Excellent link with antenna comparisons with spectrum analyzer

[EscapeVelocity]

True, but it is intriguing.

Getting 6 to 9 dB gain on VHF High from these antennas makes them very useful and competative against the VHF High/UHF combo yagis from Winegard and AntennaCraft, for a one antenna solution.

Note: Because the screens of the DB8 and the HD 8800 are not solid lengths, they dont give near the gain across the VHF High band. The Channel Master 8 bays are sure to beat them by a country mile on VHF High. The Kosmic might can unseat the CM's in that regard, though. Its longer elements are beneficial in that regard, but the CM's have 8 elements to push the signal and reflected signal through, albeit ineffeciently.

A lot of small indoor FM antennas are 1/8th wave jobs. The elements of these N-Bays are about 1/4 waves at VHF High. Quarter Wave antennas are known to perform well, like the 33" 1/4 wave FM whip. Multiply that by the number of bowties, 4 or 8, and you start to see the beauty of it.

 

[tballister]

Getting 6 to 9 dB gain on VHF High from these antennas makes them very useful and competative against the VHF High/UHF combo yagis from Winegard and AntennaCraft.

YA! THAT is EXACTLY (to me) the promise, and I enthusiastically second the sentiment.

Its the promise of being able to help stimulate market (re)acceptance of OTA. E.g., the promise of being able to get past the wife's question "You want to put THAT on the roof!?!?" (sorry, Hun). The promise of being able to transition from requiring a bunch of gaudy aluminum (uh, not in my eyes, the wife's) to requiring something not much more obtrusive than a satellite dish.

Its great.

Because the screens of the DB8 and the HD 8800 are not solid lengths, they dont give near the gain across the VHF High band.

Keep an eye on AntennasDirect. I'm under the impression they are working on a significant re-work of the DB8. The target is quite clear; its the CM4228HD's game to lose. Sometimes it better to not be the first on the market...

The elements of these N-Bays are about 1/4 waves at VHF High. Quarter Wave antennas are known to perform well, like the 33" 1/4 wave FM whip. Multiply that by then number of bowties, 4 or 8, and you start to see the beauty of it.

Its a good point; I'll integrate it into my pondering of N-Bay physics' compatibility with VHF...

 

[EscapeVelocity]

YA! THAT is EXACTLY (to me) the promise, and I enthusiastically second the sentiment.

Its the promise of being able to help stimulate market (re)acceptance of OTA. E.g., the promise of being able to get past the wife's question "You want to put THAT on the roof!?!?" (sorry, Hun). The promise of being able to transition from requiring a bunch of gaudy aluminum (uh, not in my eyes, the wife's) to requiring something not much more obtrusive than a satellite dish.

Bingo. Smaller, more compact, than a huge yagi. Wife and neighbor friendly. The guy in LA was having problems with his Home Owners Association....was attracted to the compact size of the Kosmic SuperQuad.

I bet those corner reflector extensions on your DB8 significantly increased its VHF High performance.

Your gonna love the Kosmic SuperQuad! Once you see what it can do and how small it is.

 

[EscapeVelocity]

Keep an eye on AntennasDirect. I'm under the impression they are working on a significant re-work of the DB8. The target is quite clear; its the CM4228HD's game to lose. Sometimes it better to not be the first on the market...

I could design them a fantastic 8 bay antenna, not being limited to commonly available hardware store items/materials.

If your reading this Antennas Direct, you know where to contact me! I work well in a team atmosphere.

 

[tballister]

I bet those corner reflector extensions on your DB8 significantly increased its VHF High performance.

I'm not taking that bet. I've been looking forward to seeing the result as well. Its one of the reasons I want to get the 8-Bay VHF Shootout done.

Your gonna love the Kosmic SuperQuad! Once you see what it can do and how small it is.

Maybe I vill, und maybe I von't. (But don't stop selling):director:

 

[tballister]

I could design them a fantastic 8 bay antenna ...

