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  Topic Review (Newest First)
2020-01-24 07:55 PM
rabbit73
Quote:
Originally Posted by paxplant View Post
.....Currently using an RCA preamp on the antenna, I started out with a CM 7777 but the power supply woul d get extremely hot and the RCA works just as well as the CM did.
I wonder what caused it to get that hot? I ordered 2 new RCA TVPRAMP1R preamps in sealed boxes; they both failed.
Quote:
The bowtie I've settled on is the holl_ands New UHF concept with the dimensions tweaked for max gain at my UHF frequencies of interest. At 16 dbi and a bit over I'm probably as good as it gets for a 4 Bay. Once this is in place I'll be playing with a Udi-Yagi for the VHF.
Yeah, 16 dBi for a 4-Bay is about all you can expect. Nice of you to give credit to Shintaro Uda who did the work; Hidetsugu Yagi made it popular. Yagi filed a patent without Uda's name on it.
https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna
Quote:
Thought you might like to see the 'ditch' I have to aim up through. The desirable direction is basically through the smaller tree at the end.


Thank you for the photo; that looks promising. Can you remove the small tree?
Quote:
Couldn't seem to get it to load vertical in my album though.
Sometimes that can be difficult. Forum member lenlab had the same problem:
https://www.digitalhome.ca/forum/186...ml#post3084133

https://www.digitalhome.ca/forum/186...ml#post3084283
2020-01-24 02:40 PM
paxplant Years ago I did use a Directv dish here, but when they upgraded their equipment to use SWM that ended. Currently using an RCA preamp on the antenna, I started out with a CM 7777 but the power supply would get extremely hot and the RCA works just as well as the CM did.

The bowtie I've settled on is the holl_ands New UHF concept with the dimensions tweaked for max gain at my UHF frequencies of interest. At 16 dbi and a bit over I'm probably as good as it gets for a 4 Bay. Once this is in place I'll be playing with a Udi-Yagi for the VHF.

Thought you might like to see the 'ditch' I have to aim up through. The desirable direction is basically through the smaller tree at the end. Couldn't seem to get it to load vertical in my album though.

2020-01-24 01:15 PM
rabbit73
Quote:
Originally Posted by paxplant View Post
..Found it interesting that moving my antenna about 15 ft I can get 26 but 54 drops out.... move it back and 54 comes back and 26 drops out... still fishing for the sweet spot in this confined area.
That is not unusual. The wavefront is not uniform so there will be hot spots and cold spots, and they will be different for different frequencies.





Quote:
My bad about Real channel 31, should be 36 so I'll have to do some more tweaking to broaden the peak gain to cover 569 through 604 MHz.
Thank you for the clarification.
Quote:
Cable available... that's funny, lucky to have power at the end of a power line. Only cellular service that's close to dependable is Verizon and that can be spotty.
Now I understand why OTA reception is important to you. The only other option you have is satellite TV.
Quote:
I do find that these forecast reception maps can be a bit pessimistic about the stations you may be a able to get.
The software that is used to generate signal reports is fairly accurate for LOS signals, but can be way off for 2Edge and Tropo signals.
Quote:
Would like to ask if you could comment regarding the F/B F/R projections and if these values affect the gain?
I don't do modeling, and prefer to make measurements of antenna performance. But, it is my understanding that when you model an antenna you can specify what parameter is important to you, like gain, SWR, F/B, or bandwidth. It would seem that MAX net gain with an SWR below 2.7 would be most important to you. A high F/B would only be important if you had interference from the rear like co-channel interference from another transmitter on the same channel, as old sparks said.
Quote:
A big thank you for all the wisdom you have shared!
I'm glad that you have found some of my ideas useful. I have been doing antenna experiments since I was 8; I'm now 86 and still learning. I have built and measured many ham and TV antennas.

It would help if you could get your antenna above the trees on a tower or mast when aimed at Augusta, but that might be difficult.

