software or calculator for wideband resonance antenna

You might try a radio group rather than here. Maybe uk.radio.amateur.moderated for a start.

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Rick

Sounds like you want a fixed antenna that is broadband from 2-30MHz. That's kinda the opposite of resonance. You make a resonant circuit have greater bandwidth by reducing the Q. You can do that by adding loss. Normally you don't want that. The other problem is capture area. Your 6' pipe is a fraction of the wavelength and won't work well regardless.

Bottom line, if it were possible, you would be able to buy one at any ham radio store.

Look up helical resonators. There should be plenty of info on coupled helical resonators.

I

You can get a free copy of EZNEC to model your antenna:

Your question is appropriate for rec.radio.amateur.antenna.

So you want a transmitting antenna. A transmitting antenna can be:

• Small (compared to wavelength)

• Broadband

• Highly efficient

Unfortunately you can pick only one of these parameters at a time at the cost of the two other. There are thousands of patents trying to optimize some of these parameters (e.g. CFA), but the other parameters are lousy.

For receive only antennas, for frequencies below about 10 MHz, you can sacrify the efficiency for the other parameters due to the huge band noise.A ferrite rod for medium waves can have a very bad efficiency typically a loss of 40 to 60 dB, with still adequate performance.

"One skilled in the art" recognizes that all the antenna dimensions are in relation to its intended wavelength (or range thereof). So you simply scale all dimensions: conductor size, length, diameter, pitch, everything proportional to the wavelength.

Which means, for a helix to be meaningfully helix-ey in your desired frequency range... you need one approximately as big around as a house, and twice as tall.

Needless to say, simpler designs are much more popular for 80 and 160 meters!

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

Eh, efficiency is kind of unrelated. Small leads to arbitrarily low efficiency of course, but broadband antennas tend to be quite good. Broadband antennas can also be very directional, because the antenna is simply a phased (and frequency'd..?) array of elements, and therefore launches a wave preferentially.

Bandwidth and directivity kind of go together; a small antenna can have neither, while a large antenna can be optimized for a continuum of both. (Optical telescopes probably being the best example of both, supporting from near ~mm to 350nm wavelengths, limited only by the receiver installed at its focus, and atmospheric absorption).

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

73

VE7AJX

"Norm X" wrote

One fact that I forgot to mention is that we did a frequency response curve for a prototype that did not work. It showed a narrow resonance at ~ 2.0 MHz.

73

Why is efficiency unrelated for a transmitting antenna?

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Rick

I said "kind of", and gave examples. It's certainly not a linear three-axis tradeoff, as you seemed to imply?

Efficiency is independent, in so much as:

- If conductors are ideal, then it's size independent (you can make a superconducting resonator with a Q of millions)

- You can always reduce efficiency, trivially, by throwing resistors at it

For real conductors, efficiency is hyperbolic vs. size (assuming an otherwise optimal design).

That is, asymptotically good for large antennas, proportionally bad for "small" antennas (you can always make the element smaller, but radiation resistance becomes an ever-smaller part of the total resistance).

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

You have me confused with someone else.

Resonators that aren't antennas possibly. An antenna can be broadband (and low Q) without being inefficient. Low Q implies a loss of energy from the resonator, but that is what an antenna does, radiate energy. If the radiation resistance is high relative to the reactance of the components of the resonator the circuit can be broadband and still have high efficiency. The efficiency is low when the loss resistance is high relative to the radiation resistance.

Which is highly counter productive in a transmitting antenna. Much better to raise the radiation resistance.

Now you are starting to make sense.

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Rick

Gain is usually defined as Directivity x Efficiency. People are usually interested in EiRP, which depends of the transmitter power and gain.

A ferrite rod has a similar figure of eight radiation pattern as a full sized dipole, but since the efficiency can be as low as -60 db, The gain is -60 dBd, so it is quite useless for transmitting purposes. Inputting 1 W and it radiates about uW in desired direction :-)

I have two antennas with 50 ohm flat frequency response across the whole HF range. One is connected to a UHF plug and the other to a BNC plug. They were known in the previous life as10Base5 and 10Base2 coaxial line terminators. The transmitter sees a nice 50 ohm load but the antenna doesn't radiate anything (at least I hope).

Then the separation between elements must be significant fraction of the wavelength.

I was pointing out to the OP that the expectations are too high.