Not if I get there first!! :first:

 

[Piggie]

The elements of these N-Bays are about 1/4 waves at VHF High.

Which elements? My 4221A measures 7.5 inches per element. If you take the virtual distance from tip to tip of 16 inches, that is close to a 1/4 wave at highband.

But you are comparing that to a 1/4 length of metal that is feed at it's end as a Marconi 1/4 Wave.

On the N-Bays the quarter wave you describe would be center feed. I have no antenna to compare that with except to call it an 1/8 wave dipole, that would have a huge mismatch.

Also even to presume the virtual distance from end to end of a diaganol pair in a N-Bay is continuous would not be any more true than because an DB8 has as wide of reflector it too should resonant at VHF as does the reflector of an old CM4228A..

Now. As always I could be wrong, but this idea just hit my sense of antenna sideways and why I pose an opposing view.

 

[EscapeVelocity]

except to call it an 1/8 wave dipole - Piggie

Or rather, a 1/4 wave dipole, with 1/8" segments left and right. See how I referenced the 1/8th wave FM antennas, commonly available over the years as indoor FM antennas. They arent great antennas on FM but if you ganged 4 or 8 together and then reinforced them with a 1/2 wave reflector element...then you will see a decent gain.

The DB8 has a less effecient reflector at 20" x 12 (4 altogether) The CMs have the 1"x2" mesh screen at 30x39 and solid rods at similar lengths on the new Chinese version. It's resonant at VHF High frequencies, much more so than a 20" screen. The Winegard similarly uses 2 HD 4400 screens instead of continuous single screen. Thus losing that bit of increased resonance help.

The DB8s 6.75" whisker length is also a bit smallish, for 1/8 wave at VHF High. But the bowtie design is a broadbanding technique itself.

 

[Piggie]

Or rather, a 1/4 wave dipole, with 1/8" segments left and right. See how I referenced the 1/8th wave FM antennas, commonly available over the years as indoor FM antennas. They arent great antennas on FM but if you ganged 4 or 8 together and then reinforced them with a 1/2 wave reflector element...then you will see a decent gain.

Yeah, brain fart. 1/4 dipole. sorry.

1/8 wave FM antennas? You mean a 15 inch whip? Most likely if an FM antenna has a built in telescoping whip less than 30 inches it most likely has a matching network.

The DB8 has a less efficient reflector at 20" x 12 (4 altogether) The CMs have the 1"x2" mesh screen at 30x39 and solid rods at similar lengths on the new Chinese version. It's resonant at VHF High frequencies, much more so than a 20" screen. The Winegard similarly uses 2 HD 4400 screens instead of continuous single screen. Thus losing that bit of increased resonance help.

I have always felt the reason the 4228A has VHF response is the resonance of the reflector couples into the driven elements by "force", even though the elements are tuned to UHF.

I don't know the math with out research but the impedance of a 1/4 dipole would be such a mismatch to the matching network in a N-Bay, I can't see it being anything of a tuned input. Much like if you live near a TV station you can receive VHF on a paper clip. Enough RF and anything will couple.

In other words the reflector does the work of resonating at high band. Then UHF elements just couple that energy (capacitively and probably inductively as well to a degree) to the coax.

I have never seen anywhere any reference to a 1/4 wave resonator center feed that didn't need a matching network.

Talk me down but I believe it's purely coupling between the reflector and the feed system.

The DB8s 6.75" whisker length is also a bit smallish, for 1/8 wave at VHF High. But the bowtie design is a broadbanding technique itself.

Yes the bowtie design is a take off from the old muli-wire dipoles providing a longer resonance point, agreed. But there is a limit to how far they broadband.

Antennas in general will work at odd harmonic very well, but no sub harmonics.

 

[EscapeVelocity]

1/8 wave FM antennas? You mean a 15 inch whip? Most likely if an FM antenna has a built in telescoping whip less than 30 inches it most likely has a matching network.

