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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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  #1 (permalink)  
Old 02-19-2007, 5:12 PM
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Default TV antenna for scanner reception?

Hi guys,
I don't know much about antennas, so I'm sorry if this seems like a strange question...

I'm moving into a new home, that has a VHF / UHF TV antenna attached to the roof. I'm wondering...can I plug that into my scanner to get reception on VHF and UHF fire and police bands? The line conveniently runs right into the room I want to place my radios in...we're not going to use the line for television reception, as we'll have cable TV.

So what I'm asking is, is this possible? Or will I get poor or no reception?

For an idea on target frequency, I'm primarily looking to receive 154.430 and frequencies around that.

Thanks in advance, guys.

Mike DiMunno
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Old 02-19-2007, 5:41 PM
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Yes as long as the cable is 75 ohm it will work fine. You will need to inspect the antenna and connections for damage or bad wiring. If it has 300 ohm line then you will need a 300 to 75 ohm transformer. Just buy a pl-259 to solder to the 75 OHM line and connect that to the scanner.
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Old 02-19-2007, 5:53 PM
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I can't be sure how many ohm the line is...wheather it is 75 or 300 ohms. Have a quick way for me to check this?

My scanner has a BNC connector...does Radio Shack or some other location sell a Coax-TV to BNC adapter?

Mike
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Old 02-19-2007, 6:02 PM
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Quote:
Originally Posted by jjmdimunno
I can't be sure how many ohm the line is...wheather it is 75 or 300 ohms. Have a quick way for me to check this?

My scanner has a BNC connector...does Radio Shack or some other location sell a Coax-TV to BNC adapter?

Mike
Radioshack has a coax to BNC connector. Not sure on checking the OHM's of the line then. Not sure how you would hook an ohm meter in there.
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Old 02-19-2007, 6:43 PM
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I have done it before.

You will lose a bit of signal since the antenna is horizontally polarized, but the height makes up for it.

I currently use a Radio Shack UHF antenna turned on its side to catch one of the more distant 800 MHz systems.
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Old 02-19-2007, 7:17 PM
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I have a source that tells me that you can tell the ohm rating of the line by checking what type of cable it is. If it's twinlead, it's 300 ohm. If it's coax (which mine is), it's 75 ohm.

Anyone confirm or deny this?

Mike
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Old 02-19-2007, 7:27 PM
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Quote:
Originally Posted by jjmdimunno
I have a source that tells me that you can tell the ohm rating of the line by checking what type of cable it is. If it's twinlead, it's 300 ohm. If it's coax (which mine is), it's 75 ohm.

Anyone confirm or deny this?

Mike
If it is coax, it probably is 75 ohm, but any difference will make little difference in how well your scanner performs.

Just make sure the line you are hooking to actually goes to the antenna and get on with it.

There is a possibility that the signals will overdrive the scanner, but nothing will be harmed and that problem is easily fixed.


For the record, there _is_ twinlead that is not 300 ohms and coax that is not 75 ohms. Neither is seen much if at all in TV antenna installations.
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Old 02-19-2007, 9:12 PM
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Default TV antenna

I have two tv antennas on my house, and i use them for both TV and scanner, it works great for both. (i dont have cable tv). sure it looks kinda stupid on top of my house, but who cares, i pick up southern cape cod on my scanner (im in the lakes region of NH) and i get tv channels from rhode island!
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Old 02-19-2007, 11:23 PM
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Better results if he rotated the boom 90 degrees so the elements went vertical?
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Old 02-20-2007, 1:36 AM
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Quote:
Originally Posted by mbird97x
Better results if he rotated the boom 90 degrees so the elements went vertical?
Yes, but not on a metal mast!



John K9RZZ
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Old 02-20-2007, 2:21 AM
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TV antennas are cut for the TV bands not the scanner bands. Plus being horizontal.
http://www.fordyce.org/scanning/scan...o/scanant.html
I took a large directional TV beam that is actually a VHF Log Periodic antenna with Yagi corner reflector for UHF, and completely disassembled it and respaced the elements and recut the elements for the scanner bands. but without proper test equipment and formulas I wouldn't try it. It took me trial and error and many unnecessary holes in the boom before getting it to what i think is right. And yes it works fine on a metal mast. It would be better to by the Grove Scanner beam antenna that is similiar to TV beams but designed for the correct bands.

p.s. i'm tired of reading bogus info on here. I'm not an expert but have lots of knowledge as a amatuer radio operator and long time scanner fan.
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Old 02-20-2007, 6:17 AM
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Quote:
Originally Posted by jjmdimunno
I have a source that tells me that you can tell the ohm rating of the line by checking what type of cable it is. If it's twinlead, it's 300 ohm. If it's coax (which mine is), it's 75 ohm.

Anyone confirm or deny this?

Mike

When speaking of TV antenna lead-in, yes that is correct.

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Old 02-20-2007, 8:18 AM
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Most TV antennas are of a log-periodic design to cover 54 to 220 MHz on VHF and 470 to 790 or so on UHF. There is no reason they won't work for scanners. You will lose as much as 15-20 db, especially on the higher frequencies, by having the antenna horizontal instead of vertical which will noticeably affect weak signals. If you are only listening to local repeaters I wouldn't sweat it. If you turn it so it's vertical, I would think the mast will have less affect on it than the loss from having it horizontal.

