Jeff Carter wrote:
> No sir, we could most certainly *not* debate the definition of
> resonance. As I said before, it's long-settled and accepted science.
>
As you have said, resonance is resonance is unlikely to provide a 1:1
SWR as the resistance is highly unlikely to be 50 ohms which may or may
not be a problem. Before the days of cheap, low loss coax, when open
wire fed antennas were king, this was readily accepted.
The antenna doesn't know if it's resonant or not and it doesn't care. I
wrote an article for CQ magazine back in the 70s titled, "A Verbal
Graphic Description of Antennas" which was a plain language description
of how antennas work. It gained enough attention I was given a book
offer which would have been a series similar to a number of similar
books now days.
Yagi antennas which we generally purchase and assemble with a set of
instructions do sort of care because of the multiple elements that
interact to produce gain at a particular frequency, but that is a
special case and even then the parasitic elements are usually not
resonant on the operating frequency as they depend on spacing and length
to provide a phase shift.
Many antennas work just fine with an antenna tuner at the feed point
where the cancel out reactance and set resistance to the same as the
feed line. Two examples are the random wire and center fed random wires
which work well on any frequency. This serves to eliminate the coax loss
due to the SWR which on the lower bands isn't all that great anyway.
I believe it was you that mentioned the 5.8 wave vertical which is one
of the best known verticals for the lowest angle of radiation.
Get the RF to the antenna it'll radiate it, how efficiently is a
different matter as shorter antennas are known for lower radiation
efficiency.
There is a well known article from some years back called "A low SWR can
kill you, or your antenna, or something to that effect.
> To get back to the original topic, the answer is it depends on what
> you're doing. Knowing hams as I do, my suggestion remains to throw up
> whatever sort of antenna appeals to you and find out what works and
> doesn't through experimentation.
In the early days we did just that, but as antenna tuners were almost a
necessity, almost any piece of wire worked, although those of over a
quarter wave worked better.
> Pick any antenna design out of any
> book, build it, and see if you can load it. Lather, rinse, repeat.
> One can get much more out of this than arguing theory one has never
> studied.
>
> The deeper concepts might as well be black magic for the majority of
> licensed Amateurs and it's probably best to leave it at that. The
> vast majority of us lack the proper background in theory to discuss
> the underlying concepts and that's why you see so much tail-chasing on
> these mailing lists. Somebody who's "been a Ham for fifty years" will
> say something utterly retarded and someone with an engineering degree
> will call him on it, and around we go.
>
I though most who had been hams for over 50 years realized the antenna
didn't have to be resonant and it was those that came after the
invention of the Yagi that thought differently.
73
Roger (K8RI)
> One of the FCC's reasons for allocating the spectrum to us is for
> experimentation. That is for all of us, engineers and non-engineers
> alike. Amateur radio was never meant to devolve into a bunch of
> Talmudic debate. Therefore, I say throw some wire in the air and see
> what happens!
>
> I've heard it said that the Internet is the death of Ham Radio. It
> may be, but not because of the communication afforded by the Internet.
> It'll be because we'll stop building antennas and towers and
> amplifiers and instead just argue over stuff most of us don't and
> can't understand until we all get mad and leave.
>
> Jeff/KD4RBG
> Society of Broadcast Engineers #25244
>
> ---- Original message ----
>
>> Date: Fri, 7 Aug 2009 22:37:57 -0700
>> From: "Clay W7CE" <w7ce@curtiss.net>
>> Subject: Re: [TowerTalk] Resonance is over rated
>> To: <towertalk@contesting.com>
>>
>> It sounds like we could debate the definition of resonance for days without
>> reaching a consensus. So let's get back to the original topic: is resonance
>> an important attribute of a good antenna? For example, consider a 40M
>> double-extended zepp antenna. At the feed point the impedance varies from
>> 243-j1150 at 7.0 MHz to 165-j870 at 7.3 MHz. The reactance is not zero
>> anywhere in the 40M band. Yet this antenna exhibits approximately 3 dB gain
>> over a "resonant" dipole, and as one would expect a narrower 3dB beamwidth.
>> One could argue that a double-extended zepp is actually two end-fed
>> collinear resonant dipoles whose ends are separated by 1/4 wavelengh. But
>> at the feed-point, which is the only point of visibilty that we have, there
>> is reactance and the circuit does not appear resonant and requires some form
>> of tuning network to make the transmitter happy. It does have zero
>> reactance and is resonant around 8.64 MHz, but the pattern no longer has two
>> broadside lobes, but rather 4 lobes that are approximately 45 degrees from
>> broadside and the maximum gain is now only 1.2 dB better than the dipole.
>> In this case resonance may actually be hurting us.
>>
>> The bottom line is that you have to look at a much bigger picture than just
>> the feedpoint to understand whether an antenna is effective or not.
>> Measuring feedpoint impedance and declaring victory when the reactance is
>> zero or when the SWR is below a certain point is just plain ignorant, unless
>> your only goal is good SWR and antenna performance is not important. If the
>> antenna is not resonant, you can always add a matching network to make it
>> appear electrically resonant to the transmission line and/or transmitter.
>>
>> 73,
>> Clay W7CE
>>
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