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Scanner Antenna Lighting Strike???

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dpslusser

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Hey guys im new into scanners but wanted to get an outdoor antenna. In my room I have alot of electronics (computer, tv, stereo) so their is alot of interference. I have trouble picking up freqs. in my room.
I have a few questions before I go ahead and mount an outdoor antenna. Let me give you the geography of my house though. My house is in the middle of a field. with two hedgerows on each side of the house. The closest hedgerow, has trees probably 50ft high. My problem is. Any direction I would be recieving frequencies, are in the direction from over the hedgerows. I don't no how much that would interferr. Im such it does alittle bit.

Getting an antenna up ontop my chimney would defenetly start to clear the tree tops. Plus it would get it away from the interference in my room?

The only thing im worried about is lighting strikes (hence the title of this post). My home is only 10 years old, and im really worried about lightning strikes. Having something metal up that high, in the middle of a field, you think it would attrack lightning. Thats my main concern. Any opinions?
 

jmtyra

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Hi there,

I've never messed with an outside antenna, but most of the forum replies talk about two very important things:

* No matter how elaborate, you can't prevent the damage caused by a DIRECT lightning strike. Keep your insurance up-to-date...

* Some form of grounding equipment to earth is required for non-direct hits.

Google has a ton of stuff, as do other members.
Here's a CNet link I found, has some info on it:
http://reviews.cnet.com/4520-11249_7-6264597-6.html

later =)
 

dpslusser

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jmtyra said:
Hi there,

I've never messed with an outside antenna, but most of the forum replies talk about two very important things:

* No matter how elaborate, you can't prevent the damage caused by a DIRECT lightning strike. Keep your insurance up-to-date...

* Some form of grounding equipment to earth is required for non-direct hits.

Google has a ton of stuff, as do other members.
Here's a CNet link I found, has some info on it:
http://reviews.cnet.com/4520-11249_7-6264597-6.html

later =)
Im not so worried about damage to the antenna. It would just suck if something happen to the house. And I would disconnect the equipment when im not using it. Maybe Im better off putting a 12ft high pole off in the yard instead of on the house. And just run a cable from the antenna to the house.

Do I have to ground the cable with a grounding block (F connector (found on Satellite installions))?

To ground the antenna, I just make sure a ground wire from the antenna (or mast/mount) is ran to the earth rite?

Using a scanner antenna, should be know different then someone having a outdoor VHF/UHF antenna for TV, or HAM antenna, or the "Old School" 8 foot wide satellite dish's?
 

jmtyra

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That's what I'm referring to, regarding the lightning strike: your equipment
Since lightning takes the shortest/least resistance path to ground, it's not going to be traveling down the wall of brick/etc of your home. =)

If you get even a partial hit, you're probably going to fry whatever is connected to that antenna: scanner, accessories, speakers, etc.

I can't answer your other questions, other than to say that "yes" you very much need to ground your antenna. It'll at least prevent some of the lower-end discharges that may occur on your lovely conductor (antenna) protruding as the highest point from your rooftop.

It's quite the tempting target for an electrical discharge. ::sigh::
 

prcguy

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Lightning doesn't take the path of least resistance, it distributes to multiple destinations depending partially on the conductor length, resistance, sharp bends, ground resistance and other stuff. If you have an elaborate tower grounding system and the coax has an effective ground, most of the lightning can be dissipated in something other than your equipment.
If your lucky.
prcguy
jmtyra said:
That's what I'm referring to, regarding the lightning strike: your equipment
Since lightning takes the shortest/least resistance path to ground, it's not going to be traveling down the wall of brick/etc of your home. =)

If you get even a partial hit, you're probably going to fry whatever is connected to that antenna: scanner, accessories, speakers, etc.

I can't answer your other questions, other than to say that "yes" you very much need to ground your antenna. It'll at least prevent some of the lower-end discharges that may occur on your lovely conductor (antenna) protruding as the highest point from your rooftop.

It's quite the tempting target for an electrical discharge. ::sigh::
 

dpslusser

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So whats my chances of a lightning strike?

Is it that common?

My chances of getting hit are as good as anyone else with a standard TV antenna on their roof.
 

n5usr

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Having an antenna on your chimney is only slightly going to raise the risk of being hit. Odds are, if you get hit with the antenna there, you would have gotten hit anyway. Just a couple of weeks ago, my house - with four TALL masts / antennas well above the house - was just fine, while the neighbor about 1/2 block down - with absolutely nothing on their house - got struck and the house caught fire.