No I mean an 8 inch loop. If you go to the FM antenna guide you will see a plethora of 8" loops. You will also see small log periodics that are nowhere near 1/2 waves or 1/4 waves. The FM Beambox is a classic example or 2 8" wires or a 1/4 wave dipole. They may have matching networks, but you are thinking like a ham. Sure its better to have a mathcing network if you are targeting a specific band or frequency, but Ive found that mismatch losses are very tolerable, not massive gain killers. And for example as you well know, off resonance, dipoles increase in SWR and impedance. You will always have mismatches on a broadband antenna at off resonant frequencies. Im not saying its the perfect solution, but we are talking about broadbanding (or multimoding) here, on a secondary frequency spectrum and not the primary UHF television band.

I have always felt the reason the 4228A has VHF response is the resonance of the reflector couples into the driven elements by "force", even though the elements are tuned to UHF.

Correct, the elements are not tuned efficiently to the VHF band. But they arent total duds either. The proper sized reflector doubles the signal being fed into the UHF collinear broadside array.

In other words the reflector does the work of resonating at high band.

Yes it is an efficient re radiator of VHF High band energy.

Then UHF elements just couple that energy (capacitively and probably inductively as well to a degree) to the coax.

They also bring in energy from the direct transmission.

I have never seen anywhere any reference to a 1/4 wave resonator center feed that didn't need a matching network.

Because if it is targeted to a specific frequency or band, then it will have a matching network, or you might wish to use larger tuned elements. However if you are targeting a higher frequency band as well, as your primary band, then you match to that frequency spectrum, and take what you can get at the other (in this case VHF High).

Talk me down but I believe it's purely coupling between the reflector and the feed system.

Not sure what you mean, but it is a coupling between the re-radiated signal from the parasitic element (the reflector) in addition to the primary transmission....and the UHF collinear broadside elements.

But there is a limit to how far they broadband.

True, but if you increase the classic 2 SWR and impedance limitations, that can be extended.

Antennas in general will work at odd harmonic very well, but no sub harmonics.

It is well established that 3/4, 5/8, 1/2, 1/4, and 1/8 wave antenna elements have synergy with the full wave.

--------------

I think there is some mind blocks going on with regards to classic ham radio antenna truisms, plus also ANALOG television and there requirements.

Hams like to pin down into the perfectly matched system to DX, and tweak their antennas and system to perfection.

Analog television could not for example, handle any multipath, if you wanted the perfect picture. However that isnt the case with digital. I know FoxTV was discussing the necessity of signal quality, and because of the bandwagon discussion that followed, I decided not to join in and rock the boat. But lets face it, as long as the digital tuner is staying locked on the primary or higher gain signal, then multipath does not affect the picture quality very much....not like on analog sets.

The key is to be good enough to get the 1s and 0s coming through, and above the BER correction ability of the tuner. Some margin above that is also beneficial (not only in the small increase in picture quality) but to ensure that you dont fall below the digital cliff with environmental changes affecting the transmitted signal.

So while striving for the perfectly matched recieving system is laudable, one must realize that there is a lot of room away from that perfectly matched system, free from multipath, and so on and so forth, that will do the job, especially in the digital age.

What say you?

 

[tballister]

The key is to be good enough to get the 1s and 0s coming through, and above the BER correction ability of the tuner. Some margin above that is also beneficial (not only in the small increase in picture quality) but to ensure that you dont fall below the digital cliff with environmental changes affecting the transmitted signal.

Ooooo... I don't think this is correct, EV.

First of all there is no difference in picture quality within and above the error correction capability. If the BER is sufficiently low such that errors can be corrected, you get, by definition, correct data. As the BER increases just above the correction capability, you generally experience pixellation on most receivers. Once the BER increases beyond the correction capability, receivers implement video/audio squelch and you get "Signal Lost". [I'm not sure there is a standard for a specific percentage of errored frames over a specfic interval before declaring "Signal Lost"]

Margin above the error correction threshold is the name of the game. If you want to withstand the worst of times, you need to have margin at the best of times.

