specific Log Periodic benefit

[AlphaFive]

In reading various sources about Log Periodic antennas it is very clear that a Log Periodic will handle decibel reception of a transmitter well beyond what a wideband discone can provide. That much I am clear on. What I am puzzled by is this; I find over and over the same phrase regarding Log Periodic performance "It improves the reception of weak signals". Okay, can someone tell me if those statements refer to a decibel improvement, or is there some reason the set up of elements on a Log Periodic can actually pull in a signal that may be 70 miles distant, where an average discone may generally be limited to 30 to 50 miles? In other words, can a Log Periodic have a longer distance reception range? Or is it only a champ regarding pulling in the same signal as a discone, but having decibel superiority? I clearly, absolutely, understand that this conversation can be had in only the most general terms, and every situation is different for any number of reasons. I am just trying to determine why a Log Periodic will beat a discone on any given Tuesday....I believe it, but want to know more. Thank you for your time.

 

[mancow]

Logs are sort of a like a lower gain super wide bandwidth beam. So yea, they have some gain toward the direction they are pointing.

 

[AlphaFive]

Log Periodic

I am so tempted to get one just to compare it to my discones. The best way to learn something is to do it yourself. Being located in the middle of rings of mountains is unique terrain, it might just do something crazy. It is really hard to tell about the benefit though, very few real specific comparisions... I can tell I'm going to do it. Have been relying on discones for must be thirty years, time to try something new. Take care

 

[mancow]

It's a difficult thing to compare since it all depends on your environment and what you want to hear. I have a discone (diamond I think) and a DPD Productions Log Periodic. The log definitely has better reception toward the area it's pointing but does fairly well in other areas. I tend to use it as a wideband yagi and leave it pointed toward the KC area.

I highly recommend the DPD Productions antenna. The build quality is excellent. Mine has been up there for many years and still looks and works like new.

 

[AlphaFive]

Log Periodic

Ten Roger on the difficult comparison. And thanks for giving me something to look into, I do appreciate that.

 

[AlphaFive]

Log Periodic

I went to their website. Very nice, easy to review. The products look like high quality, unfortunately the "LP" products are not being produced at the moment. Ke' sera sera, or something like that.
Still hoping someone has both, and can say if there has been a noticeable difference, over a long period of time. Thanks again.

 

[prcguy]

Think of a beam antenna like a Yagi or Log Periodic type as a telescope. Your naked eye can see a certain detail at a distance but placing a few lenses in front of your eye will bring in images you cant otherwise see. The lenses are picking up a larger capture area of light and focusing it onto the much smaller lens in your eye and ultimately your retina.

The elements in a directional antenna are like a reflector and lenses to light, taking signals that would be otherwise wasted in all directions and herding it in one direction where they are multiplied.

The effects are the same on transmit and receive where on receive the antenna looks like it has a much larger capture area and focuses signals spread over a larger area onto a smaller one, which would be the dipole in a Yagi or the active area of a Log Periodic. On transmit the power that would normally be wasted in all directions is multiplied when focused into a smaller area.

This description is probably not textbook and is more of what my brain pictures when I try to explain things.

 

[AlphaFive]

Log Periodic

Very well explained.. It takes the other information I have been reading, and put it into clear focus (no pun intended).. See if the kid in the back of the class is beginning to get this;
If I'm looking down on a map with a 40 mile radius depicting transmit sites. There will be a certain few that for different reasons a standard discone will have a difficult time processing. A Log Periodic will look at a specific area in the 40 mile circumference, and because of the nature of it's construction, receive, and process the signal in a manner that let's it be heard.
But, it is not necessarily a given that the L.P. antenna will reach out 70 miles and do the same thing, am I on the right track here?? It's not necessarily distance, but the quality of what is closest to you?

 

[mancow]

Yes that's the general idea.

 

[AlphaFive]

Log Periodic

Wasn't that from Star Trek 4? haaaaaa, Nice graphic there. Thanks for the reply. Learned something today. Hope someone else does too.

 

[chief21]

Log Periodic (LP) antennas typically have multiple elements, each cut for a different band or sub-band. This makes them desirable for commercial or government HF stations which often require extreme frequency agility. In addition, there is a certain degree of directionality since the elements share a common boom, but not as much gain as a true yagi or beam.

FYI... I just visited the DPD website and there is a note that their LP models are not being produced at this time,

 

[AlphaFive]

Log Periodic

Yes, reference the Yagi antennas, I had seen that they did have a very high gain, they sound perfect, except.... Everyone I look at has such a limited bandwidth... In order to cover an approximate 100 Mhz. to 1300 Mhz. range, a person would need several Yagi's, just not practical if you want it all and not something specific. That's what I get for being greedy.

 

[prcguy]

Maybe look at it this way. All the transmit sites on your map are light bulbs and you are in the center looking 360deg around you at night at these light bulbs. Some light bulb sites may be blocked from view due to hills or surroundings and some may be so far away that the light you see is very dim or just not visible at all. Also consider that every building, water tower or hill is a mirror that can potentially reflect some light that is partially blocked.

Now consider a broad band antenna with no gain like a Discone as your eyes and imagine what a telescope might do for some of those distant light bulbs that are a little too dim to see with the naked eye. A Yagi or Log Periodic will be like a telescope and can see into the distance better than a Discone and bring weak signals up to a level that your receiver can make use of.

