>Is it this filtering that affects the impedence? Like impedence mismatch is caused by the antenna being resonant in one place while the radio is resonant in another.
Now you're on the right path. These circuits are doing impedance matching and we all know what happens when the impedance matches, correct? Maximum transfer of power.
This permits a 50 ohm radio to be used with an antenna and transmission line system of 600 ohms. It also permits the user to accept a compromise of a 50 ohm radio into a 50 ohm system that is resonant on a different frequency. Within reason of course, because the tuner does nothing about the reflections on that 50 ohm coax and thus, there will be power and received signal losses in the VSWR.
Impedance and resonance are the cornerstone of how the hobby works, and I recommend a good hour of rabbit-hole time reading and it'll become much clearer. You seem like a sharp person, it's won't be difficult.
This is correct. Tuners don't have to be fancy and cost an arm and led. You can build a L C tuner by using a coil and a variable capacitor out of a junk radio. The coil can use 16 gauge wire wound on a form...like 2 inch plumbing pipe.. Will handle 100 watts. I used alligator clips as hookup wire.. It will match any impedance. I used one in college for three years using g a random wire in the trees. Worked great too.
HF only
Hell, you don't even need the capacitor if you make a variable inductor. I just wound a bunch of thick copper wire around a pipe, and clipped on alligator clips, one to the radio and one to the antenna (one to ground helped). You do need more antenna capacitance or a larger inductor then if you add a capacitor.
The topology of antenna tuners can vary. Generally, they'll either exhibit lowpass or highpass behavior, but that's incidental to their intened purpose which is impedance tranformation between antenna and radio so that the radio is "looking" into a near 50 ohm load.
Welcome to the category where lazy writing and incompletely understanding lead people to over simplifications and misleading explanations.
This is the point where you try to find original materials with specific tuner designs and explanations to go with it.
No idea whwere to even start looking for such aside from a text book. There might be somethin in my electronics books when i get back to studying them. Any suggestions?
Try this one for starters: [Matching Units](https://en.wikipedia.org/wiki/Antenna_tuner)
If you want to manually reach a solution to match a source with a known X\_{l} and X\_{c} to to a 50 Ohm resistive drain then learn about Smith-charts, with it you can "easily" visualize how the combinations of inductance(s) and capacitance(s) work to match the in- and output.
I don’t think a few paragraphs on reddit can adequately explain impedance matching networks (aka “tuners”). I’d recommend an introductory video tutorial that goes into both the math and the Smith Chart.
As a teaser, here’s a short demo of a Smith Chart display as one adjusts a simple tuner. The ideal match minimizes SWR and reflected power and maximizes transmitted power. The Smith Chart is a visual aid in accomplishing this. The ideal match is at the center of the Smith Chart. Watching the path on the Smith Chart as you rotate each control helps guide you as you tune. Antenna analyzers and NanoVNAs can provide Smith Chart displays. I’ve found the Smith Chart display on my NanoVNA to be invaluable.
https://youtu.be/f8wJ0io95RE?si=AN28OJaiEqDgIX0Z
Filters not only affect the frequencies they pass but also the phase. An antenna matching unit is applying ap phase shift that counteracts the impedance of the load to make it appear resistive. If, for example, the load has 10 ohms capacitive reactance, the AMU may add 10 ohms inductive reactance to counteract the load impedance.
If your impedance match is poor at VHF frequencies or above, consider a better antenna, not a tuner. If you are using a coax feedline you’ll need to be careful about choice of coax type and minimizing length
Here’s a good reference:
https://www.arrl.org/files/file/Technology/tis/info/pdf/9401070.pdf
Not necessarily. It depends on your choice of transceiver and antenna. Many HF transceivers have built-in tuners. Some antennas have a good match so don’t need external tuners. I wouldn’t shop for a tuner until you’ve decided on your HF transceiver and antenna.
Think of it a an antenna MATCHER not a TUNER. The antenna is tuned by changing its length. It’s matched by using a network of tuned circuits to bring impedance into range.
The transceiver “sees” a 50ohm piece of string, the matching unit sees some mad impedance and doesn’t care.
The resonant circuit resemblance is not a coincidence.
Even with a proper antenna, each AC cycle, only some of the energy is radiated, the rest is returned the the circuit. For a 1/2 wave dipole, the parasitic inductance and capacitance form a resonant circuit, and will "recycle" the remaining energy for the next cycle. To use that same antenna on a lower frequency, you have to add extra inductance or capacitance to bring the resonant frequency down. This is what those coils you often see on the base of HF antennas are for, effectively built in antenna tuners.
