specific Log Periodic benefit

[n2pqq]

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.

The elements where destroyed in the wind if I remember correctly.
It just stopped receiving any signal at all.

Yes it was in a very bad ice storm with high winds.

However I will say Dave from DPD is a great person.

 

[iMONITOR]

The elements where destroyed in the wind .

They're 1/4" solid aluminum, not tubing, no dimple rivets. Must have been hurricane force winds!

 

[krokus]

When I worked at a military receive site, we had LP antennas for HF, that were spec'd for 25.5 dB gain. (I do not remember if dBd or dBi.)

They were nice to use, when not being utilized for official purposes. I could pull out signals that were not present with other antennas, but were fairly picky on their aim.

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[AlphaFive]

Log Perodic

Man, I can't tell you all how much I appreciate this information. Sometimes people get cranky about something that happens on R.R. but, this is an example of what is really great about this place. I hope this is one of those threads that sticks around for awhile and can become a reference point for someone else. Way to go you antenna nuts! Thanks much and take care, Lance.

 

[Ubbe]

A HF antenna that have 25dB gain have never been designed nor constructed. It must have been 2.5dB.
Most radio/tv antennas are yagi, not logperiodic. You can tell it is a LP by the two booms it uses and that the elements are alternating between the booms for each "dipole". If the elements are attached to a single boom then it is a yagi antenna.

As long as you have the hardware and mountings from a $25 television LP antenna you can easily drill new holes and design it to whatever frequency ranges you want. Those Creative LPs are way too expensive for non professional use.

/Ubbe

 

[majoco]

There is quite a lot of misinformation in these replies.

Look at this article...

Log Periodic Antenna | Aerial Array | Radio-Electronics.Com

and the very last paragraph says....

In real terms a typical log periodic antenna might provide between 3 and 6 dB gain over a bandwidth of 2:1 while retaining an SWR level of better than 1.3:1. With this level of performance it is ideal for many applications, although a log periodic antenna will be much larger than a Yagi that will produce equivalent gain. However the Yagi is unable to operate over such a wide bandwidth.

 

[AlphaFive]

Log Periodic

Thank you for the article. I appreciate you sending it from across the globe..... I read it, and I'll go over it again to understand what I may have missed the first time. Take care way over there.

 

[krokus]

A HF antenna that have 25dB gain have never been designed nor constructed. It must have been 2.5dB.

I can only tell you what was in the tech manual, even if it sounded a bit too good to be true. I wish I could remember which brand and model it was, to look for the specs.

They looked very similar to these, with similar dimensions.

http://antennaproducts.com/product/lph-30/

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[Ubbe]

They looked very similar to these, with similar dimensions.

HF Medium/Long Range RLPA 6-30 MHz 13 dBi | Antenna Products Corporation

That antenna has 13dB gain. Remember that for each additional 3dB gain the antenna size doubles.

/Ubbe

 

[Ubbe]

You can use this calculator to input frequencies and boom lenght to see what gain you can get.
https://www.changpuak.ch/electronics/lpda.php

Input the values for a Creative logperiod antenna and see the real gain values. Remember that higher gain also gives more directivity until it mimics a yagi antenna. There's no free lunch, you always have to sacrifice something to increase antenna gain.

I would say that an antenna amplifier are the easiest way to improve performance. It will work as a buffer and feed the coax with a constant impedance and will raise the signal level into the coax so it doesn't matter what losses and irregularities in impedance you have in coax, splitter and scanners input circuits. If you have seen my measurements of scanners antenna input impedance you'll know that it can be anything from 10 ohm to 200 ohm. If you have made efforts to make the antenna and coax 50 ohm you then loose a lot of signal in that impedance mismatch, but not if you use an antenna amplifier.

/Ubbe

 

[popnokick]

prcguy wrote: "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."
Not correct... UHF channels for TV begin at 704 mHz with Channel 53 but run all the way up to 890 mHz for Channel 83. So Older TV antennas covered a much wider range than stated above. The newest, tiny flat-panel "leaf" antennas are not going to handle low VHF and MAY eliminate everything above Channel 38 (614 mHz).... but those antennas would have to have been designed after April of last year when the decision to eliminate the highest channels was made. Up until then, low power broadcast and translators were still operating in that range... and manufacturers would not eliminate channels potentially in use for those low power / translator stations. Bottom line: Get your hands on old TV Yagi antennas while you still can: they overlap the common scanner bands.

 

[prcguy]

Ok, a very old TV antenna from 30+ years ago might include public service/trunking frequencies in the 800MHz range but it still won't cover any useful VHF lo or high frequencies or 450-470 UHF.

prcguy wrote: "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."
Not correct... UHF channels for TV begin at 704 mHz with Channel 53 but run all the way up to 890 mHz for Channel 83. So Older TV antennas covered a much wider range than stated above. The newest, tiny flat-panel "leaf" antennas are not going to handle low VHF and MAY eliminate everything above Channel 38 (614 mHz).... but those antennas would have to have been designed after April of last year when the decision to eliminate the highest channels was made. Up until then, low power broadcast and translators were still operating in that range... and manufacturers would not eliminate channels potentially in use for those low power / translator stations. Bottom line: Get your hands on old TV Yagi antennas while you still can: they overlap the common scanner bands.

 

[Ubbe]

A TV yagi antenna usually drop its gain conciderable when you go above its design frequency range but not below as it is almost a liniar drop in gain. If you have 10dB gain at 600MHz and 8dB at 500Mhz you are looking at 6dB at 400Mhz. My experiance is that at high-VHF from airband 118MHz up to 175MHz it works reasonable well and is a huge improvement compared to an antenna inside the house.

If you have a combi antenna that also receives 175-250MHz its even better. If the combi antenna also have a FM radio broadcast element for 100MHz and TV single element for 60MHz it will receive even more in the low-VHF.

/Ubbe

 

[majoco]

Ubbe quoted:

That antenna has 13dB gain. Remember that for each additional 3dB gain the antenna size doubles.

It said dBi gain. i is the theoretical isotropic radiator and has a gain of 2.15 dB over a dipole, usually quoted as "dBd". IMHO nobody has built the isotropic radiator yet - as soon as you build it, it interferes with itself!

 

[AlphaFive]

LP

Theoretical Isotropic Radiator is beyond my understanding, but, I can appreciate good humor, and that was pretty good... "As soon as you build it, it interferes with itself", haaaa Thank You!