OK we have a antenna that is not resonate but with a ATU we get a good match at the radio ..now if you take the SWR meter that is now between the radio and ATU that is currently reading a low SWR and move the meter to after the ATU so its in between the ATU and the antenna will the meter still read the same low SWR??
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Will it match..... question
- Thread starter davev8
- Start date
That sounds strange, but I have never tried that. I will have to think about what is inside a tuner. It's not like an amp with an input network, then the transistors, then the output network. It's like the feed line passes straight through the tuner with variable capacitors that tap the center conductor to ground. Even an inductor in series would affect the whole circuit which includes the feed line before it and after it. Maybe someone else can elaborate, I don't know exactly what is inside a tuner. Interesting for sure.
No. If you move it between the tuner and antenna the swr meter will read the swr that you would have without the tuner. This will vary at different points on the feedline.
The SWR meter simply reads the SWR of the antenna system that is AFTER the meter. If you place the meter after the ATU then of course it will NOT read the same as it did before the ATU.
ok say we get a SWR reading presumably higher when the SWR meter is moved from between the TX and ATU to between the ATU and ANT what would happen to the SWR reading if the meter is after the ATU if we bypassed the ATU or removed it ?
The swr will be the same. Power output may now be different because the transmitter isn't working into a 50 ohm load with the tuner in bypass.
There can be a lot of variables here. Is this all theoretical or are you using a tuner on an antenna that needs to be repaired? Throw some corrosion and bad connections into the mix and who knows what will happen.
Line loss goes up with high swr, too. So if you have a coax-fed, non-resonant antenna with an antenna tuner built into the radio or between the radio and feedline, you can lose a lot of power in the feedline. Also the power-handling ability of the feedline goes down.
Ladderline is much better in that regard.
Ladderline is much better in that regard.
A Tuner only fools the SWR meter or other gear into seeing what it thinks is a good match.It does NOT actually change the SWR.If you have a 5.1 SWR without the tuner you still have 5.1 SWR with the tuner but the radio & SWR meter don't see the mismatch.
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I suggest doing some research on the conjugate match. I guess it's true that the tuner fools the transmitter or swr meter, but that isn't the entire story.
I'll take a crack at it. It took me a while to wrap my brain around it so I may not be 100% correct.
When properly adjusted the tuner gives the transmitter the 50 ohm load that it needs to work its best. The output of the tuner is also matched to the impedance at the transmitter end of the feedline. Now the output of the tuner matches the impedance of the load and maximum power transfer can occur. The tuner adds reactance to the system that is equal to but opposite of the load to cancel out reactance in the system.
Reflected power that is not lost as heat will be radiated eventually. Coax loss can be very high with high swr. A balanced feed line such as window line or ladder line will have far less loss in this situation.
https://owenduffy.net/blog/?p=11618
Lets look at what happens from a different point of view.
You have an antenna, some feed line, and an antenna tuner, before some more feed line and a radio (or perhaps the antenna tuner is built into the radio), and a field strength meter. If you tune the antenna tuner so the radio sees the lowest SWR, you have maximum power transfer to the antenna, as measured with a field strength meter (which you are not moving). If you adjust the antenna tuner so it doesn't have the lowest SWR, the field strength meter will have a lower reading, and the lower the SWR the lower the reading.
I want to point out this is the same even if you have a radio that doesn't have a high SWR protection circuit.
From the point of view of the field strength meter, you are tuning the antenna, or you are at least doing something that directly affects the antennas transmitted power.. If you claim this effect isn't from tuning the antenna, I would love to hear your explanation of what is causing this effect.
The DB
You have an antenna, some feed line, and an antenna tuner, before some more feed line and a radio (or perhaps the antenna tuner is built into the radio), and a field strength meter. If you tune the antenna tuner so the radio sees the lowest SWR, you have maximum power transfer to the antenna, as measured with a field strength meter (which you are not moving). If you adjust the antenna tuner so it doesn't have the lowest SWR, the field strength meter will have a lower reading, and the lower the SWR the lower the reading.
I want to point out this is the same even if you have a radio that doesn't have a high SWR protection circuit.
From the point of view of the field strength meter, you are tuning the antenna, or you are at least doing something that directly affects the antennas transmitted power.. If you claim this effect isn't from tuning the antenna, I would love to hear your explanation of what is causing this effect.
The DB
How does a lower (power?) reading on a FSM result in a lower (SWR) reading on the fsm?
The FSM doesn't generate any power , it (and everything past it) is a load
you are adjusting the impedance that the transmitter "sees".
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