I don't understand how there could possibly be an additional "small increase in picture quality" once margin increases above the error correction capability threshold. Unerrored and corrected frames represent a received bitstream that is precisely the bitstream generated, by definition.

Sorry.

 

[EscapeVelocity]

Uncorrupted and corrected data will omit errors and thus give a better picture quality, however it is not very noticeable by the average joe, unless he is told what to look for.

Perhaps my nomenclature is wrong, its not BER but rather pixel interpolation, that I am referencing. If you have pixels lost then the image processing can assess the adjacent pixels and fill them in, even if they may be errant the image is produced and teh next frame comes along.

 

[EscapeVelocity]

Im not a guru on BER though. I am pretty clued in on image processing.

As regards to my post to Piggie.

You could split the VHF High and UHF portions of the captured signal and then run 2 differnt matching networks on them, then recombine to the 75 ohm coax, as well, in a custom matching transformer box (circuit board baluns) that are all the rage these days, as well. But I dont currently have that kind of production capability.

EV

 

[EscapeVelocity]

In other words, BER isnt a 100% accurate correction, it allows a less than perfect image to be acceptable. You progressively move within BER towards a more and more degraded picture til you hit the cliff. However this degradation isnt all that noticeable. Most people wouldnt notice it, but its there. As opposed to a perfect reception no BER picture...with no errors.

 

[EscapeVelocity]

The difference being, that a digital video heavy into BER still looks better than what most folks received on analog, no snow, no ghosting, no herringbone, and so on and so forth.

 

[tballister]

Uncorrupted and corrected data will omit errors and thus give a better picture quality, however it is not very noticeable by the average joe, unless he is told what to look for.

Again, not quite precise. If by "Uncorrupted" you mean error free, then there is no "omit" action taking place. Error free, and corrected data are, again by definition, the exact unchanged data originally generated. There is no omit or better involved.

Perhaps my nomenclature is wrong, its not BER but rather pixel interpolation, that I am referencing. If you have pixels lost then the image processing can assess the adjacent pixels and fill them in, even if they may be errant the image is produced and the next frame comes along.

BER (Bit Error Rate) and interpolation are two different topics, really, although one may follow the other. Errors don't precisely lose pixels. For a 1920x1080 screen a pixel is one of the 2,073,600 small areas on the screen that can be illuminated independently of all others.

What an uncorrected error does cause is loss of a low level 188 byte packet out of the MPEG transport stream. Among other things, each packet contains information describing the spectral energy in a block of pixels, for example 8x8, or 64 pixels. Dropped packets trigger error concealment techniques aimed at minimizing the visible degradation due to loss of the information. Most of these techniques are pretty mathematically exotic, and some do interpolate pixel blocks, but not just individual pixels.

I understood your comment to focus on individual pixels, and I just think its a little more complex than that.

So, if I misunderstood, I apologize.

Anyway, never mind all that. Let's get back to finding a better mouse trap!

t

 

[EscapeVelocity]

Yeah, Im not a master of BER. But I do understand some of the concepts. So my terminology is bound to be imprecise and confusing.

The basic gist of what I am saying is correct. Perfect error free data produces a better picture than stuff coming out of BER, however, its not that noticeable for the average joe. And certainly worlds better than most analog, without the associated problems, due to multipath and other electrical anomalies that affect the picture seen negatively.

Error free, and corrected data are, again by definition, the exact unchanged data originally generated. There is no omit or better involved.

From what I understand this is false. Errors or omitted data are tolerated which are handled in the image processing.

Back to the mousetrap...

Im working on a prototype Hoverman tommorrow, still need to acquire tubing. Gonna try it with the fencing first. Using dimensions of the G1483. Then perhaps one scaled up a bit.

 

[tballister]

From what I understand this is false.

Hmmm..... I can tell I'm not communicating very well.

Let me try again, and start with a definition of Bit Error Rate. It is a unit-less ratio of the number of bits received in error divided by the total number of bits received over a given interval, commonly 1 second.

