Questions tagged [impedance-matching]

Questions about fixed impedance matching networks, the necessity of impedance matching, etc.

Filter by
Sorted by
Tagged with
0 votes
3 answers
49 views

SMA Connector Impedance

I am new to antennas, and am trying to create a monopole that connects to an SMA female to transmit a 2.4ghz wifi signal. I know that the antenna needs to be a multiple of 3.1cm in order to have the ...
2 votes
1 answer
49 views

Do I need an antenna tuner for new mobile antenna

I am looking to buy my first mobile antenna, for use with a 2m/70cm HT in the car. The HT needs 50 Ω impedence. I was looking at this antenna, but another ham told me that I need 1/4 wave or 5/8 wave ...
  • 219
2 votes
1 answer
54 views

cut or lengthen to reduce swr on vertical wire antenna

Have tried measuring antenna wire using formula 234/frequency for 1/4 wave vertical but this gives high swr. How do I lower swr on a wire vertical antenna. Do I Cut or Add? wire'
  • 21
1 vote
2 answers
77 views

Understanding Coax Impedance when Connected to Reactive Load

The 50 ohm characteristic impedance of my coax is only "characteristic" if it's terminated with $ 50 + 0j$ load. So when the coax is connected to an antenna that is fairly reactive like $ 23-...
  • 291
2 votes
1 answer
68 views

Yaesu FT817ND + (Bluetooth) CAT control + ESP32 microcontroller: reading SWR "programmatically"?

I am building a wireless control system for a magnetic loop antenna. The system uses an ESP32 microcontroller (that has Bluetooth and WiFi) that automatically drives the magloop capacitor by means of ...
  • 31
2 votes
3 answers
68 views

Is a UHF connector any real disadvantage off the transmitter circuit board or at an antenna feedpoint?

I have a discone antenna intended for use in the 25-1300 MHz frequency range, but it uses a SO-239 connector. Now, we know that the so-called "UHF" i.e. the PL-259 male plug and SO-239 ...
4 votes
3 answers
236 views

What is the difference between antenna input impedance and its radiation resistance?

I got to know that the input impedance of the halfwave dipole antenna is given as: Zin=1/Im* sin(β(H-|Z|)) where Im is the maximum current on the antenna( when excited with a 1 volt supply), H is the ...
  • 43
0 votes
1 answer
41 views

How do you create a DC-blocking ground-shunt that looks inductive in an "L" match?

We are optimizing an impedance match with s2p models for an LNA and found that an "L" match with a serial cap and shunt inductor will optimize to provide +3 dB of output, versus using serial ...
  • 307
3 votes
4 answers
106 views

Is it worse to use an antenna tuner on an already-loaded short monopole?

If I had a good transmatch and wanted to use a spare CB antenna on the amateur HF bands, would I be better off bypassing its tuning coil completely? One ham pastime is using an antenna tuner to match ...
7 votes
2 answers
691 views

Are "end-fed" antennas really more multi-band than dipoles?

Several "end fed" antenna kits (including the ARRL's for example) include wording suggesting that they are useful as multi-band antennas. But does feeding a wire antenna highly off-center ...
  • 12.6k
2 votes
2 answers
156 views

Measuring actual feedpoint impedance for a given frequency

Background I'm attempting to tune an antenna with my NanoVNAv2. I calibrated it using the included open/short/(50-ohm)load standards by screwing them directly onto the NanoVNA one by one and running ...
  • 381
1 vote
1 answer
63 views

Current Transformers in Series versus a Single Voltage Transformer

I've read that the commonly used 49:1 (7t:2t) auto transformer for Multi-band End-fed Half-wave (EFHW) antennas has criticisms as not being very efficient. I haven't found any other designs that ...
  • 291
1 vote
0 answers
50 views

S-Parameters Power amplifier impedance matching

I recently decided to conceive a 10W class 446MHz amplifier. I want to be able to amplify a 100mW signal into a 10W, for that i'm going for a two stages amplifier : SKY65162 to amplify the signal to ...
3 votes
1 answer
125 views

Can you think of any reason my NanoVNA says my antenna has 1.2 SWR while my radio says it has off the scale SWR?

My radio is an mcHF kit that I just finished soldering up. It receives fine, but when I went to transmit it's giving off the scale SWR. I rechecked my antenna with my NanoVNA, and it shows 1.2 SWR at ...
  • 401
3 votes
2 answers
197 views

How do you calculate peak voltage given VSWR caused by impedance mismatch in a 50-ohm system?

I would like to choose a feedline that is safe for the wattage at a given VSWR to avoid coax arcing. How do you calculate peak voltage given a peak power in watts and maximum expected VSWR from ...
  • 307
2 votes
1 answer
38 views

Whip/stub antenna sorting with SA using VSWR

I have an assortment of whip antennas for various RX & HT devices such as a 2M/70cm FT740, a Uniden race scanner 29-54Mhz/108-174Mhz/406-470Mhz/806-956Mhz, a similar Realistic Pro-32 scanner and ...
  • 21
7 votes
1 answer
318 views

Why ferrite-core transformers are wideband while air-core are not?

