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Questions tagged [amplifier]

Questions about amplifiers, typically RF power amplifiers. For low-noise amplifiers (LNAs) consider using the "lna" tag.

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What is a linear RF amplifier?

Most of the RF amplifiers advertised, and most of the questions about amplifiers, are "linear" amplifiers. What is a linear amplifier, and what other common amplifier type(s) exist that requires ...
Adam Davis's user avatar
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13 votes
3 answers
349 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 ...
philpem's user avatar
  • 131
12 votes
3 answers
5k views

Why does "high SWR" damage transmitters, instead of "impedance mismatch"?

In the audio realm, where cable lengths are insignificant compared to the signal wavelength, I would understand an impedance mismatch damaging an amplifier as follows: Take an audio amplifier that ...
natevw - AF7TB's user avatar
11 votes
4 answers
9k views

What is dBm and why is it used rather than watts?

Reading through an RF power amplifier datasheet, I found the sheet only referenced dBm output power, rather than watts. What is dBm? How do I convert it to watts? Why, or when, would you use dBm to ...
Adam Davis's user avatar
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10 votes
1 answer
343 views

How can I do direct digital synthesis of a 630m WSPR signal?

I want to do direct digital synthesis of a 630m band WSPR signal. Specifically I'd like to use an Atmega 328 chip running at 20 MHz to produce such a signal. I will use standard phase accumulator ...
Eric Urban's user avatar
9 votes
2 answers
1k views

What is the purpose of the transformer at the input (and output) of this RF push-pull amplifier

Firstly, feel free to move this to Electronics SE if it's not on-topic, but it's strongly related to ham radio and RF circuitry. Reading Hayward's classic "Solid State Design for the Radio Amateur" ...
Buck8pe's user avatar
  • 989
9 votes
1 answer
1k views

How effectively do modern transmitters protect against high SWR?

The following are fairly common knowledge: Transmitting at full power with too much of an impedance mismatch can damage your finals. If we do so inadvertently, modern radios drop the power ...
Dominick Pastore's user avatar
8 votes
2 answers
709 views

How to calculate if low-pass filtering is sufficient?

An answer on this question Suggested method for boosting 0.05 watt transmitter up to 10+ watts? suggests putting a filterless 19dB amplifier between the HackRF (or similar general-purpose SDR) and a ...
natevw - AF7TB's user avatar
7 votes
3 answers
1k 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 ...
Buck8pe's user avatar
  • 989
7 votes
2 answers
458 views

Water cooling a GS-35B in lieu of air cooling?

Does anyone know how to --or have any experience with-- water or oil-cooling the anode? Since forced-air cooling is required, the sound from the blower and the exhaust air would be too noisy for my ...
Mike Waters's user avatar
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7 votes
1 answer
1k views

Double power-handling ability of RF amplifier output transformer

I want to base the output network for a 500W push-pull HF amplifier on "A 250W Broadband Linear Amplifier" described in Chapter 17 of the 2014 ARRL Handbook. I need advice on whether and/or how the 1:...
Brian K1LI's user avatar
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7 votes
1 answer
163 views

Efficient BPSK31 amplification

I'm looking at making a portable system that can transmit BPSK31. I have a limited power budget, so I'm looking at trying to make my final power amplifier as efficient as possible. From my ...
W5VO's user avatar
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6 votes
1 answer
2k views

Suggested method for boosting 0.05 watt transmitter up to 10+ watts?

Long time ham operator here, new to this particular challenge - I have a software defined radio transceiver that I'd like to try and use to make contacts on HF, in particular 20-meters. Tuning ...
Brad Hein's user avatar
  • 198
6 votes
2 answers
465 views

Purpose and sizing of capacitors placed across RF push-pull power amplifier transformer windings

I keep finding RF push-pull power amplifier designs specified with a small(-ish) capacitor across the primary (or secondary) windings of the coupling transformers. Here's an example: This is one ...
Buck8pe's user avatar
  • 989
5 votes
4 answers
886 views

Recommended way to analyze spectrum output of a high-power amplifier?

I have a small collection of "software defined RF lab" equipment, notably a HackRF and a VNWA3. I am almost done building a 35W HF amplifier and once I've done some other testing, would like to look ...
natevw - AF7TB's user avatar
5 votes
1 answer
125 views

Why does my received power rise so much when I connect an antenna?

I am in early stages of making a narrow-band radio receiver (block diagram below). To give you an idea, I am using a simple CP-FSK based modulation scheme, and have achieved 5dB SNR with a Tx signal ...
Kraken's user avatar
  • 153
5 votes
1 answer
783 views

Using a Return Loss Bridge and Nano VNA to measure amplifier characteristics

One of the difficulties of measuring active devices like LNA and IF amplifiers with the Nano VNA is the care needed to avoid over-driving the amplifier input and, more importantly perhaps, to avoid ...
Buck8pe's user avatar
  • 989
5 votes
2 answers
284 views

Repeater Amplifiers DMR vs Analog

I have recently purchased an amplifier for my repeater. This was actually my first amplifier purchase ever and should probably have asked more questions prior to buying it. The repeater is a ...
Mike's user avatar
  • 171
4 votes
3 answers
221 views

Coax braid acting as power supply ground between radio and amplifier connected to the same supply, is this a problem?

