Tuner Efficiency Proof
Tuner Efficiency Proof
In this section I rely heavily on the SimSmith RF Circuit Analysis tool. If you have not tried SimSmith yet, I highly recommend it. SimSmith allows the user to model antennas, feed lines, circuit components and a truck load of other things. It can also display the network visually on a Smith Chart so that you can actually see how each individual component is affecting the whole system. If there is one tool that helped me understand what was happening with my feed line and my antenna tuner components, this is it. Highly recommended.
Edward Harriman (AE6TY): http://www.ae6ty.com/Smith_Charts.html
Larry Benko (W0QE): https://www.w0qe.com/SimSmith.html
First a word of appreciation for the work done by Ward Harriman and Larry Benko. Ward is the primary author of SimSmith. He has done a remarkable job of creating a tool that is both accurate and incredibly detailed. Ward has a set of introduction videos on Youtube that you can use to become familiar with SimSmith. Larry Benko has created a large number of videos on Youtube that really show off the power of this tool. I would suggest starting with Ward's video tutorials and then heading over to Larry's channel to dive into the incredible detail that this tool provides. Don't be intimidated by the tool. It is a bit difficult to master at first, but once you understand how the tool works, you'll be creating networks, modeling power consumption, observing the effect of component value changes to power and SWR across your entire network, and graphically modeling your network in a Smith Chart. It's fun and very educational.
The following is a snapshot of the SimSmith main application window. I want to familiarize you with the layout of the tool so that you can find data presented on the screen when I reference them.
In the upper left hand side of the screen is the depiction of the network that is being modeled. Each box represents a different component in the network. In this model the box on the far left (in red) is a component representing the impedance values of both my antenna and my transmission line together. For work on evaluating my own tuners, I've chosen to combine both the antenna and feed line together because it's easy to get value readings for any frequency from my antenna system using an antenna analyzer. SimSmith will allow you to model the antenna and feed line separately, which I will do below in order to illustrate a point about feed line length and its impact on impedance seen at the tuner. SimSmith allows the user to import a complete EZNEC antenna analysis for the entire spectrum from 160 - 10 meters.
To the right of the Antenna/Feed line combo component, I have the output capacitor (in cyan) for an unbalanced PI-network antenna tuner. Following the output capacitor I have the roller inductor (in magenta), the input shunt capacitor (in green), and finally the transmitter (in blue). Below the component boxes are the specific values for each component. Each value can be individually adjusted in order to observe how component value changes affect the overall network. The Smith Chart to the right is a visual representation of the entire network mapped out on the Smith Chart. The individual component colors are depicted in the arc in the diagram. Below the Smith Chart and to the left are depictions of components that can be added to your network when designing different tuners. Later, I'll show you how to use a custom component called a RUSE (Really Ugly Schematic Editor) to design lumped network components that can be added to your overall design.
What SimSmith is going to allow me to do is model real world feed line / load values against various antenna tuner models and evaluate how well each works and, more importantly, how much power is consumed in each component!!
Component Power Loss in a Pi-Network tuner
Zooming in on the network components from the previous picture, we have the screen shot above. Note the values below the colored boxes. The values of interest are "R" for resistance, "X" for reactance and "W" for watts consumed. On the far right is the transceiver that shows the SWR value presented to the transceiver from the network. As we adjust the component values, we can watch the SWR value presented to the transmitter change. It's hard to see, but I have the transceiver set to produce 2000 watts of output power at 10Mhz (30 meters). Note the SWR value at the transmitter of 1.069. This is a really good match. Also note the component values in the little boxes below the components. The two capacitor values are 91.6 pf and 58.19 pf respectively and the roller is set to 4.495 uh.
Ok, reading from left to right, we can see that of the original 2000 watts produced by the transceiver, 1.93K (1936 watts) have been transferred into the antenna and feed line. Because the feed line is lumped into this component, we can't see the losses in the feed line. We'll break that out next. Continuing on with the output capacitor we have a consumed power of 8.58 watts (not bad). In the roller inductor we have a consumed power of 54.6 watts and finally in the input capacitor we have a power consumption of 0.195 watts. All in all pretty good, but we can do better.
These power consumption numbers get significantly worse on the odd ends of the bands on 160 and 10 meters. In fact, we can model scenarios where over 200 watts (10% of input power) is being lost as heat in the roller inductor.
Component Power Loss in an L-Network tuner
Ok, here's the network layout for an L network. Note that the source capacitor has been swapped over to the load side of the roller inductor. In an L network, the shunt capacitance is always on the side of the higher impedance.
Note that the L Network is a bit more efficient. We have 1.94K watts out to the antenna, we have 8.62 watts consumed in the shunt cap and we have 53.5 watts consumed in the roller inductor. Not a huge improvement, but it does prove the point that L-networks can be more efficient than PI networks.
