E.Shell
Ultimate Member
I understand. I can't remember what I had for lunch yesterday and propagation is pretty technical anyway.
In trying to understand your perspective, I found an online article that aligns itself with the "Reflections' book, in fact references it, and explicitly explains that there are no losses other than the coax. Here is the article: "The Real SWR Page"
In this article, the author states:
a) the first trip down the coax, about 9% of the energy output from the tuner is lost to resistance and leakage in the coax.
b) the signal arrives at the mismatch and a portion, depending upon actual degree of mismatch, is reflected back.
c) whatever is not lost in the coax coming back is re-reflected at the tuner to be in phase with the outgoing signal, contributing to it's amplitude.
d) this power will echo back and forth until it is either transmitted in phase with the main carrier, or lost to coax resistance and leakage.
It even explicitly states that everything reflects back and forth between the tuner output and antenna feedpoint until absorbed or radiated and there is no other power lost, which you had stated above.
If this is what you are telling me, then, yes, OK, I agree and understand this carefully defined loss description just fine.
What it does NOT explicitly say is that it references the degraded/attenuated output at the tuner, not full amplifier output, yet that is exactly what they are doing and exactly what we were discussing.
No real harm in this, but it fails to make clear that using the tuner costs us power, sometimes a LOT of power, but always some power. Losses are quite clearly NOT confined to the coax until we pay the
The tuner provides the advantage of allowing full amplifier output, and thus greater propagation than if the amp shut itself down, but tuning a balcony rail, so to speak, is extremely costly in terms of wasted power. To say an antenna tuner is without losses is patently untrue because it is impossible.
Pretty solid rule: Insert something passive into a circuit, suffer insertion losses.
With regard to the RF current path, tuners are completely passive. They do not provide positive gain (amplify or supplement the signal in any way). Their use of input power is limited to indicators and switching and is measured in milliamps.
What I said in my first post regarding this 'energy lost/not lost in the tuner' discussion is that the tuner causes losses that increase with mismatch, and suggest that a tuner isn't 'all that' and has substantial losses associated with its use. I stand by that.
I asked rhetorical questions intended to demonstrate this fact. The recurring question has been, because the answer is the key: "Where does the heat inside the tuner come from?"
Very simple answer: Insertion losses.
The RF power output from the amplifier heats the tuner because there is current flow along a path or paths, resistance and voltage drop, which equals power loss.
This direct answer demonstrates that there are indeed tuner losses. It can be no other way. The mere presence of heat, any heat, indicates lost power because we must use power to produce heat. Because the tuner represents circuit path losses that are proportional to the "work" it must use this energy to "do", losses vary and can be substantial, as I have maintained in prior posts. Laws of physics dictate that we cannot do "work" without using energy. Valuable RF energy, in this case.
The link I posted previously with the IR imagery showed exactly what components were hot from dissipating lost RF power. RF power lost to heat....inside the tuner. Testing was discontinued due to excessive heat accumulation and concerns for permanent damage to, you guessed it, the tuner. Between tuner losses, feedline losses and a few percent lost to antenna radiation resistance, they ended up with only 56 watts radiated power from the original 100 watts generated at the amplifier output. The coax loss only theory would have us at 91 watts...
Looking at the Excel chart linked below that compiles tuner specs from the ARRL testing sessions is quite illuminating. Note the MEASURED LOSSES in various tuners at the various match points within the various frequency bands:
Summary Chart, from MatchBoxShootout page.
These are real numbers from real tests. Find your tuner and see what a 10:1, or even a 5:1 does to it with regard to forward power output. Anything lost doesn't make it to the output, so again, to say that there are no losses except in the coax is erroneous.
It is easy to see tuner losses as great as 40%, and there are commonly losses in the 20-30% range. In fact, they treat a modest 10% insertion loss like a nice place to be.
Watts are watts and a direct measure of power, whether it is a 100 watt light bulb, a 1,500 watt cube heater or a 500 watt toaster. A median value loss of 20-30% means that if you are running 1kw into one of these mismatched antennas via a magical tuner, you are burning/losing/wasting enough RF power inside the tuner to light a 250 watt floodlight.
In the case of one of the uglier mismatches "cured" by the tuner, we are saddled with 40%, 50% or even more wasteful losses within the tuner. Several went to 55% and one exceptionally high loss number was at 58%.
Oddly enough, some of them even show >10% losses when tuning into a 50 ohm load. So apparently we sometimes pay for something we don't even need...
Only after enduring this tuner loss do we become subject to the 'no other loss but the coax' assertions put forth in the 'Reflections' theory. We are then only at the mercy of our feedpoint match and how much is reflected, and subsequently lost in the coax, again and again and again.
We still cannot get something for nothing.
. While it might seem like an arbitrary number, but it is a compromise from transmission line design many many years ago. The best power handling is at z0=30 ohms, and the lowest loss was air dielectric coax with a Z0=77 ohms. So designers split the difference with a nice round 50.