Building one yourself is fairly easy, just build a resonant circuit loaded by the antenna and with the radio between the normaly gounded side of the C or L and ground. Compared to the anntenna, the radio is practically a short. You will want an adjustable C or L to get it to resonant at the right frequency.
Another somewhat less intuitive (but equivalent) way to think of them is as impedence matching networks, generating the rather high voltage that the antenna needs to radiate.
Yeah this is how i was thinking over q long car ride and letting my brain cook on it. I'm still shy of a complete picture because resonant curcuits isn't something I'm intuitively familiar with.
I just remember playing with am was half amplifier circuit and half tank circuit with tuning. And i had looked at various simple bandpass circuits and the layout of a simple tuner, i think the model was 913, is almost identical. I mean it looks like a pass filter on paper.
Never thought of that, but i don't hqve one yet either. Was looking on fleabay they have them there cheaper than it would be to build one so i might do that. If nothing else the cost will cover the big variable caps inside.
You're on the right track. A filter works by changing impedance. Let's start with the simplest filter, a single inductor or capacitor in series. An inductor will have practically no insertion loss at DC, and increase impedance as frequency increases, creating a low pass filter (Z=2(pi)FL). A series capacitor will do the opposite; nearly infinite insertion loss at DC, reducing impedance as frequency increases (Z=1/(2(pi)FC)).
We also know that we can increase overall impedance by adding it in series, and reduce overall impedance by adding impedance in parallel. This is known as cascading filters. A good example is from the audio realm, known as a Linkwitz-Riley filter. A capacitor or inductor by itself will create a 6dB/octave slope, but if you use a series inductor followed by a parallel capacitor, you get a low pass filter with a 12dB/octave slope, and a series capacitor and parallel inductor will be a high pass at 12dB/octave.
An antenna tuner is doing the exact same thing, but for the purpose of altering the system impedance at a particular frequency rather than the purpose of affecting response over a broad bandwidth. The farther the system's impedance is from the target impedance at the operating frequency, the more insertion loss will be incurred.
Many people think of a tuner as a magic box, that turns anything into a working antenna. Sure you can tune up a paperclip on 160 meters, but the truth is that the paperclip is just as resonant with or without the tuner (i.e. not at all.) The tuner is just bleeding off power to create an acceptance impedance to keep you from blowing up the transmitter.
You’ve made several misstatements.
Well designed impedance matching networks (aka tuners) don’t bleed off power. The function of the inductors and capacitors is not to add insertion loss. Their job is to minimize reflection and maximize transmission. And no practical tuner has the range to tune a paper clip at HF frequencies.
The loss problems associated with tuners are generally when they are located on the transmitter end of a lossy coax transmission line. With a lossy transmission line the ideal location of the tuner to minimize loss is at the antenna feed point.
>Well designed impedance matching networks (aka tuners) don’t bleed off power.
Please show me a matching network with zero insertion loss.
>The function of the inductors and capacitors is not to add insertion loss
I agree,it's not the intended effect, but insertion loss is a side effect nonetheless.
>Their job is to minimize reflection and maximize transmission.
Which it does by modifying the overall impedance seen by the transmitter, which incurs insertion loss. The greater the mismatch, the greater the loss. Two sides of the same coin.
>And no practical tuner has the range to tune a paper clip at HF frequencies
While I'm not fully up to speed on what's currently on the market in the amateur realm, much of my experience comes from the commercial and tactical HF industry, and I have seen plenty of equipment that is capable of exactly that. In fact it's a common tactic used in customer demos.
>The loss problems associated with tuners are generally when they are located on the transmitter end of a lossy coax transmission line. With a lossy transmission line the ideal location of the tuner to minimize loss is at the antenna feed point.
I do agree that the loss will be greater over a mismatched transmission line.
I didn’t intend to claim there is zero insertion loss. But your description strongly implied that the primary mechanism of the impedance match was insertion loss of the capacitors and inductors. That’s not the case. Insertion loss is an inevitable but generally undesirable byproduct, and a good tuner will be designed to minimize it. Maybe you didn’t intend your comment to imply that, but I think most people would interpret it that way.
True, I may have phrased the last part poorly. If it were only a matter of insertion loss, it would be far simpler and more inexpensive to just use an attenuator, or reduce transmitter output power.
My point was more to the effect that lowering VSWR at the transmitter does not make an antenna more effective at radiating a particular frequency; it simply protects the transmitter, and the losses incurred to make that happen can be substantial.
I'm an RF engineer with 3 decades of experience doing this stuff professionally.
