Questions tagged [hf]

HF stands for High Frequency and it is normally used to denote the range of radio frequency electromagnetic waves between 3 to 30 MHz.

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Special considerations when designing a PCB with signals in HF band (3 -30 MHz)

I want to design a PCB which will handle RF signals in the HF band (3 -30 MHz). Are there any special considerations when designing a PCB at these frequencies? I know higher frequency PCBs require ...
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291 views

How to understand EIRP, PSD for a given bandwidth?

I have troubles to understanding what is the meaning of parameters for transmitting power of RF-signal. So for RF signal in the same frequency band and same application, on one hand I see the max. ...
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34 views

How to tell what type of RFID tag?

I have an RFID tag for access to my apartment building that I would like to clone(buying one through strata would be 100s of dollars). I have a proxmark 3 easy and have cloned tags in the past with ...
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2answers
349 views

How to drive an AD9850 at 100 kHz/s sweep using arduino or rasberry pi?

The basic problem I am interested in doing is using an ADXXX chip to make a linear frequency sweep through the HF bands, from 1-20 MHz. The sweep rate I would like to achieve is 100 kHz/s, which ...
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2answers
85 views

Looking to make a large surface area 13.56MHz antenna with short range

I wondering about the feasibility of making a 13.56 MHz antenna that would occupy the entire rack of a shelf (5'x2'). The range would need to be small so that it only identifies entities that are ...
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342 views

High-frequency voltage amplifier (opamp) keeps clipping and oscillating

I've been working with the following very basic opamp circuit: simulate this circuit – Schematic created using CircuitLab I've built this Voltage amp a few times for a couple of low-frequency ...
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1answer
367 views

PIN-diode lowest operation frequency limitations

I have a need to implement RF switch for HF circuit (~10 - 30 MHz) and I've been browsing options for that. Electromechanical switch would of course work, but I want to consider other possibilities ...
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98 views

HF current measurement

I have an assignment, where i'm supposed to (sort of accurately) measure the current drawn by a SIM-card, in the different phases it can operate in. The current is by no means DC, as the SIM-card ...
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1answer
349 views

SMPS output noise: Why is it amplified further away from the output capacitor?

Well this is just a general question about switch mode power supplies, but i have recently built a buck converter, and read that it is very important where in the circuit you place your probes, to ...
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696 views

Understanding relay isolation specifications

I'm building a board with some relays to switch a bank of HF filters. I want to be sure I'm understanding the isolation I can expect from a given relay so as to not degrade a filter's performance by ...
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1k views

Purpose of bare copper perimiters on HF PCBs

I have seen many RF PCBs with a thick, rounded area of exposed copper going all around the PCB, like in this example: My intuitive thought is that this is for some kind of grounding or shielding can, ...
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1answer
110 views

Difficulty getting HF filter to work: maybe PCB layout?

I am trying to build a set of HF filters using the values from the Alex filters from HPSDR. I'm having difficulty getting the input impedance to be 50Ω as it should. Based on wide variations in ...
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4answers
492 views

Transmission Line Question

I have a question concerning reflections due to impedance mismatching. Now, assuming a lossless TL, the latter is modelled by sections of lumped L-C segments where L in a series (sub)element of the ...
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1answer
1k views

Suggestions about proper usage of vk-200 choke

I have an old custom-built non-switching 5V power supply (usual 220V-12V transformer + bridge + 7805 regulator + various capacitors) that I'm using to power a HF upconverter and a HF LNA. I'm ...
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1answer
329 views

Arduino+2X12 LCD to emulate a defective Kenwood HF rig display unit

I have an HF rig with a bad display init (LC7582A driver and custom LCD with 9 seven-segment numeric indicators and some icons making for a total of a 100 or so segments). The input pins of the LCD ...
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3answers
9k views

How does this Miniature Solid State Tesla Coil work?

Here are the schematics What is the use of> -Transformer (I assume it is providing higher voltage? and what does it do) -Transistor (Is it common emitter? and what does it do) -LED (What does it ...
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1answer
55 views

High-Frequency Circuits with commonly available parts [closed]

Does radio shack carry any good chips or transistors for building high-frequency amps, oscillators, or mixers? My friend and I are trying to build the coolest circuits possible with only Radio Shack ...
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1answer
3k views

Metcal: why do they heat with HF?

I got a used Metcal station from ebay for my home-lab and everything I read about soldering with it is right, it is a completely different feeling. I understood that stuff about controling the ...
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2answers
1k views

UHF RFID reader ability to recognize tags in less than 1 m reading distance

If the UHF RFID reader basic reading distance is up to 5 m, if adjusted to be less than 1 m or to be up to 1 m, can it be able to recognize all the tags? Or since it's for mid range reading, the ...
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1answer
3k views

Analyze My Homebrew Diplexer

I'm in need of a diplexer that'll separate RF signals from a single feedline to two antennas. What I designed and built was a diplexer that would allow ~38 Mhz and below out port 1, with ~38 MHz and ...