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Questions tagged [impedance-matching]

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

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How to characterize and select UHF linearly loaded antennas?

Q1.1: Why can a helix calculator not be used for linearly loaded antennas? Those online calculators suggested that the turn pitch/wavelength should be around 0.25. However, a typical linearly loaded ...
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2answers
91 views

Do I need a separate SWR meter if the transceiver has one built-in?

I'm going to buy Yaesu FT-891 as my first transceiver. I know that I can measure SWR with it if I use FM mode and minimum power, which is 5W for this transceiver. However, I don't know whether it's ...
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UHF FM power amplifier design without expensive software

I'm designing a small UHF data transceiver for the 70cm band, based on a Silicon Labs EZRadioPro Si4463 IC. Modulation is FM, 12.5kHz channel step. The concept is similar to SiLabs' AN656 application ...
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2answers
157 views

Exactly why do some SWR meters give a changing reading depending on the length of coax used to connect to an antenna?

Following is my understanding of some theory and the questions are at the end. Is this right ? ... A standing wave is an AC waveform oscillating at a particular frequency which has a varying ...
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1answer
48 views

What is the best approach for measuring return loss of a home-made 3cm horn?

Let's assume I have built a SMA-to-waveguide transition that flares out into a horn antenna. There's no flange between transition and horn, it's made of a single metal sheet. The antenna has tuning ...
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3answers
82 views

Impedance Matching between RF Amplifier Stages

I'm in the process of building a RF buffer-amplifier chain for a VFO and I'm experiencing a design issue trying to impedance match between the sections. The issue I'm having is that many (most) of ...
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2answers
160 views

Impedance matching: Why do components behave totally differently from theory?

I got stuck with impedance matching for an antenna. Any added components in the matching network gave a result totally different from what a Smith chart predicts. Let me explain this clearer. First, ...
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2answers
121 views

Lightbulb as an SWR detector?

Back in ye olden days before SWR meters and auto-tuners, how was a ordinary household lightbulb used to help tune an antenna system? What did the circuit and tuning procedure look like?
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2answers
144 views

How did hams manage to tune their antennas before VSWR meters?

In the early 20th century --back when the hobby was still new-- before VSWR meters and antenna analyzers were invented, how did radio operators know whether they were tuned for maximum power out? ...
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1answer
71 views

Is this transmission line peak voltage formula published in CQ Magazine more accurate?

In his July 2018 article in CQ magazine entitled “Lightning (and EMP) Surge Protection for HF Radios”, Steven Karty, N5SK based much of his analysis for properly specifying a GDT (Gas Discharge Tube) ...
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1answer
147 views

Impedance matching using Smith Chart and relationship to reflection

I've been reading the impedance matching chapter of Bowick's excellent RF Circuit Design book and I have a question. For those who haven't read this book (or have but can't remember!), the chapter ...
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1answer
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Understanding of NFC Reader Antenna matching

I have been designing a 20 x 20 cm square NFC reader antenna which looks like this: In order to make it work and detect NFC tags at certain distance, it needs to be matched. To do that I was trying ...
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33 views

NFC coil matching - Q factor improvement

I have been trying to match my NFC reader coil of size 20*20 cm with a three element circuit - one capacitor in series, another in parallel and one resistor in parallel. I have been using Texas ...
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2answers
91 views

Removing the whip on a 2m/70cm antenna makes no difference

Today I was trying to measure the SWR of a new aerial on my car which has 3 loading coils. Whilst doing this I took the whip out on the top to see how drastically I might have needed to cut the ...
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1answer
196 views

Input and output impedance of antenna/circuit: theory and measurement methods?

As illustrated in my previous post, I got stuck with the matching circuit between an receiving antenna and my circuit, including a rectifier and sensory circuits. I got confused with input and output ...
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1answer
128 views

Impedance matching between antenna and load - Theory and Practice?

I'm trying to do impedance matching between my PCB antenna and my circuit. My PCB antenna has a measured impedance of 49.4 - j8.1 ohms. The operating frequency is 915 MHz. The goal of matching is to ...
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1answer
86 views

How high an SWR can the USRP 2901 (B210) handle?

I connected a USRP 2901 (B210) to an amplifier I designed. The USRP seems to shutdown every time I try to transmit. I guess I messed up with the input impedance matching on the amplifier. Is it the ...
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2answers
144 views

RF signal level when the antenna is disconnected

This is question a3a1-1 from the set of practice questions in the "amateur radio Exam Secrets" book: An antenna is connected by a short feeder to the input to a radio receiver. Everything is ...
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1answer
64 views

How to consider the influence from the PCB that a small antenna is mounted on?

