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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


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