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Considering a Log Period Antenna

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habsfan70

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#1
Hello all. I need an antenna solution that will cover 150mgz, 440mgz and 800mgz rage and offer a good amount of gain I am considering the Comet CLP-5130-1N http://www.theantennafarm.com/catalog/comet-clp-5130-1n-3388.html,\ with a Strisdberg multicoupler. I am looking to monitor town and city PD agencies that run the gamut of this frequency rage. Initial post suggested beam antennas would work but I would need 2-3 of them. This antenna seems to have everything I want. It offers a wide frequency range and 10-12dbi of gain. The agencies I'm looking to monitor are just out of range. I get sporadic hits from back of the set antennas but nothing of quality. I know it's pricey but I'm not too worried about that. Let me know what you guys think. Have a great Labor Day Weekend. Ed
 
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#2
Are all of your target stations in roughly one direction? If so it might be a good solution and if not it can become a big hassle turning the antenna every time you want to hear something different.

I have a 100MHz to 1.3GHz log on a rotor at the top of my tower and I only use it now for occasional 2m simplex stuff because I don't like moving it all the time. Otherwise I have several Discones and dedicated high gain mono band antennas combined for every day scanning.

Also the gain spec on the Comet antennas is a little hyped and more in the 5 to 6dBd or 7 to 8dBi gain range. Otherwise they are well made and do a good job compared to a unity gain antenna.

If your using an antenna attached to the scanner you might climb on your roof with it and take a listen. If you can hear everything reasonably well then something like a Discone might work for you. The typical scanner Discone works very well in the VHF and UHF range but falls off a bit at 800Mhz due to the radiation pattern shifting upward above the horizon. Even a poor antenna up high fed with good coax should be way better than a back of the set antenna inside a building.
prcguy


Hello all. I need an antenna solution that will cover 150mgz, 440mgz and 800mgz rage and offer a good amount of gain I am considering the Comet CLP-5130-1N http://www.theantennafarm.com/catalog/comet-clp-5130-1n-3388.html,\ with a Strisdberg multicoupler. I am looking to monitor town and city PD agencies that run the gamut of this frequency rage. Initial post suggested beam antennas would work but I would need 2-3 of them. This antenna seems to have everything I want. It offers a wide frequency range and 10-12dbi of gain. The agencies I'm looking to monitor are just out of range. I get sporadic hits from back of the set antennas but nothing of quality. I know it's pricey but I'm not too worried about that. Let me know what you guys think. Have a great Labor Day Weekend. Ed
 

habsfan70

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#3
Everything I want is to the east. I'm going to climb up and see what I receive on the back of the set antennas. I was told discones are good but don't offer gain and that was what I needed for my particular situation. I would much rather go with a $140 discone vs a $400+ log periodic.
 
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#4
Looking at the specs, it says horizontally polarized. For your use it will need to be vertically polarized. You might try looking at the spec sheet directly at Comet and determine that it can be flipped 45 degrees....
 
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#5
I agree with PRC.
I read and I think I commented on your original post about needing an antenna. I'm not a big fan of discones, but I think maybe I didn't understand your situation well when I commented.

If you are having issues with the back of set antenna, then getting something outside and up high is probably going to make a big difference. Directional antennas work well if you want to listen to a specific area, but I'm not sure that's your best bet.

I believe in my post on your other question, I suggested what PRC said, get up on the roof with your radio and see if it works. If it does, then you won't need much to fix the issue. A simple multiband antenna with decent coax might be just the trick. Discones are certainly one option, but they are not the only one. They suffer from low gain, which can be an issue in some cases. Sounds like a discone would work for you, but you may have other options that will work.
If the 800MHz system you want to listen to is close by, you can often get away with a dual band VHF/UHF antenna and get acceptable results. Don't be too quick to limit yourself to just a discone.
 
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#6
Everything I want is to the east. I'm going to climb up and see what I receive on the back of the set antennas. I was told discones are good but don't offer gain and that was what I needed for my particular situation. I would much rather go with a $140 discone vs a $400+ log periodic.
OK, got it, everything you want to listen to is to the east. How far to the east?
Answer this:
VHF agency is this far to the east:
UHF agency is this far to the east:
800MHz agency is this far to the east:

Providing us with some details will help. I agree, discone is an option, but it's not the only option.
Back of radio antennas are pretty bad, so it probably won't be hard to fix this if you are at least getting something with the stock antenna.
 
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#9
If you can climb on the roof, after determining just how well the back of the set antenna works, I would order a discone from a reputable dealer, and climb on the roof with it and see how it works. You can return it if it doesn't do the trick.
You probably only need 2 antennas....a 145/440 dual band beam would work just fine on the commercial frequencies, and an 800 mhz beam. But your are 100% right, one antenna is easier than 2-3. Not necessarily better!
 
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#11
prcguy has given you some good advice.


That antenna appears to be horizontally polarized. I believe that for what you want you would want a vertically polarized antenna.

In general, on line-of-sight (LOS) paths, it is most important that the polarization of the antennas at both ends of the path use the same polarization. In a linearly polarized system, a misalignment of polarization of 45 degrees will degrade the signal up to 3 dB and if misaligned 90 degrees the attenuation can be 20 dB or more.