Radio waves in the VHF/UHF spectrum propagate similar to light in they are mostly line of sight but somewhat more forgiving when blocked by trees, buildings, etc. Antennas with gain will do for radio waves what lenses will do for light. In fact, at very high frequencies (like 40GHz and above) where wavelengths are small enough, actual lenses made of plastic are used to collect the radio waves over a large surface area and focus them down to a smaller area to achieve gain just like light.

Just like light, some radio signals might be too far away to be picked up or may be completely blocked by hills, so there are many factors that determine radio reception distance, just like light.

Very well explained.. It takes the other information I have been reading, and put it into clear focus (no pun intended).. See if the kid in the back of the class is beginning to get this;
If I'm looking down on a map with a 40 mile radius depicting transmit sites. There will be a certain few that for different reasons a standard discone will have a difficult time processing. A Log Periodic will look at a specific area in the 40 mile circumference, and because of the nature of it's construction, receive, and process the signal in a manner that let's it be heard.
But, it is not necessarily a given that the L.P. antenna will reach out 70 miles and do the same thing, am I on the right track here?? It's not necessarily distance, but the quality of what is closest to you?

 

[Ubbe]

A discone antenna receive signals from all directions and up from the sky. As soon as you want some gain you have to sacrifice reception from some directions, usually you select to ignore signals coming from the ground and from the sky and only concentrate on a small vertical angle at the horizon, where all the transmit towers are.

The smaller the angle you can use the higher the gain will be. If you also can be without coverage from a direction from behind and somewhat from the sides you can increase the gain even further.

A yagi antenna have a limited frequency range but great gain. One could say that a logperiodic antenna have several yagis connected in series, with each one tuned to a different frequency range. Due to the LP design the shift between frequency ranges are seemless and the elements that are tuned to the wrong frequency doesn't interfere much with the reception.

A logperiodic antenna are usually designed to have 3 active elements for a frequency and equals about 6dB gain. The lenght of the LP antenna will set how wide the frequency range can be. A 50MHz-1300MHz LP will be huge. If you can limit the range to 120-800MHz it will be much smaller.

If you don't need that much coverage to the sides you can increase the number of active elements to 4 or 5 but the it will then be much more directive. But lets say that you prefere more gain and directivity in the 800MHz range than the 120MHz range. You can then actually have 1 active element in the low range, similar to a dipole, and 5 elements in the high frequency range, like a high gain yagi, without the LP antenna becoming too large. But you probably have to build it yourself. If you get a $40 LP antenna for tv reception you can use the hardware and use the online calculators on internet and drill new holes for the elements and also adjust their lenghts to suit your own preferences.

Where I live these kind of antennas cost $25. https://www.ebay.com/itm/HDTV-TV-ou...Grade-10dBi-VHF-UHF-Log-Periodic/361707193412

/Ubbe

 

[lmrtek]

The common vhf/uhf outdoor combo tv antenna is in fact a log periodic antenna that can cover 54-900mhz

 

[dlwtrunked]

The common vhf/uhf outdoor combo tv antenna is in fact a log periodic antenna that can cover 54-900mhz

None that I have seen. A log periodic has a very specific design providing continuous frequency coverage.
And using one for VHF/UHF TV would not make sense as there is not need to cover the frequencies from about 216-470 MHz was never used for TV. All TV antennas I have seen were not designed to do that but were rather a combination of antennas for the bands but vary in their design doing that.

 

[prcguy]

I've had conversations with engineers from a couple of US TV antenna companies and they do their best to only cover TV frequencies and to produce the antenna for the cheapest possible cost. Older TV antennas at best covered 54 to 88MHz, 174 to 216Mhz and 470 to 806MHz. Current TV antennas loose the 54 to 88MHz range and the 700-800MHz range.

Even though many TV antennas are log periodic types, they skip over non TV frequencies to save $$ and reception within public service bands will be way down. That's not to say you can't modify a TV antenna by trimming or lengthening elements, but they will not have the correct spacing for the new frequencies.

The common vhf/uhf outdoor combo tv antenna is in fact a log periodic antenna that can cover 54-900mhz

 

[iMONITOR]

The Create Log-Periodic 5130-2N is a log periodic antenna for the range of 105-1300 MHz. It features 19 elements providing 10 to 12 dBi. It can be used for receive and transmit (to 500 watts). The boom length is 4 feet 6 inches and weighs only 6 lbs. It is wind rated to 90 mph. It mounts on a 1.5 to 2 inch mast. Mast and lead-in cable is not provided. A low loss N connector is utilized.

 

[n2pqq]

This is the antenna I use >

https://www.dxengineering.com/parts/cae-clp-5130-1n

I have it up about 15 feet and I mounted it vertically
this results in a very narrow beam width.
It is the best antenna I have owned .
I do use a 20 db low noise amplifier with it.
I can receive a good 65 to 70 miles

I do have a icom AH 8000 discone also
https://www.universal-radio.com/catalog/scanants/1945.html

There really is no comparison the create is far superior.

I have in the past had a omni x witch lasted one half winter.

If you are willing to make the investment you will be pleased .

For further review here is a link to some reviews

https://www.eham.net/reviews/detail/5017

The antenna is the most important part of any station.

 

[iMONITOR]

I have in the past had a omni x witch lasted one half winter.

I'm really shocked, not just surprised to hear that. Exactly what part of the Omni-X failed? I had the dual-band aircraft version of it (basically the same only tuned differently) and it was built very well and looked like it would stand up to anything for several years. I'm about to order the regular coverage model to replace it.