Questions tagged [impedance-matching]

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

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0answers
70 views

How to estimate input and output impedance of an amplifier?

I'm trying to figure out how to design power amplifiers which input and output are properly matched to 50 Ohm. My thinking was that the most bullet proofed approach would be to model an amplifier in ...
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1answer
2k 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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2answers
38 views

RF PCB Design Difference Between Controlled Impedance Track and Impedance Matching Circuit

Im new on RF circuit designing. Im designing an circuit with GSM and GPS capabilities. I know when using high frequency signals the RF traces must be impedance matched. Now what I understand is, I can ...
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1answer
64 views

impedance matching with window twinlead

Question from new ham here, regarding ways of matching impedances between a feedline and an antenna. Is it possible to fashion a broadband HF impedance matcher from a length of windowed twinlead, in ...
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1answer
106 views

How do I tune my EFHW 40-10 to have the lowest SWR in the 40, 20 and 15 meter bands?

This is a reading from my RigExpert AA-35 ZOOM of my EFHW 40-10 inverted L with radials, and feedpoint 2 feet above the ground. Any thoughts as to how I can tune or move this antenna to get the ...
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5answers
117 views

Is “coil loading” a type of impedance match?

If I have a too short dipole, or vertical, I can add a coil to lenghten in electrically. But it's my understanding that I could also do this with any other kind of match: given the complex impedance ...
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2answers
788 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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3answers
733 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 ...
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2answers
116 views

What kind of filter should be used at the output of HF linear amplifier?

I am looking for a output filter to use with a HF linear amplifier called miniPA70 which is available through several online auction sites. The circuit is available here : http://iu3idf.blogspot.com/...
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3answers
2k 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 ...
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36 views

Which specification is exceeded for a transistor output stage in a transmitter when there is a high SWR? [duplicate]

For a transmitter which has an output stage which uses one final output power transistor, when the SWR is high, it's common knowledge it seems that the output transistor can get hot and fail due to ...
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1answer
78 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 ...
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1answer
237 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 ...
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3answers
219 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 ...
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2answers
112 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 ...
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5answers
396 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 ...
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5answers
771 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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2answers
122 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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2answers
216 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 ...
2
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1answer
84 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 ...
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2answers
132 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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2answers
495 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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3answers
232 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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1answer
324 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 ...
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2answers
90 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
910 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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84 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 ...
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3answers
1k 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 ...
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1answer
162 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 ...
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3answers
924 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 ...
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2answers
272 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
65 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
83 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
937 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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163 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
534 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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2answers
165 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 ...
5
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1answer
55 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
590 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
183 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
310 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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3answers
720 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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1answer
162 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
218 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
393 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 ...
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1answer
194 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
110 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
175 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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5answers
353 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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1answer
84 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 ...