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Once an antenna is tuned, is it always tuned?

Or to put it in other terms, if carry all my stuff to one location, tune an antenna, can I leave the antenna tune at home after that?

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CISA, CISSP, Computer geek
clueless about HAM

www.linkedin.com/in/dariandunn

Unless rust gets into the coax joints or wherever the antenna parts casn get rusty, it should remain the same. Sometimes putting metal objects close to antennas will change the SWR reading. ALways check the SWR before you use the radio - always a proper practice...

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BASE: Icom IC-718 & GAP Titan DX, Yaesu FT-8800R & Diamond X50A, Magnum OmegaForce S45 & IMAX 2000 w/Astatic D104/TUP9.
MOBILE: Galaxy DX99V & Wilson 1000 w/Astatic D104-M2, Yaesu FT-8800R & Diamond NR-770.
"...The 444 in San Jose CA; the Central Gold Coast..."

When most people talk about "tuning an antenna", they are referring to using an antenna tuner. I'm guessing by your question however, that you mean actually tweaking the antenna until you get it resonant at the frequency you want? If it's the latter, then yes usually once you get the antenna where you want it, you can leave your meter at home. Sometimes weird stuff happens, though. Sometimes the tree's branch that you tied your dipole off to grows in a direction you though it wouldn't and starts to affect the antenna (that actually happened to me). Sometimes a bug crawls into your antenna's balun or matching network and sets up camp across a coil or some component and the whole thing goes to hell. Sometimes ice freezes on the thing and it all goes whack until it thaws. You get the idea. It helps to have your meter if your rig doesn't have one built in.

If your question is about using an antenna tuner to make an antenna load up, then you will always need to have that tuner with you to make it work, if that is the case.

Only if you're Baptist.

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73 de W4FCC

For clarity, I am thinking SWR.

I am thinking for man portable solution.

This may be for a mobile car antenna or wire dipole or .....

__________________
CISA, CISSP, Computer geek
clueless about HAM

www.linkedin.com/in/dariandunn

This is just a different way of saying what's already been said, not really anything new about it.
If you've 'tuned' an antenna, made it resonant and done the impedance matching, then it shouldn't need anything done to it until something changes. The first thing that comes to mind is what kind of antenna are we talking about, mobile or 'fixed'? Things can change with either, so both are subject to wondering about occasionally. Checking every once in a while is typical/normal. How often should that be? Beats me, when ever something changes or when you feel like it?
'Fixed antennas'
(I'm sort of uncomfortable whicvh that 'fixed' phrase, but whatever.) Non-moving/movable antennas tend to change less than mobile ones. That's typically because they don't move around a lot, aren't subject to the same amounts or kinds of vibrations, stresses, etc, but they do change. That's usually connected with corrosion, connections/joints, and things changing around them (growing, being chopped down, whatever). Think about that, I'm sure you can come up with as many of those thingys as I can. The simple side of that is that nothing ever stays exactly the same, and since part of that tuning is making an antenna 'comfortable' in it's environment, and since that environment is always changing... and I'm sure you can see where that's going, right? I don't know about where you live, but around my house them stinking @#$ squirrels don't seem to like antennas or the things that hold them up. So, a fairly regular check, or at least paying attention to the radio is sort of necessary. (12 ga. thingys work very well with this sort of changes. The neighbors don't like it but so what.)
Mobile antennas.
Same basic ideas, just more of them, sort of. The 'hard' mounted mobile antennas tend to not change as much as the movable kind, simply because they don't get moved as often. If a movable antenna gets moved, it doesn't hurt to check it to make sure it wasn't moved 'too much'. Since mobile antennas are subjected to more vibrations than the 'fixed' kind, it pays to pay attention to anything that can come loose on them. I don't think making a 'fetish' of tightening things is a real good idea, but doing so every so often probably wouldn't hurt. Driving under 40 miles of low hanging tree limbs sounds like a good time to re-check that antenna, you know? (Do that at the right speed and it sounds like a metalica beat-box, don't it??) Adding something metal near a mobile antenna, or doing a chop-n-channel on the roof line is another good time for antenna checking. An occasional check after really different weather conditions probably wouldn't hurt either, once anyway maybe.
So carrying around a few meters isn't something that's absolutely necessary all the time. Unless you just happen to have a few extra meters that you want to leave hooked up all the time. Or maybe have on in a radio? Then it's just a matter of paying attention to 'whaz-hap-nen wid-da ra-did-di-o', sort of. There are two kinds of "can't check, what the heck" sort of people. Those that it really bothers, and those that is doesn't. Both kinds have their 'pluses'. You decide which you are.
And then there are those antennas that are only going to be put up for fairly short period and then taken down for use at another time. With those, take your meters.
- 'Doc

Some exaggeration in the above, probably not too much... sort of.
(all puns intended)

one of my friends had a mini van he wanted to use a CB in. He bought a brand new CB antenna with a mag mount, and no matter what he tried he couldn't get the antenna to tune. Eventually we took the antenna off and put it on another vehicle, swr was 1.2:1 with no adjustments, put it back on the minivan and the swr was sky high again. It turned out that the mini van was made from some strange alloy (no idea what) that wasn't very conductive. The mag mount didn't stick very well to it either. It just goes to show that in some situations strange things can happen, so it never hurts to carry that meter with you and just check that swr.

Like the others have said, in most situations most antenna's will not require any adjustment.

In your friends case, the problem was that mag-mount, not the conductivity of whatever kind'a metal the van was made from. A mag-mount requirement is that it sticks to what you set it on, which means that the metal is ferrous. If you cn make that thing sit on aluminum, it would work just fine too, but magnets don't stick to aluminum so a mag-mount seldom works very good that way, falls off.
[That mag-mount and a metal vehicle provide the two plates of a capacitor which is the only reason why a mag-mount works at all. That 'capacitor' is the connection to the other half of the antenna, the vehicle's metal body. The greater the distance between the magnet and the metal, the smaller that 'capacitor' and the less 'connection' you have. 'Distance' is measured in REALLY small amounts between the plates of a capacitor, as in sheet of paper thicknesses, sort of. A layer of fiberglass would be quite a large number of sheets of paper thick, see where that's going?

"Like the others have said, in most situations most antenna's will not require any adjustment." ... Like it or not, 'those others' are mistaken. If you change both of those "most" words in that quote to "some", it would be less mistaken, and change that "any" to "much", I'd agree with it. Unless you're just sooo @#$ lucky you can't believe it, all antennas may need some adjustment to be right. Of course, if you have an antenna that does it's own adjustments all by it's self then you got the exception to that 'rule'.
You are right about that meter, the do come in handy.
- 'Doc