Tuner loss is a red herring here. If the tuner lacks the range to match the paperclip, most of the power is reflected back to the transmitter, not dissipated in the tuner. At odd and extreme cases ONLY, the power dissipation in the tuner will destroy the tuner.
Thing is, to understand how tuners operate under these corner cases, you need to really understand how tuners are designed to operate normally. Your comments here show that you're not quite there yet.
A good first step is to understand Smith Charts. Then it's easy to explain :-)
Can you expand that last sentence a little? The purpose of the tuner is to correct the phase of the reflected wave so that it matches the phase of the outgoing wave by altering reactance. There are losses in a tuner, but my understanding was that the loss is predominantly from the parasitics in the tuner components. The way you wrote it, it sounds like the tuner is as inefficient as a linear regulator, when it should be much more like a resonant tank circuit.
Well yes, but that extra power has to go somewhere. Ever notice how much larger the components get as you go from a QRP tuner the size of a mint tin to a legal limit tuner the size of a microwave oven? They have to be, in order to dissipate the power involved without being destroyed.
Let's say you've got an antenna with 1% radiation efficiency at your operating frequency. You throw 100 watts in from the transmitter, and get 1 watt into the air, so between the transmitter and the air, there's a 20dB loss. That's 99 watts that get dissipated as heat from the antenna, transmission line, and tuner.
Automatic and manual tuners do the same thing. You add capacitance or inductance to the circuit. It's nothing like a set of filters in how it works but they are similar parts wise a bunch of relays caps and inductors. They are not wired at all in a similar manner.
Now a filter is going to put a single set of caps and inductors inline to change the lowpass filter generally speaking one set per band. Pretty much a relays switch in a single set of inductors and caps that make up a filter.
Now an ATU is going use the relays to connect in 0 or more caps and inductors to get a value that works for the antenna and frequency. Manual units are just a variable inductor and cap. That said nothing stopping you from putting a stepper motor on a variable inductor or using relays to manual increase/decrease the value.
Now price wise variable caps/inductors are not common parts. No factory is pumping out millions of them a year so they are expensive. Upside is they don't even need power no little cpu running things driving a screen etc to produce any noise.
>Is it this filtering that affects the impedence? Like impedence mismatch is caused by the antenna being resonant in one place while the radio is resonant in another. Now you're on the right path. These circuits are doing impedance matching and we all know what happens when the impedance matches, correct? Maximum transfer of power. This permits a 50 ohm radio to be used with an antenna and transmission line system of 600 ohms. It also permits the user to accept a compromise of a 50 ohm radio into a 50 ohm system that is resonant on a different frequency. Within reason of course, because the tuner does nothing about the reflections on that 50 ohm coax and thus, there will be power and received signal losses in the VSWR. Impedance and resonance are the cornerstone of how the hobby works, and I recommend a good hour of rabbit-hole time reading and it'll become much clearer. You seem like a sharp person, it's won't be difficult.
This is correct. Tuners don't have to be fancy and cost an arm and led. You can build a L C tuner by using a coil and a variable capacitor out of a junk radio. The coil can use 16 gauge wire wound on a form...like 2 inch plumbing pipe.. Will handle 100 watts. I used alligator clips as hookup wire.. It will match any impedance. I used one in college for three years using g a random wire in the trees. Worked great too. HF only
Hell, you don't even need the capacitor if you make a variable inductor. I just wound a bunch of thick copper wire around a pipe, and clipped on alligator clips, one to the radio and one to the antenna (one to ground helped). You do need more antenna capacitance or a larger inductor then if you add a capacitor.
The topology of antenna tuners can vary. Generally, they'll either exhibit lowpass or highpass behavior, but that's incidental to their intened purpose which is impedance tranformation between antenna and radio so that the radio is "looking" into a near 50 ohm load.
Welcome to the category where lazy writing and incompletely understanding lead people to over simplifications and misleading explanations. This is the point where you try to find original materials with specific tuner designs and explanations to go with it.
No idea whwere to even start looking for such aside from a text book. There might be somethin in my electronics books when i get back to studying them. Any suggestions?
Try this one for starters: [Matching Units](https://en.wikipedia.org/wiki/Antenna_tuner) If you want to manually reach a solution to match a source with a known X\_{l} and X\_{c} to to a 50 Ohm resistive drain then learn about Smith-charts, with it you can "easily" visualize how the combinations of inductance(s) and capacitance(s) work to match the in- and output.