Here are a couple of lightning-related links I have bookmarked:
http://members.cox.net/pc-usa/station/ground0.htm
http://www.polyphaser.com/technical_notes.aspx (This is rather technical!)

Also, it is not necessarily required to get above the hedgerow. Just being outside, away from the noise inside the house, makes a HUGE difference. Only the very weakest of signals is going to require clearing the trees. If you can hear them somewhat inside, you'll be just fine once you get outside no matter the height.
 

dpslusser

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n5usr said:
Also, it is not necessarily required to get above the hedgerow. Just being outside, away from the noise inside the house, makes a HUGE difference. Only the very weakest of signals is going to require clearing the trees. If you can hear them somewhat inside, you'll be just fine once you get outside no matter the height.
What about the attic? I probably shouldnt have it 12 feet above the chimney. lol. How high should I go? Just clearing the top maybe?

I work for Radioshack (yes I no not all their products are good), but I can get the Scanner Discone antennas that they sell, rather cheap, and their rated pretty good. Links below for the two that they have? Which one should I get.

http://www.radioshack.com/product/index.jsp?productId=2103160&cp=2032052.2032075.2032078.2032098&parentPage=family
http://www.radioshack.com/product/index.jsp?productId=2103641&cp=2032052.2032075.2032078.2032098&parentPage=family
 
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n5usr

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The higher you go, the less obstructions there are, the better / stronger signal you will have. I would at least clear the top of the roofline, as some roofs have metal in them (foil backing to insulation or shingles, etc) and all roofs will attenuate signals somewhat but still - being outside even below the roofline is still better than inside with all the noise.

Another option, as you mentioned the attic, is to just put the antenna in the attic. Hang it as high as possible inside, and you'll still be better than down in the room with the noise-makers. And your antenna doesn't have to stand up to the elements, you don't have to have a mount strong enough to withstand the wind, the feedline doesn't have to be waterproofed.

I'm personally partial to the full-on discone, but I've read plenty of posts here that said the smaller version works well too.
 

dpslusser

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How much better reception am I going to have being outside? Compared to in the attic?

Being in the attic I should probably have the Full Discone for better reception and outside, the smaller antenna should be fine rite?

PLUS having it in the attic may be less likely to lightning stirkes.

How would I suspend something like that though?

IS RG/58 cable fine enough for the run (quality wise)?
 
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schnit

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Lightining absolutly does choose the least path of resistance to ground, and if you have a metal object high in the air and circumstances are right, your antenna will be struck. When you choose to put up and ariel, you should always assume that your antenna will be subject to lightning stikes and make sure you have a ground block and ground rod (at least 4") in place to lesson your chances of getting your equipment destroyed. Thats all you can do, plain and simple, there is no sure fire way to eliminate your "chance". If you are really that worried about it, you could simply disconnect the bnc connector when your not using your scanner or when you expect inclimate weather in your area. I have my outdoor antenna connected to my Uniden BC796D and its a pretty pricey piece of radio (at least for me it is) and thats what I do.

BTW, like with any antenna, terrestrial (trees, buildings, ets) are a major factor in how much better your reception will be. If you can, always put your antenna outside and up high. I have never had very good luck with attic antennas, the reception has never seemed to be much better than what I already had in the back of the set.
 
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dpslusser

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schnit said:
Lightining absolutly does choose the least path of resistance to ground, and if you have a metal object high in the air and circumstances are right, your antenna will be struck. When you choose to put up and ariel, you should always assume that your antenna will be subject to lightning stikes and make sure you have a ground block and ground rod (at least 4") in place to lesson your chances. Thats all you can do, plain and simple, there is no sure fire way to eliminate your "chance". If you are really that worried about it, you could simply disconnect the bnc connector when your not using your scanner or when you expect inclimate weather in your area. I have my outdoor antenna connected to my Uniden BC296D and its a pretty pricey piece of radio (at least for me it is) and thats what I do.
Ya, I am going to disconnect it for equipment sake.

So which antenna should I go with? The big one or small one? I guess it depends on the area that I am in. The big one has some reviews of grabbing signals 100 miles away. But it is also 50 dollars more.

And how about RG/58, is it a good enough cable for scanners?
 

schnit

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Almost forgot, if you can pony up for it, try to get your hands on some LMR400 cable. It is extremely low loss cable but is a but pricey. Your local ratshack wont carry it, you'll probably have to get it orr the net. I have the little cheapy antenna from rat shack but great cable and I have outstanding reception for 60 miles or more.
 

dpslusser

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schnit said:
Almost forgot, if you can pony up for it, try to get your hands on some LMR400 cable. It is extremely low loss cable but is a but pricey. Your local ratshack wont carry it, you'll probably have to get it orr the net. I have the little cheapy antenna from rat shack but great cable and I have outstanding reception for 60 miles or more.

