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-   -   Low VHF antenna designs (http://forum.tvfool.com/showthread.php?t=16656)

JoeAZ 11-Aug-2019 9:58 PM

Low VHF antenna designs
 
Greetings everyone.
Since it is near impossible to purchase a low VHF band specific
antenna, It would be nice to have the information to build one.
Personally, I'd prefer a Low Band VHF antenna that covers Rf 2-6.
Currently, I've been using FM antennas to receive Rf 6 with fairly
good results. I'm finding FM antennas harder and harder to find
for purchase. Please include specific spacing, reflector, director
measurements. Appreciate your help!!

GroundUrMast 12-Aug-2019 1:06 AM

You're right Joe... Finding any commercially made L-VHF antennas has become nigh-on-impossible. I've just finished installing 4NEC2 antenna modeling software on my new computer so as I get back up to speed with it expect me to offer a few contributions to this thread. In the meantime, there are a few calculators available online.

Examples;
https://www.changpuak.ch/electronics...enna_DL6WU.php
https://www.changpuak.ch/electronics/Dipole_folded.php
https://www.changpuak.ch/electronics...da_antenna.php
http://www.vk5dj.com/yagi.html
https://www.qsl.net/4nec2/

JoeAZ 12-Aug-2019 11:20 PM

Really appreciate your information. I cannot help but
wonder if a low band VHF antenna, that covers Rf 2-6,
would differ from the channel specific designs you
provided????

GroundUrMast 13-Aug-2019 12:09 AM

Quote:

Originally Posted by JoeAZ (Post 62047)
Really appreciate your information. I cannot help but
wonder if a low band VHF antenna, that covers Rf 2-6,
would differ from the channel specific designs you
provided????

I need to get back up to speed with 4NEC2 still... But I expect to prove you right. There are a few things that can be done to broaden the frequency response of an antenna. The first that comes to mind is to use larger diameter elements. I'd also like to experiment with the length of the director elements.

rabbit73 13-Aug-2019 7:12 PM

2 Attachment(s)
Quote:

Originally Posted by JoeAZ (Post 62047)
Really appreciate your information. I cannot help but
wonder if a low band VHF antenna, that covers Rf 2-6,
would differ from the channel specific designs you
provided????

I also think that would probably be true. The bandwidth of a Yagi can be increased by increasing the element diameter and adjusting the spacing of the elements, but it will probably be at the expense of gain.

If you need even more bandwidth, the next step up would be a Log-Yagi which has log periodic active elements combined with parasitic elements. An example would be the VHF-High section of an RCA ANT751.

https://i.imgur.com/0HMm9FY.jpg

And finally, for the greatest bandwidth you would need a Log Periodic antenna design. Examples would be the VHF-High section of the Winegard HD7698P and the VHF-High/VHF-Low section of the Winegard HD-8200U.

https://forum.tvfool.com/attachment....3&d=1565736363

https://forum.tvfool.com/attachment....2&d=1565726635

The small extensions that you see on some of the 8200 VHF elements allow those elements to function on 2-6 AND 7-13.

rabbit73 13-Aug-2019 11:43 PM

Here is a file from holl_ands for a channel 3 to 5 Log-Yagi that has two active elements and a parasitic reflector and directors. Note that the gain curve is fairly flat across the design bandwidth, as opposed to a Yagi that has a gain curve that rises from the low end to the high end.
http://imageevent.com/holl_ands/logy...0elch35logyagi

This is the Antennacraft Y-10-2-6 Log-Yagi. The design is deficient for channel 2.
http://imageevent.com/holl_ands/logyagi/y1026

JoeAZ 14-Aug-2019 12:03 PM

I really appreciate all your suggestions and information.
Toying with the idea of producing antennas currently
either hard or impossible to find new. There are several
places in Phoenix that could make the components and
a place here in Prescott that could assemble the components
on the cheap. I just don't know if I want to undertake such
an ambitious project at this time in my life.....

rickbb 16-Aug-2019 7:06 PM

Just the design and testing phase would be time consuming.

After you get all that nailed the rest is just building and shipping.

