Motorola Spectrum Antenna for Scanning

[ScottBL]

Hi All,

I have a question about an antenna I was able to get my hands on for free. It came from a Motorola unit and all the antenna says on it is "Spectrum" on the bottom rubber piece. The actual metal part of the antenna is 32" long and the antenna including the base is 3 feet. I was wondering if this would be able to be used with my scanner and if so what frequencies it would receive. Also, if it cant be used with my scanner, are there any modificaitons that I can do to the antenna to make it work? I am looking to scan primarily 40-50 mhz as well as 150-160 mhz and I also occasionally scan 410-420 mhz.

Thanks!

 

[jimg]

Hi All,

I have a question about an antenna I was able to get my hands on for free. It came from a Motorola unit and all the antenna says on it is "Spectrum" on the bottom rubber piece. The actual metal part of the antenna is 32" long and the antenna including the base is 3 feet. I was wondering if this would be able to be used with my scanner and if so what frequencies it would receive. Also, if it cant be used with my scanner, are there any modificaitons that I can do to the antenna to make it work? I am looking to scan primarily 40-50 mhz as well as 150-160 mhz and I also occasionally scan 410-420 mhz.

Thanks!

Look inside the coil and see what frequencies it is specifically made for, i.e. 40-50, 150, 450-470 mhz, etc. This will give you an idea of what you may expect to receive best on that antenna. As I remember, this is a mobile antenna, so you will also need an NMO mount and cable assembly to use it.

 

[N5TWB]

Spectrum is a brand of antennas that has nothing to do with Motorola except for perhaps being attached to a Motorola radio system using a New MOtorola (NMO) mount. Before they went to 800 EDACS, the Oklahoma City PD had a bunch of these on their cars with a VHF-Hi system. They appeared to be made well and you should probably expect good performance from it in whatever band you find on the bottom/mounting coil.

 

[ScottBL]

So i looked at the antenna a little further looking for some sort of frequency marking. I unscrewed the mount that was on the bottom and bingo i found the frequency. It reads 42-50. Is this the only frequency the antenna will now work for? And also I am looking to make this an outdoor antenna for the house, will I be able to use the existing vehicle mount or are there other modifications I will need to make?

Thanks for the replies this really helps! Been scanning for 3 years and still consider myself a newb!

 

[mmckenna]

42 - 50 MHz is what the coil was designed for. The length of the whip will determine the exact frequency the antenna will resonate at. This is of primary concern for transmitting, however it will play into reception slightly. It isn't uncommon for antennas to resonate well at other frequencies, also. A 5/8's wave VHF antenna will act like a 1/4 wave in the VHF low band.
So, this antenna will work best on the VHF low band, somewhere around 42 - 50 MHz. It may work well in the VHF high band, also. Likely it won't be an outstanding performer on the UHF or 800MHz bands, but it will receive something.

You can use it as a base antenna, but it will work better with a ground plane underneath it. Most mobile antennas are designed to have the metal trunk lid or vehicle roof underneath it to provide the ground plane. Since this is likely a base loaded 1/4 wave design, you'll get much better results by recreating this. An easy way to do this is to install the NMO mount on a large metal sheet, hardware cloth (chicken wire), or add 3 or more lengths of metal rod or stiff wire attached to the ground portion of the mount and extending out horizontally under the antenna. Ideally, for VHF low band, you would want 1/4 wave worth of ground plane underneath the antenna. The metal rods or wires should be around 60 inches each, but do what you can

 

[ScottBL]

Great thanks for the help! I knew I could count on the RR forums to get the info i needed!