For example, the T1 Transmission System ubiquitously deployed throughout the North American telephone system has a bit rate of 1.544 Mbps. If there were 1 bit error in every second the Bit Error Rate would be 6.5E-07. If there were 1 bit in every 10 seconds the error rate would be 6.5E-08, and so on. [In even simpler terms, if the transmission system's bit rate was 1 million bits per second, then 1 error every second would be 1E-06, 1 error every 10 seconds would be 1E-07, and so on].

So when I said "Error free, and corrected data are, again by definition, the exact unchanged data originally generated.", I meant successfully corrected data, and thus a total BER of 0, and thus exactly the picture originally encoded.

I stand behind that statement.

When I said "There is no omit or better involved. ", I was just trying to introduce a little more preciseness into your statement "Uncorrupted and corrected data will omit errors and thus give a better picture quality, however it is not very noticeable by the average joe, unless he is told what to look for."

When I referred to the word omit I was simply trying to clarify that "Uncorruppted and corrected" data does not have any errors - there is nothing to "leave out", or "omit" from that data.

When I referred the word "better" it was because the impression I took from your words was that somehow the clarity/detail/resolution would somehow improve for correct data, and it was just a bit odd. I mean clarity and/or detail/resolution are characteristics of the coding algorithm and I assumed these are the things you meant about "quality". Perhaps that word is the root of any misunderstanding, because its a little undefined.

You are either error-free, or you are not.
- You compression data is not error free when the error rate exceeds the ability of the error correction to restore precisely the original bits.
- When this happens at modest levels, blocks of information are lost, resulting in the visual effect that I know as pixellation.
- When this happens excessively, well, you know what happens.

To say that one more way:
- If there are no transmission errors, or the transmission BER is low enough that the errors are correctable, the quality you observe is exactly the quality rendered by the encoder, no more, no less.
- In the presence of errors it is not clarity/detail/resolution that suffers, but rather loss of information and thus pixellation, or worse the blank screen, and I submit pixellation is noticeable by every average Joe.

If you want to define not seeing pixellation as better quality than seeing pixellation, then I would agree with your statement. But like I said, I generally consider quality to be defined as things like clarity/detail/resoultion, so the statement struck me as a little strange, and I was just trying to help with some clarification.

No Big Deal. Let's move on... opcorn:

 

[EscapeVelocity]

No problem, Im not here to belabor that point, especially since Im not an authority on BER and Error Correction.

The main point being that the Analog is more sensitive to multipath signal interference, and other electrical anomalies.

 

[Piggie]

No I mean an 8 inch loop. If you go to the FM antenna guide you will see a plethora of 8" loops. You will also see small log periodics that are nowhere near 1/2 waves or 1/4 waves. The FM Beambox is a classic example or 2 8" wires or a 1/4 wave dipole. They may have matching networks, but you are thinking like a ham. Sure its better to have a mathcing network if you are targeting a specific band or frequency, but Ive found that mismatch losses are very tolerable, not massive gain killers. And for example as you well know, off resonance, dipoles increase in SWR and impedance. You will always have mismatches on a broadband antenna at off resonant frequencies. Im not saying its the perfect solution, but we are talking about broadbanding (or multimoding) here, on a secondary frequency spectrum and not the primary UHF television band.



Correct, the elements are not tuned efficiently to the VHF band. But they arent total duds either. The proper sized reflector doubles the signal being fed into the UHF collinear broadside array.



Yes it is an efficient re radiator of VHF High band energy.



They also bring in energy from the direct transmission.



Because if it is targeted to a specific frequency or band, then it will have a matching network, or you might wish to use larger tuned elements. However if you are targeting a higher frequency band as well, as your primary band, then you match to that frequency spectrum, and take what you can get at the other (in this case VHF High).



Not sure what you mean, but it is a coupling between the re-radiated signal from the parasitic element (the reflector) in addition to the primary transmission....and the UHF collinear broadside elements.