Some people with a similar location have found improvement with a high gain Yagi like the Antennas Direct 91XG or the Solid Signal HDB91X and a preamp, but I'm not certain it would help you. You are using a preamp now, aren't you?





You can click on Map for a channel in your report to see the coverage map. If you click on Transmitter Distance for a channel, it will show the terrain profile.
2020-01-24 01:13 PM
old sparks
Quote:
Originally Posted by paxplant View Post
Would like to ask if you could comment regarding the F/B F/R projections and if these values affect the gain?
Gain is developed by reducing reception from other directions, including the rear of the antenna. Having said that, you're not building a satellite or EME array where a high F/R ratio is desirable to improve G/T.

IMO, as long as you don't have any interfering signals or noise from the rear, I would concentrate on maximizing gain (and return loss) at the frequencies of interest.
2020-01-24 11:42 AM
orbot You should be able to improve the F/B and F/R values by using a smaller grid spacing on your reflector. That also may increase gain a bit, but also swr, so you might want to move the 4-bay further away from the reflector if swr is "too high". The gain values in those pictures seem kind of high for a 4-bay, did you run the Average Gain Test before calculating the results?
2020-01-24 11:15 AM
ExDilbert One thing the posted map doesn't appear to take into consideration is signal refraction. That could explain what is being observed. I can get a couple of channels several miles behind a hill due to refraction. It shows up on the channel coverage maps on TVFool.
2020-01-24 10:29 AM
paxplant Thank you for the information,
The reception maps pretty much agree with real life, I can get Virtual channels 6 and 54 pretty good (even with the Hoverman I have up now). Used to get Virtual 26 too but ever since that station was bought by Spectrum they reduced power. Found it interesting that moving my antenna about 15 ft I can get 26 but 54 drops out.... move it back and 54 comes back and 26 drops out... still fishing for the sweet spot in this confined area.
My bad about Real channel 31, should be 36 so I'll have to do some more tweaking to broaden the peak gain to cover 569 through 604 MHz.

Cable available... that's funny, lucky to have power at the end of a power line. Only cellular service that's close to dependable is Verizon and that can be spotty.

I do find that these forecast reception maps can be a bit pessimistic about the stations you may be a able to get.

Would like to ask if you could comment regarding the F/B F/R projections and if these values affect the gain?

A big thank you for all the wisdom you have shared!
2020-01-23 10:01 PM
rabbit73
Quote:
Originally Posted by paxplant View Post
Oh my, you were so right... I hadn't checked the impedance setting, with it set to 300 it looks much better!
Thank you for checking; that's excellent!
2020-01-23 08:10 PM
rabbit73
Quote:
Originally Posted by paxplant View Post
Thanks Rabbit73,
I was wondering about the affect of the nasty looking F/B F/R curve, any recommended cures?
That's not too bad; holl_ands didn't do much better with his new UHF FF-4
https://imageevent.com/holl_ands/mul...yscreenreflopt

Quote:
I attached the rabbitears info just to add a little humor to your day (I guess it'll work by pasting the link in?).
It works; thanks for the report. I see what you mean; your location isn't very good for OTA reception. You have very weak signals, terrain interference, and trees make it worse.
Quote:
The channels I can get most of the time are virtual 6 and 54 and I'm trying to add 26 which I can get when there's a low cloud ceiling. I can also get channel 12 but conditions have to be right.
I'm a little confused.

It is the real channel number (also called physical channel or RF channel) that determines what antenna is needed.

VHF-Low, real channels 2-6
VHF-High, real channels 7-13
UHF, real channels 14-51

The virtual channel number (like 5.1 or 5-1) is a holdover from the analog TV days to maintain the identity of the station, and is what the TV displays. By convention, the virtual channel number is given in the decimal form to keep it from being confused with the real channel number.

https://www.rabbitears.info/searchma...study_id=47926



Quote:
I may come back later and add a separate VHF, but for now this is the best I've been able to do with a simple 4 Bay bowtie with a flat screen grid tweaked for 557, 569, and 575 MHz.
557: is real RF channel 28, what callsign do you mean, WJBF?
569: is real RF channel 30, WAGT ?
575: is real RF channel 31, ?

