Fractal TV Antenna Research & Development - Page 23 - Canadian TV, Computing and Home Theatre Forums

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post #331 of 341 (permalink) Old 2017-05-19, 01:55 PM
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Originally Posted by majortom View Post
OK got it... his link, buried within tags, only shows up when you use 'quick reply', 'quote message text', and 'advanced'. that is quite annoying, isn't it..
Yup, very annoying, but I thought it needed to be done so that holl_ands and others could see the Regolith images to properly comment on the Regolith model.

Maybe Regolith can use a different way to show his images, next time.

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2017-05-19 at 02:13 PM.
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post #332 of 341 (permalink) Old 2017-05-19, 05:05 PM
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The above posted *.html File [which EVAL generated] contains (almost) EVERYTHING you would want to know about the Design, incl. 4nec2 File, Dimensioned Drawing, Raw/Net Gain and SWR Freq. Response(s) and Results Text Summary which I posted above. About the only thing I would want is to ALSO see RAW GAIN in the Azimuthal Gain Plots...beware they currently ONLY display NET GAIN....which is VERY RARELY of interest:
http://photos.imageevent.com/holl_an...Fixed.nec.html

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #333 of 341 (permalink) Old 2017-05-20, 05:16 PM
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Smile Many Thanks

Many thanks to majortom, holl_ands, rabbit73 and nikiml for all the good work you have done in response to my posts to this thread. I will definitely be using jpegs for future images. I have visited your websites often and picked up many good ideas.

Just to summarize: my summer project will be to put up two antennas in Sequim, WA. One will face north to pick up Victoria and Vancouver stations and the other will face southeast to pick up Seattle stations. I currently have an old long-range antenna I picked up many years ago at Radio Shack. It sits on top of a rotor and works OK. I can pick up most of the available UHF stations from Canada depending on atmospherics but only two VHF stations from Seattle, channels 9 and 11. The main problem with my current setup is that the digital decoder box has to be retuned every time I change the direction of the antenna. A little bit of a pain in the neck for me, but this seems to be nigh impossible to figure out by my wife and my out of town guests (mostly her relations). My goal is to have a static antenna array so my technologically challenged relations can just turn on the TV and not have to fuss with the rotor and the digital decoder box.

My plan is to use a GH10 ala nikiml to pick up Canadian UHF. The toughest station to get is CBUT-DT ch 43, 100 miles away. Hopefully a SBGH will do it, but I will consider a DBGH if need be.

I used to get many Seattle stations until VHF low went away. Now all I get are channels 9 and 11. There is another VHF channel (13) in the south Sound but too many mountains block this source. The big three Seattle stations – KOMO, KIRO and KING – though on the same compass direction as ch 9 and 11 are all on UHF these days and therefore probably unattainable.

For Seattle I will first try the 4 bay Koch fractal. Using 4nec2 I was able to adjust the reflectors to create a 15 dB spike at 640 MHz to try and pick the three UHF channels while maintaining an 8.5-9.0 dB bump at around 190-205 MHz. Alas, according to the TVfool plot I am about 5-6 dBs below the power threshold for picking up any of these stations. Perhaps a masthead amp will do the trick. I have used a similar 4 bay Koch fractal without reflectors or amps to pick VHF and UHF in the Tucson area from about 45 miles away. That works great there.

If the 4 bay Koch fractal doesn't work I will go with the fractalized GH VHF antenna, not 300Ohms' version but the Koch fractal version which majortom put on nikiml's website (see page 21 of this thread). My reason for going fractal is strictly size. The Koch version with reflectors has a 6' by 6' form factor while 300Ohms' version is about 15" taller. Nikiml's GH4 VHF is over 9' tall and his short GH4 VHF has a form factor of 4' by 7.25'. All of the shorter/smaller/fractalized versions of nikiml's original GH4 VHF antenna have gains of 12-13 dBs according to 4nec2. I guess I will see if modeling agrees with reality.

To tie the two antennas together I will use a Televes, 3 Input, Mast Mounted, Combiner/Amplifier. It has inputs for two UHF and one VHF antenna. It comes with a power injector and each input can be adjusted to increase or decrease gain. I will try different input combinations for the antennas mentioned above to see which works best.

