7 votes

Receiving through a linear amplifier

Every linear amplifier designed to work with a transceiver has a bypass circuit which switches the antenna between the amplifier and transceiver. When transmitting, the transceiver connector is ...
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7 votes

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

The GS-35A tube is the liquid cooled version of the same tube. Some hams have fabricated their own version of a liquid cooling jacket to replace the fins on the GS-35B: The designer of this jacket ...
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6 votes

what are the alternatives to LM387 and SA602AN?

LM387 is just a really old, ordinary op-amp as far as I can tell. It has a funny pin configuration, so if you have a PCB already made you need to make modifications. I suggest cutting the traces, ...
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6 votes
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Recommended way to analyze spectrum output of a high-power amplifier?

Professional-level dummy loads generally have a "sampling" port that provides a reduced level signal for analysis. You should be able to create something similar.
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6 votes
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33cm 5W(effective output power) tx amplifier for ATV (HamTV)

DVB-T signals are OFDM (orthogonal frequency division multiplexing), which means that you take your symbols, put them in a vector, put that vector through a discrete fourier transform, and get the ...
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6 votes
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What is the purpose of the transformer at the input (and output) of this RF push-pull amplifier

T4 is just this idea: simulate this circuit – Schematic created using CircuitLab Sometimes it's done this way: simulate this circuit The primary of XFMR1 is equivalent to T4 from the ...
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6 votes

Impedance Matching between RF Amplifier Stages

There is no need to "pin" an interstage impedance. You may directly transform from the native output impedance of one stage to the native input impedance of the next without going through an ...
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6 votes
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Signal power measurement

If the frequency counter is measuring -5.3 dBm, then before 20 dB of attenuation the power was 20 dB more than that, so 14.7 dBm. "dBm" means decibels relative to 1 milliwatt. 14.7 decibels can be ...
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6 votes

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

If I understand the description correctly: simulate this circuit – Schematic created using CircuitLab If that's all it is, I wouldn't say it's any big deal. Whenever you have multiple paths to ...
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6 votes

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

Step away from RF for the moment, and think about the basic operation of a single-supply transistor amplifier, or even a voltage regulator. simulate this circuit – Schematic created using ...
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5 votes
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AN762 Amplifier Transistors

The tests they are referring to are for amplification characteristics like linearity and stability, not continuous thermal dissipation. That said, unless you've constructed the thing in such a way ...
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5 votes
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Suggested method for boosting 0.05 watt transmitter up to 10+ watts?

There is nothing especially unusual about this situation: a modulator in most radios will output only some very tiny power which then goes through multiple amplification stages. You just don't have ...
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5 votes
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Why does "high SWR" damage transmitters, instead of "impedance mismatch"?

The VSWR isn't the problem per se, it's just the impedance that appears at the transmitter's terminals. Take the load at the end of the transmission line, transform it according to the electrical ...
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5 votes
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building a relay for 5.8Ghz?

Let's work an example. Say the aircraft transmits at 1 watt, or 30 dBm, on 2.4 GHz. The aircraft is 500 meters away, giving a free space path loss of 92 dB. Between transmit and receive antennas ...
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5 votes
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HackRF + Amplifier = HF/VHF QRP Radio?

Just to answer the second part of the question, you do not want an amplifier that has too wide a bandwidth, mainly to lower the complexity (and hence also the cost) of the amplifier. All users of ...
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5 votes
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Power Amplifier Balun Question

I believe it's a misprint. Comparing the drawing showing the construction of the balun with its schematic representation, it does appear the dot on the lowermost winding (terminals 2 and 5) is ...
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5 votes
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is KPA100 a good amplifier for Yaesu Vx-8Dr

and welcome to ham.stackexchange.com! Sorry, but the Elecraft KPA100 won't work at all with the Yaesu VX-8DR. The VX-8DR is a handheld that runs on the 6m/2m/1.25m/70cm bands; the KPA100 works on ...
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5 votes
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Voltage Converter for Amp

120 volts times 20 amperes = 2400 watts. That would mean this amplifier would have to be more than 42% efficient to avoid popping the breaker. That's pretty unlikely. Check the specs for the amplifier ...
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5 votes
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Toroid Coupling Issue in Common-base Amplifier

The problem is most likely the type 43 core material. It is quite lossy at 21 MHz and is a poor choice for the auto-transformer. Unlike a transmission line transformer, the auto-transformer relies on ...
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5 votes

Increasing communication range by boosting output and input power

Is it possible to do without the power amplifier at TX ... by using a high gain antenna for RX? It is. You need another 27 dB (37-10) of antenna gain in addition to whatever you included in your ...
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5 votes
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What safety procedures should be followed when developing and testing a high power amp?

Get yourself a dummy load. If your gut is telling you your doing something stupid you're doing something stupid. Keep the power supply switch near by. Always assume it's live. If you have doubts about ...
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4 votes

what are the alternatives to LM387 and SA602AN?

The SA602AN looks to be still available from many of the usual distributors. (Check octopart.com or findchips.com to see which distributors have them in stock.) The LM387 is apparently long obsolete....
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4 votes
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Will an Internal Antenna Tuner work with an external HF amplifier?

Yes, you'll need an external tuner, unless your antenna is already matched sufficiently well to 50 ohms. The objective of the tuner is to transform the impedance seen by some signal source, like your ...
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4 votes

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

I entered your circuit into LTSpice and made some test runs to verify the following: In order to get reasonably accurate Fourier analysis, you need to simulate at least 20 cycles. I prefer 50. And, ...
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4 votes
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Why does an RF Amplifier fail when the SWR is high?

A high SWR implies the load impedance is significantly different from 50 ohms, violating the design specifications of the amplifier. Yes, there is power reflected in a feedline. But it's not this ...
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4 votes

How does the Maximum Power Transfer Theorem relate to RF power amplifiers?

The maximum power transfer theorem tells you how to design a load to extract the maximum possible power from a given source. It does not tell you that the source will survive this treatment, and it ...
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  • 22.9k
4 votes

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

Simply put, the LNA amplifies everything that comes into it. If you think about it, it's actually kind of amazing. It's dragging its output value up and down in response to nanosecond-by-nanosecond ...
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  • 8,833
4 votes

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

If I were to design an amplifier, I would always design an amplifier with low noise anyway. Nope! For a power amplifier, you'd do a different tradeoff; the noise figure of that amplifier nearly doesn'...
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4 votes

What is an optimal amplifier arrangement with ham radios?

All modes @ Mike Waters So, clearly, then your only choice is to modulate at low powers and then amplify the modulated signal: Devices that affect a high-power signal do exist (for example, high-...
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4 votes

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

An anecdote: I had problems with my station which included computer-radio interconnections; some of my devices (RTL-SDRs) would lock up when I powered on my Yaesu FT-897. I eventually tracked this ...
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