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wide range scanner dipole?

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country85
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wide range scanner dipole?

Post by country85 » Tuesday, 02 November 2010, 19:57 PM

I know theres already a post about scanner dipoles but I have some what of a different/more specific question. I live in an apartment (a cb'ers and shortwave listeners no mans land). I have a uniden bearcat scanner that works fairly well with the little piddly 2 foot job that comes with it. I would like to make a simple dipole for it, but I would like to have a wider frequency range. the local channels around here range from the 130's all the way up to the mid 800's, I'm scared that if I make a dipole designed for one certain frequency that I'm not going to be able to pick up everything I want to. I was thinking that I should shoot for the middle of my desired frequency range, around 450mhz and make the dipole around that.. any advice? thanks guys :compress:


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Re: wide range scanner dipole?

Post by Ronin » Tuesday, 02 November 2010, 20:22 PM

You could try a Fan dipole. There is plenty of information on them on the internet. You could be creative with mounting it, but the construction is pretty simple. just measure and cut wire for three sets of dipoles for about the middle of each of the three bands you mentioned and connect all three of them to your coax or feedline (for coax, one leg of each three bands to center conductor and the other three to the shield). Mount it vertically and it should work pretty well. A friend of mine had used a fan dipole on ham radio for years made of 3 conductor Radio Shack antenna rotor wire and it worked nice.

Try to keep the feedline run to the scanner as short as you can since there is considerable line loss at 800 mHz.

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Re: wide range scanner dipole?

Post by 'Doc » Wednesday, 03 November 2010, 0:41 AM

For anything in the VHF or higher bands, antenna height will make more difference than anything else will. Frequencies in the VHF and higher ranges are definitely more 'line of sight' than lower bands, meaning the distance to the RF 'horizon' is the limiting factor in most cases. Having an antenna resonant on a particular band will certainly help though. That 'fan' dipole will help, but not as much as additional height (not a couple of feet, but maybe a dozen or more). Polarization is also going to make a sizable difference in what you hear. Almost everything in the VHF or higher regions is vertically polarized, so making that dipole vertical is a nice idea. Getting that antenna outside will make a difference too, less 'stuff' that signal has to go through to get to the antenna. Of course, if that signal is from the wrong side of that building, inside/outside won't make a huge difference anyway. Oh well.
In general, an antenna for the lowest frequency will tend to work 'better' for higher ones, than the other way around. That's a 'practical' thingy, so do what's practical for you.
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country85
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Re: wide range scanner dipole?

Post by country85 » Wednesday, 03 November 2010, 8:12 AM

thanks for the advice guys. I've also been looking into these "snoop" antenna's they sell on ebay, has n e one had one or does n e one know how to make one? I think there just a wire would wood dowel inside a piece of pvc pipe but I"m not sure

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Re: wide range scanner dipole?

Post by drdx » Wednesday, 03 November 2010, 9:09 AM

Your best bet for what you want will be a discone. It will do exactly what you want to do. You can make one or buy one. Look them up. For that frequency range you could make one out of an aluminum pie pan, some aluminum foil, a toilet paper or paper towell tube, and some cardboard since it is an indoor antenna, very very simple and fun. Look them up, read around. The discone is one of the best non popular antennas out there. You can even transmit on them.

A discone for your needs would be about the size of a table lamp- 23 inches or so in diameter and probably 2 feet tall.

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Re: wide range scanner dipole?

Post by Night Crawler » Wednesday, 03 November 2010, 15:10 PM

drdx wrote:Your best bet for what you want will be a discone.
I agree here's something similar if cut for the length shown it will cover the vhf and uhf bands for it to cover up to 800mhz make a third radiator and radials cut to 3 1/2 inches.
http://www.qsl.net/na4it/dbgp.html

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country85
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Re: wide range scanner dipole?

Post by country85 » Wednesday, 03 November 2010, 19:29 PM

what would the center radaditors have to be in length? just so i double check i should have 3 in the center then the 4 3 1/2 rods on the side?

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Re: wide range scanner dipole?

Post by Night Crawler » Thursday, 04 November 2010, 7:52 AM

Construct the antenna as shown then add the 800mhz element.

You need 3 radiators (top elements) one at 19 inches one at 6 1/2 inches and one at 3 1/2 inches. Spread the 19" and 6 1/2" apart a bit and mount the 3 1/2" in the center between the two.

2 radials (bottom elements) two at 19 inches two at 6 1/2 inches and two at 3 1/2 inches to add the two 3 1/2 inch radials drill a hole between where the 19" and 6 1/2" radials are connected on the SO-239 connector and mount them there so you will have a total of six radials (bottom elements) two at 19" two at 6 1/2" and two at 3 1/2".


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