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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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Old 03-28-2006, 7:34 PM
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Default Thru-the-glass CB antennas

How good are thru-the-glass CB antennas? Do they even compare to a regular magnet-mount antenna?

I'm looking for a CB antenna that is very discret an non-noticable anyone know anything about those adapters that turn your car antenna into a CB antenna?


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Mark
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Old 03-28-2006, 7:42 PM
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Stay away from the glass mount CB antennas.
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Old 03-28-2006, 8:55 PM
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I agree
They can ruin your finals on your rig.
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Old 03-29-2006, 5:37 AM
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Even with a near perfect alignment of the contact buttons on the outside and inside couplers, there is STILL a chance of an extremely high Standing Wave Ratio (SWR) due to impedance mismatch from external sources. Some auto glass manufacturers use a 'tint' that contains a metallic element. Also, the chrome trim and metal parts that surround a window can affect the resonance of the glass mount.

Using glass mounts at higher frequencies is not much of an issue if installed correctly, but at 27 Mhz., there are just too many variables to allow proper operation in most cases.

The same holds true for the AM-FM-CB antenna interfaces. They do not allow for any critical tuning for proper resonance and may ultimately damage your transmitter.

A compact Mag Mount with center loading is OK if you do not wish to drill holes in the vehicle.

Why not go the full opposite: Drill a 2 inch hole in the back fender along with three 3/8 inch holes and mount a 102 inch whip, 6 inch spring and ball mount... ( Just kidding!! ).
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Old 03-29-2006, 8:29 AM
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Quote:
Even with a near perfect alignment of the contact buttons on the outside and inside couplers, there is STILL a chance of an extremely high Standing Wave Ratio (SWR) due to impedance mismatch from external sources.
My Radio Shack through glass was installed 6 years ago and the standing wave is still 0 at nearly 4 watts.
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Old 03-29-2006, 8:49 AM
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Quote:
Originally Posted by fmon
My Radio Shack through glass was installed 6 years ago and the standing wave is still 0 at nearly 4 watts.

My oil can dummy load has a low SWR. But that doesn't make it a viable antenna.
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Old 03-29-2006, 10:35 AM
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Quote:
Originally Posted by Highlander_821
My oil can dummy load has a low SWR. But that doesn't make it a viable antenna.
Meaning but both are resonant and not damaging the transmitter as suggested by RevGary. However, the through glass is radiating a mile or so down the highway making it viable, while the tin can might be reaching the end of your car at best.
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Old 03-29-2006, 8:09 PM
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What other kinds of CB antennas can a person get that are very discrete?
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Old 03-30-2006, 5:54 AM
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You might wish to scan the links below and others at Google, until you find something that is right for your application. However, disguise antennas are notorious for poor operation.

http://www.omesbs.com/communication/index.htm

http://www.electronicsoutpost.com/cbantennas.htm

http://www.walcottcb.com/index.php?cName=antennas

http://www.radioshack.com/sm-magnet-...i-2103575.html
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Old 03-30-2006, 7:23 AM
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All true fine fellows.

Mr. Mark, Ever heard CB at 27mhz referred to as being in the 11 Meter band? This is because a full wavelength of radio wave transmission at these frequencies is 11 meters long. That's over 33 feet. So you can figure it's not practical to make and operate verticle antennas that are 33 feet tall. There are 5/8 and even 3/4 wave verticle antennas for base stations but they are over 20 feet tall.

Now you go mobile. The antennas must be even shorter. Those 9 foot long skinny stainless steel antennas you see are 1/4 waves and work well.......but they're still 9 feet long ! To make antennas for these frequencies shorter you have to start adding coils to have an appropriate length of conductor contained therein....but the shorter the antennas get then unfortunately the less efficiency they have and the result is you get less talk and hearing range out of them. The glass mounts will be the smallest to keep them lightweight. Yes they work but you shouldn't have any dreams of "getting out " any good distance.

I've never heard of an "adapter" to convert AM/FM antennas to include CB, only a whole antenna REPLACEMENT that LOOKS like an AM/FM ant. and fits the same hole ect. I guess they're still around. Search the CB antenna selling places and look for them.

Now may I ask why you want to do this? Don't want anybody to know you're a CB'er? Well that would be amusing and I can understand your predicament. Don't want anyone to know you have a CB in the car as it would be a target for theft? You gotta be kidding us right? Only the most depraved crackhead would think a CB is valuable and they would quickly learn this lesson when they found out that nobody would give them 5 bucks for a CB anymore. Only thing else I can come up with is that you don't want to muff up the looks of your vehicle with an (embarrassing) CB antenna. Oh well too bad. If you've going to be a serious radio operator needing serious performance then you're going to have to have serious equipment and there's never been any way around that and there never will be.

good luck
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Old 03-30-2006, 8:52 AM
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Quote:
Originally Posted by ReceiverBeaver
All true fine fellows.

Mr. Mark, Ever heard CB at 27mhz referred to as being in the 11 Meter band? This is because a full wavelength of radio wave transmission at these frequencies is 11 meters long. That's over 33 feet. So you can figure it's not practical to make and operate verticle antennas that are 33 feet tall. There are 5/8 and even 3/4 wave verticle antennas for base stations but they are over 20 feet tall.

