CB Antenna Repair Help

[angelofwar]

Well, I grabbed this magnetic mount CB antenna at a local thrift store for $1.95. The only issue with it is that the top post is "broken" off (not really, since it was merely held in by a setscrew, but, it wasn't on when I bought it). Now, I've seen common sizes on the net for 21" and 38"...however, where does the measurement start? Also, since the top-post was missing, I replaced it with a thin brass rod, measured the whole thing to 21", and snipped the brass rod off from there. I'll give you all the measurements, but I was wondering basically, where my measurement needs to start for the end product.

And here's the middle piece labelled as the antenuator on the first pic:

Also, on a side note, it appears to me, to be maybe a Radio Shack get-up...any educated guesses as to make/model?

Thanks in advance for any help!

 

[angelofwar]

Anybody? I can do the math based on the wavelength/freq, I'm just not sure where the meaurment needs to start. The base of the magnet? Base of the spring???

 

[kb2vxa]

The math starts in the load coil. Since it's unknown also is the answer. Toss it, there isn't enough radiator in that type of antenna to make it much more than a dummy load.

 

[LtDoc]

I think your best bet would be to find a way to measure the amount of coil, the inductance, in that "attenuator" thingy. With that information you could determine how much shorter than 1/4 wave length the overall length of the antenna would be. Split the length of that into a bottom and top part of the antenna, put that "attenuator"/coil in the middle of it and you'd have your antenna.
Or, keep adding to that top section until the thing finally works somewhere near the channel you want to use it on. That's probably your best bet. What would the final length be? I have no idea. I'd have to guess longer than what it is now, but who knows how much longer?
There's a third option, as suggested, throw it away and get an antenna. So how determined are you in making it work??
- 'Doc

 

[angelofwar]

Thanks for the help you two. I should be able to measure the copper coils pretty easy, using a "thread" count if you will. I will try to get a better pic up, but, with zero markings on it, I will just have to find something that looks similar, and try to dig the specs up. Thanks, and I'll get back to ya once I get a little more info.

 

[angelofwar]

I think your best bet would be to find a way to measure the amount of coil, the inductance, in that "attenuator" thingy. With that information you could determine how much shorter than 1/4 wave length the overall length of the antenna would be. Split the length of that into a bottom and top part of the antenna, put that "attenuator"/coil in the middle of it and you'd have your antenna.
Or, keep adding to that top section until the thing finally works somewhere near the channel you want to use it on. That's probably your best bet. What would the final length be? I have no idea. I'd have to guess longer than what it is now, but who knows how much longer?
There's a third option, as suggested, throw it away and get an antenna. So how determined are you in making it work??
- 'Doc

Yeah, I just like bringing things back from the grave. So, I need to add the length of the coil to the over-all length to find the true length of the antenna? And just do my antenna math from there? It's for a cheap set-up in the garage, and only cost $1.95 (plus, I'm on a budget right now), so I'm pretty determined. Thanks again for the help...once I get all the measurments, I'll try and do some math, and see what happens. I've seen similar models, but thewy ranged from 17.7", 21", 24", 26". But, I'll get back to ya'll. Thanks for the help!

 

[angelofwar]

Got a new SWR meter...but I'm getting higher than a 3...no matter what (except when my hand is really close to the antenna...I have it sitting on a metal gun safe. Can the cables be bad, or is this antenna complete crap???

 

[WA0CBW]

This isn't going to be easy!

Any combination of coil size and antenna length could be used to get the antenna to resonate at a specific frequency. Assuming this antenna was (is) designed for the CB band you need to get an antenna analyzer (such as an MFJ259) and adjust the length of the stinger until the antenna resonates in the CB band.

BB

 

[kb2vxa]

Apparently nobody here has experience with this type of antenna as I have. That's why I said "toss it" because all that work won't produce an antenna worth its salt. Bottom line here is the NEW one I had looked good on the meter but couldn't get out of the yard.