I have a Kenwood TH-D72 and I just got an old Radio Shack HTA-20 2m amplifier to use with it. They're both powered from a sizeable 3S2P Li-Ion battery pack and they work great together for the most ...
MoTLD's user avatar
  • 736
4 votes
3 answers
503 views

High-Z RF amplifier for magloop RX vs Q-factor

I've noticed that increasing load on magloop reduces it's Q-factor, it becomes less selective. Traditional way to approach this is reducing size of pickup loop, or alternatively, using transformer. ...
BarsMonster - R2AYN's user avatar
4 votes
4 answers
2k views

Why does an RF Amplifier fail when the SWR is high?

Exactly why does an RF output transistor fail if the SWR is bad ? Is it A because the impedance mismatch between the transmission line and the antenna results in maximum power not being transferred ...
Andrew's user avatar
  • 3,683
4 votes
1 answer
241 views

Really a Class C design?

In the March 2000 QST there was an article on the Tuna Tin QRP transmitter, which I thought I might build: The text describes Q2 as a C Class amplifier, but I just can't see how that can be true. &...
Ian_B's user avatar
  • 43
4 votes
2 answers
907 views

Reduction in transceiver power output into high SWR

How much do transceivers drop their output power, when the SWR is high? Most amateur solid state amplifiers or transceivers are (fully?) protected against high SWR, by a circuit which reduces the ...
tomnexus's user avatar
  • 11.3k
4 votes
2 answers
400 views

Pi Matching circut for tube PA - what values?

I am working on my 80m and 40m CW transmitter and ran into a problem: I need to match the high impedance of PL504 to 50ohm coax, a Pi match seems to be the best, but I don't know how to calculate ...
thegamebusterpl's user avatar
4 votes
1 answer
263 views

What is unique about a Low Noise Amplifier (LNA)?

What is so special about a low noise amplifier? If I were to design an amplifier, I would always design an amplifier with low noise anyway. Why is it emphasised as being “Low Noise”? What are the ...
user5349's user avatar
  • 251
4 votes
1 answer
453 views

What is the average fade margin required for proper operation at 2.4 GHz?

I have two radios. Sensitivity is -84 dBm and transmitting EIRP is +30 dBm. How much distance should I expect? I want it to be somewhere near about 2-3 km. Is it possible?
user40713's user avatar
  • 225
4 votes
0 answers
120 views

Checklist for QRO remote setup

In a few weeks I'm hoping to set up a solid state linear amplifier at a remote shack that I've set up at the house of a friend who lives in a rural area. I've been connecting to this shack remotely ...
Jeremy Gilbert's user avatar
3 votes
3 answers
1k views

Under what circumstances does intermodulation become an issue in a filter after LNA setup?

I'm reading about using software-defined radio for picking up ADS-B signals at 1090MHz. There is this blog which considers (among others) a setup as follows: ...
JJJ's user avatar
  • 133
3 votes
3 answers
914 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 ...
Andrew's user avatar
  • 3,683
3 votes
2 answers
149 views

What safety procedures should be followed when developing and testing a high power amp?

I'm designing a 300W power amplifier using the MRF300AN from NXP targeting a center frequency of 146 MHz. Obviously I need to keep my fingers out of it and test into a dummy load, but generally ...
KJ7LNW's user avatar
  • 723
3 votes
1 answer
1k views

Receiving through a linear amplifier

I want to build a simple amplifier using those Mitsubishi modules (like the RA30H1317M or other RA parts). I know this might seem like a very obvious question, but I am unable to find the answer after ...
Synaps3's user avatar
  • 425
3 votes
3 answers
2k views

The amplifier does not work for hack rf one

Good day! I ask for help with repairing the hackrf one amplifier. Doesn't work at all. Accepts signals without amplifier, and LNA and VGA adjustment in SDR sharp works too! But when I put a tick on &...
Антон's user avatar
3 votes
1 answer
1k views

33cm 5W(effective output power) tx amplifier for ATV (HamTV)

I am searching for a 5W effective output power TX amplifier that I can use with my BladeRF to send DVB-T Signals for ATV (33cm band). Can someone tell me on what things I have to look for when buying ...
maxbit89's user avatar
  • 273
3 votes
1 answer
342 views

Power Amplifier Balun Question

Second (and last hopefully) question on the classic Solid State Design for the Radio Amateurs (SSDRA) book by Hayward et al. Again it's a power amplifier circuit (Chapter 4, pg. 66), and again it's ...
Buck8pe's user avatar
  • 989
3 votes
1 answer
322 views