While experimenting with end-fed antennas I've made two 1:49 transformers. The first one has an air core, as shown in the article by John, M0UKD. This transformer doesn't even work as a transformer ...
2 votes
3 answers
132 views

Ferrite unun transformer to match antenna resistance loads of <50Ω?

For LF/MF (2200m/630m), I am interested in the situation of a vertical antenna with capacitance hat top-loading, where the vertical antenna is VERY short compared to wavelength, and the antenna is ...
2 votes
1 answer
93 views

Reasons for an antenna tuner at the transmitter other than transmitter protection?

An antenna tuner colocated with the transmitter may be required to prevent transmitting into an SWR higher than the allowed specification for the transmitter, or if the transmitter might overheat or &...
  • 12.6k
1 vote
2 answers
142 views

How do you calculate the impedance of a parallel-wire balanced feedline (ladder line)?

I've looked around and maybe I'm just searching for the right terms to find the answer. I know that the impedance of ladder line has to do with the distance between wires: What is the generalized form ...
  • 307
5 votes
5 answers
170 views

Antenna tuner at the transceiver output confusion

I am a bit confused. Let's take a HF transceiver for example. My understanding is that the output impedance of the transmitter is 50 ohms. The impedance of the coaxial cable feedline is 50 ohms, and ...
1 vote
0 answers
118 views

Crystal Filter Impedance Matching

I downloaded a 2-meter receiver schematic using an IC for the dual conversion IF strip. The first 10.7MHz IF uses a crystal filter with a terminating impedance of 1800//5pF. The output impedance of ...
  • 161
3 votes
2 answers
86 views

Impedance miss-match short vs long section?

Let's say there is a 50 Ohm transmission line coming from a transmitter, suddenly the transmission line is spliced into a 300 Ohm line. From what I've learned a partial reflection occurs at this point....
3 votes
1 answer
97 views

Calculating SWR for a dipole

I have a dipole wire antenna that is tuned to 14.0 MHz so that it has an SWR there of nearly 1:1. Is there a mathematical formula by which I can compute the expected SWR for other frequencies? I would,...
1 vote
1 answer
355 views

Common-mode choke (CMC) hurting my SWR. Live with it? Drop the choke?

I have been using a Par EndFedz Mk2 Trail Friendly 40/20/10 though using the matchbox from an EndFedz EF-QUAD (with Vibroplex’s blessing) so I could transmit at more than 25W. On all three bands I ...
5 votes
2 answers
145 views

Is tuning at all useful for an antenna that is already resonant?

Say you have a resonant antenna that also has a tuner. Does this help at all? Can your antenna be "fine tuned" ?
6 votes
6 answers
373 views

Does an SWR higher than 1:1 necessarily cause additional heat in the transmitter?

Each of the 3 answers to SWR of 1.5 -- use internal antenna tuner or not? in one way or another suggest that an SWR of 1.5:1 will cause additional heat in the transmitter: The radio may heat up a bit ...
3 votes
3 answers
400 views

SWR of 1.5 -- use internal antenna tuner or not?

My IC-7300 has an internal antenna tuner that can handle a SWR of up to 3:1. The other day I noticed that a frequency I was transmitting on (the 40m FT8 frequency FWIW) has an SWR of 1.5 (was my first ...
3 votes
1 answer
120 views

Do you need to analyse the SWR of your radio repeatedly? Or periodically? If so, Why?

Let us assume that I have an adjustable antenna, between 160m - 6m. And let's also assume that using an antenna analyser I have estimated the SWR for that antenna for a specific frequency. If my ...
  • 169
1 vote
3 answers
174 views

SWR erratic based on time of day

I have an odd issue - SWR swings wildly, like a loose connection (there are no loose connections), on 17 and 15 M, only mid-afternoon local. I have made contacts as far as Japan (from central NC) at ...
1 vote
1 answer
122 views

How to understand same SWR but different Tx/Reflected power

I'm tuning a wire dipole. Cross-needle SWR meter shows the same SWR on the lower end of the band as on the higher end. However, the needles move much higher on the lower end. They cross on the same ...
  • 291
1 vote
1 answer
494 views

How to take to account impedance mismatch losses when cascading 2-port networks as RF System?

