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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Bypass caps on RF board: why are there three different size caps in parallel?

Take a look at this evaluation board for a variable gain RF amp (datasheet): J5-J10 are intended to connect to DC power (with the exception of J6, which is a DC analog control voltage). All of these ...
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Why do OOK transmissions have bandwidth?

With on-off keying, you have a single carrier wave at a constant frequency transmitting its presence or absence. Now I understand that the crystal will not be perfect so you will have some minimal ...
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What is 2-FSK modulation?

In the documentation for a radio chip, I keep seeing the term 2-FSK, which seems to be a modulation scheme. My understanding is that in FSK, data is encoded by emitting a carrier wave on a number of ...
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Does the impedance of a PCB track matter if the length of the track is far smaller than the wavelength of the signal?

I have a PCB with tracks of no controlled impedance. The longest track is shorter than 1/5000 of a wavelength. Does the impedance of the track even matter? If not, then at what length would I need ...
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Using copper clad for RF projects

As a novice reading "Build Your Own Transistor Radios" by Ronald Quan I was kind of mystified by the author's statement that using "vector" board would be easier than using prototype boards, but the ...
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At what cable length does matching the impedance at the ends of the cable become important?

I'm building a base for a PMT that outputs pulses of width <=1 µs. In Hamamatsu's PMT handbook it states on pg. 112 (emphasis mine): When using a photomultiplier tube which is not a fast ...
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Smith Chart Explanation

I'm working on designing some hopefully simple RF (912 MHz) attenuators. I need a few different levels of attenuation but each different attenuator can be fixed. I have prototyped one using just off ...
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Why does holding my car's RF remote to my head extend its range?

I'm in my parking lot and just a little too far from my car for the remote to work... But if I hold the remote up to my chin, and then suddenly it works. It sounds dumb until you try it, but it ...
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What are the advantages of CPW over microstrip?

I have to use a coplanar waveguide (CPW) for a project which is going to characterise small amounts of tissue. I have never used CPW before. What are the advantages of using CPW? What would be some ...
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Low-power wireless module strategy

I'm designing low-power sensor modules which will be spread over a reasonably small area. The modules are all battery powered and should operate for a decently long time without having to recharge/...
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Can I merge two impedance matching circuits?

I've got an RF transceiver (Nordic's nRF24L01+) which shows a typical circuit to match its antenna output to a single ended 50 ohm impedance. I've also got a chip antenna which comes with an example ...
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Why does my GPS and Wi-Fi work inside a sealed copper clad box?

I have just finished assembling a Raspberry Pi-based project into a DIY box made from copper clad FR4 PCB, with the edges soldered together and the copper surface connected to ground. I expected, ...
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DC Blocking capacitors - What value to choose

I am in the progress of ordering parts for a LNA board (2.4GHz, based around the broadcom/avago MGA-635P8). I was following the manufacturer's component list in the datasheet for their evaluation ...
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Does it ever make sense to use a 50Ω input with 10X scope probe?

I'm at the point in my learning where one discovers measurement setup for a scope at RF frequencies is quite a bit more involved than I thought :) I see the importance of thinking about the probe + ...
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1answer
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Antenna matching network. What? Why? How?

I'm designing a small board featuring a transmitter in the 900 MHz band. Since RF is definitely not my strongest subject, I'm basically trying to follow all the datasheet recomendations regarding ...
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642 views

15MHz photodiode PCB, feedback requested

I've developed a 2-layer 15MHz photodiode amplifier board. The first stage is a transimpedance amplifier using AD8065. The second stage is using a current-feedback amplifier, THS3091. Power is +/-12V ...
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What is the importance of the \$50\Omega\$ resistors in this RF op-amp circuit?

From the TI application note RF and IF amplifiers with op amps: The source says "The 39-pF capacitor provides peaking to compensate for some high-frequency roll-off, but better IP3 performance can be ...
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Differences between a planar coil and coplanar waveguide to create a local 1D AC magnetic field

Coplanar waveguides (for example picture look here) are often used in research to create a local in-plane magnetic field. Now if compared to a planar microcoil like this, driven by a AC voltage in ...
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Impedance Matching Differential Signals

I'm designing a circuit with RFICs using differential signaling. I'd like to keep noise to an absolute minimum. Let's use the mixer (LT5560) as an example. All of the reference schematics match to 50 ...
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A poor man's alternative to a network analyzer for antenna matching

I'm doing a small board with a 915 MHz transceiver. A small helical antenna is used, which is located on board with a very short path (10 mm) from the IC, including balun and a matching network. There ...
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What is the purpose of holes on edge of the PCB?

Here is a photo of one of Texas Instrument's RF EVMs. Please pay attention to edge of the PCB that has multiple tiny holes. I marked 3 of them with a red circle on the photo. What is the purpose/...
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Could induction thaw ice?

Last week we had very cold weather; and as a result there were lots of frosted pipes (iron and plastic). I spent a lot of time defrosting metal pipes with a torch, but could not do the same with ...
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Very high speed counter (around 1.5 GHz to 2 GHz)

I am thinking of a device that can measure the distance of an object from a sensor using a radio transmitter and receiver pair. I'm thinking of using a counter at the sensor side, with a fixed-...
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What will it take to build a DIY 2km (city conditions) RF transmitter (433Mhz)?

This is my first question on this site. I am not an electronics/electrical engineer so pardon my depth of knowledge. I am trying to build an RF transmitter/receiver. These are my end goals : a text (...
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Measuring direction of object (or angle of signal origin)

I am interested in somehow tracking the "compass" direction of a moving object from a reference-station -- in other words, something similar to submarine sonar systems (although I'm unsure how those ...
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RF Wakeup - Battling power consumption

I am currently using two nRF24L01+ (2.4 GHz RF transceivers) together with two AVRs to create a keyless entry system. My problem is battery lifetime when using a CR2032 battery to power the key. The ...
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How is a 50Ω “back-termination” accomplished on a scope probe line?

