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Author Topic: Internal tuner vs external tuner efficiency  (Read 2560 times)
KD2CJJ
Member

Posts: 368




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« Reply #15 on: May 14, 2013, 01:41:58 PM »

Again thanks for another good dive into the abyss!   Here is an article by the ARRL which supports your argument; though they do not call out the differences between an impedance match and a conjugate match they describe these differences and their affects related to SWR.  http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf

One interesting story is that my father had an issue with a Tarheel antenna where he had an impedance match but NOT a conjugate match thus his SWRs were 1:1 fine but the antenna was no where near resonance as it did not  have "ears".  He was using a SWR meter to tune the antenna and was scratching his head as to why the antenna was not resonating if he was getting a 1.0:1 SWR.  In 99% of the cases this is fine to tune an antenna using a SWR meter - so for both of us and as you can clearly see from the thread I posted no one could figure out why the antenna was not resonating.  Being a new student to antenna theory I had him use his antenna analyzer.  He was focusing on SWRs but was dismissing reactance.  After a quick test we clearly saw that the antenna was reactive with a with an impedance match.  Further tuning the system allowed us to finally get the antenna system to become a conjugate match and an impedance match.
Please correct me if I am misinterpreting any terms or concepts.


Question:
Now my understanding is that even though an antenna is Zero reactance is still may not be resonant on certain frequencies.  How is this possible?
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73

Mike
KD2CJJ
W5DXP
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Posts: 3540


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« Reply #16 on: May 15, 2013, 06:52:23 AM »

Now my understanding is that even though an antenna is Zero reactance is still may not be resonant on certain frequencies.  How is this possible?

Let's state some principles to see where the confusion is coming from. From The IEEE Dictionary:

"resonance (5)(A) (radio-wave propagation) The rapid increase or decrease of the (signal) amplitude as the excitation frequency approaches one of the natural frequencies of the system."

For resonance, we must have an inductive reactance and a capacitive reactance that are equal in absolute magnitude such that energy is being exchanged between the two types of reactances. In other words, the two different types of reactances are neutralizing each other such that the total reactance in the system adds up to zero leaving one with a pure resistance. That's what we are doing when we adjust a tuner for a 50 ohm Z0-match at the tuner input. In a low-loss system, when we achieve that Z0-match, we are causing the signal amplitudes to peak at the antenna thus radiating the maximum available power.

An ideal dummy load presents a purely resistive impedance but is not resonant because it does not meet the above definition.

The purely resistive value at resonance can have any value, e.g. 1 ohm, 10 ohms, 50 ohms, 100 ohms, ... There is nothing magic about 50 ohms.

Almost all SWR meters are calibrated for 50 ohms and the SWR reading will be 1:1 only when a value of 50 ohms exists. A 1 ohm resonant circuit will indicate a 50:1 reading on an SWR meter. A 100 ohm resonant circuit will indicate a 2:1 reading on an SWR meter. A 50 ohm SWR meter is worthless for determining resonance except for a 50 ohm value at resonance, i.e an SWR meter cannot be used to detect resonance at any other resonant resistive value except 50 ohms.

A grid dip meter can be used to detect resonance at virtually any resonant resistive value.

On a 50 ohm SWR meter, a resonant value of 10 ohms will indicate an SWR of 5:1. With a non-resonant value of 20+j20 ohms, it will indicate an SWR of 3:1, i.e. a non-resonant value of impedance can give a lower SWR reading that a resonant circuit.

Point is: When we adjust our antenna systems for lowest SWR, we may not be adjusting them to resonance.

An ideal system-wide conjugate match exists only in a lossless system which is impossible in the real world.

A system-wide near-conjugate match can exist in a low-loss real world system.

High losses in a real-world system prevent a system-wide conjugate match from being achieved. For instance, if the resonant impedance looking into the transmission line is one ohm, almost half the power from the transmitter will be dissipated in the tuner and a lot more in the coax with the 50:1 SWR.

Hopefully, I have touched on the source of the confusion.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
NO9E
Member

Posts: 382




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« Reply #17 on: May 15, 2013, 08:07:48 AM »

It all depends on the antenna and the range of the internal tuner. In a nutshell, the internal tuner is more convenient. Major differences arise when the antenna is badly unbalanced and shows high common currents. With the external tuner, one can have a balun between the radio and the tuner. Such a balun can be very simple as it works at low SWR. With internal tuner the balun needs to be connected to the antenna and must be able to tolerate high SWR with low losses.  With some loads such a balun can absorb nearly all the power sent to the antenna.

