you have worked in an RF lab for an antenna company? Care to divulge which one?? Or was this just academic experience?

Rick
 

DW-77

DTVUSA Member
#30
So DW, now we know you are an engineer. Glad to have you aboard! Are you also saying you have worked in an RF lab for an antenna company? Care to divulge which one?? Or was this just academic experience? Rick
Never worked for an "Antenna Company". Took RF courses in college and did hands on gain and radiation pattern measurements on antennas. Worked in a design lab for RF equipment after graduating, and have been working with wireless carriers for many years.
 
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#31
I took a look at the maps of the area Paul Anderson's signal reports were from. Most of his reported signal paths were largely over water no trees, hills, or building in the way over large parts of the signal path. While the use of a good antenna system would be required, and signal would be somewhat weather dependent such signal paths do look possible to me. Having a good location played a large part in the results he got. Most of my personal experience has been exploring VHF/UHF signal paths using amateur radio equipment. VHF/UHF FM is not a weak signal mode and is normally good for only about 50 to 70 miles line of site at the low power levels used. Less than 50 watts. My observation was by using a small directional antenna when weather conditions were favorable for it over 100 miles was possible on an almost predictable basis. The propagation mode was tropospheric enhancement, and is quite common across the Wyoming desert in temperature inversion prone areas, and probably more common across large bodies of water. Tropospheric ducting is very rare in my part of the world, and is what I would call an interesting but useless phenomenon. While my experience has been with low power FM I do believe that such signal paths will support ATSC signals. What I experienced was very location dependent, but had I not tried I would not have known that such signal paths are even possible. Reliable Tropospheric Scatter for ATSC signals? I'm not one to say it couldn't happen in the correct location with a good antenna system. To sell the Idea that a high priced antenna system can produce amazing reliable results at any location is a bit far fetched.
I did need to do a bit of review reading, and from the descriptions I read Tropospheric Scatter is unlikely to support ATSC signals.
Tropospheric Propagation | Susquehanna Astronomical Society
Tropospheric DX Modes
Steve
 

DW-77

DTVUSA Member
#32
... Okay kids -- I have been enjoying your numerical 'Chess game' ... but has it crossed your minds that your 'theoretical' results have very little to do with reality?
Based on my experience, serious mismatches between theory and reality happen, 9 times out of 10, because the "theory" was either incorrect, or incorrectly applied. Occasional "magic" outcomes are exceptions.

... Antenna height NOT GAIN usually wins. My (enormous) 16-Bay Hoverman proved to be a crap antenna compared to my (tiny) DB-2 because it was too large to be raised high enough to capture signals AND because it captured too much multipath. Plus, the Hoverman's tremendous gain could not overcome the lack of signals at the lower height. Screw 'assumed' dB gain numbers. I can receive a translator 86 miles away on a tiny DB-2 elevated to a crazy height which proves my point.
If your point is that an antenna must first be in the "right place" (where there is incoming RF signal), and then have the right gain, I agree. Receiving antennas are made to receive signals not to create them out of nothing. Your 16 bay Hoverman may not be "a crap antenna" after all; it sounds like it was not a good match for the location, though.
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#33
... If your point is that an antenna must first be in the "right place" (where there is incoming RF signal), and then have the right gain, I agree. Receiving antennas are made to receive signals not to create them out of nothing. Your 16 bay Hoverman may not be "a crap antenna" after all; it sounds like it was not a good match for the location, though.
DW,

I raised my 2-Bay about 52 feet above ground level on a "50 foot" telescopic push-up mast with a rotor and side-mast without any guy wires. Raising a sixteen Bay to the same height, even for testing would be scary: one puff of wind and down comes the whole works.

The 'alleged' gain of a sixteen Bay (in theory) should equal (or better) the minimal gain of a two Bay at a lower height and at 30-ish feet, it didn't come close. Zero reception on the same stations, because the signals were 22 feet higher and "gain" made NO DIFFERENCE.

It is like Real Estate, except its in the air above your property: LOCATION, LOCATION, LOCATION!

As you said (paraphrased) you need to find the (height) where the data stream is available to be collected. I see the arguement about alleged antenna gain as a straw man's claim or assumption: until an antenna is actually tried in a particular location, no one can claim it will work at any location before actually trying it at that specific location.

Regarding your out of context quote, Hoverman antennas and their variations are not crap, they are excellent designs: they are great for some locations, but certainly not at my location per my physical testing here and the results of my tests.