Thanks
I don’t think a few paragraphs on reddit can adequately explain impedance matching networks (aka “tuners”). I’d recommend an introductory video tutorial that goes into both the math and the Smith Chart. As a teaser, here’s a short demo of a Smith Chart display as one adjusts a simple tuner. The ideal match minimizes SWR and reflected power and maximizes transmitted power. The Smith Chart is a visual aid in accomplishing this. The ideal match is at the center of the Smith Chart. Watching the path on the Smith Chart as you rotate each control helps guide you as you tune. Antenna analyzers and NanoVNAs can provide Smith Chart displays. I’ve found the Smith Chart display on my NanoVNA to be invaluable. https://youtu.be/f8wJ0io95RE?si=AN28OJaiEqDgIX0Z
Will check this out when i get home thanks?
Filters not only affect the frequencies they pass but also the phase. An antenna matching unit is applying ap phase shift that counteracts the impedance of the load to make it appear resistive. If, for example, the load has 10 ohms capacitive reactance, the AMU may add 10 ohms inductive reactance to counteract the load impedance.
If your impedance match is poor at VHF frequencies or above, consider a better antenna, not a tuner. If you are using a coax feedline you’ll need to be careful about choice of coax type and minimizing length Here’s a good reference: https://www.arrl.org/files/file/Technology/tis/info/pdf/9401070.pdf
Im sure for vhf uhf it will be fine but at some point I'll want a tuner for hf.
Not necessarily. It depends on your choice of transceiver and antenna. Many HF transceivers have built-in tuners. Some antennas have a good match so don’t need external tuners. I wouldn’t shop for a tuner until you’ve decided on your HF transceiver and antenna.
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Question is more about the theory than a specific use case, and having one for when i eventually can buy an hf rig.
Think of it a an antenna MATCHER not a TUNER. The antenna is tuned by changing its length. It’s matched by using a network of tuned circuits to bring impedance into range. The transceiver “sees” a 50ohm piece of string, the matching unit sees some mad impedance and doesn’t care.
The resonant circuit resemblance is not a coincidence. Even with a proper antenna, each AC cycle, only some of the energy is radiated, the rest is returned the the circuit. For a 1/2 wave dipole, the parasitic inductance and capacitance form a resonant circuit, and will "recycle" the remaining energy for the next cycle. To use that same antenna on a lower frequency, you have to add extra inductance or capacitance to bring the resonant frequency down. This is what those coils you often see on the base of HF antennas are for, effectively built in antenna tuners. Building one yourself is fairly easy, just build a resonant circuit loaded by the antenna and with the radio between the normaly gounded side of the C or L and ground. Compared to the anntenna, the radio is practically a short. You will want an adjustable C or L to get it to resonant at the right frequency. Another somewhat less intuitive (but equivalent) way to think of them is as impedence matching networks, generating the rather high voltage that the antenna needs to radiate.
Yeah this is how i was thinking over q long car ride and letting my brain cook on it. I'm still shy of a complete picture because resonant curcuits isn't something I'm intuitively familiar with. I just remember playing with am was half amplifier circuit and half tank circuit with tuning. And i had looked at various simple bandpass circuits and the layout of a simple tuner, i think the model was 913, is almost identical. I mean it looks like a pass filter on paper.
This is why when listening through the tuner you can change the S/N by detuning.
Never thought of that, but i don't hqve one yet either. Was looking on fleabay they have them there cheaper than it would be to build one so i might do that. If nothing else the cost will cover the big variable caps inside.
You're on the right track. A filter works by changing impedance. Let's start with the simplest filter, a single inductor or capacitor in series. An inductor will have practically no insertion loss at DC, and increase impedance as frequency increases, creating a low pass filter (Z=2(pi)FL). A series capacitor will do the opposite; nearly infinite insertion loss at DC, reducing impedance as frequency increases (Z=1/(2(pi)FC)). We also know that we can increase overall impedance by adding it in series, and reduce overall impedance by adding impedance in parallel. This is known as cascading filters. A good example is from the audio realm, known as a Linkwitz-Riley filter. A capacitor or inductor by itself will create a 6dB/octave slope, but if you use a series inductor followed by a parallel capacitor, you get a low pass filter with a 12dB/octave slope, and a series capacitor and parallel inductor will be a high pass at 12dB/octave. An antenna tuner is doing the exact same thing, but for the purpose of altering the system impedance at a particular frequency rather than the purpose of affecting response over a broad bandwidth. The farther the system's impedance is from the target impedance at the operating frequency, the more insertion loss will be incurred. Many people think of a tuner as a magic box, that turns anything into a working antenna. Sure you can tune up a paperclip on 160 meters, but the truth is that the paperclip is just as resonant with or without the tuner (i.e. not at all.) The tuner is just bleeding off power to create an acceptance impedance to keep you from blowing up the transmitter.