Now you go mobile. The antennas must be even shorter. Those 9 foot long skinny stainless steel antennas you see are 1/4 waves and work well.......but they're still 9 feet long ! To make antennas for these frequencies shorter you have to start adding coils to have an appropriate length of conductor contained therein....but the shorter the antennas get then unfortunately the less efficiency they have and the result is you get less talk and hearing range out of them. The glass mounts will be the smallest to keep them lightweight. Yes they work but you shouldn't have any dreams of "getting out " any good distance.

I've never heard of an "adapter" to convert AM/FM antennas to include CB, only a whole antenna REPLACEMENT that LOOKS like an AM/FM ant. and fits the same hole ect. I guess they're still around. Search the CB antenna selling places and look for them.

Now may I ask why you want to do this? Don't want anybody to know you're a CB'er? Well that would be amusing and I can understand your predicament. Don't want anyone to know you have a CB in the car as it would be a target for theft? You gotta be kidding us right? Only the most depraved crackhead would think a CB is valuable and they would quickly learn this lesson when they found out that nobody would give them 5 bucks for a CB anymore. Only thing else I can come up with is that you don't want to muff up the looks of your vehicle with an (embarrassing) CB antenna. Oh well too bad. If you've going to be a serious radio operator needing serious performance then you're going to have to have serious equipment and there's never been any way around that and there never will be.

good luck

Pearls of wisdom right there, I agree with all of that.
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Old 03-30-2006, 9:44 AM
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Alright put it this way, I just bought a $15,000 2002 Monte Carlo SS, I just don't want to ruin the cool look of my car, I have a magnet mount antenna I used on my old Ram-Charger but when I took then antenna off it made a permenant ring where the base was on my roof. I don't want this to happen to this car nor do I want a giant ugly antenna on it.
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Old 03-30-2006, 10:03 AM
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The only advice I can give you is this:

If you want to communicate on CB (WHY you would want to do so is a topic for another thread) with any reliability or distance, don't use a through the glass antenna.

Will a through the glass antenna work? Yes - any antenna will work to one degree or another - but its performance will be less than most people would desire.

If you’re interested in why this is so, please PM me.


Quote:
Originally Posted by mark2117
Alright put it this way, I just bought a $15,000 2002 Monte Carlo SS, I just don't want to ruin the cool look of my car, I have a magnet mount antenna I used on my old Ram-Charger but when I took then antenna off it made a permenant ring where the base was on my roof. I don't want this to happen to this car nor do I want a giant ugly antenna on it.
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Old 03-30-2006, 12:15 PM
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OK Marko, Ya gotta nice ride and you don't want to muff it up. No problem. So find ya one of the AM/FM replacement antennas and use it. It will work a goodly percentage better than one of those tiny little glass mount jobs.

BTW, you owe each of the thread responders here $5 for forcing us into another conversation about CB radio :-)
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Old 03-30-2006, 3:42 PM
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Larsen NMO-27, Cable, and L-bracket. Three small holes inside the trunk or hood opening. Take it off and no one will ever know it was there.

Antenna and cable
http://www.radialllarsen.com/docfile...LowMidBand.pdf


L bracket (page 8)
http://www.radialllarsen.com/docfile...ASB6Mounts.pdf

I would post a pic BUT mine is in the trunk of the new car waiting for the weekend to get reinstalled.
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Old 03-31-2006, 6:55 PM
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Hi guys,

"My Radio Shack through glass was installed 6 years ago and the standing wave is still 0 at nearly 4 watts."

There is no such thing as "standing wave 0" because it's a ratio of power going to the antenna to that reflected by it. It can be no less than 1:1 and that's a theoretical, perfect value. The best that can be achieved in the real world is 1.1:1 even on a purely resistive dummy load. It seems what's confusing you is the scale begins with 1, not 0.

As someone said quite nicely a mag mount is the best you can do under the circumstances BUT don't expect the SWR to remain constant unless you leave it undisturbed. It will vary depending on any slight variation in positioning as will it with any transmitting antenna. Hams have found that nothing beats permanent mounting, otherwise all else is a compromise.

Oh Rev, you reminded me of a friend who long ago had a 102" whip and a bumper mount having a weak spring. You can imagine the sway, I laughed myself silly once as he rounded a curve and it smacked a lady square on the butt.
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Old 03-31-2006, 11:01 PM
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Quote:
Originally Posted by mark2117
What other kinds of CB antennas can a person get that are very discrete?
Depends on what you want - one that's discrete or one that works.

An antenna much less than 1/8 wavelength long is useless. That's about 54" on CB. You can toss all the gimmicks you like on a much shorter one - base coils, center coils, cow catchers, bangles and beads, and you still have the same thing - a dummy load.

There are some newer designs that are a little more discrete and actually work - like loops and top hats (an antenna that looks like a short version of Lincoln's beaver stovepipe hat) - but you design and build them yourself after learning the theory. You won't find anything like that at your local "Would you like a cell phone to go with that?" emporium.
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