Your tellin me!! 80 some bucks for a 50ft. I don't think I have to go that good of quailty. Its pretty said if the cable connecting the equipment and antenna was the most expensive thing. Lol. Whats some other good grades?
 

dpslusser

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The other thing I was looking at was a PreAmp. I have a preamp for VHF/UHF, its ment for TV antennas. Will seomthing like this work on a scanner antenna, with the rite adapters?
 

hydrolocked

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dpslusser said:
Ya, I am going to disconnect it for equipment sake.

So which antenna should I go with? The big one or small one? I guess it depends on the area that I am in. The big one has some reviews of grabbing signals 100 miles away. But it is also 50 dollars more.

And how about RG/58, is it a good enough cable for scanners?

Simply disconnecting the antenna from the radio may not be good enough.




If:

you don't have decent quality lightning protection on your coax (look up Polyphaser)

your lightning protection ground isn't tied to ground by the SHORTEST, STRAIGHTEST, LARGEST POSSIBLE conductor (minimum 12 AWG, though ground STRAPS are considered to be better, typically - less inductance per foot)

you don't have lightning protection on EVERY wire entering the house (Cable TV, sattelite, TV antenna, telephone, power service entrance, etc. etc. etc.)

you don't have the coax, chassis of the radio, etc. tied to ground

your "radio" ground isn't tied DIRECTLY to the building ground (which it MUST be, per N.E.C., and as required by MIL-HDBK-419, for further reference)

your radio ground isn't tied to the building ground by the SHORTEST, STRAIGHTEST, LARGEST POSSIBLE conductor

you aren't protected.



Lightning WILL take the MOST DIRECT PATH to ground. this may not be the shortest DISTANCE, but will be the path of least IMPEDANCE (not just resistance - Lightning is usually modeled as an AC waveform, so inductance is a HUGE factor in your grounding system - a low impedance at DC may be hundreds of ohms at higher frequencies!!!)



as far as your coax, you want the lowest loss cable you can afford. LMR-400 may not be what you want to spend (It used to be about 30 cents a foot) - RG 6 MAY work.

For a 50 foot run, i'm willing to bet RG6 will do just as well as LMR-400 (you may not even notice the difference, but this is VERY dependant on WHAT you're trying to listen to, how far away it is, what the terrain is like, tetc. etc. etc.)

Larger coax doesn't afford lightning protection, but feeting the antenna under your roof with coax that has 3 dB of loss over 50 feet will make an improvement over an old piece that may have 8 dB of loss.
 

hydrolocked

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dpslusser said:
The other thing I was looking at was a PreAmp. I have a preamp for VHF/UHF, its ment for TV antennas. Will seomthing like this work on a scanner antenna, with the rite adapters?
yes, with the correct adaptor, i have used these quite successfully with scanners. the issue you may have is that once the signal is gone (lost in the coax), you may not be able to bring it back to where your scanner can find it.

The mast mount preamps are best.

the worst you can do is to try it.
 

dpslusser

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hydrolocked said:
yes, with the correct adaptor, i have used these quite successfully with scanners. the issue you may have is that once the signal is gone (lost in the coax), you may not be able to bring it back to where your scanner can find it.

The mast mount preamps are best.

the worst you can do is to try it.
What do you mean lost in the coax?
 
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Rat shack antenna

I have the small RAT SHACK antenna and a RAT SHACK brand 50 foot run of RG-6 low-loss antenna cable with ground wire. I'd have to say my anteena is only about 15 ft off the ground and only about a foot over my roof. And despite the trees being another 50 ft above the antenna, I'm pulling in signals at least 50 miles away. For being on a budget my set up works great with my BCT15. So no complaints on my end with the setup. hope I could help
 

hydrolocked

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coax has loss.

if your signal is attenuated by our coax beyond the sensitivity of your receiver - you can't bring it back

(say your signal comes into the antenna at 10 millivolts, and your scanner needs 1 millivolt - if you loose 10 mV in the coax due to loss, you have 0 mV - the signal is gone, no preamp in the world will bring it back, unless you put the preamp at the antenna, to boost the signal to 50 mV, then you have 40 mV at the receiver - plenty to receive, to take this further if you have 1/2 mV at the receiver, and put a preamp at the receiver to boost the signal to 10 mV (or even 5) then you'll be OK.

these numbers are totally bogus, but just to make a point. most receivers operate in microvolts, and most losses are measured in dB, which is a log scale - not linear.
 
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