I will report back to this thread later this summer with the results of my project. Thanks again.
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post #334 of 341 (permalink) Old 2017-05-20, 06:54 PM
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Thank you for the details about your project; very challenging.

Out of curiosity, I did a generic tvfool signal report for Sequim:
TV Fool

Would it be possible for you to do a report based on your location, which wouldn't show in the report?

Maybe you already posted a report link, and I missed it.

You can do a report here:
TV Fool


Quote:
The main problem with my current setup is that the digital decoder box has to be retuned every time I change the direction of the antenna.
Some tuners can add a channel after scan, like on my Sony TVs, to avoid the need to rescan after changing direction.
Quote:
Alas, according to the TVfool plot I am about 5-6 dBs below the power threshold for picking up any of these stations. Perhaps a masthead amp will do the trick.
It is impossible to receive signals with a Noise Margin below -15 dB, because they would be below the thermal noise floor. If you are able to receive a signal below NM -15 dB, either the tvfool report is wrong, or the signal has received enhancement from tropospheric propagation.


If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2017-05-20 at 07:39 PM.
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post #335 of 341 (permalink) Old 2017-05-20, 09:36 PM
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rabbit73

Maybe I'm on a fool's errand on this project, but I will try it just the same. If after putting up the new antennas my reception hasn't changed for the worse and I can still get the stations I get now, I will still count it as a win having eliminated the big rotor and all the infrastructure it requires.

Funny thing about the TV Fool channel table, I get channels 9 and 11 much better than the numbers would seem to indicate. I have gotten occasional hints of KING-DT by the digital decoder box but have never had enough signal strength to even pixelate the channel. Your Noise Margin graph seems to indicate that I will never pick up the Seattle UHF channels from my site in Sequim. If that is indeed the case, look for a home built HDTV antenna for sale coming to a flea market near you. Ha ha.

Thanks for the feed back.
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post #336 of 341 (permalink) Old 2017-05-21, 02:11 PM
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I don't think you are on a fool's errand. You will not be happy until you find out what is possible at your location, and you will learn a lot.

I encourage antenna experimentation, and learn something every time, especially when it doesn't work. Then I have to figure out why.

The tvfool report is only a computer simulation, and is often way off with 2Edge signals, especially with rough terrain.
Quote:
Your Noise Margin graph seems to indicate that I will never pick up the Seattle UHF channels from my site in Sequim.
It indicates that it is impossible to receive signals that are below the Thermal Noise Floor at -106 dBm. If a signal is stronger than that at your location for whatever reason, you do have a chance of receiving it.
Signal Strength, Signal-to-Noise and Other Related Topics

An antenna with a lot of gain can't "pull it out of the noise" below -106 dBm. And a preamp certainly can't do it because it adds its own noise which degrades the SNR. First, the antenna must increase the signal strength, which it does without decreasing the SNR, to allow for the minimum required SNR of 15 dB and the noise figure of the preamp. Then the preamp can make the signal strong enough to overcome the tuner noise figure and the distribution losses.

This means that the signal must be at least -91 dBm to allow for the minimum required SNR of 15 dB. This is what the tvfool report calls 0 dB NM. You can see that the difference between the NM and the signal power is a constant of 91 dB.

The report assumes that you are using a preamp, which will bury the tuner noise figure in the amplified noise floor. But, if you are not using a preamp, you have to allow for the tuner noise figure, which is about 6 dB. That means the minimum signal without a preamp must be at least -85 dBm (NM +6 dB) where most tuners drop out.


If you can not measure it, you can not improve it.
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post #337 of 341 (permalink) Old 2017-05-21, 02:23 PM
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You can get an estimate of your system performance by doing a System Noise Figure calculation. Here is the calculation for the Weak Signal DX NM diagram:



with a little tweaking, maybe you can do even better:


If you can not measure it, you can not improve it.
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post #338 of 341 (permalink) Old 2017-05-21, 04:41 PM
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Thanks for the image of your tvfool report. It's hard to read because it isn't very sharp, but that's because the forum says your album image can't be any wider than 600 pixels.

