Questions tagged [impedance-matching]

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

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1answer
83 views

Trying to understand the work of 4:1 coax balun

Let's consider the following picture (source): When current passes the half-wavelength matching section it changes the phase to the opposite, this is why we get +V and -V in the feed point, 2V ...
2
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3answers
89 views

Tweak antenna resonant frequency higher

This is a very simple question and I'm sure if I had a bit more background knowledge, I could figure it out myself. Let's say I have a 1/4 wave vertical antenna that is slightly too long, but it is ...
6
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2answers
89 views

Why aren't “ghosts” and intersymbol interference due to unmatched impedance (high SWR) a concern for HF receivers?

In amateur radio, we care about impedance matching when we need to keep the load within the equipment's specification (for best performance, or just to avoid damaging a transmitter), when we want to ...
2
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2answers
61 views

How to estimate a dipole feedpoint impedance?

An ideal dipole, at resonance, will have an impedance around 73 ohms. A folded dipole, around 280 ohms. How can I calculate the impedances when not at resonance? Let's assume I have a span of 15M in ...
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5answers
130 views

How to match low impedance of NVIS Dipole?

I want to match a 50-ohm coax feed wire to a 40-meter NVIS half-wave dipole. NVIS antenna examples I've found are usually based on a regular dipole (72 ohms in free air). However the impedance drops ...
2
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1answer
51 views

Output impedance of TAPR QRPi?

I'm a newly licensed amateur and have decided to start out by trying WSPR on a Raspberry Pi equipped with TAPR's 20m QRPi. The QRPi write-ups I've read always talk about long wire antennas but I'd ...
2
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2answers
68 views

resonance vs resonator in antenna

Resonance in electronic means: reactance of zero. (maybe wrongly/correctly someone's calling the minimum VSWR, the resonance of antenna! and this cause confusion) I've heard in Antenna Design for ...
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3answers
85 views

How does the Maximum Power Transfer Theorem relate to RF power amplifiers?

The Maximum Power Transfer Theorem says that maximum power transfer occurs when the source impedance equals the load impedance, when the power transferred to the load is 50%, the other 50% being ...
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2answers
124 views

Understanding RG6-75 ohm Cable Impedance

Here is my measurement to a piece of RG6 cable. It is around 30cm cable. On the shield is written COAXIAL CABLE 5C-2V 75 ohm. From my measurement I got data as below: From that table, we can see that ...
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1answer
75 views

Can I connect a 75 ohm antenna to a 50 ohm radio?

I have been looking for an affordable yagi antenna to use with a dual band handheld radio and I came across some very inexpensive VHF/UHF (HDTV) antennas. They are all 75 ohm though. Is it ok to use a ...
5
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2answers
74 views

Better SWR bandwidth

Good day, I have a Kenwood TS-480HT with a Wolfriver coil and a stainless steel whip in my car. I find that on 40 meters I can get the SWR at around 1.4 (using an MFJ 269) at 7.1000 MHz. But the SWR ...
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3answers
146 views

Using 75 Ω instead of 50 Ω coax feed

Can I replace my old 50 Ω coax with RG6? It's cheaper and less loss at VHF/UHF. I would match by L/2 multiples of coax to repeat input and output impedance or L/C matching networks at each end. Is ...
8
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3answers
717 views

Impedance ratio vs. SWR

The specs of the Elecraft T1 tuner say, that it can match a 10:1 SWR. What does that mean in terms of impedance ratio? What antenna impedance can it match to 50 Ohm then? Or is it not that easy?
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73 views

Matching a 188 ohm antenna to an unbalanced input that expects a 50 ohm antenna

I am new to RF field and trying to use an Archimedean Spiral Antenna design from this paper to capture 915MHz RF for the P2110B power harvester chip. The estimated antenna impedance is 188 Ohm (see ...
5
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3answers
486 views

What is the proper way to electrically wire in a loading coil to a vertical antenna?

I am trying to put together a vertical pole style antenna with a loading coil housed at the base using a plan very similar to the one described in this ARRL article. I am trying to understand how to ...
2
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1answer
78 views

Why SWR significantly changes with adding 10-30 meters of coax in presence of RFI choke?

I've build a verical for 40M band using a fishing rod as a mast, 6 radials and an RFI choke (FT240-31 ring, 8 turns of RG58, W1JR winding according to the article by Steve Hunt). When I measure SWR ...
5
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2answers
205 views

Can I have a signal generator on while it's not connected?

The unit in question is an Elecraft XG3 test signal generator. It puts out anywhere from -107 dBm to 0 dBm. Is it safe to have these signal generators on and transmitting while not connected to ...
5
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3answers
358 views

Determining Impedance With An Antenna Analyzer

I need some help interpreting some information from my antenna analyzer (RigExpert AA-35). I want to use the information to impedance match my AM receiving antenna system to AM radios. No ...
9
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3answers
445 views

RigExpert AA-35 - Interpreting The Information

I have a new RigExpert AA-35 antenna analyzer. 1st one I have had & 1st time trying to use an analyzer on an antenna. My questions are very basic and general, but I am having difficulty in ...
5
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2answers
143 views

What additional information do I get from an RF ammeter, as compared to a regular SWR/wattmeter?

I've grown up using SWR/power meters. They're "simple" devices: They show forward and reverse power, and show the standing wave ratio. They, however, do not show antenna efficiency. New hams are ...
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2answers
61 views

What would the power at output at a distance of 1cm when transmitted at a power of 1dBm from the transmitting antenna?

If the transmitter and receiver are placed one centimeter apart, what would be the power at the receiving end if the tranmission power is 1dBm? Consider an omnidirectional antenna. And if it is a ...
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1answer
74 views

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 ...
5
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2answers
390 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 ...
8
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0answers
131 views

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
370 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 ...
5
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1answer
52 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 ...
5
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3answers
329 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 ...
3
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2answers
178 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, ...
2
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2answers
193 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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5answers
559 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? ...
4
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1answer
123 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) ...
5
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1answer
195 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 ...
3
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1answer
248 views

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 ...
0
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1answer
135 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 ...
1
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2answers
106 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 ...
0
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1answer
903 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
570 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 ...
3
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1answer
145 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 ...
5
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2answers
163 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 ...
2
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1answer
76 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
70 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 ...
4
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5answers
220 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 ...
5
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2answers
1k 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
191 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, ...
8
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1answer
227 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 ...
9
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1answer
184 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 ...
3
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1answer
819 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 ...
2
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3answers
444 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 ...
2
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3answers
429 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 ...
2
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2answers
129 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?