Also note that we have a lower SWR reading at the transmitter as well.
Component Power loss in a T-Network tuner
And now the T network. Things are looking pretty good here and it should be pretty clear why most tuner manufactures use a T network in their design.
In this model the feed line / antenna sees almost the full power going in at 1.98K watts. The load cap is consuming 1.41 watts, the roller is consuming 13.5 watts and the source cap is consuming 3.31 watts. SWR at the transmitter is 1.014. Nice. Can we do better? Let's see.
Component Power loss in a Symmetic PI-Network
Now we're getting somewhere. We're down to 1.021 SWR at the transceiver, we're transmitting 1.99K watts to the load and we're losing 10.1 watts in the load cap, 9.49 milli-watts in the roller inductors, and 0.671 watts in the source capacitor. Note that in parallel, the roller inductors combine to form an inductance that is lower than either one of the rollers individually. The funny looking block in the middle is the RUSE block, which looks like this when opened up.
This is how SimSmith allows for all kinds of circuit diagrams to be created and added into a network.
Ok, the take away from this is that the Symmetric Pi-Network tuner is definitely the most efficient (power wise) than the other networks. The question is, is it worth the additional expense of a symmetric roller inductor system? For me, it's about the efficiency, and reduction of heat. I don't like the fact that in some scenarios I could be burning up 200 watts of power in my roller inductor. Depending on the construction of the inductor, this could actually lead to a fire and there are plenty of those stories out on the forum pages.
Feed Line Length Influence on System Impedance.
Ok, one more thing before we're done. Let's break out the feed line separately and see what we can do by altering the feed line length and type. The illustration above shows the Antenna impedance as the light green "X" on the right of the diagram. The red line is the influence of the feed line on the impedance of the system. The cyan line is the load cap, the magenta line is the roller, and the dark green line in the middle of the Smith Chart is the source cap. By varying any of these values, including the feed line length, we can change the overall impedance of the system. I wanted to dwell on this a bit because I have had several discussions with Amateurs on various forums concerning feed line length and how it impacts your transmission system. In the case of a perfect match throughout the system, i.e., 50 ohm load, 50 ohm cable, 50 ohm transceiver output, the length of the coax cable is inconsequential. But! In the case of any system where the impedance between the feed line and load (antenna) doesn't match, the feed line becomes an impedance transformer itself and has a severe impact on SWR at the transceiver. This is how some amateurs have actually built matching networks, by literally using different lengths of ladder line for each band they want to work. Ok, enough words, here are some more picture.
Figure #1 (Feed line = 14 feet)
In this example the feed line is 14 feet long. The values of the 2 caps and roller have been adjusted to provide a good match. The values of these components will not be changed in the following figures. Look what happens to our perfect match as the feed line length is changed from 14 feet to 20 feet (an addition of only 6 feet) in Figure #2. The SWR at the transmitter is now well outside of the 2.0 SWR circle represented by the black dashed line.
Figure #2 (Feed line = 20 feet)
Figure #3 (Feed line = 46 feet)
Note that the SWR is almost back to that in Figure #1 with the addition of more feed line length. Cap and rotor values have not been touched.
Figure #4 (feed line = 65 feet)
And finally with more line added the feed line impedance is once again well away from the 2.0 SWR circle. The caps and roller values have not been changed.
Ok, observe what is happening here as additional feed line length is added. In figure #1 with only 14 feet of cable, the total system presents a near perfect match to the transmitter (as evidenced by the dark blue circle in the middle of the Smith Chart. Impedance = 50+0j). As we add length to the feed line, the entire system changes as the feed line acts as an impedance transformer. These changes in feed line length have a huge impact on our final impedance and SWR reading. Note that by adding length to the feed line, it essentially follows a circle around the chart as the length approaches various percentages of wavelength of the frequency that we're on. Because of this, we can add or subtract length from the feed line in order to affect SWR. In fact, we can change the feed line length and potentially end up with a 1:1 SWR ratio. Why? Because a transmission line is modeled as a set of segments. Each segment has specific fixed inductance and capacitance values. As we add or subtract segments, the total number of capacitive and inductive contributors to our overall impedance changes, which affects the impedance of the entire network.
One more thing to note. In figure #4 it's clear that as the feed line length increases, the impedance of the feed line follows a circle relative to the percentage of wavelength distance. But, also note the circles are not right on top of one another. This small variance is due to attenuation in the feed line itself and this is one of the things that most impresses me about SimSmith. SimSmith comes with a catalog of various open wire and coaxial cables that can be used to model feed lines. Each selection comes with the full values for velocity factor, attenuation per foot, etc... So, when you include the correct feed line length in your model, you can be assured that you are modeling reality.