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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.

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3answers
155 views

Measure impedance of PCB antenna with very small ground plane

I have recently been designing different PCB antennas with very small ground planes due to design restrictions. I use a VNA to measure the impedances, but am having trouble measuring them correctly. ...
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1answer
63 views

Choosing between ipex connector and SMA Connector for LoRa, LTE and GPS

I have completed designing of PCB with LoRa (868 MHz), GPS and LTE (1800 MHz). Earlier version of my PCB had this SMA connector. But now the PCB will be placed in enclosure and I am thinking to ...
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1answer
131 views

What is needed link budget? [closed]

Assuming I want to send a signal 1 km away from a 2.4 GHz antenna with 5 DBI gain and recieving antenna of 2.15 DBI gain. What is the minimum needed power at the receiver (not the minimum transmitter ...
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3answers
160 views

Does a Crystal Radio coil require enameled wire or insulated turns?

When creating a coil for a Crystal Radio, why do I have to have insulated windings? Why does it matter if the individual turns touch each other? When it "shorts out" in this context, what does that ...
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5answers
309 views

Why are cell towers so high? [closed]

Why do cell towers need so much height? Does the height increase antenna gain because it may provide directionality?
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1answer
56 views

Single tone signal generation at microwave frequency with best phase noise and spurious performance

What is the best way to generate a single tone signal with best phase noise and spurious performance? Is frequency multiplication the best way? single stage multiplication or multi stage ...
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1answer
263 views

Why microwave links on cell towers have high frequency?

Why microwave links are in the higher microwave spectrum (I don't know exactly but I guess it's around 20-40GHz). If by Friis Equation higher frequencies have lower range then why use higher frequency ...
4
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1answer
172 views

How can I reshape this PCB antenna so that I can still use it with the given circuit?

I'm borrowing the RF design from the MICRF114 Development Kit. Here's user guide- http://ww1.microchip.com/downloads/en/DeviceDoc/50002433A.pdf The circuit I'm using is on p. 35 and the antenna ...
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1answer
55 views

How does adding more coils to an AM tuner coil allow it to tune Shortwave?

I have seen several tutorials about how to turn an AM radio into a Shortwave radio. They add more coils to the inductor (is that the correct name for the tuning coil?). Here is one example, https://...
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2answers
55 views

Direction Coupler

While testing a direction coupler (i am testing 30 dB DC ), I found that when I am giving signal at port 1 and output at port 2 (through port), it provides insertion loss and at coupled port its ...
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1answer
150 views

How can a phone transmit the signal back to tower? [closed]

If cellphones have such a low power transmitter (around 200mW for LTE) and also doesn't have directionality then how can they talk back to the tower even though they are so powerful and built ...
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2answers
87 views

How to derive voltage applied to an antenna, where transmitter power is known & identical tx/rx antennas are used with known gain/impedance?

Question: Imagine a transmitter + transmitter antenna with the following characteristics: 433Mhz transmitter transmitting 10dBm Into an impedance matched (50 ohms) antenna, omni-directional, 3dBi ...
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4answers
1k views

RF vs. audio of the same frequency

From an article by an engineer at Cisco Systems: An RF signal can have the same frequency as a sound wave, and most people can hear a 5 kHz audio tone. No one can hear a 5 kHz RF signal. Why not?
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1answer
141 views

Do the FCC's regulations make any sense?

I have read on the following page that the maximum permissible exposure MPE standard FCC have is 1 mW/cm2 for RF wave above 1500 MHz for general population. http://www.rfcafe.com/references/electrical/...
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1answer
128 views

What is this RF Frontend IC?