I face this issue in portable situations where the antenna is a vertical wire and 1-2 radials. One setup is IC7000 with Z11Pro tuner. The jumper and the control cable to the tuner are both wrapped 10 times around a toroid. Never any evidence of RF current or heating from 160 to 10. The other setup is K3 with internal tuner and an external balun. Smaller baluns are getting hot on some bands really fast.

Ignacy, NO9E




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KD2CJJ
Member

Posts: 368




Ignore
« Reply #18 on: May 15, 2013, 08:30:38 AM »

OK.... Therefore to achieve resonance we must have AND WILL HAVE a 0 Reactance and there is NO WAY to achieve resonance without 0 Reactance ( inductive reactance and a capacitive reactance that are equal) but does not constitute maximum power transfer.  So in a lossless system to achieve maximum power transfer and resonance the source and load resistive component of impedance must match with a 0 reactance , this ultimately constitutes a conjugate match.

Now my understanding is that even though an antenna is Zero reactance is still may not be resonant on certain frequencies.  How is this possible?

Let's state some principles to see where the confusion is coming from. From The IEEE Dictionary:

"resonance (5)(A) (radio-wave propagation) The rapid increase or decrease of the (signal) amplitude as the excitation frequency approaches one of the natural frequencies of the system."

For resonance, we must have an inductive reactance and a capacitive reactance that are equal in absolute magnitude such that energy is being exchanged between the two types of reactances. In other words, the two different types of reactances are neutralizing each other such that the total reactance in the system adds up to zero leaving one with a pure resistance. That's what we are doing when we adjust a tuner for a 50 ohm Z0-match at the tuner input. In a low-loss system, when we achieve that Z0-match, we are causing the signal amplitudes to peak at the antenna thus radiating the maximum available power.

An ideal dummy load presents a purely resistive impedance but is not resonant because it does not meet the above definition.

The purely resistive value at resonance can have any value, e.g. 1 ohm, 10 ohms, 50 ohms, 100 ohms, ... There is nothing magic about 50 ohms.

Almost all SWR meters are calibrated for 50 ohms and the SWR reading will be 1:1 only when a value of 50 ohms exists. A 1 ohm resonant circuit will indicate a 50:1 reading on an SWR meter. A 100 ohm resonant circuit will indicate a 2:1 reading on an SWR meter. A 50 ohm SWR meter is worthless for determining resonance except for a 50 ohm value at resonance, i.e an SWR meter cannot be used to detect resonance at any other resonant resistive value except 50 ohms.

A grid dip meter can be used to detect resonance at virtually any resonant resistive value.

On a 50 ohm SWR meter, a resonant value of 10 ohms will indicate an SWR of 5:1. With a non-resonant value of 20+j20 ohms, it will indicate an SWR of 3:1, i.e. a non-resonant value of impedance can give a lower SWR reading that a resonant circuit.

Point is: When we adjust our antenna systems for lowest SWR, we may not be adjusting them to resonance.

An ideal system-wide conjugate match exists only in a lossless system which is impossible in the real world.

A system-wide near-conjugate match can exist in a low-loss real world system.

High losses in a real-world system prevent a system-wide conjugate match from being achieved. For instance, if the resonant impedance looking into the transmission line is one ohm, almost half the power from the transmitter will be dissipated in the tuner and a lot more in the coax with the 50:1 SWR.

Hopefully, I have touched on the source of the confusion.
Logged

73

Mike
KD2CJJ
W5DXP
Member

Posts: 3540


WWW

Ignore
« Reply #19 on: May 15, 2013, 07:25:12 PM »

So in a lossless system to achieve maximum power transfer and resonance the source and load resistive component of impedance must match with a 0 reactance , this ultimately constitutes a conjugate match.

It a little more complicated than "0 reactance". At any point in a conjugately matched system, if the impedance looking toward the load is R+jX then for a conjugate match to exist the impedance looking toward the source must be R-jX. Those two reactances still exist but since they are equal in magnitude and opposite in sign their effects cancel just as they do in an LC series resonant circuit.
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
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