# Questions tagged [rf]

Short for Radio-Frequency. Frequencies at which radiation (intentional or not) plays a role. Typically associated with wireless communications, but also relevant for high-speed PCB design.

2,257 questions
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### Microphonic SAW transmitter?

I built this very simple SAW transmitter, with a simple "spring" antenna for the right frequency. To test it, I tuned a portable receiver to around 433.92Mhz and fine tuned it until I heard silence. ...
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### Reactance of a dipole antenna

I am interested in calculating the input impedance $Z_{in}=R_{in}+jX_{in}$ of a dipole antenna numerically. However, I am unsure how I would compute the imaginary part of the impedance ($X_{in}$). ...
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### Conversion Gain Definition for DSB-SC Upconversion

If I multiply a baseband signal $A cos(C\omega t)$ and a carrier signal $B cos(D\omega t)$, the result is $\frac{AB}{2} [cos(C-D)\omega t+cos(C+D)\omega t]$, which is a double sideband, ...
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### I cannot find information about some chips in 3 stage LNA circuit

Hi, here you can see 3-stage LNA circuit. I want to know information about two chips(6 pins) with R8 mark at the top. Also, 4 chips with D4 mark with 3 pins at right side. Is there anyone who has a ...
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### What kind of Modulation? Who transmits on 850 MHz (LTE-Uplink or GPRS?)?

Hey, I found an interesting Signal on 850MHz (in Germany). It is not symmetric and very strong (relative to many others due to bad antennas). On the right side the bandwith is permanently used, on the ...
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### Cheap RF 433.92MHz design, PCB track antenna [duplicate]

I'm doing a RF remote control project using a PCB with microcontroller and with simple onboard antenna layout as transmitter and a 433.92MHz receiver RWS-371F-6 model. Here is the datasheet of the ...
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### 160MHz Ambient Office Noise?

I've got a shielded tent in our office and I see one ambient element I don't have a good explanation for. We see some ambient noise at 700MHz - 800MHz which I guess is cell-band noise. But there is ...
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### On purpose shorted capacitor in schematic

I've come across this schematic from an RF device where I've spotted some weird configuration of capacitors. There are, all around the schematic, some shorted capacitors which I can't figure out what ...
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### RF Design / Calculations - 433.92MHz, PCB antenna, values of capacitors

I'm doing a RF remote control project using a PCB with microcontroller and with simple onboard antenna layout as transmitter and a 433.92MHz receiver RWS-371F-6 model. Here is the datasheet of the ...
181 views

### Tube transmitter tuning

I am trying to tune/tweak/repair this transmitter for a friend of mine. It is oscillating, and it has rf power on the antenna, but it just doesn't seem as "strong" as it should be. The diagram says ...
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### Minimizing reflection coefficient of a low-pass filter

I'm trying to figure out (with not a lot of success) as to what I need to consider when I want to minimize reflection coefficient below a certain point. I'm trying to design a low-pass shunt stub ...
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### S21 VNA Connector & Cable Loss?

I've tuned plenty of RF devices using my VNA for impedance matching. But I've never done an S21 measurement. I have a shielded tent with some connectors and SMA cables that are going to introduce ...
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### Tube transmitter plate current meter question

Can I install the mA meter in this schematic directly in the circuit? This is the high voltage plate supply and there is RF on it. The diagram doesn't specify if there is any circuitry to adapt the ...
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### RF Antenna Matching circuit and PCB design for 868 MHz SigFox device

I'm designing a Sigfox sensor device based on WISOL/SFM10R1 a SigFox verfied module by WiSOL and Atmega328. I need to understand the parameters for 868 MHz RF Antenna Matching circuit and PCB trace ...
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### How can I design a high speed RF peak detector?

The diode-capacitor solution would not work in my application because the operating frequency of my circuit is about 1.4GHz. So what is an alternative solution that would work in such high frequencies?...
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### Phased array receiver circular polarization

In a phased array system, what will have to change in a receiver's architecture if it needs to work for both linear and circular polarization? I saw in one article it is said "Supports automatic ...
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### How same frequency signal with different power are produced?

My router have settings to configure transmission power and as i know energy of a signal is given by $$E = h\nu$$ where $E$ is the energy of the signal, $h$ is Planck's constant, $\nu$ is ...
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### (Antenna impedance matching) How to find the load impedance

I'm working on a project that requires impedance matching and I'm going to match a 50 Ω antenna to a RF amplifier SST12LP22. However, I'm not sure how can I get the impedance of the amplifier from the ...
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### In this Foster Seeley discriminator, what is the purpose of capacitor C3?

I understand the whole circuit, except for the use of capacitor 3. What's its purpose in here?
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### How does this transmitter work/how to tune it?