This about as sharp as you can get it within the forum limits:



unless you do it in two parts like this:





which is why I use an image host or give the link to the report.

I did an estimated report based on your image; I think it's pretty close:
TV Fool

It would be more useful if you had posted the active link to your report, which would allow us to click on a callsign to see the terrain profile. For example, this is for KING. The transmitter is on the left, and your location is on the right behind a mountain.
TV Fool



Quote:
My goal is to have a static antenna array so my technologically challenged relations can just turn on the TV and not have to fuss with the rotor and the digital decoder box.
That will be difficult, but it isn't impossible, if the signals are available from each antenna before combining. Combining two UHF antennas aimed in different directions doesn't always work, in spite of what the preamp and antenna marketing descriptions claim.

If it was easy to do, CATV systems wouldn't have to do this:



If you are willing to settle for 9 and 11 from Seattle, you can combine a VHF antenna aimed at them with a UHF antenna aimed north with a UVSJ, and you are done.
Stellar Labs Deep Fringe Directional Antenna VHF-Hi HDTV 174 - 230MHz | 30-2476 (302476) | Stellar Labs

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2017-05-21 at 07:47 PM.
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post #339 of 341 (permalink) Old 2017-05-22, 07:38 PM
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KING on Ch48 will NEVER be received...it has NM = -27.7 dB...ain't gonna happen, even with Ultra-Low NF Preamp, Tall Mast and Stacked Antennas.....and the Coup de Grace: Adjacent Ch49 has NM = 24.7 dB, which is 52.4 dB STRONGER than Ch48....so you would need a LOT higher F/R Suppression than is typically possible. Also note that even if you carefully selected a UHF Antenna with a Deep Null Directly to the Rear [e.g. A-D 91XG] to Null out Ch48, you would Lose about 3 dB in Forward Direction since they are NOT exactly 180-deg apart in direction.

An EXTREME Antenna System is lucky if it works with NM's in the negative teen's....or BETTER....

You wouldn't lose ANY Resolution, if you simply did a COPY/PASTE of TVFool's Results URL (WebAddess at top of WebBrowser) directly into a post on this Forum....Easy/Peasy. And FMFool added a similar capability, except it now provides a Results WebAddress as an embedded link that can you can simply COPY/PASTE into a Post.

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #340 of 341 (permalink) Old 2017-06-05, 03:57 PM
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Thanks to all of your input, I have been convinced that UHF reception from Seattle is a not realistic for my site. The main reason I would like to be able to view KING, KOMO or KIRO is for local news and weather. Victoria and Vancouver news and weather is not particularly relevant to Sequim, WA. We seem to be just outside their realm of interest.

So I have modified my plan somewhat. For Seattle I will put up the Deep Fringe VHF-HI antenna suggested by rabbit73. $35 is not a bad trade off for the savings in materials, labor and time for constructing my own VHF antenna of whatever style. Plus this antenna has better results on 4nec2 than antennas of my own design. It should pick up channels 9 and 11 just fine. For Canadian TV I will put up the 4 bay Koch fractal antenna (Ruckman) with screen reflectors. It seems to have slightly better performance predictions from 4nec2 than the GH10. However, if I get too much interference from 800-900 MHz, I can replace it with a GH just as easily. Finally, I will also put up a 5 director yagi with corner reflectors pointed at Port Angeles to try and pick up K30FL-D CH30, a KIRO TV (CBS) station. I will build this antenna myself . The boom length is just under 4 ft. and will fit nicely on my roof with the other antennas.

I will report back sometime in August after everything is up and hopefully working.
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post #341 of 341 (permalink) Old 2017-06-05, 08:34 PM
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Quote:
I will also put up a 5 director yagi with corner reflectors pointed at Port Angeles to try and pick up K30FL-D CH30, a KIRO TV (CBS) station.
That might work; it's worth a try. K30FL has a short tower and the FCC Longley-Rice coverage map shows spotty coverage in your area.

tvfool terrain profile for K30FL:

TV Fool

Here is a different terrain profile:



Here is a close up coverage map of your area:



which came from here:
RabbitEars.Info

If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2017-06-05 at 09:00 PM.
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