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7 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 ...
Phil Frost - W8II's user avatar
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 ...
Glenn W9IQ's user avatar
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7 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 ...
Phil Frost - W8II's user avatar
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 ...
Marcus Müller's user avatar
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, ...
Phil Frost - W8II's user avatar
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.
Dave Tweed N3AOA's user avatar
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 ...
Phil Frost - W8II's user avatar
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 ...
Glenn W9IQ's user avatar
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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 ...
Phil Frost - W8II's user avatar
6 votes
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Really a Class C design?

So, my question is: Is Q2 operating in Class A or Class C? This is an OOK transmitter (on-off keying) where both oscillator and final amplifier are keyed. Keying only the final amplifier (with ...
glen_geek's user avatar
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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 ...
Phil Frost - W8II's user avatar
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 ...
Scott Earle's user avatar
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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 ...
Phil Frost - W8II's user avatar
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 ...
Hamsterdave's user avatar
  • 1,844
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 ...
rclocher3's user avatar
  • 9,242
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 ...
Phil Frost - W8II's user avatar
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 ...
Glenn W9IQ's user avatar
  • 18.6k
5 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 ...
Kevin Reid AG6YO's user avatar
  • 24.6k
5 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 ...
hobbs - KC2G's user avatar
  • 12.5k
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 ...
Graham G8URP's user avatar
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 ...
Ben Madison KO4UXC's user avatar
5 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 ...
Kevin Reid AG6YO's user avatar
  • 24.6k
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 ...
Phil Frost - W8II's user avatar
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, ...
Brian K1LI's user avatar
  • 7,868
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....
rclocher3's user avatar
  • 9,242
4 votes

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

Since writing this answer, I've learned this explanation isn't entirely accurate. I'm leaving it because it's not entirely wrong, either. Ultimately, it is impedance mismatch (really, too low an ...
Phil Frost - W8II's user avatar
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 ...
Phil Frost - W8II's user avatar
4 votes

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

The objective of specifying a 50 ohm load isn't to generate maximum power per se. The transmitter is subject to damage from excessive current or voltage. The currents and voltages will depend on the ...
Phil Frost - W8II's user avatar
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'...
Marcus Müller's user avatar
4 votes

What is an optimal amplifier arrangement with ham radios?

Pretty much every design I've looked at in detail (I'm not a radio engineer or electronic designer, but I've looked at circuits with an eye to building them) does the modulation before any power ...
Zeiss Ikon's user avatar
  • 4,097

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