I have used a few 433MHz ASK transmitters. They're cheap, readily available, and work reasonably well. Based on this application note from Murata I tried to build my own. I replaced the NE68030 ...
111 views

### How does this simple FM slope detector work?

I understand what happens from the diode onwards, it's a rectifying amp and a low pass filter that filters any unwanted frequencies from the carrier, but what is going on in terms of voltage between ...
237 views

### How to measure radio signal strength

I am building several types of radio antennas, and I would like to test which is the most effective. I am wondering: What is the best way to measure the strength of the received signal? It is at ~...
96 views

### designing Low-Pass Transmission Line Stub Filter

I'm trying to design a Low-Pass transmission line stub filter, and I have a few question regarding it. I'm rather new to RF-circuit design, so please bear with me. If my desired specs include the ...
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### Absorber effect on EM RF pattern

If I have an omnidirectional antenna and put a perfect reflector plane near it (in the near field), it will obviously change its radiation pattern in the direction opposite the reflector. ...
178 views

### Sub 1 GHz communication - long range at 500kbps. Is my range estimate roughly correct?

When researching long range medium bitrate RF comms I came across the TI range. The TI CC1201 transceiver claims -97dBm sensitivity at 500-1000kbps. If the system is on the 868MHz band which is ...
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### How to link 3 RF transceivers to 1 antenna

I'm not an RF designer, so excuse the newbie question: How would I link three transceivers, say WiFi and two separate bluetooth transceivers, to a single antenna. I have found a 3-way combiner ...
27 views

### What causes the fail-safe bit to be set in the SBUS protocol?

What causes the fail-safe bit to be set in the SBUS protocol? I know that the when the link between the transmitter and receiver is lost, the fail-safe bit is set, however, what constitutes a 'lost ...
59 views

### Bitstream autocorrelation? - comparing two bitstreams - BER?

I am sending a PN9 sequence from a sender to a receiver and want to compare the received bitstream (RB) to the sent one (SB). I am assuming that the transmission will get distorted and want to somehow ...
114 views

### What is the fastest SiC MOSFET?

I would like to know what is the fastest SiC FET greater than or equal to 10A in a TO-247-3 package. Currently I am using a C2M0280120D. My switching speed is 7 MHz. I want to know if there is a ...
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I'm working in an office with a Wi-Fi router, desktop, and a few cell phones making RF noise. I have an 8 feet long by a 3-feet wide table, and I have an Aaronia BICOLOG 30100 + spectrum analyzer + ...
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### Drivers for high power RF switches

I am currently working on an RF project and using a high power RF SPDT switch. The control voltages of this switch are between 0V/-40V. If the control voltage is 0V, then the corresponding path is ON ...
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### High SNR FM demodulation

So I need to demodulate the FM signal from a sensor with highest SNR possible, at least 70-75 dB. IF is 10.7 MHz, max. deviation is 200 kHz but I can change those values if needed. Baseband signal ...
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### Layout questions on RF design based around vendor patch antenna

I'm struggling with a basic antenna design around a 868 MHz patch antenna. The datasheet of the vendor is particularly sparse in regards of layout guidelines. A rough preliminary sketch of the layout ...
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### Output from a system of cascade connection with Wilkinson's divider and Quadrature hybrid

So I have this system, with $f=3GHz$ $b = \frac{λ}{4}$ $a = 0<a<b$ and I want to know the output at ports 2 and 3. I'm wondering how exactly I should approach it, and if my sketch is ...
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### How is companding different from pre-emphasis and de-emphasis?

What I know is that interference increases linearly with frequency and thus noise power is concentrated at higher frequency. So, to reduce noise, pre-emphasis and de-emphasis filters are used which ...
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### Suitable antenna for XBee S3 PRO 900hp working at 900MHz frequency

We are currently working on a project using 3 XBee modules. One is like a data center or the master of the other two XBees. We did a range test with a master and a slave XBee on an open field using a ...
127 views

### How to decrease nrf24l01 transceiver range?

I've just got my Nrf24l01 but then I found out that the working signal range for the module is 100m and above. Our real intention for the module is to let the nrf24l01(Receiver) out of range for about ...
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### Unleveled vs Leveled RF Power

I'm reading over a manual for a RF generator and I've come across the terms leveled and unleveled RF power. I'm curious what the difference is between leveled RF power and unleveled RF power.
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### JFET colpitts oscillator - very unstable

I've designed, simulated and build this simple JFET colpitts oscillator and I couldn't get it to work with real parts. I didn't have BF256B jfet model so I simulated it using some generic one. The ...
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### Finding Z-parameters from a two-port network and using them to find S-parameters

So I have the two-port network and I want to find out the Z-parameters of it (and later, use that to find the S-parameters). For the assignment, $R_x=8Ω$. From what I understood, I should null ...
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### s-parameter matrix analysis

So I'm trying to figure out how I can analyze S-parameter matrices. The i. should be pretty straightforward, though I'm not 100% sure if I am correct with what it means. I'm assuming that there's ...