Antenna Reuse experiment

[techforce5]

The antenna we will be talking about is 16 feet long and was 8 feet wide before I stripped the Vhf wands off. The one in the pictures.
I was wondering if anyone could help me out? I have been around the old type Tv antennas my whole life and remember helping my father install them on our home when I was a small boy. I thought I knew alot about them but it seems I don't. I am 76 and since I think that if I haven't learnt by myself by now I definitely need advice. Please make your answers in layman's terms as I don't know any of the complicated school terminology .
Since there is no more Vhs signal broadcast now I am trying to get rid of the unneeded Vhs part of my old antenna. My reasons for this are to reduce wind resistance, ease of handling when installing and and also I hope to beef up it's capability for signal receiving capability . I plan to add some short Uhf (I'll call them wands) and I plan on adding another Wing section with the strip of short flat 6 inch wands on the end I am stripping of the Vhf hardware . I stopped that process to take pictures so to try and explain what I found. Since I no longer have the installation manual for this antenna and for the changes I am trying to make I need to clarify a few things to understand how the antenna functioned originally. And how I will apply my alterations.
If you look closely at the pictures you will see some red tape on the left and near the tape you will see yellow paint on what appears to be two temperate sets of wire connecting studs. It seems that the Vhs part was isolated by plastic insulators and interconnected with bare aluminum wire running down the center of the antenna joining all the Vhf wands. On the the right where the red tape is you will also see some yellow paint and on the back side of where the yellow paint is two more posts to connect wires for the Uhf side of the antenna. This would make it two separate antennas on one frame?
I have always only had one coax cable running from the Tv to the antenna and connected to one set of wire connecting posts . I can't remember which set . Going back to my observation that both the Vhs and Uhf were isolated from the other doesn't that mean there should be two separate coax connecting one to the Vhs posts and one to the Uhf posts ?
If that is the case how would I have been able to join the two cables and reduce them to one lead to go back to the Tv? That being said since I am eliminating the Vhs section of the antenna wouldn't I install the new wing and additional wands directly to the aluminum frame with no need of the bare aluminum wire nor any insulators that ran the length of the Vhf section? In other words any additional wands and wing I add at this point would mount directly to the bare aluminum frame and I would just connect coax to the Uhf end wire posts using the flat wire to coax adapter and this then would utilize the whole antenna as one entire Uhf antenna without the need for the bare aluminum wire in the center running down the center nor plastic insulators ? I am now wondering if I ever had this antenna wired correctly to utilize both a Vhf and Uhf signal ?
First I need an explanation of how it would have been wired correctly upon inhalation when new . And then the answers to my changes and new creation. I hope you can understand the information that I am trying to supply here as it is confusing for me to even try to write it.
Thank you, Rick

 

[merlin]

These are the log periodic types, plus a UHF Yagi. Each is combined with a splitter for the single coax.
As a scanner antenna, it will work well if you mount it with the element vertical. It will be directional so keep a rotator in mind.
I butchered an old Winegard for the longest elements for my local ATSC channel 3 to 6. I found that a folded dipole works a bit better.
UHF channels here are a hard catch because those come from translators with not much power.
You can separate the VHF from UHF without changing the characteristics of the log periodic, but removing any elements will change that significantly. Effectively making a dipole that has a narrower bandwidth.
Note the reflector elements are missing on this antenna.
Perhaps research VHF log periodic antennas and Yagi antennas.

 

[techforce5]

There are no Vhs signals left around here everything is uhf Digital. Do you know anything about the rest of my questions in my first post?
The flat tail end wands are 6in and then there are a few others on the wing that measures 16in. and 23in. Is that the size I should fill in with where I removed the Vhs?

 

[Ubbe]

The longest elements at the rear are for the 50MHz band and are of a Yagi type, but elements are connected together in a cross phase shift pattern that makes it possible to reduce the distance between elements to half to make the antenna shorter, the type of connection you see with bow tie antennas to make them smaller in size.

The 500-700MHz UHF part at the front will be extremely directive with all those elements and are also of a Yagi type.

The mid part of the antenna are for the VHF band 175-250MHz and another section to the side in parallel are for the FM radio 88-108MHz band and also connects all four antenna bands together to one coax. I see no log periodic antenna design, all are Yagi.

There are plenty of elements for each band to make it very directive and will only be usable for scanner monitoring if sites are in one specific direction and are in the 45-60MHz band, or above 175MHz in VHF or above 500MHz in UHF but below 700MHz.

If I would modify it for scanner use I would chop off the antenna from the front UHF part to only leave 2-3 elements left at the middle. The same number of 2-3 elements left for the 88-108MHz part and cut their lengths to 160MHz. For the 175-250MHz I would do the same, 2-3 elements and cut their length to 450MHz. The distance between remaining elements on the boom should really need to be shortened to make it more effective, or only use one element as a single dipole type of antenna with no gain or directivety.