Jim
 
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DW-77

DTVUSA Member
#34
... The 'alleged' gain of a sixteen Bay (in theory) should equal (or better) the minimal gain of a two Bay at a lower height and at 30-ish feet, it didn't come close. Zero reception on the same stations, because the signals were 22 feet higher and "gain" made NO DIFFERENCE. Jim
Jim, you are right: if there is no signal in a certain place, more gain will make no difference. At your location, those extra 22 feet seem to be what it takes to go from "total darkness" to "light", and all the credit goes to you for finding the solution.
 
#35
A Theory

It sounds like Jim did a noise margin (NM) calculation, based on ideas you can find on TVFool and elsewhere, and found that his 16-bay Hoverman "should" have worked better at 30 feet than his DB2 at 52 feet. Based on this, he's concluded that gain figures are generally suspect, and perhaps the entire science of radio communications is just a little wobbly.

But the calculation of NM recommended on TVFool, and which you often see in user posts, is just an approximation. For example, the "noise" referred to is nothing but the normal thermal noise (heat) that exists everywhere. There's no attempt to adjust for the artificial electrical noise in the city versus the country, or the artificial noise close to the ground (if any), versus artificial noise high in the air.

But there is artificial noise wherever people hang out -- more and more so, as fluorescent lights saturate our cities. So why would artificial noise have a greater effect in the city than in the country? The inverse square law works the same on noise as it does on the original signal, right?? Right. That's the point.

Ever notice that transmitters tend to be high in the air, far from any noise, and especially high within the city? As long as the source of noise is closer to receiver than transmitter, the inverse square law says noise becomes less significant relative to the desired signal, as the distance increases. Relative to thermal noise, distance always decreases NM, but relative to artificial noise, distance can actually make a signal cleaner and easier to receive. Distance can actually increase noise margin. :cool:

Don't believe me? Try this simple experiment. Most of us have an AM radio in the home and some source of noise, such as a laptop or a microwave oven. Move the radio (or the noise, whichever is easier) close together and tune in a station so the noise is considerable, but where you can still hear voices in the background. Now line up your hardware so noise source is in between transmitter and radio in a straight line, like this:

Radio <- Noise <- Transmitter.

Now move your radio farther and farther away from the noise, keeping everything in a straight line. The farther you move away from the transmitter, the clearer the signal you will get!

Granted that's an extreme example, because the noise is much, much closer to the receiver than the transmitter. But as long as artificial noise is any significant distance from the transmitter, the inverse square law says an even greater distance can easily improve the SNR, and the NM right along with it. And this will never show up on a Fool report. :gramps:

But the curvature of the earth ensures that the main sources of artificial noise will be some distance from any transmitter over 70 miles away. A signal that becomes dirty, by traveling through the heart of a nearby city, is unlikely to reach one hundred miles, even with one or two refraction edges. Any signal that gets that far will have radiated horizontally at first, or at an upward angle. For that reason, if you want to get a Milwaukee station from anywhere north of Green Bay, the artificial noise you need to worry about does not come from Milwaukee; it comes from Green Bay.

I am saying that someone who wants a Milwaukee station is better off 100 miles north of Green Bay than 10 miles north of it. And Google Maps tells me Anderson's Fishing Camp is over 100 miles north of Green Bay. Also, nearly the entire path to both cities is over Lake Michigan. That's also true for Muskegon.

The Fishing Camp is located on a large body of water ensuring a large distance between the receiver and any possible artificial noise in the direction of the transmitters. I say this has much more to do with Anderson's success than any tropo-scatter phenomenon, or ganging together precisely the right antennas to squeeze out an extra dB or two of gain.

It also might explain Jim's story. If there's a source of man made noise on the ground, then getting the antenna way up high will have much more impact than the regular NM calculation reveals. Also, if height is necessary to clear some tall trees, once again the number you get by adding antenna gain to NM in a Fool Report is bound to be deceptive.

By definition, all scientific theories are disprovable through counterexample. But I'll need a lot more data before I :flush: the concept of gain, or discard communications theory altogether!

Rick
 
#37
A test to see if the site is accepting new posts today.

Actually, I wanted to bump post #35 above. What writing! What a great theory, eh?? :first: I keep thinking I'll write up a detailed calculation with the inverse square law to show what I mean. Plus I have some old sources showing the great stress ham radio operators used to lay on reception in the country versus the city -- specifically due to man-made electrical noise. Maybe I'll get around to it tonight.

R.
 
F

FridaFrida

Guest
#38
I grew up in Door County, WI & we would often get Chicago UHF channels with just an indoor O loop on the back of the TV. It is because of Lake Michigan that the signals go so far, he would not get Madison & I do not think the setup would work as well in a non-Nautical situation.
 
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