CB Firestick Experiment

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screamin72

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I did a little experiment this evening. Was quick to put together. I used a white 11m firestick antenna and added 5 feet 5 inches of wire to the thread of the firestick. At the opposite end of the wire is into 6 feet of 50 ohm Rg-58 double shield coax. I wanted to try to get better reception indoors For Shortwave.

It seemed to receive fine.

I have no test equipment. Can someone with the same parts as I mentioned piece one together like mine and find out where it is resonant at?

Edit: Forgot to mention I have it mounted to a 7 foot 3/4th inch by 1-1/8th inch wood thing.

I can hear the pile up on 20 meter amateur at 14255 khz upper side band. Some kind of contest.

Seems to do ok mounted in the vertical position.
 
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mmckenna

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If the CB antenna is a loaded 1/4 wave design, there is about 9 feet of wire in there. Add the 5.5 feet, and you've got 14.5 feet. That works out -very roughly- to about 16MHz of 1/4 wave goodness.

There are likely a lot of variables involved, but that should be close enough.
 
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screamin72

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testing testing the antenna

If the CB antenna is a loaded 1/4 wave design, there is about 9 feet of wire in there. Add the 5.5 feet, and you've got 14.5 feet. That works out -very roughly- to about 16MHz of 1/4 wave goodness.

There are likely a lot of variables involved, but that should be close enough.
Its the Firestik about 2 feet in length with a coil form.

It seemed to do well at 14mhz and i heard eam's on 8992 11175 and 15016. Not real loud but loudest was at 8992 probably propagation.

I encourage anyone else to try this with new designs. This be a compromise antenna.
 
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screamin72

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Need a better idea.

I doubt you're the first to try such a thing. Props for using what you have to make improvements!
I sat here and thought about trying to find some kind of metal tubing at 5ft 5" with 5/8th's inch threading inside the tubing to see if it gives it a bit more bandwidth. I am also thinking the inductance of the Firestik can either be adding to or taking away from performance on different bands. It appears to be electrically resonant at 16mhz but with rg-58 doubles shield that roughly 14 mhz accounting for velocity factor.

I did want to say the wire is the same wire in Ethernet cable. I have another stretch of wire at the same length connected to shield of the coax slung out the window with e weight to keep it straight.The weight is plastic. Not heavy enough to snap the wire and wont break the solder connection.

I am aiming at the inductance of the Firestik with the 5ft 5" of wire put together what is it doing? Did I decrease or increase inductance? What did I do to it's capacitance?
 
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nanZor

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You may want to look at how I used capacitive "top loading" instead of inductive base loading on a cb antenna to get it to resonate near 14 mhz. Although I was interested primarily in amateur monitoring, merely changing the lengths of the top load can put it anywhere you like:

Although my cb antenna is different from the firestick, see the pics several messages down in the page to get to the "top loading" part.

http://forums.radioreference.com/amateur-radio-antennas/242671-radio-shack-hf-vertical-kit.html

What I'd try is pulling the top cap off the firestick, and running some wire from the tip in a "T" configuration, such as adding 5 feet of vertical wire to it, and hanging a "flat top" horizontally to the top of that. Of course you'll have to find a way to support that additional wire.

Let's suppose the total length of your firestick vertical with the additonal vertical wire is now 8 feet tall. On the top, is a horizontal pair of wires about 4 feet on each side. You can lengthen or shorten those wires as needed. Or simply add more vertical wire. Or use a "capacity hat" of a spoke of smaller wires instead of the two wire flat-top.

The big advantage here is that capacitive top-loading is far more efficient than bottom inductive loading.

The one thing I'm not sure about is that the firestick you have seems to be a 5/8 wave, with an internal matching circuit, so not sure how that would affect your setup with the additional wire added to the tip. Still, worth a shot, and you can end up with a clean coax connection from the rig to the firestick connector.
 
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Firestik advertises 5/8 th wave antennas. They claim 6dB of gain.

I've never really taken the fiberglass antennas apart (I usually run Larsen nmo based antennas or a tram dual band 10/11m antenna). They're not going to be capacitive loaded like the Larsen's. My bet would be that they are inductive based. Some simple 5/8 designs are physically 3/4 wave long but only physically 5/8 wave before the actual loading coil.
 

prcguy

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Even the 6 and 7ft Firesticks are well under 0dBd gain, even on a proper ground plane. In the 70s I remember testing lots of CB antennas and nothing at the time beat a Shakespeare or Avanti 9ft fiberglass whip, the kind that just has a straight copper wire running the full length inside the fiberglass. That doesn't mean much to this thread of using them for SW reception but what the heck...
prcguy

Firestik advertises 5/8 th wave antennas. They claim 6dB of gain.

I've never really taken the fiberglass antennas apart (I usually run Larsen nmo based antennas or a tram dual band 10/11m antenna). They're not going to be capacitive loaded like the Larsen's. My bet would be that they are inductive based. Some simple 5/8 designs are physically 3/4 wave long but only physically 5/8 wave before the actual loading coil.
 
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