102" stainless whip

[rwlack]

Guy's , Need some help here I cant remember how much coax to use with 102" stainless whip ... I keep thinking 20 ft in order to get a good SWR

DX99V Galaxy

 

[packrat]

Use whatever length that reaches from the antenna to the radio. There are no magic lengths.

 

[office888]

Use whatever length that reaches from the antenna to the radio. There are no magic lengths.

This.

Trim antenna height as required to meet your required match.

-Richard-

 

[rwlack]

Thanks for the input . But i have never trimmed a whip always done SWR by coax length.

 

[Peddler]

I've always used 18ft ... never trimmed a 102.

 

[Chop]

I've always used 18ft ... never trimmed a 102.

ditto.

 

[loosecannon]

rwlack,

the cutting coax thing is a myth that has been propagated for a long time now.

it comes from a misunderstanding of why your SWR meter might read different with a change in coax length in a certain antenna installation.

the truth is, if changing your coax length changes what your SWR meter says, then you definitely have a mismatched antenna, and changing the length of the antenna is the only way to fix it.

think about it for a second.
why did they invent coaxial cable in the first place?
why not just use speaker wire or another two conductor cable?

the reason coax cable was invented was so that any length of cable could be used without affecting the tune of the antenna.

do some reading here in the forum on SWR and coax length and you will be greatly enlightened. you will also start fights on the CB radio. LOL

to answer your question, a 102" whip that is properly installed is already the correct length and any length of coax will work just fine.
LC

 

[Marconi]

This.

Trim antenna height as required to meet your required match.

-Richard-

888, why would you advise rwlack to cut a 102" whip unless he wants to work high in 10 meters? A 102" is already on the borderline of being on the short side for CB.

 

[GnG8d]

888, why would you advise rwlack to cut a 102" whip unless he wants to work high in 10 meters? A 102" is already on the borderline of being on the short side for CB.

Agreed, most people need to add a spring to get into CB range.

THIS
is why people cut coax to tune swr, and it shows why it doesn't help anything but the meter.

 

[mackmobile43]

Agreed, most people need to add a spring to get into CB range.

THIS
is why people cut coax to tune swr, and it shows why it doesn't help anything but the meter.

The 102'' whip was created with the 6'' spring in mind otherwise you'd just purchase the 108'' whip, it's as simple as giving the consumer what he wants.

One being the exact length antenna and the other an antenna that works but has a springy thing some cber told him he needed.

 

[Peddler]

Must have been an old CBers ... He probably had a springy thingy and not a stiff whip.

 

[W5LZ]

There are two conditions to meet to have a correctly 'tuned' antenna (makes no difference what kind of antenna). The antenna should be resonant and there should be a good impedance match to the rest of the system (feed line and transmitter). That antenna's length or loading determines resonance. Resonance has nothing to do with impedance matching, it has to do with getting rid of any reactances in that antenna. Those reactances do not contribute to radiation efficiency so are detrimental to that antenna producing a good signal.
The other part, matching impedances, will have to be done with any and all antennas. There isn't any antenna that has a 50 ohm input impedance without some type of impedance matching being done at the antenna's feed point. Using the characteristics of particular types of coax to make that antenna's input impedance seem to be 50 ohms to the transmitter is certainly possible. It's called a 'conjugate match'. It is 'usable' but never efficient. You will have the same losses as without using that 'magic' length of coax. Your SWR meter may read a nicer number, but the mismatch is still there. Why? Cuz you are reading the SWR in the wrong place, at the transmitter end of the feed line instead of at the antenna feed point where the mismatch is.
What about changing the antenna's length to adjust impedance? You can find a length that will have a reactive component that in combination with some resistive component will make what that SWR thinks is 50 ohms impedance. But there are two things that length adjustment does. It introduces some reactive characteristics, and it destroys the resonance of the antenna. You got a nice SWR reading, but the efficiency of the antenna just flew out the window. Why does that sound sort of self defeating? It is self defeating, don't mistake that!
Nothing new in any of that, it's been a proven fact for a very, very long time. Don't agree with it? Fine, don't agree with it. It's still a fact though, not an opinion, but a fact.
- 'Doc

 

[packrat]

 

[Chop]

i had an old 102" whip laying around so i cut the stud off of it and attached this:
Stud for 102 in. CB Ham Radio whip antennas - eBay (item 310213960476 end time Jul-14-10 16:59:55 PDT)

then i measured it out to 9' and slapped 18' of rg8x on it and my swrs are flat, completely flat across the board.

 

[Beetle]

i had an old 102" whip laying around so i cut the stud off of it and attached this:
Stud for 102 in. CB Ham Radio whip antennas - eBay (item 310213960476 end time Jul-14-10 16:59:55 PDT)

then i measured it out to 9' and slapped 18' of rg8x on it and my swrs are flat, completely flat across the board.

Doesn't mean that the antenna is actually radiating efficiently, though. A good dummy load shows "flat" SWR (not "swrs") over a wider spectrum than your antenna.