This is based on my past experience when I was involved with LMR, almost everything was vertically polarized. Have they maybe gone to circular polarization, like much of the FM broadcast band stations?


I had to step away from my computer and mass-man beat me to it.
 
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#12
Let me rephrase that:
Do you hear what you want to hear on VHF? How's the signal quality with the back of set antenna?
Do you hear what you want to hear on UHF? How's the signal quality with the back of set antenna?
Do you hear what you want to hear on 800? How's the signal quality with the back of set antenna?
 

habsfan70

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#13
Long Island is relatively flat. UHF comes in poorly, VHF is 50/50, some nights good some not good, 800mgz not all all. Got a couple of hits on my deck on the 800mgz. nothing to speak of.
 
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#15
Oh yes! But it would be nice to prove the signals you are interested in can be received at your house before you spend any $$. If you can pick up all your wanted stuff on the roof with your existing equipment, even very weak, then there is a good chance a dedicated antenna on a mast will work out.

It would be really nice if you could borrow an antenna and coax for a test.
prcguy

I'm starting to get what you're saying. An antenna with 10ft of mast on the peak of the roof will invariably outperform a back of the set antenna.
 
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#16
Long Island is relatively flat. UHF comes in poorly, VHF is 50/50, some nights good some not good, 800mgz not all all. Got a couple of hits on my deck on the 800mgz. nothing to speak of.
So, something to consider....
Two way radio systems are designed for radio coverage in the area they are licensed for. Usually the license will say something like X km radius around point y. Point Y is usually the repeater site, or center of a multi site system. FCC and frequency coordinators do it this way to limit coverage to the necessary coverage area. This lets frequencies be reused by other agencies. Technically, the mobile and portable radios are only permitted to transmit inside the area where they are licensed.
Designing a radio system to cover its intended area takes some work. The antenna system design, RF power levels, etc. are all part of the equation. By using RF power levels and antenna design, a system designer can maximize coverage inside their operations area. The coverage outside the licensed area is sort of a bonus for scanner listeners.

Since the radio systems you want to listen to are probably designed for agencies outside your immediate area, it's going to take some effort to get the coverage you want.
As suggested, it would be a really good idea to take the radio with back of set antenna up on the roof, or where ever you are going to mount the antenna, and see if you can receive the agencies you are trying to listen to.
The back of set antenna is going to be a poor performer as it's nowhere near tuned to the frequency you want to listen to. But, it can tell you if there is something there to listen to.
Inside the house with the stock antenna you have a couple of things working against you:
1. You are low down, so your "radio horizon" is pretty close, probably a few miles.
2. Metallic building materials, copper pipe, house wiring, etc. can all block signals.
3. Local noise sources inside your house, like consumer electronics, can drown out the weak signals.
By getting the antenna outside and up high, you are addressing these issues.
The higher up you can get your antenna, the farther it can "see". Since the frequencies you want to listen to are (for the most part) line of site, the farther your antenna see the more it's going to pick up, even stuff you cannot hear inside the house.
Getting the antenna outside in the clear gets you away from foil backed house insulation, vapor barriers, metal lath in plaster walls, wiring and plumbing. Some roofing materials can be metal also, so even installing in the attic isn't always going to work.

Taking the radio on the roof will tell you and us a lot.

If you can pick up what you need from there, mounting a suitable antenna on the roof, preferably on a pole, fed with good coaxial cable and properly grounded is likely going to be what you need.
In fact, you might be very surprised what you can pick up with a good outdoor antenna.

Key is, picking the right antenna, installing it correctly and using suitable coaxial cable to get the signal down to your radio with the minimal amount of signal loss.
There's some math involved here that can help figure this out, but we need to know if the signal is there in the first place. From there we can figure antenna gain, feed line loss, etc. to help you figure out the right parts list to do what you need.

One option that hasn't been mentioned is that you can get an old outdoor TV antenna and turn it sideways and mount it on the roof. The old TV frequencies covered portions of VHF, UHF and 700-800MHz. Old TV antennas were often a combined log periodic. You can find them cheap, and they'll work quite well. Also, you can use the standard RG-6 tv/cable/satellite TV coaxial cable to connect it to your antenna.
 
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#17
Looking at the specs, it says horizontally polarized. For your use it will need to be vertically polarized. You might try looking at the spec sheet directly at Comet and determine that it can be flipped 45 degrees....
The CLP-5130-1N can be installed either horizontal or vertical. I've got 2 of them, both vertical.

Depending on how far your FM transmitters are, you might be able to receive good sigs with a Discone. The reason I'm using the Log P. is all my monitoring is VHF & UHF AM signals in the military band where signals are weaker and my listening targets are 100 - 300 miles away. I do have a discone, they work fine but the CLP-5130-1N works much better.
 

chief21

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#18
Another option... Grove used to sell a product called a scanner beam, which was essentially a multi-band yagi intended for typical scanner frequencies. I'm not positive, but I think another company might have continued offering them when Grove went out of business. If you can find one, it might solve your problem for less cost.

John AC4JK
 

habsfan70

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Thank you all for the time and effort put into the posts. The knowledge you guys have shared with me has been invaluable. You guys are the best. Enjoy the upcoming holiday weekend. Ed
 
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