Mobile coil antenna "spring" change length?

[hammer0630]

I need to get over my pick up roof with a coil antenna and would like to use a spring to help soften any tree branches etc and help with a little more height and am wondering if the addition of a spring at the base radiates as an antenna which would not be good and does it change the SWR?

 

[hammer0630]

.

 

[midnight special]

i use a military spring from way way back with my 102 inch whip so the antenna can be resonant on 27 mhz ... 102 + 6 equals 108 plus the 1 1/2 inch ball mount makes it 109 1 1/2 inches.... the spring becomes part of the antenna, so swr might change some... but adjusting the whip down some will get it back on... remember to get as heavy duty spring as you can weak spring will make antenna lean back in the wind and swr go kinda flacky..... 73s midnight special

 

[Oatmeal]

Not sure what antenna u maybe using with a coil, but I ran a 10K and mounted it on the back side of my tool box, the mount I used was flush with the box between the lids.....and I had the 27" shaft and single coil, this put the coil up 8" above the cab of the truck....

You maybe be able to use some pipe fitting, or get one of those extension made for antennas......think a spring may let the antenna flop to much, unless you can find one of those big ol heavyduty pot belly spring, those suckers are stiff to bend....haven't seen them for like 10 years or so..

 

[hammer0630]

I bought a Browning BR-89 mobile antenna. It has a 16" stainless steel shaft and 2 flat coils made of aluminum and has a total length of 70". It will replace my current antenna that is mounted to my tool box passenger side. 16" is exactly where the first coil on the bottom measures level with the roof. I bought a heavy duty stainless spring 3" but it is not the pot belly one. I am also replacing the coax and the antenna mount where the coax and antenna join together on the tool box. So basically anything below 16" such as a spring if it does radiate RF will not be radiating properly.

 

[jazzsinger]

Most springs have a braid runs up the middle for continity so would detune the radiator which many use to advantage having bought 102" whips that are too short. Hope that helps.

 

[W5LZ]

Think of it this way.
You usually 'tune' a mobile antenna by adjusting it's length. So, if you change that antenna's length by adding a spring to it, you just 'un-tuned' that antenna (if it was 'tuned' before adding that spring). If you add some then you have to remove some to stay 'tuned'. That 'some' that you add/remove may not be exactly the same length, it can vary a little according to where it's being added/removed. Above or below that coil for instance.
- 'Doc

 

[hammer0630]

The spring is not critical so I will not be using it. Since hearing that a spring does become a antenna basically I think a lot of people may have over looked this factor. This is a shame since I bought a Stainless Steel spring which should have longevity with out corroding but it is not worth changing the performance of the antenna.

 

[midnight special]

my spring that i have had for so many years (since 1976) is an old military/public service one,,, it is rusty in spots and it never was chromed it actually was galvinized,, the wire that runs up inside of the spring is what is important,,, if it breaks from constant banging up on stuff or simply rusts makes the spring worthless,,, ever once and a while i will squirt some oil in side of it to help keep the braided wire inside of it from corroding .... other advantage of my spring is it takes the banging but doesnt lay down at highway speeds like some others i have seen... 73 midnight special

 

[hotrod]

The spring is not critical so I will not be using it. Since hearing that a spring does become a antenna basically I think a lot of people may have over looked this factor. This is a shame since I bought a Stainless Steel spring which should have longevity with out corroding but it is not worth changing the performance of the antenna.

the spring wont change the antennas performance . however it may change your swr slightly
being your adding lenth your swr on 40 may rise a lttle. cutting off /filing off a few inches
off bottom of stinger will correct this. id try it and see what it does . but drive around a bit
makes sure the spring doent make the antenna flop around as this would be a reason to
NOT use the spring.if not then trim up whip for tune. also goto gunnyspucks.com they have a solid 6 inch riser that will
screw into where yor spring would go aswell.

 

[jazzsinger]

Think of it this way.
You usually 'tune' a mobile antenna by adjusting it's length. So, if you change that antenna's length by adding a spring to it, you just 'un-tuned' that antenna (if it was 'tuned' before adding that spring). If you add some then you have to remove some to stay 'tuned'. That 'some' that you add/remove may not be exactly the same length, it can vary a little according to where it's being added/removed. Above or below that coil for instance.
- 'Doc

It would really depend on antenna used, a resonant tuned antenna then the whip would require trimming, but a 102" whip that is physically too short to start with may well benefit from adding a spring or 3/8 extension. The braid inside also ensures that if the spring (coil) is conductive it doesn't add inductive reactance by shorting it out.

 

[W5LZ]

Now read that post again. This isn't about a 102" whip, but a loaded antenna.
- 'Doc
On second thought, it would apply to any antenna, loaded or not. If you add length to a 'tuned' antenna then you can expect it not to be 'tuned' any more, you changed it's length. It has nothing to do with the spring being a 'coil' because of the shorting strap inside.

 

[jazzsinger]

Now read that post again. This isn't about a 102" whip, but a loaded antenna.
- 'Doc
On second thought, it would apply to any antenna, loaded or not. If you add length to a 'tuned' antenna then you can expect it not to be 'tuned' any more, you changed it's length. It has nothing to do with the spring being a 'coil' because of the shorting strap inside.

maybe if you'd read the first sentence instead of leaping in trying to make me look wrong, you'd have realised i knew it was a loaded antenna,

as i said, " it depends on the antenna"

then i went on to explain how it affects a whip that's physically too short, which most US cb'ers are familiar with, to show that if he uses a resonant i.e. tuned antenna, adding it will make it too long and detune it.

So like i said, "IT DEPENDS ON THE ANTENNA".

If your going to nit pick, do it with someone that doesn't know more than you

and I was the one who mentioned the shorting braid which does affect it. The coil is shorted out by it.

I don't even know why I argue with you, you still haven't figured how a swr meter works despite being told by several people, hundreds of times, you might baffle others with bullshit, but i'm a wee bit more clued up than most people :headbang:headbang:headbang

 

[W5LZ]

And it would also benefit you if you don't assume the one you are talking to isn't as smart/informed as you are. Don't read more into what was said than was actually said.
- 'Doc