Firestick Antenna Question

[K8BBL]

I have a 5' Firestik on my truck CB. It sits in the left front corner behind the cab. I have had no issues since it is more than 3' above the cab and there are 2 ground straps attaching the stainless mount to the body (so please don't tell me to move it, that's not the issue). The issue/question: I can get a 1.2 SWR on channels 1 & 40 however; as soon as I put the red rain cap (the one that came with the antenna) on the adjustable tip it goes to approx 2.55. I set up a ladder and took the rain cover off/on 5 times. Each and every time I was able to get 1.2-1.3 without the cap and it went to ~2.55 with the cap. I even changed radios, same issue. Has anyone else seen this issue? I'm hesitent to leave the rain cap off but don't see much other choice. I do have the 'O' ring to seal the antenna threads.

 

[prcguy]

You typically see a small change when putting the cap on and it depends a little on how much heatshrink you removed to expose the wire. A bunch of exposed wire turns will have more cap effect than just one turn. Putting on the cap should lower the resonant frequency slightly.

I would find the sweet spot without the cap then with the cap and see if the lowest VSWR reading is about the same at both frequencies. If it is and the sweet spot is at a lower frequency with the cap on then you can trim a little more wire off and put the cap on and repeat until you get the lowest VSWR where you want like around ch 19 or 20 with the cap on.

 

[slowmover]

FIRESTIK TIP TIP

Bonding

You do have a separate SWR meter, right?

Tech-Docs Index

 

[slowmover]

Skipshooter Antennas - S6

A better quality (and longer) antenna will help

Need a CB antenna wizard

Firestik is not in the same room as Skipshooter.

As a truck driver I’ve had my share of buying FS. The money goes into advertising & distribution. It’s adequate.

But I have (5) pairs of Skipshooter Antennas.

They’re not expensive. A bargain, IMO, when this design-type of antenna is wanted.

Unless otherwise, I recommend “Clear” (Natural) color as it blends in easiest.


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[slowmover]

Note: Future

The vast majority of pickup truck CB installations I come across are almost as bad as the vast majority of big truck installations.

What you’ve described is a poorly-performing radio rig compared to what you could have.

I’m not a fan of mag mount antenna, but a WILSON 5000 mag on the roof would far exceed what you have at present.

— The permanent mount upgrade is pretty close to being the best of what’s possible.

Access the roof underside through the interior light cut-out. Avoid framing. Cut, set, fish coax down B-pillar to run to radio.



The grannies running dirt-caked & tired minivans with a permanent mount Wilson while escorting OVERSIZE loads will out-talk nearly everyone on the highway with an ordinary dual-final radio. They can hear a good deal farther than you as well.

— Clean 12VDC power POSITIVE straight from BATT, and shortest NEG to firewall or seat bolt.

Need to RF Bond all four corners of bed to frame; bed to cab + cab to frame and hood hinges as a minimum (with two points on exhaust as well).

** Lay out on paper what’s necessary and consider it. My experience is that there’s no substitute. Given wet and/or winter weather driving in West Virginia you’ll find it pays for itself pretty quickly. **

This is a vehicle upgrade by every definition.

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[K8BBL]

Slowmover I appreciate all the info but given my situation I have to leave the mounting as is. With that said, I have a friend who has a 5' Skipshooter. Actually he has a dual setup and we're gonna borrow one and try it. And yes I use a separate SWR meter (MFJ digital, same one I use with my HF rig).

Here's an FYI for anyone else who uses these antennas ....

I sent this same question to the Firestik tech guys. This is their answer:
"Common and reoccurring scenario ....
Turn the screw down a couple of turns, put the cap on and retest. The cap must be on for all tests ... it adds capacitance to the antenna and that shifts the frequency.
I usually rub the sides of my nose with a finger and rub it on the top of the antenna ... body oil helps when sliding the cap on and off. Don't twist the cap when removing or installing ... go straight up and straight down so you won't mess the solder joint at the top. "

I did what they said and took prcguy's suggestion to tune on the middle channels and all is well. I'm at 1.2-1.4 thru the whole band with the rain cap on. (I didn't realize it added capacitance and is allowed for by design). I can live with that.
I found it interesting that the tech guys said this is a 'Common and recurring scenerio'.

 

[prcguy]

Adding the plastic tip doesn't exactly add capacitance, anytime you cover a bare or mostly bare wire with insulation or an outer dielectric it effectively lengthens the wire and lowers the resonant frequency slightly. If you tune a whip or dipole that is bare metal or wire then cover it with heatshrink it will resonant at a lower frequency.

On the firestick you are only affecting a very small area and a few turns of wire with the cover but apparently the end of the antenna is very sensitive to the the change and probably due to the very high impedance at the tip.

 

[Groundhog1960]

I run the 7 ft firestik in the same location with an old 1960's barrel spring my Dad owned and it does a really god job. Had to trim the wire a little at a time but finally got it down to a 1.1 on channel 1 and 1.2 on 40. Of course it's quite a bit up over the top of the pickup cab.