5

Reactance is the imaginary part of impedance. Together with the real part, resistance, impedance describes how a given load will respond to an AC voltage or current source. While for DC analysis resistance alone is sufficient for this purpose, for AC analysis we need to know not only the magnitude of the voltage or current, but the phase angle between them, ...


4

First you don't necessarily have to do anything. The SWR is below 3 for the bands and most transceivers can handle that OK. If you want to try to get the resonate points inside the bands you will need to lengthen the wire. it is usually a good idea to start with too much wire and trim the length to bring the resonance down, but in your case it look like the ...


4

It is not an either/or situation. Impedance controlled traces make feedlines of a known characteristic impedance, just like most coax is 50 or 75 ohms, and ladder-line is often 300 or 450 ohms. As a rule of thumb, any trace or wire longer than 1/10th the wavelength has to be considered a transmission line, in which case you must know the characteristic ...


4

The short answer to your question is, "Yes." Every change made to an antenna is likely to change the feedpoint impedance: lengths, diameters and configurations of driven and parasitic conductors; positions, values and parasitic characteristics of "loading" circuits; distance from ground and "nearby" conductive structures, including near-resonant feedlines; ...


4

Remember the time-honored engineering adage: Better is the enemy of Good Enough. It is difficult to imagine any practical value to inserting a matching network between your generator or feedline and your antenna: 49.4 - j8.1 ohms equates to an SWR of less than 1.2:1 on a 50$\Omega$ line, already a very good match. Given the relatively large tolerances and ...


3

I don't think the "matching to free space" should be taken so literally. I've never seen an actual equivalent circuit in a textbook or used it to derive any property of an antenna. Sure an antenna is the interface between the transmission line (which has an impedance) and free space (which also has an impedance, same units but different in nature). ...


3

Take three 1/4 wave sections of 75 ohm coaxial cable (let's say RG11) and solder together. You now have a 1/4 wave section of 25 ohm. Doing the math (25 * 25) / 12.5 = 50 ohm. Now use any 50 ohm coxial cable length to the radio. Ps: don't forget to take into account the 75 ohm cable speed factor to calculate the 1/4 wave section. Good luck. Luiz PY4ACP


3

Anything done to get the antenna impedance closer to 50 ohms (or whatever the design might call for) can be called an impedance match, loading coils included. However I would note: many loading coils aren't exactly equivalent to an inductor at the feedpoint. Quite often, the loading coil is not at the base of the antenna but rather somewhere in the middle. ...


3

According to Vincent D. Matarrese's Master's thesis, "Tapered radio frequency transmission lines" (Portland State University, 1992), there is a long history of using tapered-impedance transmission lines in matching systems. It's much too big a topic to review in an SE post, but the thesis is loaded with references for exploration. The Delta match is an ...


3

Well, according to the spec tables in the manual the thing expects a 50 Ω antenna impedance. Mismatch means a loss of signal energy. How much exactly depends on the length of the 75 Ω transmission line – this makes a system much harder to design predictably. I wrote all the following (up to the next horizontal line), then stopped to wonder "what might ...


3

I think the problem you will run into is that people will want this to be plug and play. They may not have a directional coupler, or know or feel like to calibrate it and all that other stuff. Even if they do it, they may wonder if they did it right and if the reading will be accurate or not. I think you will need to handle this part in your design and ...


3

An antenna that's Pretty short (0.08 wavelength), Not tuned, Mag-mounted to an inadequate counterpoise, Indoors with who-knows-how-much metal in its near field, could certainly have a 5:1 or worse SWR, which is enough to "peg the needle" on most meters I've seen.


2

Smith chart shows that 50 Ohm antenna (assumed perfect 50 Ohm real!) connected to 75 Ohm coax cable can result in impedances between 50 and 112.5 Ohm. SWR 1: 1.5. So this so far not mentioned possible solution in this thread may be usefull for your problem: for a single frequency, or for a small frequency band, the use of cable with a multiple of half ...


2

The noise you hear in your headphones is coming from the antenna. When you tune the antenna and minimize the SWR, the losses between the antenna and the receiver are minimized, thus more of the noise received by the antenna makes it to the receiver, and you hear more noise in your headphones. (Assuming of course the receiver is set to a mode where power is ...


2

Missing in this discussion is the fact that optimum power matching does not necessarily correspond with optimum noise matching. Antenna tuner alignment on band noise is possible when the input impedance of the receiver is 50 Ohms real. Then maximum received noise corresponds to correct antenna tuner alignment.


1

As per Phil's answer, the idea that a matched system is most efficient from a system level perspective is undeniable. However, at VHF and UHF the receiver noise is well above the noise received by the antenna, so then without doubt less mismatch means better system signal to noise ratio. Also, i imagine that the signal to noise ratio probably changes for ...


1

Let's assume the answer to your question is yes: an antenna can be mismatched to free space. What would that look like? Well, the feedline, let's say it's 50 ohms, is matched to the antenna's feedline port, so no reflection there. But at the mismatch to free space there'd be a mismatch, generating some reflection. Is this any different than the antenna being ...


1

S11 is one of the S-parameters. It uses 1 port on the VNA to look into something and look at the reflection coming back to determine reflection coefficient / VSWR. If the device was calibrated properly then it can also tell you the complex impedance of what it is "seeing". To calibrate you have to use open, short, and load (99% this is 50 ohm), but ...


1

To add to Phil's answer: if your antenna, source and transmission line (the impedance controlled traces) are all of the same impedance, you don't need an impedance matching circuit. Most common impedance for RF applications is 50 ohms. The impedance matching circuits are only there to connect two systems with a different impedance to each other. Creating ...


1

A "loading coil" in series with its feedpoint terminals can offset the capacitive reactance of an electrically short set of radiating wires (where the jX term of the feedpoint impedance R -jX is zero ohms at the operating frequency). However the loading coil value and its physical location in the antenna system have much less affect on matching the R term ...


1

Yes. A vertical antenna element shorter than λ/4 at the required frequency would be capacitive. The inductive reactance of the loading coil at the base of the antenna would offset the capacitive reactance of the short antenna and make it resonant at the required frequency. Likewise with two loading coils at the feed point of a short dipole. A tuner would ...


1

ngspice is free and can read and write S2P models. You can also just open the file with a text editor and read the S-parameters manually. With the appropriate skill and care, you can then manually calculate the desired matching with no electronics software at all.


Only top voted, non community-wiki answers of a minimum length are eligible