05-02-2024, 04:44 PM
Pete
An ATU is simply-put an impedance matching device, yeah I know that's not news.
The complex load impedance reflected by your 132ft wire antenna, some unknown value of capacitance and inductance values transforms into a R+jx (inductive reactance) or R-jx (capacitive reactance) equivalent impedance at ONE frequency, and the complex impedance changes as soon as you utilise the antenna at a slightly different frequency, even as little as 10KHz different.
Then insert the unknown characteristics of a 49:1 UN-UN at any specific frequency (because they are never 'perfect') and you introduce a variation in the R+jx or R-jx impedance of the basic antenna, stepped down by an approximation of 49:1 to TRY to match to a 50 ohm transmission line. But guess what : if the antenna doesn't actually present as 49x50 (2450 ohms) at the selected frequency then the complex impedance presented is no-where near 50 ohms. That introduces power losses and power reflected back to the ATU and thence the radio/transmitter.
So from all that, you are asking whether the capacitors should be meshed - or not, and how much - rather than MEASURING the impedance presented at the end of the coaxial line and seeing what the actual SWR, and preferably the capacitive and inductive values, being presented to the ATU is like. So that is the proverbial "how long a piece of string" question in an electronic form.
It could be that the antenna actually presents a very low impedance at 15M, let's assume that is 300 ohms (or 294 to make it easier), so the 49:1 brings it down to 6 ohms nominal - which the ATU might cope with despite being a complex R+jx or R-jx value.
Just as likely is that the antenna could present a very high impedance, if the antenna wire perchance be a multiple of half waves at the given frequency (or near to it), so maybe it presents 50000 ohms of R+jx or R-jx, where the R is near-zero and the impedance is totally inductive or capacitive. Even transformed down by 49:1 to try t match 50 ohms, the load/antenna system has nowhere it can dissipate energy/power because it is only the Radiation Resistance component that radiates power. So the SWR remains at infinity, or near to it, and nothing works.
Supplied tables mean nothing as they assume a 'reasonable' load impedance, and they only really provide a guide as to which position for the inductor setting !
Without looking back at my previous forum posts to you, I have indicated before that a single antenna (wire/whip/..) is not going to work for all bands regardless if you want it to - or not.
Instead of asking what to mesh capacitors, do some technical reading plus some actual measurements so that you are starting from an informed point of view. Even then, the only person who can help you solve it is YOU.
Doug VK4ADC
Hint here : 'nanoVNA' devices can help you solve this !
https://nanovna.com/
https://nanorfe.com/nanovna-v2.html
An ATU is simply-put an impedance matching device, yeah I know that's not news.
The complex load impedance reflected by your 132ft wire antenna, some unknown value of capacitance and inductance values transforms into a R+jx (inductive reactance) or R-jx (capacitive reactance) equivalent impedance at ONE frequency, and the complex impedance changes as soon as you utilise the antenna at a slightly different frequency, even as little as 10KHz different.
Then insert the unknown characteristics of a 49:1 UN-UN at any specific frequency (because they are never 'perfect') and you introduce a variation in the R+jx or R-jx impedance of the basic antenna, stepped down by an approximation of 49:1 to TRY to match to a 50 ohm transmission line. But guess what : if the antenna doesn't actually present as 49x50 (2450 ohms) at the selected frequency then the complex impedance presented is no-where near 50 ohms. That introduces power losses and power reflected back to the ATU and thence the radio/transmitter.
So from all that, you are asking whether the capacitors should be meshed - or not, and how much - rather than MEASURING the impedance presented at the end of the coaxial line and seeing what the actual SWR, and preferably the capacitive and inductive values, being presented to the ATU is like. So that is the proverbial "how long a piece of string" question in an electronic form.
It could be that the antenna actually presents a very low impedance at 15M, let's assume that is 300 ohms (or 294 to make it easier), so the 49:1 brings it down to 6 ohms nominal - which the ATU might cope with despite being a complex R+jx or R-jx value.
Just as likely is that the antenna could present a very high impedance, if the antenna wire perchance be a multiple of half waves at the given frequency (or near to it), so maybe it presents 50000 ohms of R+jx or R-jx, where the R is near-zero and the impedance is totally inductive or capacitive. Even transformed down by 49:1 to try t match 50 ohms, the load/antenna system has nowhere it can dissipate energy/power because it is only the Radiation Resistance component that radiates power. So the SWR remains at infinity, or near to it, and nothing works.
Supplied tables mean nothing as they assume a 'reasonable' load impedance, and they only really provide a guide as to which position for the inductor setting !
Without looking back at my previous forum posts to you, I have indicated before that a single antenna (wire/whip/..) is not going to work for all bands regardless if you want it to - or not.
Instead of asking what to mesh capacitors, do some technical reading plus some actual measurements so that you are starting from an informed point of view. Even then, the only person who can help you solve it is YOU.
Doug VK4ADC
Hint here : 'nanoVNA' devices can help you solve this !
https://nanovna.com/
https://nanorfe.com/nanovna-v2.html
Doug VK4ADC @ QG62LG51
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.