We would need to know what frequencies you need to receive and from what directions, to suggest a proper modification or a totally new antenna, like a logperiodic 100-800MHz antenna or perhaps a discone that receives from all directions if signal strengths are acceptable at your location.

/Ubbe

 

[merlin]

The mid part of the antenna are for the VHF band 175-250MHz and another section to the side in parallel are for the FM radio 88-108MHz band and also connects all four antenna bands together to one coax. I see no log periodic antenna design, all are Yagi.

Never saw a TV antenna with a 88 to 108 Mhz elements. This design has such broad bandwidth it coveres the FM band nicely.
The OPs antenna is like a combination of antenna designs, Yagi and log periodic, and the 'V' cofiguration is a 3rd design that broadens bandwidth and gives more polarity span (sort of a discone flavor). As is this will work well above 150MHz to 250 MHz. Lets not forget reasonance at higher frequencies.
You cross couple of dipoles, spaced 180° apart, that doubles the gain, just like log periodic.
I wold not modify a log periodic into a V configuration, the whole complicated maths would change.

 

[Ubbe]

I agree, this antenna are something special. The rear part are low VHF, the middle part high VHF with FM radio band going next to it in parallel and the front part are UHF. It's like an Antennacraft ST-2 antenna that combines several different frequency bands but this one uses Yagis instead of dipoles.

Logperiodic antennas are something different and works as a self adjusting Yagi with only a small number of the elements on the boom in resonance, and in the correct wavelenght from the front where the coax are attached, so that 2-3 elements at a time are effectively receiving the signal and delivers it into its two booms in opposite phases and the rest of the elements outside the frequency band are dead. A Yagi have almost all elements involved in the reception and can have issues when trying to make it broad banded.

/Ubbe

 

[merlin]

I agree, this antenna are something special. The rear part are low VHF, the middle part high VHF with FM radio band going next to it in parallel and the front part are UHF. It's like an Antennacraft ST-2 antenna that combines several different frequency bands but this one uses Yagis instead of dipoles.

Logperiodic antennas are something different and works as a self adjusting Yagi with only a small number of the elements on the boom in resonance, and in the correct wavelenght from the front where the coax are attached, so that 2-3 elements at a time are effectively receiving the signal and delivers it into its two booms in opposite phases and the rest of the elements outside the frequency band are dead. A Yagi have almost all elements involved in the reception and can have issues when trying to make it broad banded.

/Ubbe

Yes, you are right, the confusion here is this antenna is a mix of 3 different designs.

 

[prcguy]

Looking over the pictures I see the TV antenna is the type with angled VHF elements and I believe that design uses a set of elements for two frequencies, one at the fundamental lower frequency and again at 3X that frequency where the radiation pattern would be skewed off at an angle. To compensate they bend the elements back to split the difference between the two different frequencies to get a useable pattern.

The angled elements are not ideal for reusing the antenna for a ham or scanner project. Even if you could a log periodic design will have specific lengths and spacing between elements for a particular frequency range. You can cut down elements of a TV antenna to work at new frequencies but you cant easily change the spacing which was calculated for TV channels and not amateur or public service stuff. Also, the elements on most TV antennas are the worst quality being very thin sheet metal rolled into a tube but the seam is open, you cant even call it aluminum tubing. I would send the old TV antenna off to the dump and forget about using it for anything else unless you want to make yourself unhappy and regretful for all the time wasted thinking it was a good idea.

 

[techforce5]

The longest elements at the rear are for the 50MHz band and are of a Yagi type, but elements are connected together in a cross phase shift pattern that makes it possible to reduce the distance between elements to half to make the antenna shorter, the type of connection you see with bow tie antennas to make them smaller in size.

The 500-700MHz UHF part at the front will be extremely directive with all those elements and are also of a Yagi type.

The mid part of the antenna are for the VHF band 175-250MHz and another section to the side in parallel are for the FM radio 88-108MHz band and also connects all four antenna bands together to one coax. I see no log periodic antenna design, all are Yagi.

There are plenty of elements for each band to make it very directive and will only be usable for scanner monitoring if sites are in one specific direction and are in the 45-60MHz band, or above 175MHz in VHF or above 500MHz in UHF but below 700MHz.

If I would modify it for scanner use I would chop off the antenna from the front UHF part to only leave 2-3 elements left at the middle. The same number of 2-3 elements left for the 88-108MHz part and cut their lengths to 160MHz. For the 175-250MHz I would do the same, 2-3 elements and cut their length to 450MHz. The distance between remaining elements on the boom should really need to be shortened to make it more effective, or only use one element as a single dipole type of antenna with no gain or directivety.

We would need to know what frequencies you need to receive and from what directions, to suggest a proper modification or a totally new antenna, like a logperiodic 100-800MHz antenna or perhaps a discone that receives from all directions if signal strengths are acceptable at your location.

/Ubbe

Here is the channels I will want to receive. You will have to enlarge it. I am after the cluster of multiple stations that are shown inline plus a few of the others scattered. Thanks