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Old 02-08-2012, 09:47 AM   #1
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Antenna Specialities - CB antenna concern

Hi all
I'm looking for some info from all you antenna experts

I found several old (20 plus years) vehicle mount total length 35" or so CB antennas around the place and plan to use one or two of them. The gray plastic end (I assume the loading coil to get the antenna to the needed 102" or so) is about 6" long. Using a DC ohm meter I read a dead short from the center pin to the outside portion of the connector on two of them and a complete open circuit on a third.

Sure would hate to connect a short to the radio's output stage.

Exactly how is that loading coil connected to the "PL-259" style connector?
And then on to the short steel antenna

What is normal when measured with a DC ohm meter?
I am thinking since I have several to grind one apart and see for myself if no one can help

Thanks for the comments
Ken
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Old 02-08-2012, 06:27 PM   #2
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Loading coils frequently are grounded.
Here is a test circuit: Take a 12 volt dome or parking light bulb and put it in series with the center conductor of the PL-59 connector ( you may have to buy some stuff at Radio-Shack). Transmit, if the bulb lights up, your antenna is shorted. If it only glows or just gets warm, then the antenna is OK.
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Old 02-09-2012, 07:52 AM   #3
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That is normal for that type of antenna.. DC short, RF 52 ohms. I have used that company's products. Though not for CB.

The gray base is a combination device, (Balun and loading coil in one) if you do not understand those terms think "Transformer" and though not exact, it will be close enough as it "Transforms" not so much voltage but Impedeance, it also takes care of balanced/unbalanced issues (the difference between some antennas and the feed line) which is another function a transforme can do.

NOTE that I believe these antennas are designed to work over a ground plane, I do not think they are "no ground plane" antennas. But that is suspicision.

Antenna Specialists products are common in industry, they are very well built, I used to see their VHF antennas on police cars fairly often.

This would not work so well today, but back in the 70's I once told the police radio tech how to make an undercover car so they could use a good antenna and not be discovered. Put about a dozen antennas on it, all different sizes and types, Half a dozen mics and "I'm a CB-NUT" bumper stickers. Of course only one mic and antenna actually work. (The Motorola mic). They never did it. but they all laughted. (They were all Ham radio operators too, same as me)
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Old 02-09-2012, 09:18 AM   #4
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Thanks guys
Your comments are greatly appreciated
I do indeed understand Balums, Transformers, Impeadance matching, Etc.
Good to hear the measurement of 0.3 Ohms at DC is normal and when operating at about 30Mhz all is well with 50 Ohms or there abouts
Yes they are ground plane antennas - they do require a ground plane
Heard the non ground plane antennas are not much good
One of the antennas is different as in open circuit - guess that one is defective
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