SWR problem when using cap on FirestikII antenna

[Coalsmoke]

Hey guys, tonight I was re-tuning my Cobra 29 to the Firestik antenna with a screw tunable tip on it. For some reason when I put the rubber boot / cap back on the tip it throws the SWR off in the higher channels (on the ch 40 end of the spectrum). As far as I know, its just rubber or plastic in this boot, no metal. Its got me confused I covered the screw end of the antenna with a layer of electrical tape and it barely made a difference, so I left it at that for tonight so it will work for tomorow, but I'm really wondering about this cap. Specifically, without the cap, my SWR at ch1 was 1:1. 3 and a half and at ch40 was at 1:1. 4, with the cap the ch40 SWR jumped to 1:2. 1, with the black electrical tape instead of the cap, the SWR at ch40 is 1:1. 4and a half, which is respectable enough for my needs. The ch1 SWR stayed pretty low regardless of what was covering the tip of the antenna, which tells me that the cap is effectively lengthing the antenna, but other than that I'm unsure of what's going on

 

[p-Bar]

sounds like there are some metallics in that cap. Try hardware store and buy a rubber cap see if that makes a differance.

 

[Pawpaw]

This is a known issue on the Firestik Tech-Help site: http://www.firestik.com/Tech_Docs/Setting_SWR.htm



Specifically, it says, "All measurements should be taken with antenna tip on, unless you do not plan to use the tip in normal use. "



In other words:



1. Take SWR measurement.



2. Remove cap.



3. Make adjustment.



4. Replace cap.



5. Repeat.





Bob

 

[Coalsmoke]

Pawpaw, thanks for the info, it's much apprecated. I have read though the firestik site before but obviously my good (but very short memory) missed that part about tuning with the cap on I wonder if the antenna is designed to be run with teh cap on, because my SWR readings are slightly higher now than when I first set up the antenna and radio. or at least so I thought. Then again, it could be that memory thing again Thanks again guys.

 

[RockinJ]

I tuned my Firestik ll just as the mfr (and PawPaw) had recommended and I'm at about 1:1. 4 with the rubber cap installed. The antenna is a 4-footer and is mounted on the first stake pocket behind the cab on the driver's side (not a bad SWR reading for that location).

 

[Pawpaw]

Corrosion can affect your SWR. Every year or two it's a good idea to disassemble and clean the coax & antenna attachment points as well as any grounds. A little conductive grease, like is used on battery posts, can stop or at least slow down corrosion.



I'm running two 4-foot Firestik II's in the front stake pockets, using the Firestik offset mounts (I have a bed cap). I managed to get my SWR down to 1. 2 on Channel 19. It's a bit higher (1. 4 or 1. 5) on 1 and 40.



I'm using these: http://www.firestik.com/Catalog/FS-USA.htm



I insist on using the caps to keep water out of the antenna tip. In addition to corrosion, water could also lead to damage if it gets in there and freezes in the winter.



Bob

 

[Coalsmoke]

Corrosion can affect your SWR. Every year or two it's a good idea to disassemble and clean the coax & antenna attachment points as well as any grounds. A little conductive grease, like is used on battery posts, can stop or at least slow down corrosion.



I'm running two 4-foot Firestik II's in the front stake pockets, using the Firestik offset mounts (I have a bed cap). I managed to get my SWR down to 1. 2 on Channel 19. It's a bit higher (1. 4 or 1. 5) on 1 and 40.



I'm using these: http://www.firestik.com/Catalog/FS-USA.htm



I insist on using the caps to keep water out of the antenna tip. In addition to corrosion, water could also lead to damage if it gets in there and freezes in the winter.



Bob

Bob, that's something I never thought about, water and winter freeze-up. Thanks for the tip. I'm going to get that cap back on before it gets cold here. It sure makes for a PITA though to tune the antenna always having to put the cap on. I've got my ch. 19 SWR down to 1:1. 1, but my antenna is mounted up front in the middle fender area.