Homemade Wire Antenna For Pro-95

[xusmarine1979]

Hello all. I have a question regarding to a wire antenna. I no longer use my old RS mobile scanner antenna so I cut off the base of it. I want to make a hanging wire antenna for my 95 so I can hang it in my livingroom. I really don't have the choice of putting it outside because I rent and don't want to be drilling or anything.

Right now my antenna will consist of a 12guage 18" wire for VHF. Two 6" 12guage wires for UHF High, and two 5' wires for low-band. I can't remember who it was that told me how to set it up, but I want to make sure. I attach the 5' pieces to the shield, right? I just want to make sure. If any hams have any suggestion, I'm all ears. TIA.

 

[kf4lne]

Since you are using it for RX all you really need to do is cut wires for the bands you want to listen to and connect them to the center conductor. You can ad a ground plane if you want, but it isnt absolutley required. Cut the ground plane the same length as the longest element and arrange them angled down at about 45 degrees. Look here for some antenna ideas. These are primarily amateur radio antennas, but they work for scanning too, probably better than the average cheap antennas that are available for scanning.

http://members.fortunecity.com/xe1bef/vhf-uhf-antennas.htm

 

[xusmarine1979]

Thank You Sir.

 

[xusmarine1979]

So for the low-band, do I need to connect it to the shielding wire? Actually, what is the technical term for that?

 

[kf4lne]

Ok, it works like this. All of your signal will be in whatever is connected to the center conductor of the coax, so you connect all of your wires for the various frequency ranges to the center conductor and connect your ground plane radials to the shield. So the VHF-LO, VHF-HI, UHF and 800/900 elements will all connect to the center conductor and you will have 2 radials connected to the shield. Since almost all of what you will hear will be transmitted using a vertically polarized antenna you will want your antenna to be virtical too. Keep in mind that these types of antennas have no gain over a dipole but it will be more sensitive that the typical commercially made 25-1300(BS) antennas. You can use this formula to cut the lengths of wire for each range you want to hear. VHF-LO antennas will have a narrow bandwidth compared to 800/900MHz elements so cut the elements to the center of the range you want to hear. Examples are below the formula


234/freq in mhz=element length




VHF-LO (30-54) element length of 66 inches
VHF-HI and Air (108-174) Element length of 20 inches
UHF (400-512) Element length of 7 inches
800/900MHz will use the UHF element since it is almost a 1/2 wavelength antenna for that range


You can further tune this idea to the ranges you want to hear most by adding additional elements for teh ranges you want to hear or removing elements for ranges you arent listening to.

 

[xusmarine1979]

Ahhhh, thanks for clearing that up. You answered exactly what I wanted to hear. Thanks again Sir.

 

[kf4lne]

You are quite welcome. Just FYI..I have been building antennas for nearly 15 years both as a hobby and to make a little extra money on the side. For the same money most scanner listeners invest in a commercial made 25-1300MHz antenna that is only resonate on a few freq ranges and just a peice of metal on the rest you can build a much better antenna that will be customized to the listening you want to do. Just takes a little time and reading. those measurements I gave you are for the middle of the ranges most scanners are able to receive.

 

[xusmarine1979]

I just have a question on the wire. As I mentioned the guages, it's copper and stranded. Not sure what brand, I got it from some of the electricians from work. They said it should work ok.

 

[kf4lne]

As long as it conducts electricity it will work fine.

 

[xusmarine1979]

K, thanks again Sir.

 

[xusmarine1979]

One thing I've noticed in the past on the UHF high, with the wire antennas, is that sometimes it doesn't recieve that well. I have two wires for UHF, do I need to add some more wires, or length or what do you recomend?

 

[kf4lne]

Except for my low band antenna my antennas are made from 14 ga. solid copper wire and a SO239 connector. great little antennas and if needed I can use them all to transmit on the amateur band they are cut for. Antennas work like this..Raio waves have lengths, this is why amateur bands are called 6 meters or 2 meters and such because that is the rounded meter length of that frequency. Antennas have to be "cut" for the frequency range they are being used for. The simplest antennas to make are the dipole and the groundplane. The way you make them is to "cut" your antenna elements to the length of the frequency you want to receive. Since one antenna can be used for a range of frequencies like the element lengths I gave you, you dont have to have a element except for a few ranges instead of for hundreds of frequencies. With receiving antennas as long as its close to resonance it will work. Your antenna (if built with those measurements) will work for the 30-54MHz range, 108-174 range, 400-512 range and 800-900 range and it will also be usable as a transmit antenna on the 6 meter, 2 meter and 70 centimeter amateur radio bands. Basically your antenna will be the same as the old Radio Shack 3el groundplane scanner antenna they used to sell, the one that had 3 vertical elements spaced about 2 inches apart and 3 ground plane radials spaced at equal distances apart. Very good antenna, but not very well made and it didnt hold up to the weather too well.

 

[kf4lne]

The reason UHF is hard to receive is because the higher you got in frequency the more line-of-sight it gets. The suggestion for better UHF reception would be to build a gain antenna for that range butthat takes some antenna knowledge and proper tools. The antenna you are building is a basic ground plane antenna and is what is known as a unity gain antenna, meaning it has no additional gain over a half wave dipole cut for teh same frequency ranges. This is a bit better than most scanner antennas since an antenna made to receive that much spectrum is a comprimise and is only going to work well on small portions of the overall range wheras a multi-band antenna like yours wil work well over the ranges it is cut for and will work ok for the ranges it is not cut for. But as for getting better RX of UHF signals you may want to buy a basic TV antenna amplifier from radio shack, they have one that works great for maybe $30 and it has a gain adjustment on it so you can set it to a level that wont overload the scanners front end. Another thing about devices designed to receive such a wide freq range is that the electronics inside are also better at some ranges than at others. My scanner is an awesome VHF-HI and UHF receiver but it isnt as good for VHF-LOW and 800MHz. Your scanner may just be optimized for another range, especially if it is a trunking scanner, a lot of those are optimized for the 800MHz ranges and drop off the lower you got in frequency

 

[kf4lne]

Your antenna should look like this when you are done
http://www.azuma.ath.cx/kf4lne/stuff/scannerant.jpg

 

[xusmarine1979]

Cool. I'll just have to mess with it and see what it does. It should help alot. My town is on VHF and doesn't have a repeater, that's the main reason why I wanted to build a better antenna. Again, thanks for taking the time to help.

 

[kf4lne]

Your are quite welcome. Also, something else that will hinder your UHF reception...the walls of your house are going to cause a lot of signal degradation so be sure you install that antenna ona wall on teh side of the room closest to the majority of your weaker signals so you will be able to hear them better

 

[xusmarine1979]

I know the perfect place. Thanks again.

 

[kf4lne]

Check this jewl out. This is a duplicate of the UHF/800 MHz antenna I have on the roof and it is a great performer. I made this during the time we traded posts

 

[kf4lne]

Hmmm. It didnt post my pic...so here it is again on the web...

www.azuma.ath.cx/kf4lne/stuff/450-800.jpg

 

[xusmarine1979]

I don't see anything Sir.