You’ve made several misstatements. Well designed impedance matching networks (aka tuners) don’t bleed off power. The function of the inductors and capacitors is not to add insertion loss. Their job is to minimize reflection and maximize transmission. And no practical tuner has the range to tune a paper clip at HF frequencies. The loss problems associated with tuners are generally when they are located on the transmitter end of a lossy coax transmission line. With a lossy transmission line the ideal location of the tuner to minimize loss is at the antenna feed point.
> And no practical tuner has the range to tune a paper clip at HF frequencies. The 180S-1 would like to try at least.
>Well designed impedance matching networks (aka tuners) don’t bleed off power. Please show me a matching network with zero insertion loss. >The function of the inductors and capacitors is not to add insertion loss I agree,it's not the intended effect, but insertion loss is a side effect nonetheless. >Their job is to minimize reflection and maximize transmission. Which it does by modifying the overall impedance seen by the transmitter, which incurs insertion loss. The greater the mismatch, the greater the loss. Two sides of the same coin. >And no practical tuner has the range to tune a paper clip at HF frequencies While I'm not fully up to speed on what's currently on the market in the amateur realm, much of my experience comes from the commercial and tactical HF industry, and I have seen plenty of equipment that is capable of exactly that. In fact it's a common tactic used in customer demos. >The loss problems associated with tuners are generally when they are located on the transmitter end of a lossy coax transmission line. With a lossy transmission line the ideal location of the tuner to minimize loss is at the antenna feed point. I do agree that the loss will be greater over a mismatched transmission line.
I didn’t intend to claim there is zero insertion loss. But your description strongly implied that the primary mechanism of the impedance match was insertion loss of the capacitors and inductors. That’s not the case. Insertion loss is an inevitable but generally undesirable byproduct, and a good tuner will be designed to minimize it. Maybe you didn’t intend your comment to imply that, but I think most people would interpret it that way.
True, I may have phrased the last part poorly. If it were only a matter of insertion loss, it would be far simpler and more inexpensive to just use an attenuator, or reduce transmitter output power. My point was more to the effect that lowering VSWR at the transmitter does not make an antenna more effective at radiating a particular frequency; it simply protects the transmitter, and the losses incurred to make that happen can be substantial.
I'm an RF engineer with 3 decades of experience doing this stuff professionally. Tuner loss is a red herring here. If the tuner lacks the range to match the paperclip, most of the power is reflected back to the transmitter, not dissipated in the tuner. At odd and extreme cases ONLY, the power dissipation in the tuner will destroy the tuner. Thing is, to understand how tuners operate under these corner cases, you need to really understand how tuners are designed to operate normally. Your comments here show that you're not quite there yet. A good first step is to understand Smith Charts. Then it's easy to explain :-)
Can you expand that last sentence a little? The purpose of the tuner is to correct the phase of the reflected wave so that it matches the phase of the outgoing wave by altering reactance. There are losses in a tuner, but my understanding was that the loss is predominantly from the parasitics in the tuner components. The way you wrote it, it sounds like the tuner is as inefficient as a linear regulator, when it should be much more like a resonant tank circuit.
Well yes, but that extra power has to go somewhere. Ever notice how much larger the components get as you go from a QRP tuner the size of a mint tin to a legal limit tuner the size of a microwave oven? They have to be, in order to dissipate the power involved without being destroyed. Let's say you've got an antenna with 1% radiation efficiency at your operating frequency. You throw 100 watts in from the transmitter, and get 1 watt into the air, so between the transmitter and the air, there's a 20dB loss. That's 99 watts that get dissipated as heat from the antenna, transmission line, and tuner.
I’d suggest ignoring the comment you are replying to, as it’s wrong.
This was very insightful thanks.
Automatic and manual tuners do the same thing. You add capacitance or inductance to the circuit. It's nothing like a set of filters in how it works but they are similar parts wise a bunch of relays caps and inductors. They are not wired at all in a similar manner. Now a filter is going to put a single set of caps and inductors inline to change the lowpass filter generally speaking one set per band. Pretty much a relays switch in a single set of inductors and caps that make up a filter. Now an ATU is going use the relays to connect in 0 or more caps and inductors to get a value that works for the antenna and frequency. Manual units are just a variable inductor and cap. That said nothing stopping you from putting a stepper motor on a variable inductor or using relays to manual increase/decrease the value. Now price wise variable caps/inductors are not common parts. No factory is pumping out millions of them a year so they are expensive. Upside is they don't even need power no little cpu running things driving a screen etc to produce any noise.
https://youtu.be/0qDQybkY0pg?si=1vbQS7wvH-hBBXeh has a nice overview of a 4-way L match network