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Antenna for a Motorola CDM1550 LS+
- Thread starter sam55671
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What frequency are you operating on? You need an antenna specific for the frequency your radio operates on, not just a 4ft antenna.
You could use a 1/4 whip which is about 4 inches long. Or you could get a collinear type antenna with some gain, they usually have a loaded coil in the center and are about 2 feet long or so. What type of mount do you have? There are many choices out there, Google is your friend.
mmckenna
I ♥ Ø
How are you determining you need a "long" antenna? Is it aesthetics? Is it because that is what someone else is using? Is it because you think you need the additional gain?
Antennas are frequency dependent. You don't necessarily purchase them by the length, you purchase them depending on exactly what frequencies you'll be using.
As stated above, for the frequency range you are using, you'll need an antenna that is resonate on those specific frequencies.
You could choose a 1/4 wave antenna, which will be a few inches long and provide zero gain, but has a nice radiation pattern. You could choose a 5/8th's wave antenna that will be about 12 inches long, have about 3dB of gain and have a slightly more compact radiation pattern. You could chose a co-linear design that will be longer, have higher gain, but will have a very tight radiation pattern.
What you really need to do is take a close look at what your department is using on their apparatus. Radio systems, specifically repeaters, are designed to provide coverage over a given area based on a number of variables. Usually, the coverage is determined by placement of the repeater, antenna height and antenna gain. System coverage shouldn't really be determined by the end users antenna choice. Keep in mind that these repeater systems are usually designed to provide a certain level of coverage for a hand held radio running 4-5 watts with a very inefficient antenna. Likely, the fire apparatus has an antenna on the roof that has been deemed suitable for the radio system. Take a look at that type of antenna as your choice. If it works on the fire trucks, it should work well for you.
Also, going with a much higher gain antenna when it isn't necessary can actually cause some issues. With higher gain antennas, you could be putting out more power than necessary and could conceivably cause interference to co-channel users farther away.
Also, depending on your local terrain, higher gain antennas are not always the best choice. Sometimes lower gain antennas will outperform higher gain antennas.
In other words, don't just pick an antenna based on looks and gain figures.
mmckenna
I ♥ Ø
Here's some more:
1/4 wave: About 5 inches tall. http://www.theantennafarm.com/catalog/larsen-nmoqw450-801.html
Wideband co-llinear, about 35 inches tall: http://www.theantennafarm.com/catalog/larsen-nmowb490c-3220.html
5/8th's wave, about 19 inches tall: http://www.theantennafarm.com/catalog/larsen-nmo4703cs-3218.html
1/4 wave: About 5 inches tall. http://www.theantennafarm.com/catalog/larsen-nmoqw450-801.html
Wideband co-llinear, about 35 inches tall: http://www.theantennafarm.com/catalog/larsen-nmowb490c-3220.html
5/8th's wave, about 19 inches tall: http://www.theantennafarm.com/catalog/larsen-nmo4703cs-3218.html
mmckenna do you think this is a ok one? http://www.theantennafarm.com/catalog/laird-technologies-b132s-766.html
mmckenna
I ♥ Ø
Yeah, it's a quarter wave antenna.
The specs on that page show it being 21 inches, but that's the measurement for it being tuned to the lowest frequency (132MHz for that one). For the frequencies you are using, it'll be -much- shorter when you trim it to be resonate on your frequencies. Probably 5 or 6 inches. With the antenna that short, the spring usually isn't necessary, so you could really go with a much more basic antenna.
As for the trimming...
The antennas should come with a cutting chart. The chart will tell you what length to cut the whip to for use on your frequencies. This is required, not optional. Your antenna must be trimmed to be resonate on the frequencies you would be using. If the antenna isn't resonate on the frequencies you are using, the reflected power back into the radio will eventually damage it, or at minimum result in very poor performance. Ideally you'd want to cut the antenna to the recommended length and then check the resonate frequency with a return loss meter, or an SWR meter that is designed for that portion of the UHF band (CB SWR meter isn't going to work right).
The specs on that page show it being 21 inches, but that's the measurement for it being tuned to the lowest frequency (132MHz for that one). For the frequencies you are using, it'll be -much- shorter when you trim it to be resonate on your frequencies. Probably 5 or 6 inches. With the antenna that short, the spring usually isn't necessary, so you could really go with a much more basic antenna.
As for the trimming...
The antennas should come with a cutting chart. The chart will tell you what length to cut the whip to for use on your frequencies. This is required, not optional. Your antenna must be trimmed to be resonate on the frequencies you would be using. If the antenna isn't resonate on the frequencies you are using, the reflected power back into the radio will eventually damage it, or at minimum result in very poor performance. Ideally you'd want to cut the antenna to the recommended length and then check the resonate frequency with a return loss meter, or an SWR meter that is designed for that portion of the UHF band (CB SWR meter isn't going to work right).
mmckenna thanks I might just buy a 1/4 antenna that is pre tuned. Will this one be ok? http://www.theantennafarm.com/catalog/laird-technologies-qw470-798.html
mmckenna
I ♥ Ø
Yes. and at $6.95.
I use 1/4 wave antennas on most of my stuff at work and on most of my personal vehicles. The bonus of a 1/4 wave antenna is that they are very broad banded and trimming them isn't as critical. I've got a VHF 1/4 wave on the roof of my truck and I've put it on an antenna analyzer at work. Useable from 144 well up to 170 MHz as is.
I use 1/4 wave antennas on most of my stuff at work and on most of my personal vehicles. The bonus of a 1/4 wave antenna is that they are very broad banded and trimming them isn't as critical. I've got a VHF 1/4 wave on the roof of my truck and I've put it on an antenna analyzer at work. Useable from 144 well up to 170 MHz as is.
Currently I have two CDM-1550LS+ mobiles in play, one uses an old Antennex Phantom style antenna and the other uses a cheap whisker style Laird Technologies antenna. Both bought through Tessco.
Work great as long as you keep a ground plane under them. Antennex is lip mounted on a car trunk and the whisker is using a metal angle bracket on a fence post for the antenna mount. Both work well for several miles.
Work great as long as you keep a ground plane under them. Antennex is lip mounted on a car trunk and the whisker is using a metal angle bracket on a fence post for the antenna mount. Both work well for several miles.
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