This is a picture of the PCB for a Tile Bluetooth tracker. I cant find any info on this chip, and I've looked for a while for the logo. here is a closer picture. The logo looks like three ticks, ...
5
votes
1answer
131 views

Design of cavity filter

I try to design a Chebyshev bandpass filter for 6 GHz as a coaxial cavity filter. I know that the filter can be designed with the aid of the coupling coefficients between the resonators and the loaded ...
1
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1answer
87 views

Alternative wireless technology for passive RFID tags

I am working on a project where I have 3 boxes and a RFID reader (mfrc522) attached at the bottom of each box. I keep my wallet/keys/etc in these boxes and a LCD screen displays what is in each box ...
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2answers
106 views

Why FM has larger range than cellular network [closed]

I can receive FM signal about 50km away from the transmitting station but I lose signal from cell towers in about few km (1-3km)
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0answers
178 views

Semtech LoRa sx1276 transceiver IC: modifying its reference matching network

After reading the following post: sx1276 Understanding matching network and having some followup questions, I wondered if I could just remove all the passives (optimizing PCB real state) and go from ...
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0answers
84 views

Reflection on a matched transmission line

A matched load with source using a transmission line (assume real load and matched using quarter wave transformer) should not have any reflection ideally. But we can see that the load impedance is ...
-3
votes
1answer
58 views

How cell sites work? [closed]

In Mobile communication, how do cell sites communicate to each other to the point when they reach the cell site which is connected to the other mobile phone when I make a call . What is the medium of ...
1
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0answers
45 views

Active phased antenna array for Wi-Fi efficiency compared to a directional antenna?

I'm interested in mesh networking of poorly controllable autonomous aerial vehicles (like blimps), so i wonder whether it is viable to use a phased antenna array versus a few traditional directional ...
0
votes
1answer
86 views

How can I calculate power consumption of the amplifier from its datasheet?

In datasheet of the transistor, CGHV40100, I could not find the power consumption of its. How can I calculate the power consumption? Datasheet of the CGHV40100
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1answer
64 views

Track impedance for CC1101 transceiver

I'm trying to make my own board for a CC1101 transceiver that will operate at 915 MHz. To do that, I'm just copying the reference design layout from the ...
1
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3answers
154 views

Methods for confirming on both sides that a signal was received in one direction

Say there are two devices (A & B) that talk to each other (full duplex). For the sake of this example, let's say the medium is RF (wireless). If device A sends a message to device B, what ...
0
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1answer
62 views

How to bias MOSFET for finding S-Parameter simulation?

I wanted to use a BSIM4 model of NMOS in my circuit. I got the correct dc biasing point, certain VDS,VGS and IC. But I am having issues measuring S-parameter data for MOSFET amplifiers. I simulated ...
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2answers
55 views

How to make BJT/MOSFET work in RF?

I am trying to design an amplifier with a transistor model. I followed some basic tutorials online (http://microwave.eecs.utk.edu/ECE545_files/02_Lab_2.pdf) and designed a transistor model for BJT/...
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1answer
47 views

Does the Si4731 / Si47xx provide the necessary info to fetch left/right demodulated audio levels?

I'm working on a project which uses an Si4731 broadcast radio receiver IC (Si47xx family) and which calls for left & right demodulated audio level meters based on a source FM broadcast signal. I ...
0
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1answer
65 views

Help identifying type of LC oscillator

I am trying to understand the RF transmitter (Q1) part of this schematic: (source: https://fccid.io/KUJCE9001/Schematics/Schematic-Diagram-171495.pdf) What type of oscillator is it? Colpitts, Harley,...
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2answers
89 views

How to detect RF / Wifi radio device nearby

I wonder if there is a way to detect if there is any RF/WiFi radio ON nearby? I'm configuring an ESP8266 12E module in STATION MODE (not Access Point) to connect to a Wifi network (any Wifi network). ...
0
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3answers
86 views

Is a modern radio wave broadcasting station a very fast spark gap transmitter?

In a spark gap transmitter, is that a "real" radio wave that is produced? I know you can hear it on an AM radio, if you are close to the gap, but is it a radio wave the same as from a radio station? ...
2
votes
1answer
106 views

Power amplifier simulation and real time experiment mismatch problem

Thanks in advance to anyone who will take the time to read my first post here. At present, I am doing a simulation of a power amplifier in LTSPice. The schematic and relevant files are uploaded in a ...
0
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1answer
128 views

Why does a classic envelope detector produce a negative voltage for some periods, when high frequencies are put in?