I would be most concerned with the age and quality of the coax and the connections at the antenna.

Having said all that, just hook the darn thing up and see if it works. It can't hurt anything. You can always go back and make improvements later.
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Old 02-20-2007, 8:42 AM
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Put it at 45deg and you will only loose 3 dB or so on TV (Horz) or LMR (Vert).

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Old 02-20-2007, 9:34 AM
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In the 80's Grove sold a book on converting a television antenna into a scanner beam. I bought one and will try to dig it up. A television antenna is 300 ohms. Radio Shack sells a 300 ohm twin lead input to 75 ohms coxial adapter for $4.99 Most new television antenna come already with one. The instructions indicated that you mount the antenna vertically (turned 90 degrtees)because most signals on VHF/UHF is vertically polarized. Although a scanner input is 50 ohms their is a mimimum loss of gain(less than 1db) since it is receive only.
To get the antenna to mount vertically, you had to re-drill the holes in the center were the boom meets the mast. They advised using a short plastic boom standoff to prevent interference from the mast. The wire connecting the elements was cut-off and re-attached. Eg the longest left side element # 1 was connected to the next adjacent element #2 but on the right side. This was repeated as the elements tapered to the shortest elements. The 300/50ohm adapter was then attached at the end of the smallest elements were the wires ended. Basically a log periodic. I tried one with a $40 RS antenna and it worked as good as a log periodic that cost $299.
There was certain disdavantages. The television band starts at ch2 roughly 60MHZ. Coverage from 108-250Mhz was excellent. Elements was not cut for some gaps in the spectrum were TV chls does not exist aka 250-400Mhz. Reception was good all the way to 800Mhz. I mounted this on a antenna rotator in NY and was able to pick up CT in the north and NJ/PA in the west/south. I was still able to hear a good deal of mil traffic. Basically I was able to hear more than on my discone & 1/4 wave 20-015 RS antenna could pickup or even hear, and ended up using it as my primary antenna to zone in on faint signals from my other antennas. Most of these antennas are easy to find cheap/not used anymore on rooftops. The disadvantage was that there was not guaranteed seamless coverage from 30-1200Mhz like most commercial log periodics.
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Old 02-21-2007, 2:06 PM
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All the great information is much appreciated guys...

So let's just sum it up with this one question. I have two choices (so says my fiancee):

1. Use the roof antenna for the scanners, which will be located in the basement (finished basement, but still below ground level).

2. Use no outside antenna at all, and simply use indoor antennas which are placed in the basement with the scanners (like I said before, below ground level).

So, in your experienced opinion, which will be better for receiving VHF 150-160Mhz?

I'm going to try it anyway, but I'm just looking for some expectations...

And changing that antenna is not an option, because we're renting the house, and the antenna is not actually mine...

To give you guys an idea of the condition of the wiring and antenna however, the prior residents of the home were using it for TV, and had a clear picture for all broadcast channels in the vacinity. Antenna was installed around the mid 1990's, when the home was built.

Thanks everyone.

Mike DiMunno
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Old 02-21-2007, 2:17 PM
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Quote:
Originally Posted by jjmdimunno
All the great information is much appreciated guys...

So let's just sum it up with this one question. I have two choices (so says my fiancee):

1. Use the roof antenna for the scanners, which will be located in the basement (finished basement, but still below ground level).

2. Use no outside antenna at all, and simply use indoor antennas which are placed in the basement with the scanners (like I said before, below ground level).

So, in your experienced opinion, which will be better for receiving VHF 150-160Mhz?

I'm going to try it anyway, but I'm just looking for some expectations...

And changing that antenna is not an option, because we're renting the house, and the antenna is not actually mine...

To give you guys an idea of the condition of the wiring and antenna however, the prior residents of the home were using it for TV, and had a clear picture for all broadcast channels in the vacinity. Antenna was installed around the mid 1990's, when the home was built.

Thanks everyone.

Mike DiMunno

Considering she is your fiancee, and not your wife, you forgot option #3!

.
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Old 02-21-2007, 4:08 PM
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"2. Use no outside antenna at all, and simply use indoor antennas which are placed in the basement with the scanners (like I said before, below ground level)."

That's not an option.

:^]

John K9RZZ
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Old 02-21-2007, 4:18 PM
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How about scanners in the basement, antennas on ground floor, inside the house, hidden in the corner of a closet?
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Old 02-21-2007, 4:23 PM
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Quote:
Originally Posted by jjmdimunno
All the great information is much appreciated guys...

So let's just sum it up with this one question. I have two choices (so says my fiancee):

1. Use the roof antenna for the scanners, which will be located in the basement (finished basement, but still below ground level).

2. Use no outside antenna at all, and simply use indoor antennas which are placed in the basement with the scanners (like I said before, below ground level).

So, in your experienced opinion, which will be better for receiving VHF 150-160Mhz?

I'm going to try it anyway, but I'm just looking for some expectations...

And changing that antenna is not an option, because we're renting the house, and the antenna is not actually mine...

To give you guys an idea of the condition of the wiring and antenna however, the prior residents of the home were using it for TV, and had a clear picture for all broadcast channels in the vacinity. Antenna was installed around the mid 1990's, when the home was built.

Thanks everyone.

Mike DiMunno
I would expect the rooftop antenna to beat the snot out of any antenna in the basement or on the ground floor.
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