AN762 Amplifier Transistors

According to the MRF421 or MRF454 transistor datasheets, used in the AN762 HF amplifiers say that the transistors are "100% tested for load mismatch at all phase angles with 30:1 VSWR". Further, in ...
user5418's user avatar
3 votes
1 answer
131 views

RFID extension cable

I am trying to build an extension cable to relay an RFID signal (125kHz) to various distances (2,5,10m). I am using 2 identical antennas at the two ends of a 75Ohm coax cable, and I also put 2 ...
gcaglion's user avatar
3 votes
1 answer
130 views

Why is my experiment to produce 3rd order harmonics by saturating a receiver not working

I've been trying to devise an experiment to produce a third order harmonic in radio receiver that's been saturated, but I'm not seeing the expected results. My understanding of the theory is that when ...
Frank's user avatar
  • 349
3 votes
1 answer
207 views

Replace transistors in MiniPA amplifier kit

I recently purchased a MiniPA 100-watt HF amplifier kit. It is a class AB push-pull amplifier and uses the MRF 9120 transistor. While doing some reading on this amplifier kit I noticed some ...
pg1989's user avatar
  • 133
3 votes
1 answer
77 views

What is the difference between an RF amplifier's DC or quiescent operating point and the RF operating point?

I chose the resistor values in the following schematic to set the DC bias point of VCE=6V and IC=5mA because the transistor data sheet gave the S-parameters at 162MHz for these values. I learned how ...
Thomas L's user avatar
  • 193
3 votes
1 answer
87 views

How do I couple two VHF Small Signal Amplifiers together?

I have managed to build single stage VHF amps ok using the transistor's S-Parameters to determine the load and source reflection coefficients for a specific gain and stability considerations. Simple ...
Thomas L's user avatar
  • 193
3 votes
2 answers
102 views

Link margin calculations with two antennas and two low noise preamplifiers

Background - UHF - 434-438MHz Two identical crossed Yagi's mounted on rotator. Currently, I have a low noise preamplifier after combining cables from the two antennas (T connector + matching stub). ...
user80551's user avatar
  • 201
2 votes
4 answers
3k views

what are the alternatives to LM387 and SA602AN?

I am building a 20 Mhz RF receiver out of the NASA radio JOVE instruction manual and they have recommended the use of LM387 as an audio amplifier. SA602AN as mixer IC:
Mathav Raj's user avatar
2 votes
1 answer
77 views

How can a low-impedance load can damage a FET final amplifier?

I believe I understand how an excessively high impedance can damage a final output power MOSFET (voltage rises until avalanche breakdown). But how does an excessively low impedance do that? If the ...
Noji's user avatar
  • 487
2 votes
2 answers
2k views

Why does a Class-C non-linear power amp distort SSB but does not distort AM?

Can someone tell me why exactly a transistor non-linear power amplifier will amplify an AM signal without noticeable distortion, but will distort an SSB signal, giving the familiar scratchy sound ...
Andrew's user avatar
  • 3,683
2 votes
1 answer
216 views

How much does a RF amplifier use of its input power?

I've been casually aware that signal gain can be added in "stages" but never really considered how that might actually work in practice. And it seems that some RF amplifiers really prefer to ...
natevw - AF7TB's user avatar
2 votes
1 answer
509 views

Hypothetical question: Repeater with power amplifier

This is my first time ever asking a question on stack exchange or any stack site, so please be gentle if I missed something here. I am currently working on building a UHF (GMRS) repeater, and while ...
hairlesshobo's user avatar
2 votes
3 answers
4k views

Will an Internal Antenna Tuner work with an external HF amplifier?

I am a new General and don't quite understand how Antenna Tuners work other than changing the impedance ratio between the radio and the antenna. So my question is - Do I need to buy a new tuner if ...
Khris Kramer's user avatar
2 votes
2 answers
369 views

RF6886 high power amplifier maximum reverse power

I'm designing a circuit which uses the RF6886 amplifier IC. What is the maximum reverse power that the amplifier can sustain? At what reverse power will the amplifier die?
heisenburg007's user avatar
2 votes
2 answers
706 views

How to supply high voltage to an amplifier in a safe way?

The grounded-grid amplifier that I am looking at requires 1100 volts Max. How do I safely deliver this rated voltage without getting hurt? Should I consider a alternative amplifier? By request here ...
Ben Madison KO4UXC's user avatar
2 votes
1 answer
328 views

FET for low voltage class E amplifier

I'm building a small APRS radio for a high altitude balloon, and I'm thinking of using an Si570 (3.3 V CMOS) at 144 MHz to drive a small class E amplifier. I'm looking for about 1W output power. I'm ...
Rodney Price's user avatar