Except for the after the sale customer service call headaches of course. lol

GroundUrMast 19-Aug-2019 6:11 AM

Here is another online calculator, for designing a Log-Periodic-Dipole-Array.

https://hamwaves.com/lpda/en/index.html

eggman531916 3-Nov-2019 6:04 AM

As always, there is good information here. Recently, a station that used to broadcast on RF 46 switched to RF 6 and now I find myself trying to figure out what to do. I've built probably close to a dozen or so UHF antennas, from M4's to a DBGH (currently on the house), but I've yet to try and tackle a L-VHF. Mainly because there has never been a need until now. I knew the station was going to make the switch, but I didn't care when it was only a religious station. But about a month before they switched, they added ION and Bounce to their line up and now I want to get it back. Has anyone as of yet tackled one of these monsters? If so, how did it work out for you?

OTAFAN 3-Nov-2019 7:58 AM

Quote:

But about a month before they switched, they added ION and Bounce to their line up and now I want to get it back. Has anyone as of yet tackled one of these monsters? If so, how did it work out for you?
Hi eggman:

I have two commercially produced moderate to compact size antennas with L-VHF extensions here in SOCAL LA/OC. The RCA ANT3037XR (actually built by Winegard for RCA) and the Winegard HD7000R, one each for my two Samsungs, 2013 40" and 2017 32". There are several low powered stations on Mt. Wilson above LA, broadcasting on the L-VHF frequency right now and one full powered station, KWHY 22 (display, physical 4) at 35kW power (yes, that's right!) which carries Retro TV on KBEH 63-3. Since part of my TV viewing includes Retro programming, that was why I put up those antennas. Plus, there might be possibilities of other stations moving to L-VHF in the future or increasing their signal. Nothing firm at the moment, just chatter from the NET. I'm in a strong to moderate signal area, 35 miles south of Mt. Wilson, so I get excellent (100%) reception from KBEH which transmits off the KWHY 22 tower. So, yeah it's worked out well for me.

I hope this helps answer your query. I know you mentioned you build your own TV antennas, so I can't really help you with that issue if that's what you were looking for.

Anyway, all the best.....

Tim 4-Nov-2019 2:08 AM

Quote:

Originally Posted by eggman531916 (Post 62380)
As always, there is good information here. Recently, a station that used to broadcast on RF 46 switched to RF 6 and now I find myself trying to figure out what to do. I've built probably close to a dozen or so UHF antennas, from M4's to a DBGH (currently on the house), but I've yet to try and tackle a L-VHF. Mainly because there has never been a need until now. I knew the station was going to make the switch, but I didn't care when it was only a religious station. But about a month before they switched, they added ION and Bounce to their line up and now I want to get it back. Has anyone as of yet tackled one of these monsters? If so, how did it work out for you?

I don't know how far you are from the antenna, but you could try a simple dipole antenna for 85 MHz. Each leg should be about 2.75 ft in length. You could feed it directly with RG-6.

Or if you need more gain, try a 3 element Yagi antenna. I expect you would get about 6 dB gain out of a 3 element Yagi as compared to a dipole.

You can use this calculator for the measurements (note: measurements in meters)
https://www.rfwireless-world.com/cal...alculator.html

Or this one has measurements in feet and inches plus measurements for additional director elements if needed:
http://www.wc7i.com/yagi_calculator.htm

eggman531916 4-Nov-2019 3:17 PM

Thank you for the information guys. I do want to try and build one to see if I can pull it off. But my plans may be on hold until the spring. I am roughly 30 miles from the towers of the Altoona antenna farm in PA, but due to the mountains, all my signals are 2 edge. I'll give it a shot as soon as I can. Thank you again.

rabbit73 4-Nov-2019 5:44 PM

Quote:

Originally Posted by eggman531916 (Post 62387)
I am roughly 30 miles from the towers of the Altoona antenna farm in PA, but due to the mountains, all my signals are 2 edge.

What does your TVFool signal report look like?

Tower Guy 4-Nov-2019 8:06 PM

Hi eggman.

What material would you like to use to build your channel 6 yagi?

I did a design that uses 3/4” hardline from a CATV scrap pile for the elements. I’ll send you the dimensions if you have access to that material.

I have also built a bidirectional V beam from simple wire. A full rhombic is another option.

In hilly areas such as yours the location of the antenna makes a significant difference. I have seen antennas in the side yard on a 10’ pole work better than the roof.

