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Re: Measuring R,X Resonant Frequency

 

This is the typical case if mixing concepts.Its very crear that the amplifiers don?t have a 50 ohm resistor inside , un less you live in a very cold place and need some extra heating… My idea were to show that has no sense to worry about resonance and minimum SWR in this case and also consider the source impedance that differs of Z2 on VNA. The minimum SWR that shows the VNA is a calculation using the calibration standards , If you really would like to know the SWR over the transmission line there are other methods because the coaxial cables has not exactly 50 Ohms and if we condider the system as unidirectional the only purpose is to transfer the maximum power to antenna the minimum SWR must to be measured over the transmission line. In the other hand the output impedance of an amplifier don’t only define his efficiency, this is other concept mixing.


Ing. Patricio A. Greco
Taller Aeronáutico de Reparación 1B-349
Laboratorio de Calibración ISO 17025 AREA: RF/MW
Gral. Martín Rodríguez 2159
San Miguel (1663)
Buenos Aires
T: +5411-4455-2557
F: +5411-4032-0072
www.servicios-electronicos.com.ar

On 21 Jan 2025, at 13:24, Fran?ois via groups.io <18471@...> wrote:

You are right to ask yourself. There is one fundamental thing that you forget, that the TX -> line -> Antenna system is only adapted in one direction.

The antenna adaptation devices (box for example) only serve to bring 50 ohms to the TX terminals. Fortunately, the Tx does not have 50 ohms of internal impedance but only one or two ohms, otherwise the efficiency would be catastrophic.

If when looking back at your antenna you see 50 ohms, your antenna looking towards the TX does not see 50 ohms.

On the other hand, once your agreement is complete with your coupling box, if you turn the coupling box over, that is to say place 50 ohms in place of the TX and look, with a NanoVNA, through the antenna base, you will see the same impedance as that of your antenna. This is a way to preset a remote adapter.

Keep in mind that if the generator impedance is fixed you will get the maximum power out of it in a combined load (50% efficiency). But if you are left free to choose the internal impedance of the generator, whatever the load, the maximum power will come out of the generator if its internal impedance is zero (100% efficiency).
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F1AMM
Fran?ois
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