Antenna Tuning

[MadisonMod]

Hello. I have a question about tuning an antenna. Is it better to use an air variable capacitor or a roller inductor "18f" with a choke to change impedanc, to Obtain a lower match ? Please share experience and suggestions. Thanks

 

[Crawdad]

What type of antenna are you tuning???

 

[MadisonMod]

Predator 30k

 

[AudioShockwav]

Predator 30k

Is that the model with the 3/4" tube for the top whip ?
It should tune as is without a matching device at the feed point by adjusting the tube.
How do you have it mounted?

73
Jeff

 

[Captain Kilowatt]

It depends on the impedance. A series inductor will lower the resonant frequency as well as make the bandwidth narrower. A series capacitor will electrically shorten the antenna and make it resonant higher in frequency. You really need both an inductor and a capacitor because simply adding one component introduces a reactance that must be cancelled out by an equal and opposite value of reactance. Then there is the question of which component to place in series......the cap or the coil........and which to put in as a shunt to ground........again the cap or the coil. One way allows you to match to a higher impedance, while the other way allows you to match to a lower impedance. A single cap or coil MAY be all you need but we cannot tell you based on what you have told us so far. We need to know your intentions (trying to make a multiband antenna?) or simply tweak the bandwidth?

 

[nomadradio]

Umm, so why do you need a tuner on that antenna? Never had one, but I thought it was famous for having a low SWR and being fairly broad banded.

Putting a tuner in line with an antenna that's already tuned just fine only wastes power. Probably not enough to matter, but what is the objective here?

73

 

[AudioShockwav]

Its Kales heavy duty 10 k with a larger insulator and uses 3\4" tube for the top section in place of a flexible whip.
It should tune around 64" total length for the CB band as long as its mounted properly.
Put some Nolox on all the set screws, that's the only issues I have ever had with his antennas.
After years exposed to the weather they can corrode and seize up.

73
Jeff

 

[linearone]

Any single coiled cb antenna mounted on the vehicle roof in the middle will usually tune to around 1.2-1.3 : 1 swr. Antennas without a coil will usually tune to slightly below that to maybe 1.2- 1.1 something. Impedance when measured on an mfj or something will usually be 37-40 ish ohms.

If you use a shunt you can usually get 1.0 50 ohms. Cbers are scared to see a coil going to ground so they dont do it. Any base loaded antenna like a sirio or a wilson has a shunt matching network built into the base. They usually have a connector like a so-239 for mounting to provide the needed ground to the antenna.
The "regular" style of isolated antenna stud, like a 3/8-24 stud, ball, or puck mount does not provide for that. You can however take a trip to the hardware store and make whatever u want.