Resonant Frequency of Antennas - Jim W6LG

..or at least voltage maxima!

My first RF fire was my last: like you, I forced myself to learn more and get with the system

Insertion loss equals heat. Heat equals flame. Flame equals fire. Hihi!

73 Jim!

Chip W1YW

 

Hey Chip,

What do I know. It's just a hobby for me

"The insertion loss of a tuner more than offsets any minor increase in power afforded by mismatch, when the SWR is less than about 1.5:1 to 1.7:1"

In my opinion, it's the losses in the transmission line between the output of the tuner and the antenna being matched that's the bigger factor versus the (negligible) insertion loss of the tuner.

When using a transmatch/tuner to introduce the inductance and or capacitance to a non-resonant load, the circulating currents are kicked back to the antenna. There is a resulting high SWR on that line.

That's why guys favor balanced line for their multiband doublets and similar antennas. And for this reason guys use remote tuners like the SGC230 at the feedpoint on non resonant loads.

If the energy were being dissipated in the tuner, it would heat up. The only time I had a tuner overheat was when I had it wired wrong at Field Day.

Hey, but what do I know. I'm just a casual operator hobbyist and a tradesperson layman. I'm not a celebrated contester or amateur radio author, nor did I complete any college credits for mathematics or engineering.

It's come to my attention my participation in this thread could be construed as interloping and inflammatory.

So I respectfully apologize for this unintended perception.

Chip, upon review of your QRZ profile, you're obviously a vastly more successful and experienced operator.

So I retract my statement that your previous comments are "poorly written and conceived."

Thanks for your comments.

 

"Just a hobby fior me..."

You make a hobby of dissing people--incorrectly?

Jim does a great job of explaining this stuff. I especially love his 'radio ready' voice. VERY 'broadcast' quality.

If you don't know a subject well, then grab a chair and listen for a change. It's a huge turn off when people who are knowledgeable on a subject are dissed. Very 'cancel culture'.

You are a bright fellow; enjoy your fellow hams' knowledge base. It will make it enjoyable for you too.

Have a nice day and HNY.

73
Chip W1YW

 

w9ac,

nice antique cards, I have a 1920's non filled out virgin qsl card here from 9BRP in virginia minnesota along with some early to late 1930's cards from my father-in-law and his brothers who all shared the same call, w9rtn, and In all of these pre WWII QSL cards there is no mention of the operating frequency.

Just curious does anyone know why the frequency of operation or wavelength was not written on any of these early qsl cards?

Also all of these qsl's have 73's on them except one qsl that is made from a piece of birch bark from w9pcu, 2 sister hams, on ISLE ROYALE Michigan dated Sept 13th 1934, this card has 73 written on the birch.

 

My personal favorite: "You're full quieting" .... on DSTAR.

 

Also, 73's was not used exclusively at all. Use of 73's and other mistakes caused amateurs to be called "plugs" and or "hams". We could have been plug radio instead of ham radio. 73, Jim W6LG

 

I am always skeptical of SWR readings on transmitter meters. If you can read SWR with your VNA, then check the features of the RigExpert or any of the other analyzers to see if they really add anything more than you already have with the VNA. My most used Ham tool besides the DVM and soldering iron is the RigExpert AA-600. It's very portable, includes all of the bands that I care about, will analyze several bands at once, provides complex impedance and has helped me to troubleshoot dozens of antennas. I've also used it to locate breaks in coax lines as it has the equivalent of a TDR which is accurate enough to narrow down the area of the break/impedance problem. It was expensive...there are cheaper analyzers out there from Youkits, MFJ and others...but I have never regretted the purchase and it gets used a lot.

 

I never erect an antenna without connecting a dedicated power and SWR meter to the feedline. They're not that expensive anymore (they were years ago, but no longer), and they're vital to make sure your settings are right, your antenna system is intact, and you're not going to blow the much more costly output stage of a radio. I'm also a big fan of remote tuners such as the SGC SG-237 and Icom AH-4. Without them, you're likely squandering power instead of getting it out there into the ether.

 

Chip,

It's not often that I talk out of turn, and I'd estimate my ratio of listening to speaking is, conservatively, about 9 to 1.

However, I recognize my position in the food chain, and am cognizant that my comment was disrespectful. Again, I respectfully withdraw it.

With hope the crow eating is satisfactory.

73.

 

Looking forward to more, friendly chats and best to you in 2022!

73
Chip W1YW

 

Maybe they had nothing to say!

Heheh!

 

Heard two "resident" antennas and a "ten over five" signal report while tuning around this afternoon. Also, a lot of hams wanting to start their antique airplanes by yelling, "Contact!"

 

If it's good enough for The Old Man, it's good enough for me.

http://hamgallery.com/qsl/country/USA/Connecticut/1aw.htm

 

I was able to find this post from Reddit that explains how impedance mismatching induces power reflection.

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It's like an elastic collision. I think sound is the most intuitive way to imagine it. Sound is the movement of atoms- imagine two individual atoms at the edge of a sound wave. One moving, one still. The moving one hits the stationary one and transmits the wave into it. If the atoms have the same weight, the wave transmits perfectly. If the atoms have different weights -the weight of gas particles is way less than metal particles, for instance- it bounces. That's exactly what happens in a reflection.

This isn't totally accurate, as the "weight" of an atom in a solid actually has a lot more to do with the stiffness of the material, but its a pretty accurate representation. When a wave in a gas hits a solid, the particles only have enough inertia to cause a tiny distortion in the solid. The atoms in gas particles move long distances in a sound wave (up to a centimeter), but they don't have much "oomph". In a solid, a very loud sound wave causes the atoms to move a few picometers, but they have an incredibly large amount of force behind them.

So the difference that causes a sound wave to reflect is the ratio of "push" (force/inertia) to "move" (displacement). That ratio is the impedance. In light (impedance = refractive index), this is the ratio of the speed of light in a vacuum to the speed of light in the material (the "push" is always the same, but the "move" isn't always). In sound, its the ratio of acoustic pressure to the flow rate of the gas. In electricity, its the ratio of voltage to current.

A high impedance material is very resistant to push- solids have high acoustic impedance (when you tap a solid, the atoms inside only move a little), rubber has high electrical impedance (for a voltage, very little current flows).

So in a transmission line, when a wave goes from a low impedance to a high impedance, it is going from a zone with a low voltage and high current into a zone where a high voltage is needed for current to flow. So the low voltage hits that transition, and suddenly all of that current doesn't have enough voltage to pass through the high impedance. It has nowhere to go except to bounce backwards, and it pulls the voltage of the transmission down as it passes.

Vice versa applies for high to low. The current is insufficient, so the excess voltage bounces backwards. It's only when the voltage/current ratio in both lines is the same that neither current or voltage get bounced.
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From hwillis, about 5 years ago

 

ROFL