Virtual 6.1 is WJBF ABC, real 42, moving to 28 during Repack phase 8 1/18/2020 to 3/13/2020
Virtual 54.1 is WFXG Fox, real 36, staying there
Virtual 26.1 is WAGT NBC/CW, staying on real 30
Virtual 12.1 is WRDW CBS, staying on real 12; you will need a very good separate VHF-High antenna
Quote:
Very constrained on mounting location/height and by dense 100+ ft trees from 95 deg to 225 deg and another stand of trees from 270 deg over to about 70 deg. I've tried several time for the stations at ~ 222 deg but guess I can't get past the edge of trees that are blocking that direction.
Not good; trees block TV signals.
Siting the antenna
scroll down to Trees and UHF









Umm, do you have cable in your area?
2020-01-23 04:48 PM
paxplant Oh my, you were so right... I hadn't checked the impedance setting, with it set to 300 it looks much better!

2020-01-23 02:23 PM
paxplant Thanks Rabbit73,
I was wondering about the affect of the nasty looking F/B F/R curve, any recommended cures? I attached the rabbitears info just to add a little humor to your day (I guess it'll work by pasting the link in?). All three frequencies of interest are at 300 ohms, sorry about the overlay there. The channels I can get most of the time are virtual 6 and 54 and I'm trying to add 26 which I can get when there's a low cloud ceiling. I can also get channel 12 but conditions have to be right. Very constrained on mounting location/height and by dense 100+ ft trees from 95 deg to 225 deg and another stand of trees from 270 deg over to about 70 deg. I've tried several time for the stations at ~ 222 deg but guess I can't get past the edge of trees that are blocking that direction.

https://www.rabbitears.info/searchma...study_id=47926
2020-01-22 06:33 PM
rabbit73 Thank you for the images.

Your SWR of 6 is too high. It will cut your Raw Gain figure way down for less Net Gain.

Your previous post stated 300 ohms, but you have the ohms in the SWR curve window covered by a 540 MHz label. Did you set it for 50 ohms instead of 300 ohms?

Your design looks like a modification of holl_ands NEW-UHF [470-608 MHz] Free-Form 4-Bay (NU-FF4) Bowtie Antennas with Flat Screen Grid Reflector:
https://imageevent.com/holl_ands/mul...yscreenreflopt

What are your whisker lengths?

I would still like to see a signal report.
Quote:
Originally Posted by paxplant View Post
Getting ready for a repack scheduled for February. I may come back later and add a separate VHF, but for now this is the best I've been able to do with a simple 4 Bay bowtie with a flat screen grid tweaked for 557, 569, and 575 MHz. Gain of 16, impedance ~ 300, SWR ~ 6 at all three frequencies.
557: Real RF channel 28
569: 30
575: 31

What are the callsigns?
2020-01-22 02:14 PM
paxplant Thanks for the information. Constructive/instructive comments appreciated since I'm still learning. Created an album and uploaded pictures, now I'll try to add them...



2020-01-21 04:23 PM
rabbit73 You can make a forum photo album and post from that. The width is limited to 600 pixels. You can also use an image host like imgur.com and link from that.

How to create a photo album for use on the Digital Forum
https://www.digitalhome.ca/forum/52-...tal-forum.html
2020-01-21 02:19 PM
paxplant Well I've messed with this long enough an have to push the button to start building. Getting ready for a repack scheduled for February. I may come back later and add a separate VHF, but for now this is the best I've been able to do with a simple 4 Bay bowtie with a flat screen grid tweaked for 557, 569, and 575 MHz. Gain of 16, impedance ~ 300, SWR ~ 6 at all three frequencies. I have the screen shots to post but I don't know what's involved in setting up a URL for them. For a 36 x 42 size it'll work out for me.
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