I'm trying to learn how to correctly calculate (cascade==RF system cascading) the connection of 2-port networks, taking into account mismatch losses. For example There is a first 2-port network, its S ...
0 votes
0 answers
32 views

Titan antenna VSWR and radio problem

I just installed a new Titan DX antenna and I am using psk31 with fldigi. When I transmit on 20m at 14072, the SWR is 1.65 and it shuts off my computer and the radio keeps transmitting. However, on ...
-2 votes
2 answers
302 views

Can an end-fed be fed with an Isolation transformer? [closed]

Typical half-wave end-fed antenna kits include either a 9:1 or 49:1 toroidal balun or unun, which is a transformer for impedance matching, but with one primary winding endpoint (for the coax shield) ...
  • 12.6k
3 votes
2 answers
68 views

When is it relevant to consider a trace as a RF transmission line

I'm building a simple Greinacher based RF Power meter for the PMR band i.e 446MHz. I intend it to work as a confirmation device and not something really acurate. The circuit is quite simple: The led ...
5 votes
5 answers
406 views

(When) does a transceiver re-reflect 100% of reflected power?

There has been a long discussion of one question here. Phil, W8II and I agreed that it's better to post a separate question. There are several sources (some editions of "The ARRL Handbook", &...
0 votes
3 answers
151 views

What happens to the signal level if the antenna has high SWR?

I'm currently reading "Reflections: Transmission Lines and Antennas" by M. Walter Maxwell, W2DU. This book explains well why the energy is not lost because of high SWR during transmitting, ...
0 votes
1 answer
101 views

What type of Cable Should I use between a Long Wire antenna and a Transmatch?

I installed a Yaesu System 600with a MFJ Versatuner 2 on my 31ft sailboat and Idont know what type of cable should I use between the MFJ and the long wire antenna I have on my back Stay. Any ...
2 votes
2 answers
347 views

Do VNA (nano) suffer the same effect of coax length to swr, as swr meters do?

A SWR meter will vary in swr with coax length if unbalanced as your coax length is around 1/2 wave length multiple. Does a VNA ( nanoVna ) in this case experience the same effect, (obviously assuming ...
4 votes
3 answers
770 views

Is testing SWR *practically* less important for 2m/70cm than HF bands?

Totally new amateur operator and I've noticed that a lot of material e.g. Your Tube videos, blogs, forums when discussing metering VSWR mainkly seem to be talking about HF bands. I also see fewer VSWR ...
  • 151
1 vote
1 answer
113 views

Antenna Tuner Range

I have a Kenwood TS-480S and a Kenwood TS-870S both with built in antenna tuners. On the TS-870S I have a ZS6BKW multiband antenna and on the TS-480S I have a vertical whip with two counterpoise lines ...
  • 87
0 votes
1 answer
62 views

Estimating SWR based on multiples of resonant length

I am planning to buy a Xiegu G90. It has an internal tuner that can tune up to SWR 5:1. Does anyone know if I have a resonant antenna on 40m, what I will have for a SWR on 80m?
0 votes
1 answer
57 views

Software to model autotransformer matched end fed dual band, 4nec2?

I have several ground independent dual band antenna of different makes, but they all have the same type of matching circuit to make them ground independent / radial-less and match say 5/8 elements, ...
4 votes
1 answer
539 views

Debugging SM0VPO's spiral loop antenna build

I had built SM0VPO's spiral loop antenna. And here it is. Recently I got myself a NanoVNA to see how finnicky it is to be tuned with that poor man's tuning cap. I brought it from 12 MHz into the 14 ...
6 votes
6 answers
615 views

If receive performance doesn't depend on SWR, then how can I tune my manual HF antenna tuner by band noise?

The popular question "What is the relationship between SWR and receive performance?" asks if a receiver with a well-matched antenna (low SWR) beats a receiver with a poorly-matched antenna, ...
  • 8,942
4 votes
4 answers
508 views

Is an antenna always matched to free space impedance?

In this thesis the following model for an antenna is proposed: It is seen as a 2 port network, in which only port 1 is accessible (port 2 is an imaginary connection between the antenna and the free ...
  • 279
1 vote
1 answer
115 views

Obtaining input/out impedance from S-parameters for a L network

This L network intend to transform Z1 to 50ohms. The design was made using a smith chart: The s-parameters plotted (S11 red - S22 green) in the smith chart is done sweeping the frequency from 200MHz ...
4 votes
2 answers
1k views

What is antenna reactance?

I have a V5000 antenna and I’m tuning it but can’t get the Reactance (X) on my MFJ 259B down. Resistance is at 50 ohms, SWR reading 1.2 to 1.3 (I don’t give that much credence) but the Reactance (X) ...
9 votes
1 answer
449 views

How effectively do modern transmitters protect against high SWR?

The following are fairly common knowledge: Transmitting at full power with too much of an impedance mismatch can damage your finals. If we do so inadvertently, modern radios drop the power ...
0 votes
1 answer
97 views

Obtaining S parameters using S11 measurements?

Is it possible to obtain the S-parameters of a circuit with only S11 measurements (S11 measurement with a VNA)? My gut tells me that it should be possible by connecting open, short and characteristic ...
  • 153