True, but if you increase the classic 2 SWR and impedance limitations, that can be extended.



It is well established that 3/4, 5/8, 1/2, 1/4, and 1/8 wave antenna elements have synergy with the full wave.

--------------

I think there is some mind blocks going on with regards to classic ham radio antenna truisms, plus also ANALOG television and there requirements.

Hams like to pin down into the perfectly matched system to DX, and tweak their antennas and system to perfection.

Analog television could not for example, handle any multipath, if you wanted the perfect picture. However that isnt the case with digital. I know FoxTV was discussing the necessity of signal quality, and because of the bandwagon discussion that followed, I decided not to join in and rock the boat. But lets face it, as long as the digital tuner is staying locked on the primary or higher gain signal, then multipath does not affect the picture quality very much....not like on analog sets.

The key is to be good enough to get the 1s and 0s coming through, and above the BER correction ability of the tuner. Some margin above that is also beneficial (not only in the small increase in picture quality) but to ensure that you dont fall below the digital cliff with environmental changes affecting the transmitted signal.

So while striving for the perfectly matched recieving system is laudable, one must realize that there is a lot of room away from that perfectly matched system, free from multipath, and so on and so forth, that will do the job, especially in the digital age.

What say you?

I say, ham radio only accented my understanding of antennas. It has grown since those days also.

Here is what bothers me. You are taking true things about antennas and extrapolating them beyond their normal usefulness.

Mismatches in SWR on receive to me also are WAY over played. I already did a thread post about how even a 3:1 which would fry some transmitter at full power is only about a db of loss on receive. Not even noticeable even in analog reception of TV, AM, FM. With a good receiver you might tell the difference in CW and SSB.

So I am not arguing that a non perfectly matched system won't receive. Heck I have a 3 element yagi up now on the test jig that picks up all the Gainesville UHF at 25 to 37 miles away. It has to be grossly mismatched.

But in this example of my 3 element the difference between the way I see it and you is you might say "see it works at UHF too". I say the UHF signals are strong enough they are being picked up by the high band elements. After all the driven element on the thing is just a dipole that is a 3/4 wave on each side of the dipole that is know to resonant around 100 plus ohms.

But I say when you start talking about antennas that are subharmonics of a 1/4 dipole, you either are matching it even to some degree to the feedline or the signal is just strong enough it works.

Are those 8 inch elements for FM more than likely have a matching network.

One of the most popular CB antenna was the base loaded 1/4 wave. They were only about 30 to 40 inches long, where as a full wave was 108 or so. They worked. Why? they had a matching network.

I can match a paper clip to a TV with the right matching network. I once lived on a dairy and could not put up anything tall, but their was a mile or more of fence. I hooked up the center of some RG8 to the fence and grounded the shield to a rod. Then went along the fence for several hundred feet in each direction and boned sections together. I didn't do anything on the higher bands but I could talk to all the local nets on 3.9 MHz. I even had some use of 7 MHz. That fence was tuned to who the heck knows what. I made the fence resonant with a tuner.

Look I understand your points, about things working that you would not think would work. Coupling between elements that at first you would not presume would happen. But I guess it's the way you are saying that to me dilutes the entire discipline of talking about antennas. I don't want to become the strict only if in a book like some of the AVS discussions but I don't want to see things that might mislead someone that knows little or a novice to think, why even measure a dipole? Just take 2 pieces of wire and hook them to a coax and you have an antenna. Where in fact it is an antenna and feedline, it moves to far away from keeping some since of the facts. If you want to use random wire for an antenna your reception will be greatly improved if it's even closely matched to the feedline.

If you take many of the classic TV antennas and do models on them like that guy does at ham radio web site, you find the can range from 90 to 500 ohms across the channels they are advertised to work. And since they are classics we all know those same antennas work well. So I am not talking about mismatches that small.

I am also biased with my physics and math background. If we want to propose something new that works such as an 1/8 wave dipole working well without a matching network, there needs to be some proof to the postulate.