I'm playing around in ngspice & trying to understand envelope detectors for ham radio. I'm pumping 150Mhz into the circuit described below - I'm expecting it to go positive in proportion to ...
2
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2answers
54 views

Help Shielding RF Anechoic Chamber - FM Stations

a collegue and I acquired a surplus small anechoic chamber (8 ft x 8 ft) for making some pre compliance test measurements, and we're running into the issue of FM Stations being only attenuated around ...
0
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2answers
60 views

Do I need to consider RF power splitters for signal <1kHz?

I need to tap a signal on a BNC cord to record it with a Labjack ADC. The signal is very low frequency, as the FFT shows. I was planning on using an RF power splitter to add a line to the Labjack. ...
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2answers
99 views

Converting from OOK to ASK at 433MHz

I need to convert messages sent from a device using OOK modulation to ASK so it can communicate with another device that modulates in ASK. I can't modify either of those devices. I was wondering if ...
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0answers
38 views

Finding output SNR using Noise figure

am trying to solve this question below: So I did find the system's overall noise figure to be 2.3 = 3.68dB, and you are more than welcome to verify it. However, my problem now is to find the output ...
2
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2answers
101 views

Using audio instrument cable for 1MHz transmission

I'd like to transmit digital data together with an audio signal along an instrument cable. In more detail, I'd like to send MIDI data and the audio signal of a guitar on a single cable. The rationale ...
0
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1answer
42 views

Why real part of load change as we look through transmission line?

As we move from an imaginary load towards generator through a transmission line, we can see that real and imaginary part of that impedance changes. In fact, an ideal transmission line is comprised of ...
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1answer
149 views

Mounting orientation recommendations for PCB spring antenna?

I have been looking at 868MHz through-hole spring antennas for an application, but I can't seem to find any sort of information in datasheets regarding layout recommendations. Here's the most ...
0
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1answer
68 views

How can I measure my smartphone transmitted power? [closed]

I was wondering if I can measure my phone's transmitted power with an SDR by tunning in the transmission bandwidth but then, I'm not sure how to know whether this power is coming out of my phone or it'...
0
votes
1answer
195 views

Impedence Matching of Antenna and Coaxial Cable

There is a scenario based question which is confusing for me Antenna had four rods each 15cm arranged as a plus sign. its brass shielding was cut and it had two 75 ohm coaxial cables in it. one 10 cm ...
0
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1answer
63 views

Correlation EMF / DNA

What is the current state of independent (of producers) studies about the correlation between EMF (with particular reference to mobile devices) and interruption of human DNA? Are the declared SAR by ...
0
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1answer
43 views

How does Return/Insertion loss work for wireless devices if there’s no cable?

I understand return loss is the ratio of how much signal is reflected in a transmission line. But for wireless devices there is no cable. So how is this measured? So is the impedance mismatch for ...
1
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2answers
108 views

RF range at 169 Mhz

I'm planning a sensor network for agriculture (that apparently doesn't exist yet in this form) and I'd like to understand the possibilities of the radio link. A good number of in-the-field soil ...
3
votes
1answer
487 views

Why is this BJT Schmitt trigger producing a sine wave?

I am trying to build a Schmitt trigger from a pair of BJTs to convert a sine to a square wave. The sine wave is from a Colpitts oscillator running at over 150 MHz. I want to measure the ...
2
votes
1answer
61 views

How to connect terminals like Ground Lugs and Feed-throughs?

Feed-throughs, ground lugs, and similar terminals are often found on RF test equipment. What is the standard way to connect these to wires-- wrap stranded wire and solder? Is there a part that assists ...
2
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1answer
91 views

BLE and Bluetooth Classic Coexistence?

we are designing a fairly compact PCB for a communications device. We are looking at using BLE as a link for voice to a separate microphone, and BT Classic to be paired with a smartphone. We are using ...
0
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0answers
69 views

Derive required carrier to noise or signal to noise from receiver sensitivity on FM receiver

Can I extrapolate the required C/N based on reported receiver sensitivity? I'm plotting coverage for a repeated radio system for handheld radios. The system is analog, FM narrow band. I've ...
0
votes
1answer
51 views

LC Network in Microchip's LoRa Gateway

I am reading the microchip's LoRaWan Gateway manual. On Page 48, I got stuck at receiving side on the LoRaWan RF circuit. It ...