I've just been watching Jim Williams' very excellent video on Measuring Switching Regulator Noise. At 1:58 Jim mentions a "50Ω back termination" in the probe setup that looks something like this (but ...
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900 MHz vs 433 MHz for urban environments

At ranges of a few hundred meters, will there be an appreciable difference in performance (ie range, bit rate) between 900 MHz and 433 MHz for digital applications in an urban environment? Forgot to ...
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Long range (~15 km) low baud-rate wireless communication in a mountain environment (no LOS)

I'm trying to implement a point-to-point communication system in a mountainous environment where the base station and the client are at least 15 km apart, without any line of sight (LOS). The ...
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Possibility of an extremely directional antenna

I'm fairly new to RF technology, but a direction-finding application has come up where a highly directional antenna can offer a convenient solution, so I started searching for such antennas. Most, ...
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When and why did 5.8 GHz become an ISM band?

It's common knowledge that the 2.4 GHz band was set aside for industrial, scientific, and medical (ISM) purposes due to its use in microwave heating. From what I've found, the United States proposed ...
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Why do we not care about matching the input impedance of non-RF amplifiers?

Talking about BJT topologies: A common base amplifier is always given as an example of an amplifier with very similar characteristics to the CE amplifier but with the low input impedance. simulate ...
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What connector is similar to U.FL but has no pin?

I am trying to identify this connector style: Look at the two RF micro-coax connectors on the left, just next to the PCB antennas. They look identical to U.FL or IPEX but have no central pin. What ...
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Does an antenna's radiation pattern characterize its ability as a receiver?

In other words, would a directional antenna used as a receiver be more sensitive to signals coming from one direction, or be equally sensitive to signals from all directions?
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When is it appropriate to use ferrite beads?

In a lot of circuits, I've seen ferrite beads on the Vdd lines to microcontrollers. For my high speed dsPIC33F (80 MHz, 40 MIPS) microcontroller, should I have ferrite beads on the Vdd lines or should ...
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258 views

Optional feature in PCB layout of MMCX board edge connector. What's it for?

I'm designing a circuit requiring MMCX board edge connectors, specifically using the Molex 73415-0961 jack. When looking through the datasheet for suggested PCB layout, I see mention of an additional ...
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771 views

What are these rectangular sidebands on my local FM radio station?

I recently bought an inexpensive USB software-defined radio dongle, and have been poking around my local spectrum: The above image is one of the local FM radio stations (88.7 Mhz, to be specific). I ...
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Improve range of 433MHz RF link

I have a system comprised of a wireless sensor which transmits temperature readings to a main base. The wireless sensor system is made up of: 12F683 pic to take the temperature reading (manchester ...
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1answer
670 views

Preferred balun location? (Are differential microstrips preferrable to single-ended?)

I'm designing a PCB with a transceiver that has differential signal pins for rf. These differential signals travel to a balun, which transforms them into a single-ended signal (50-Ohm characteristic)....
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What does sequences like 1-3, 1-10, 1-3-10 etc in a spectrum analyzer mean?

I have read in a paper explaining spectrum analyzer basic 'When selecting the RBW(resolution BW), there is usually a 1-10 or a 1-3-10 sequence of RBWs available. More RBWs are better because this ...
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How does this quartz antenna work?

I picked up something called a quartz antenna at a surplus store for $2.75 so I could tear it apart. This is what I found: There were two small cardboard boxes filled with loose quartz crystals ...
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Placement of RF module for better performance

I am using a standard RF module (i.e., Bluetooth-module-on-PCB), which has a PCB-trace-type anntena. It is in turn to be soldered onto my main PCB. The whole thing will be powered by a standard Li-ion ...
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High Frequency Characteristics of Solder-Filled Vias

If a via gets plugged with solder, does this destroy its ability to pass high frequency (RF noise) currents? Since there is no longer a surface along which the high frequency currents can travel due ...
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1answer
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50Ω Impedance Matching with Signals Through Vias

I'm working on an IoT board and it is all laid out (LTE, GPS, BLE, WIFI - 30mm x 30mm -- VERY TIGHT). As a design concession, I have to use vias to route some of the RF signals. There's no other way ...
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How does a closed loop antenna work?

There are many videos and explanations about dipole antennas and the theory seems to make sense. But when I see closed loop antennas I am very confused. None of the material I can find about antennas ...
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806 views

Helical antennas and orientation

A batch of questions here really (if it helps I'm operating at 433.92MHz): How should I orient a helical antenna with respect to my board (i.e. my "ground plane") to get the best range performance? ...
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Implementing a network of RF receiver/transmitters

I should make it clear tha I'm not an electronics buff, although I did do Electronics for my A-Levels (and got an A) I have 2 cats named Ollie and Tiggy. I don't want them going towards the road for ...
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How strong is the electrical field inside a microwave oven?

I'm interested in figuring out the approximate peak electrical field strength inside a microwave oven. The question is not so much about the exact number, but rather what reasoning to use to work it ...
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Wideband matching network design

I have read about matching networks, authors usually will describe a target impedance to be presented, to say, the output of an amplifier, and then they design the matching network. To widen the ...
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670 views

How do IR rangefinders accomplish centimeter precision without high speed / high cost parts?

I'm currently working on a system that requires an RF rangefinder with ~15 cm precision, over a range of about 50 meters. My research into the field has shown that I'll need complex and expensive ...

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