The small antenna itself has an $S_{11}$ of -3 dB around MICS band (verified with simulation and network analyzer). In application, the antenna is mounted on a transceiver PCB of 30*15*0.8 mm which ...
2
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1answer
57 views

Inductors for Impedance Matching

I need to impedance match an IF mixer circuit to a 10.7MHz crystal filter. One of the inductors was calculated to be 44 $\mu$H. So I need a relatively large value inductance in a small package to fit ...
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5answers
145 views

Coax cable as antenna for 5 watt handy

For a normal 5 watt handy working in VHF or UHF freq with 50 ohm antenna , is it possible to use a same length coax cable instead of a stub antenna, so as to work like a crude antenna. Will this only ...
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2answers
406 views

How can the design of an RF filter also encompass impedance matching?

I'm installing an antenna which will require a matching network. (A fixed network: the load will not change.) I'm also building some low-pass filters to reduce transmitted harmonics. It would be a ...
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1answer
90 views

Intermittent High SWR

Using a Cushcraft MA5B beam, when I apply high power from an amplifier, the SWR will go up and down intermittently. Something is breaking down at high power (200-500 W). I have a new coax feedline, ...
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1answer
95 views

SWR Measured at the Transmitter versus SWR at the Antenna

It is fairly well understood that due to transmission line losses, the SWR as measured at the transmitter will be less than the SWR at the antenna. Some of the new antenna analyzers and some vector ...
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1answer
147 views

Does Coax Limit the Maximum SWR a Transmitter 'Sees'?

A recent discussion about SWR led to the assertion that a length of coax cable will ultimately limit the SWR to which the transmitter will be exposed. By experimenting with an SWR calculation tool ...
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1answer
515 views

Is ladder line necessary when using a non-resonant dipole through a tuner?

I've heard if I have a dipole of some arbitrary length, or a random wire, the SWR can be very bad. An antenna tuner can present a decent match to the transmitter, but the SWR on the feedline will be ...
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3answers
274 views

SWR, overall, is too high

This is a sort of follow-on question from my tuners in series question. The problem I am ultimately trying to solve is this: I am using a manufactured end-fed, half-wave 40m antenna. The ...
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3answers
227 views

How do I set up my radio for an antenna tuner?

I recently acquired an MFJ Versa Tuner II model MFJ-949D as well as a Kenwood TS-430S radio. The instructions for the tuner state (in part): For optimum operation of the MFJ-949D, the transmitter ...
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2answers
119 views

Antenna experimentation

I want to make a DIY antenna for my Kenwood TH-F6A. Is there any danger of damaging the radio (i.e. by trying an antenna that is unsuitable), or is it safe to experiment?
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3answers
565 views

What is the output impedance of a typical solid state ham transmitter?

I've often heard that the output impedance is 50Ω, and the load impedance should be matched to that and also 50Ω. While the reasons for the load impedance to be 50Ω are clear, is the output impedance ...
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1answer
98 views

What kind of losses do you get from an LC network matching the antenna's impedance?

If you have a transmitter that is perfectly on your frequency but you have an antenna with some impedance what types of losses, and of what magnitude, will you expect from a tuner in between your ...
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2answers
678 views

3 way coax split / impedance match

I would like to split a coaxial feed line 3 ways, maintaining 50 Ω impedance. I know how to do this 2 ways; you use 1/4 wavelength 75 Ω coax as matching stubs. I know how to do this 4 ways; you do 2 ...
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1answer
123 views

Dual Band Antenna Matching

I am building a wideband dual band omni for school. My antenna is about 2m long. The antenna length basically has two sections (divided by ports) - from 0 - 1.8m (This length is for 20-180MHz) and ...
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3answers
142 views

Do stub matching techniques still produce some loss?

I am using a double stacked Yagi-Uda antenna with about 57 Ω impedance. The 50 Ω feed line (coaxial) cables are combined using a tee connector. I observed, at the output of the tee connector, an ...
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1answer
107 views

How is impedance matching related to balance and common-mode currents?

Does a good impedance match imply good balance and lack of common-mode currents? Does a poor impedance match imply poor balance and excessive common-mode currenst?
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961 views

Why is the risk of damage to a transmitter due to a mismatched antenna at lower frequencies greater?

A quick follow-up to this answer ... If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies ... I'm sorry to be so dense, but uh why is the risk ...
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1answer
286 views

What is this matching technique called?

I've had this suggested to match 50 ohm coax to a lower feedpoint impedance, like a vertical, especially mobile shortened verticals. What's it called? simulate this circuit – Schematic created ...
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1answer
1k views

How to combine two 50 Ω antennas such that they appear as one 50 Ω load?

I'm looking for a simple way to impedance match an array of two 50 Ω antennas so that when they are combined they appear as one 50 Ω load. Assume that both antennas are identically constructed, are ...
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6k views

Why do I need to tune an antenna?

I've heard that when an antenna is set up, it needs to be tuned to reduce reflective power back into the radio. Is this always necessary, and if so how would I go about tuning it?