3: Bow tie antenna for reception of WCBS 608 MHz
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- เผยแพร่เมื่อ 11 ก.ย. 2024
- How to scale the bow-tie antenna to other frequencies and some alternatives for better reception.
The plate (in MMANA simulated with wires) could be made easily with the side from an old box, just cover it with aluminium foil.
And of course use good (low attenuation) coaxial cable. If the cable is longer, a pre-amplifier is recommended.
Used links for calculation:
3g-aerial.biz/...
MMANA-GAL (basic version is sufficient): gal-ana.de/basi...
Keep it simple! Bowtie best gain for the entire UHF band would be 18" width total with a 24" reflector with spacing between the feeds about 1 to 2 inch apart.
Thanks for your addition!
Hi: Thank you for taking the time to try and answer my question, but I am afraid it does not. I think there has been some misunderstanding, again.
First of all, those "inch" measurements that I used in my question, for instance, the 7.28" width, ARE from one of those calculators. I had already converted the resulting mm to inches for my own purposes as I work in inches. Sorry. And perhaps I confused the issue further, because I also called it "width" as the resulting "length" is the width of the bowtie, sorry.
Let me try asking a different way, using your results: You come up with a wire length of .083 for a bowtie designed for WCBS TV New York, which is UHF channel 36, broadcasting at 608 mhz. If I built a bowtie using them, to those dimensions, it would have .083 length elements, as you say.
BUT that is not even close to the recommended length of the elements for a UHF TV antenna anywhere within the range of UHF broadcast frequencies! Recommended are, as I pointed out (depending on the designer or manufacturer) anywhere from about 9.5 inches to 12.5 inches (241 mm to 318 mm). However, your result, and my results from the same calculators you used, give figures like this .083 meters, which is 3.26 inches! If you note, that is (very) approximately half of my original question, where I used 7.28". The difference we arrived at is simply the difference of which calculator we used... I have gotten @ your results, also.
I fear this will still not be understood, somehow. Maybe I'll distill it down to one, simple, question:
"Why do the bowtie dimension calculators return segment lengths about 80 to 100 mm, when the builders, designers and manufacturers of UHF TV antennas use segment lengths of about 241 to 318 mm?".
For instance, look at the antennas of Michael at Cosmic Antennas, or Danny Hodges (he uses 10" elements), and others. For that matter, just search for UHF Television bowtie antennas. The segments are always at least 9" or 10" (228.6 mm or 254 mm), to about 12.5" (318 mm). They are always FAR larger, by multiples, than these calculators return.
Thanks again for trying to understand this. You are not alone in missing my point here... I came across a great many others, similarly confused. If no one can answer or explain it, I'll have to simply build an antenna with the common dimensions used "out there", because NOBODY build UHF TV antennas to the size the calculators return. That cannot be correct, or they would.
Hi, the Bow-tie antenna I showed in my video's is just a single element. I am not sure if I found the antenna’s you suggested, many of them are not for just a single frequency but for the whole UHF TV band. In review of such antenna (th-cam.com/video/m1b5h0IKqh4/w-d-xo.html ) is even mentioned it is also for the VHF channels… ? (But there is an additional option with a smaller dipole for UHF?).
The UHF-TV band is between 470 and 700 MHz. In wavelength that is from 640 mm to 430 mm. That is a large span! Half a wavelength multiplied by 0.7 is 223 mm to 150 mm. So if you are at the top of the band you need (for optimum performance) a much shorter element then for the lower part of the band.
The element lengths that you mention are not in this range and I can not explain why, you could ask them what antenna theory underlies it (and if the results proved by measurements).
What I also see that several designs use stacked antenna’s with the reflector plate, not oll bow tie but also whiskers. Stacking should not influence the length of the individual bow tie antenna’s but if built correctly, it would give more gain than a single element.
However, if you have the materials (they are not expensive): just try what will give you the best results.
And be aware of the polarization: the ones that I saw offered are shown in horizontal polarization and if I am informed well, WCBS uses vertical polarization. So you need to tilt those antenna’s 90 degrees side wards.
Keep in mind: wonder antenna’s do not exist. Designs of antenna's that are small, offer lot of gain and broadband should ring bells ;-)
Keep an eye on my channel for the moment I will make a video about the basic principles of antenna’s.
@@chrix2381 Thank you again for attempting to answer the question, but for some reason I don't understand, I am not able to properly explain the issue to you.
Yes I do understand everything you say in your answers... in the video, and in the recent answer just above. I do know all this pretty well after watching many videos, and looking around the web. And "no" this is not about me hoping for a "wonder antenna". And yes, there is a range of UHF stations/frequencies, as you correctly relate, and yes there is no ideal antenna, and one must make choices for the range they are interested in.
The question is entirely different here, and I am sorry I would not know how else to explain it, other than how I already have. Well maybe I'll try one more time:
When one uses these calculators and calculations to determine the proper dimensions of a UHF bowtie antenna, the resulting measurements are far, far, smaller than any of the antennas made or used for ACTUAL UHF TV reception. Entirely different. The resulting measurements, from those calculators, is entirely and completely off the range of sizes actually used for that range of UHF antenna designs that is used, in practice. The results do not even overlap, at all, and would result in antennas that are far tinier than anything actually used or selected.
It is that disparity which is the question: Why? Nobody builds anything that small, and I doubt they would work as I've seen the tests for the larger size bowtie antennas, and they need to be 9" to 12.5" (each side of the bowtie). So I doubt the little 3" to 4" bowties the calculators come up with, would even work at all.
@@proto57 I understand that you are faced with differences that you could not explain. Neither could I.
I have seen calculators that gave strange results, therefore I simulated it with MMANA. That is a serious simulation application, not a few formula’s that come up with some numbers.
A single dipole is half a wavelength long (as stated in every basic antenna handbook) en for thicker elements (like Bow tie) this length is reduced. In this example with a factor of about 0.7.
I showed measurements with these dimensions in video 2.
If others make their elements a lot longer, it means that they are for a longer wavelength = lower frequency.
I would suggest those others how they came up to their element lengths, why are they so different then basic antenna theory and are these antenna’s measured on their frequency with respect to resonance and gain?
If they do not come back to you with the results, you know enough. If you get a serious plausible answer, please let me know, very curious about that.
@@chrix2381 Well then it will remain a mystery for now, anyway. But thanks again.
Did you look at Michael's antennas at Cosmic Antennas? His are representative of what is always done out there, and would probably explain my issues better than all my words. I can't link in your comments, but if you search for cosmic antenna diy bowtie you will see them. I did write to him with a couple of questions, but have not heard back.
But as I said, searching TH-cam, and the internet, will show a great many DIY and commercial UHF bowties, all demonstrating the issue. Meanwhile, I am going to make my two bowtie to Michael's dimensions, with 12.5" elements as shown in his "12x15 Two-Bay Bowtie" plans. These are typical dimensions, and he has found they work well, as he says, for "... it works very well for ALL CURRENT UHF frequencies (14-36) tested out to 30+ miles, post repack.", and, "4NEC2 MODELING across all available UHF 470-608MHz.
Raw Gain 12.25-13.81
Net Gain 11.83-12.61
SWR 1.95 good, above Rf 29, SWR 2.92 high, if you have many channels above 29 the FF4 may be a better choice for you."
So like you, I would rather know the "why" of it, and come up with my own figures. I don't like just blindly copying the results of others... but, in this case, I have to. But also, given the many great reviews of these antennas, with these measurements, I don't think I can go wrong.
Rich.