Goo goo gachoo.

rabbit73 5-Nov-2019 12:35 AM

Quote:

Originally Posted by eggman531916 (Post 62380)
Recently, a station that used to broadcast on RF 46 switched to RF 6 and now I find myself trying to figure out what to do. I've built probably close to a dozen or so UHF antennas, but I've yet to try and tackle a L-VHF. I knew the station was going to make the switch, but I didn't care when it was only a religious station. But about a month before they switched, they added ION and Bounce to their line up and now I want to get it back. Has anyone as of yet tackled one of these monsters?

Is that WKBS?
https://www.rabbitears.info/repackch...=&lss=&status=

https://www.rabbitears.info/market.p...=13929#station

The strength of the WKBS signal at your location will determine what type of Channel 6 antenna you will need. On the plus side, VHF signals can make it over rough terrain better than UHF signals. On the minus side, the noise level from electrical interference is high on VHF-Low, requiring a stronger signal with sufficient SNR above the noise.

Tower Guy is correct; try different locations for your DIY CH 6 antenna.

I made some measurements of electrical noise on all three TV bands; it was highest on VHF-Low:

https://i.imgur.com/aAU1EBY.png

This is what the noise looks like on VHF-Low at my location. The signal had to be at least -8 dBmV (-57 dBm), which is a fairly strong OTA signal equivalent to 34 dB NM on a TVFool report, for reliable reception:

https://i.imgur.com/DwQNtji.jpg

Signal diagnostics:

https://i.imgur.com/eiRXzRu.jpg

Channel 3 folded dipole antenna:

https://i.imgur.com/6qYVZsO.jpg

rabbit73 5-Nov-2019 1:09 PM

3 Attachment(s)
cambria county on AVS extended the rear elements on his RCA ANT751 to be able to receive WQED from Pittsburgh. It moved from 13 to 4.

https://www.avsforum.com/forum/45-lo...l#post58584134
Quote:

Originally Posted by cambria county (Post 58584134)
I extended the rear elements on my Rca-751 antenna to get Wqed 13 (rf-4). It works very good at my location. I am about 58 miles from Wqed tower.

Quote:

I made the rear elements about 48" each side. I used elements from old antenna's. Just used flat screwdriver and pliers to open seam where the slit is. Slid onto existing element and ran foil tape around it. Before I did this, Wqed was not decoding on the Zenith box. It was very close to opening. That is when I got the idea to extend back elements for rf-4 aka Wqed. I was suprised how strong it was after I did this. On another note, I ordered stellar labs version of the Rca-751 and the fringe yagi 30-2476. Wtov 9-Steubenville not quite strong enough to decode with Rca-751 here. (90 mile signal). I think the 30-2476 will get the job done. Hopefully, I can shoot for Wtrf-7 Wheeling, also. The cw-rf 11 is real easy to get here for some reason. Fox 8 comes in very strong with the rca-751.
https://forum.tvfool.com/attachment....4&d=1572963758

Those elements are a little too long for channel 6; should be more like 33 or 34 inches on each side.

This is what the Winegard HD7000R looks like with the VHF-Low extensions added:

https://forum.tvfool.com/attachment....5&d=1572964727

https://forum.tvfool.com/attachment....6&d=1572966677

JoeAZ 5-Nov-2019 5:16 PM

Another option would be to use an FM antenna, especially for
Rf 6. You cannot beat the price..... and it works very well
for a 500 watt, Rf 6, translator at 20 miles away.

https://www.newark.com/stellar-labs/...ING-Electrical

rabbit73 5-Nov-2019 6:51 PM

That's a good idea.

eggman531916 6-Nov-2019 5:11 PM

http://www.tvfool.com/?option=com_wr...90386ebd6201d7
My TVFool report. It's not very accurate as these are the old listings and the channel I'm trying to get isn't even on there BEFORE the switch. Actually, my NBC station used to come in on RF 34 which isn't on the report either. They switched to RF 35 around the same time and signal now cuts in and out. Maybe an LTE filter is needed? I don't know. I haven't had a chance to try anything yet. Hopefully over the weekend. I apologize as I just now have only had a chance to check the thread and am getting ready to run out the door to work. I'll look over everything everyone has posted ASAP. Thank you all.


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