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Old 12-Sep-2015, 1:21 PM   #1
4.6 Explorer
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What's the difference???

I have seen a few various designs of 8 bay constructions. and they all have various gain factors.

Some of the more common 8 bay have the driven elements that look like simple wires, basically the thickness of coat hangers (I say that loosely).
I see other driven elements that have a more flattened appearance and then I have seen other 8 bays that have the flattened loop appearance. Keep in mind that these are all new and not the home made versions.

Of course every manufacture will put its twist on design to make its claim of the better antenna.
But, what part of the antenna actually determines the overall gain.

1) the number of driven elements can certain be a factor but right now I am referring to 8 bays only.
2) the design of the driven element, Wire bowtie, flattened bowtie or flattened loop.
3) all the spacing involved where the driven element sits with respect to the reflector and distance between elements.

I'm sure some one might com back and suggest that all these factors play a part of the overall gain. BUT, are there any particular factors that make for a high gain antenna. At this point I am not referring to construction differences because we have seen cheaply built antennas and we have seen well built antennas and those have an affect on price.

No, right now I only question what determines the gain?
Attached Images
File Type: jpg flattened bowtie.jpg (73.2 KB, 382 views)
File Type: jpg wired bowtie.jpg (64.3 KB, 388 views)
File Type: jpg flattened loop.jpg (120.0 KB, 401 views)

Last edited by 4.6 Explorer; 12-Sep-2015 at 1:31 PM.
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Old 14-Sep-2015, 11:23 AM   #2
Stereocraig
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Quote:
Originally Posted by 4.6 Explorer View Post



No, right now I only question what determines the gain?
Short version:
Boom length and the number of directors.
Reflectors.
# of properly phased driven elements.

Roughly analogous, to a funnel. How much signal can it scoop?
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Old 14-Sep-2015, 12:12 PM   #3
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Craig: I can certainly understand that concept for any type of Yagi having various 'boom' lengths multiple directors, flat or corner reflectors. Or, for a log periodic or regular delta wave and simple dipole design
But for all these different and seemingly the same, 8 bay type antennas I see various styles of driven elements. Then we see on the advertising and/or the packaging where they claim various gain factors.

I suppose the question is: what determines the various gains on these 3 different types of driven elements "collectors". I'm only referring to the 8 bay flat bowtie shown in the pictures I submitted.

I also sense a lit bit of BS coming from the manufactures based on "under ideal conditions". When I say "BS" (carefully crafted words). I simply refer to claims 'the way they are written' in order to mislead the average person that has no RF background, Joe Average Consumer. Even legal beagles can't correct these claims unless they, too, have an RF background.

So, strictly on 8 bay reflector antennas, how do they determine the different gains, between brands for each 8-bay.
I can certainly understand and appreciate construction differences that would allow one antenna to be more durable than another and hold up to bad weather, hence they are built differently mechanically, But, when they all seemingly look alike with subtle differences, what changes the gain?
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Old 14-Sep-2015, 1:35 PM   #4
Stereocraig
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Different styles, will perform differently, at different frequencies.
Some mfrs., just might be hand picking the results, that make their product out shine the rest.

One industry that has been pulling this BS for decades, is audio.
Some cheesy brands, will claim that their amps will put out say, 500 watts, when in fact, they're only consuming, maybe 200 watts max.

Yeah, we get bombarded by these BS claims, from the time we get up, 'til the time we go to sleep.
It's all in the way things, are worded and how much people accept it as reality.
It's also, pretty much the same words being used, over and over.
That and the fact, that nobody questions anything, anymore.

Stick w/ name brands and you should do OK. (Remember, I said:"Should" =D

The only true test, is for us to see how it performs, in real life.

Last edited by Stereocraig; 14-Sep-2015 at 1:44 PM.
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Old 14-Sep-2015, 2:19 PM   #5
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Oh, now you're referring to politicians at large . re the BS.

There're all kinds of design I'd like to play with mainly for those distant transmitters (and a I have a couple in mind). Problem is, at my age ,climbing that 40ft tower multiple times for a tweak here or a tweak there can play on your abilities.

I'm sure you've done some Youtube searches and those guys don't say much any differently than we read. Then we see the novices that don't really have a clue, poor editing and bad grammar.

The basics are obvious and I'm sure they have been mentioned a gazillion times on this forum. Height, directional aim, gain, good cabling and connectors and a longer list.

And, yes, you're correct. One manufacture will design and build an antenna that resonates best on one frequency only and the other frequencies are so-so, but they capitalize on the gain of that one frequency.
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Old 15-Sep-2015, 1:33 AM   #6
rabbit73
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Your question is off-topic for this thread which is for database updates. Better to have posted it here:
Special Topics
http://forum.tvfool.com/forumdisplay.php?f=9

or here
Help With Reception
http://forum.tvfool.com/forumdisplay.php?f=7

But I will try to answer it now.

Quote:
But, what part of the antenna actually determines the overall gain.