• Accept matched conditions at those frequencies you actually intend to transmit on, possibly use separate antennas for each band

• Accept low efficiency and use very much transmitter power (1 kW)

• Move to a detached house with lots of space for antennas or use remote transceiver over the internet.

Sorry, what upsidedown implied... :-p

For sure, the resonators that are, aren't being used as antennas, and presumably their Q is high /specifically because/ they are even worse antennas than such a high Q might imply! :)

But it also implies that if one were constructed of a superconducting coil and parallel plates, open to space and allowed to radiate, and designed so the radiation resistance is a considerable fraction of the total loss, then it would be, well, right about Q times smaller than a wavelength-scale antenna would be.

So that's what I was getting at.

To say nothing of bandwidth, of course: such an antenna would be truly useless, hardly being able to carry CW traffic! :-)

Sometimes, dampening is useful to smooth the transition from abrupt geometry changes and reflections, like at the mouth of a horn antenna. The extended bandwidth, flatness and SWR might be more beneficial than the cost of midband loss. But this is really only relevant to lab applications where flatness is more important than efficiency.

Certainly not something you'd do for a broadcast application!

Yeah, the great thing about wideband antennas is, they usually have quite excellent matching to free space, around 140 ohms (which still needs some matching to a 50 ohm line, but oh well).

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com

Get the ARRL Antenna Book and read the parts about mobile HF antennas. There is no such thing as a small and efficient antenna with decent bandwidth.

In aviation, there are MF beacons (NDB, locator) which have to us very short antennas compared to wavelength. The frequencies are around 300 kHz, with corresponding wavelengths around 1 km (0,625 miles, 3300 feet). The antennas are about 20 m high with a 6 meter diameter top capacitance hat. The efficiency is around 1 %, even with a respectable amount of radial wires in the ground.

--

Tauno Voipio, (OH2UG)

There is a practical example in aviation NDB beacon antennas. They are of necessity short compared to the wavelength (1 km), as there is no way to erect a 250 m stick in the middle of an approach funnel. The antennas are 20 to 40 m high with capacitive top hat loading and a very high Q, so that the AM modulated Morse code indentifier is sent at

400 Hz instead of the more customary 1050 Hz, to pass the modulation sidebands better.

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-TV

Still not with you. When you say, "designed so the radiation resistance is a considerable fraction of the total loss", I think you've mangled something again. I would assume the superconductor has no loss resistance so that the radiation resistance is the only resistance in the loop.

I have been reading a lot on loop antennas and small transmitting loops are common. It is hard to achieve high efficiencies and a wide bandwidth because of the limitations of using non-superconductors. However, such a loop can be designed in a much smaller space than many other types of antennas. Clearly they work or no one would build them.

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Rick

There are many commercially available compact magnetic transmitting loops that would fit into an ordinary balcony, but they are not very useful below 10 MHz.

3 m diameter loop bent from a single 18-25 mm OD copper tube might have an efficiency of about 1 %. The problem is the variable capacitor, which has to handle several kilovolts. The best solution is to use a dual high voltage capacitor with the both ends of the loop soldered/welded into the two stators of the two capacitors. The two capacitors are now in series, so reducing the required voltage ratings. The loop current flows from one rotor through the capacitor axle to the other rotor, no current flows through the slip connections. The rotor slip connections might be connected to ground to reduce noise on reception or avoid electric shocks if tuned when the transmitter is on.

Better than two variable caps is one with a butterfly construction. Each rotor plate is between two stator plates at each end so no current flows through the axle at all, just through the plates. That is assuming a vacuum variable cap is not your first choice.

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Rick

Not so. You expect too much of a disabled senior citizen. However, I guess you missed my aside where I stated that we did a frequency response curve for a prototype that did not work, and found a narrow resonance at 2.0 MHz, the beginning of the desired band. So the Subject: line is well worded, given observations and prior art. Prior art is derived from a US Patent, which has failed to attract attention in the ham world.

Let's say sometime about electricity as know in 1971. The ARRL handbook shows a capacitance hat as just that, either a wide metal pie plate or a circular plate of aluminum. Back in the good old days people didn't really understand Coulomb's law or its implications. For two parallel plates charge is distributed evenly but for one plate, charge goes to the circumference. A pie plate or aluminum plate wastes metal and is less efficient than a more enlightened idea. I'm not making any ad homonyms, I'm just saying that progress happens.

That is why I am relying on a US patent. I'm doing original work, apparently, but I am not doing patent infringement.

73

VE7AJX