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 ...
- 136
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 ...
- 18.3k
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 ...
- 50.8k
6
votes
Accepted
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 ...
- 50.8k
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, ...
- 50.8k
6
votes
Accepted
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 ...
- 14.6k
6
votes
Accepted
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.
- 1,210
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 ...
- 18.3k
6
votes
Accepted
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 ...
- 50.8k
6
votes
Accepted
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 ...
- 611
5
votes
Accepted
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 ...
- 1,824
5
votes
Accepted
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 ...
- 50.8k
5
votes
Accepted
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 ...
- 50.8k
5
votes
Accepted
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 ...
- 4,429
5
votes
Accepted
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 ...
- 50.8k
5
votes
Accepted
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 ...
- 8,982
5
votes
Accepted
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 ...
- 50.8k
5
votes
Accepted
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 ...
- 18.3k
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 ...
- 306
5
votes
Accepted
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 ...
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 ...
- 23.7k
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, ...
- 7,743
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....
- 8,982
4
votes
Accepted
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 ...
- 50.8k
4
votes
Accepted
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 ...
- 50.8k
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 ...
- 23.7k
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 ...
- 10.7k
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'...
- 14.6k
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-...
- 14.6k
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 ...
- 23.7k
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