1) the number of driven elements can certain be a factor but right now I am referring to 8 bays only.
2) the design of the driven element, Wire bowtie, flattened bowtie or flattened loop.
3) all the spacing involved where the driven element sits with respect to the reflector and distance between elements.
1) The number of elements is certainly the most important, but since you have limited your question to 8-bay collinear arrays (the proper name for the category), how you combine the two 4-bay arrays can affect the gain. If you combine the two 4-bays with a splitter in reverse, the maximum gain will be 2.5 dB; 3 dB for two 4-bays combined minus 0.5 dB combiner loss. There are other ways of combining two 4-bays that have lower loss if you are concerned about the last 0.1 dB.

Maximum combining gain will only be realized if the wavefront presented to the antenna is uniform and the plane of the antenna is perpendicular to the wavefront.



2) All those shapes will give the same gain at the design frequency if they are resonant at that frequency, but as you move away from the design frequency the gain curve will be different. The array will have less gain at frequencies below the design frequency and more gain above the design frequency, but "thin" elements will have a narrower bandwidth and "fat" elements will have wider bandwidth.

A collinear array has greater bandwidth than a yagi because it has a lower "Q," as defined by the max allowable SWR, and the fatter elements make the Q even lower.

Each bay consists of a collinear pair of half-wave dipoles that form a full-wave dipole. Each end of a half-wave dipole is a high impedance point, so where it connects to the vertical phasing line, the support point must be well insulated for low loss. Screwing the inner ends of the "whiskers" to wood can cost you 2 or 3 dB.

3) The spacing between the elements and the reflector is usually 0.2 to 0.25 wavelength at the design frequeny for max gain. A larger reflector can increase gain and so can a non-flat angled reflector.

The vertical spacing between the bays is usually 1/2 wave at the design frequency. When the antenna is operated at frequencies above the design frequency, the gain will increase because the vertical spacing and the elements become longer in terms of wavelength, with the max gain at 5/8 wave. As you move even higher in frequency the gain will decrease because the vertical spacing is more than when the capture areas of each bay just touch, and the element lengths are so long that the main lobe splits into two parts.

So, you can see that it is possible to construct an antenna for a specific frequency that puts the peak of the gain curve where you want it, which is not the same as the design frequency of an antenna that is for a whole band with the design frequency at the center of the band.

Have you looked at mclapp's website?
http://m4antenna.eastmasonvilleweather.com/index.html

Have you looked at the files by holl_ands?
http://imageevent.com/holl_ands/multibay/8bayrefl
sample gain curves
http://imageevent.com/holl_ands/mult...yrefl/cm4228hd
http://imageevent.com/holl_ands/mult...=0&w=1&s=0&z=4
Attached Images
File Type: jpg 4BayCurrentFlow.jpg (42.8 KB, 1396 views)
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Last edited by rabbit73; 15-Sep-2015 at 9:57 PM.
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Old 15-Sep-2015, 10:41 PM   #7
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Thank you Rabbit
I sent another reply to you yesterday thanking you but somehow it didn't go through.

The information you provided certainly adds to what it is I needed to know.

I have two 8-bay collinear arrays stacked on top of each other aimed east to capture the Buffalo and Grand Island stations about 50 miles away. Decent signals for the most part with occasional drops outs due to weather time of day (or whatever). Those two are also using a preamp CM 7778;
one simple 4bay to Capture Toronto towards the north and another Yagi that aims west for a single station.
Presently the single 4bay is not hooked up, yet
Because I'm below an escarpment the western transmitter is hard to capture and it's only about 4 miles away. I do get it but a very weak signal.

When I bought a used 8 bay a weeks ago the mechanical properties of the used 8 bay were in terrific condition but the simple combiner that came with had fried due to a light lightning strike or eddy current. No burn marks anywhere but the coax wires inside the combiner popped like fuses.
I simply rewired as original and put it back in action. I do have more gain and adding the preamp certainly helps even more so.

I copied that concept to make a second combiner by stripping an existing two-way splitter and wiring the same as the original one.
So, right now, I have the western facing Yagi into one side of the combiner and the two eastern facing 8bays with a preamp to the other side of the combiner down by the TV set it self.

That's all that's active so far. My plan is run a third coax line from the 4-bay and create a 3 way combiner and hopefully capture an almost 180 degree signal pattern.

yes? No?

What would you advise?

Thanks thus far to all you guys.
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Old 16-Sep-2015, 12:34 AM   #8
rabbit73
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What started out as an antenna theory question has turned into a reception problem question. I quoted your question and have given my answer on the Help With Reception thread:
http://forum.tvfool.com/forumdisplay.php?f=7

Please go to:

My Answer to "Need Help with Combining Antennas" Post by 4.6 Explorer
http://forum.tvfool.com/showthread.php?t=15747

You will get more help there, and ADTech might have a better answer that I have overlooked. He works for Antennas Direct and has a lot of experience with 8-bay antennas because they make the DB8 and the newer DB8E.
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If you can not measure it, you can not improve it.
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Last edited by rabbit73; 16-Sep-2015 at 11:14 AM.
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