To answer the first question, it depends on your point of view. I have seen both methods used by hobbyists. For example, shortened mobile antennas that are 5 foot long are often referred to as shortened 1/4 wavelength antennas, and some people don't bother to put the shortened. The Imax 2000 has been shown to be electrically 1/2 wavelength, yet it is still considered a 5/8 or, for those that worship a certain length, the so called "almighty .64". If you have a 5/8 that has a coil as you said that makes it an electrically shortened 3/4 wavelength, people still call it a 5/8 wavelength antenna, although in reality these are actually very rare. Most 5/8 wavelength antennas are actually impedance corrected electrical 5/8 wavelength antennas, there typically is not electrical shortening involved.
Further still, and this is really nothing more than snake oil, some fiberglass mobile antenna manufacturers will call their shortened 1/4 wavelength antennas 5/8 because they were wound with a 5/8 wavelength physical length of wire, but this is nothing more than marketing.
I could actually go on here, I guess the short answer is it depends on the person and what they are trying to sell you.
Anything that measures as X = 0 on an Antenna Analyzer/VNA/whatever is self resonant by the definition of self resonance. Some people put an additional requirement of it also needs to be near the impedance of the coax it is attached to, but there is nothing on the engineering side that supports this idea. This is part of something I call the "coaxification" of radio users, essentially people who are dependent on the limits of coax and can't see anything beyond.
You will note that bot freecell and I have both used the phrase "self resonant". This is key as what most hobbyists call resonance is more accurately defined as self resonance, and is in reality a special case. I don't recall freecell using this phrase before this thread so I have to give him props for this change. Any impedance can be made resonant with a matching circuit of some sort, although this isn't always efficient. In general, if the length of the element/antenna is less than 20% of a wavelength (say a 5 foot CB antenna), it is generally more efficient to use some form of loading up on the antenna over a matching circuit.
Just a note here, it is also technically accurate to call "self resonant" just "resonant" as self resonance is a part of resonance. The thing is, when a hobbyist talks about "resonance" they are almost always referring to "self resonance".
Don't fret over this, as I stated above, you will never notice the difference between the low SWR and the self resonant points performance wise. Also, if you have an antenna that gets a low SWR without some form of matching, the low SWR point will always be close to the self resonant point. As self resonance is required for a perfect SWR match, if you have such a match one of two things happened, either the self resonant point lined up with the SWR match point, or you have something else affecting the reading, including but not limited to to many losses or common mode currents on the feed line. This is, of course, assuming there is no other form of matching in the antenna system.
I agree with this as in the hobby world this is a common length that is used from MF all the way through VHF, and even beyond those limits. I would be curious as to why he said such a thing, but he does say some strange things sometimes so I just put it in that category.
That is a good question. I'm not so sure that a 1/4 wavelength antenna, by itself, is self resonant. Every time we set up a 1/4 wavelength antenna, electrically shortened or otherwise, there is always something attached to the shield side of the coax, and if there isn't the antenna simply doesn't tune without drastic help. That being said, I haven't really researched this directly... yet... so I will hold off on any opinion at this time. I know a lot of people jump to the 1/4 wavelength sections being self resonant, but may simply be them ignoring the part of the antenna attached to the shield side of the coax...
A lot of people think this way, but I do not.
On the topic of resonance, I have two additional comments. The first is a quote from the 23'rd edition of the ARRL Antenna Book, page 1-6 and I'm pretty sure it is in other recent versions as well.
In the charts I showed above, the addition of the feed line and its losses had noticeably more of an effect on overall gain than weather or not you were near the "resonant" part of the antenna. Further, those losses were not based on reactance/resonance, but SWR.
Another thing I've noticed recently, if you look up resonant vs non-resonant, if its written by an engineer for other engineers, they will almost always say that resonance doesn't matter, while the hobbyist writing for hobbyists will almost always say it does, so take that for what it is worth.
The DB
