14

Google defines "linear" as "arranged in or extending along a straight or nearly straight line." Wikipedia tells me that "linearity refers to a function or relationship which can be graphically represented as a straight line". Such systems can be described by an equation of the form $y=mx+b$. In the case of RF amplifiers, the relationship is the input ...


10

What is dBm? dBm stands for decibels relative to one milliwatt. Decibels represent multiplicative factors, or ratios; by establishing a specific reference level they can instead be used as absolute values: 0 dBm is 1 milliwatt, 3 dBm is approximately 2 milliwatts, etc. How do I convert it to watts? Convert the decibel value to a scale factor and ...


7

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 connected to the input of the amplifier, subsequently the output to the antenna. When receiving, the amplifier circuit is disconnected and the antenna is connected ...


7

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 correctly highlights the challenges of selecting and maintaining the liquid medium since it is exposed to the full anode high voltage. Deionized water will ...


6

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.


5

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 time-domain signal you want to transmit. Now, this is fine and all, but OFDM hence has a high Peak-to-average power ratio. Which means that your amplifier needs ...


5

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 all the stages. Building a little amplifier to take your 50 mW and amplify it enough to drive a typical linear amplifier could be a fun little homebrew project, ...


5

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 perhaps there is 10 dBi gain, so the power received at the relay is: $$ 30\:\mathrm{dBm} - 92\:\mathrm{dB} + 10 \:\mathrm{dB} = -52\:\mathrm{dBm} $$ Meanwhile, the ...


5

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 radio spectrum (including radio amateurs) must not cause any interference to other users of the radio spectrum, and that means that out-of-band transmissions must ...


5

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 question. Since T4 provides the collector load for the transistors, it's a factor in voltage gain. For a differential-mode input, the collector currents correspond to ...


5

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 intermediate transformation or termination. When designing an interstage transformer, the general design rule is to ensure that the inductive reactance of each winding ...


5

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 the ham bands between 80m–10m. What's more, the KPA100 is really meant to be part of the Elecraft K2, and isn't meant to be a stand-alone amplifier. You ...


5

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 to get its current requirements, then double it to account for the voltage conversion, and add some more for converter inefficiencies. A voltage converter ...


5

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 the coupling of the two coils to partially occur by passing flux through the core. The complex permeability of type 43 material indicates high losses for this ...


4

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 that the transistor's thermal dissipation capacity is severely derated, it is very rarely heat that kills finals, at least in the short term. While severe and ...


4

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 radio, or the amplifier. The amplifier will already be designed to have a 50 ohm input. Your radio, transmitting into that, is designed for a 50 ohm output, so ...


4

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, scraping off the solder mask, and soldering wires in place with the right layout. Look for datasheets on the internet for the pin configuration. For old stuff ...


4

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 backwards. If we build it like the schematic suggests, consider the application of a differential mode input on the balanced side: simulate this circuit – ...


4

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 changes in its input, reproducing signals at every frequency up to its bandwidth limit. A good amplifier is as linear as possible (meaning its output is ...


3

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. A quick web search didn't reveal any pin-for-pin compatible parts still being manufactured, so if you're using the printed circuit board from the kit, then ...


3

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 impedance) that damages transmitters. The thing to realize is the impedance seen by the final power transistors in the amplifier (the part that usually breaks) isn'...


3

As answers already posted show, there are a variety of solutions to this problem. But, a very simple one is an old timer ham radio operator's "trick". Popular back in the late 1950s and 1960s as "the only way" to hook up an oscilloscope (which also usually had low power input needs) to a high power amplifier was to use a regular PL-259 coaxial connector. ...


3

No. An audio amplifier is not designed to have the bandwidth to amplify RF — it will not pass or amplify signals much greater than audible frequencies, which would require significantly different design. In fact, if it did amplify RF, it would be a potential source of RF interference by amplifying incidental noise on the input. If you did find an amplifier ...


3

I would encourage you to reconsider this project as it not simply a matter of paralleling all of the tubes to double the output power. When you parallel more finals (807's in this case) the input and output impedance of the stage will decrease. This will require a redesign of the output circuit of the final stage at a minimum. If it has input filtering/...


3

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, you need to add a SPICE statement setting plotwinsize=0 to eliminate data compression that compromises Fourier analysis. The "polarity" of V6 needs to be PULSE(...


3

Actually, any amplifier is non-linear but has a linear region. The linear region is a region of power input to the amplifier. If you use the amplifier at an appropriately low power level, it works as linear in this region. You can find the linear region in the datasheet for the amplifier.


3

Your question can be answered by the Friis transmission equation. One way to write it is: $$ P_r=P_t+20\log _{10}\left({\frac {\lambda }{4\pi R}}\right) $$ Where: $P_r$ is the received power (in dBm) $P_t$ is the transmitted power $\lambda$ is the wavelength $R$ is the distance between the antennas, in the same units as wavelength Wavelength at 2.4GHz is ...


3

Are there specific problems or equations that are easier to deal with in dBm vs watts? Decibel units, dBm being an example of such, provide a more intuitive measure of some property that responds logarithmically, like power frequently does. Consider, if you are transmitting now with 1W, and you add 1W more, you have doubled your transmit power. That's a ...


3

Transmit range involves a number of factors. Propagation At 100 MHz your signal range will be largely limited by line of site (LOS) although you may experience some fringing and reflections. This means that no matter how much you increase the transmit power, you cannot predictably increase your range beyond LOS. Increasing the altitude of the transmit or ...


3

TL;DR: Sat TV equipment, 75Ω, probably analog. Obsolete. If anything, keep smallest switch matrix. It's commodity satellite TV equipment. Let's go through this: a Bias injector (hence the different voltages next to each port) and satellite dish control signal multiplexer (DiSEqC uses control signals at 22 kHz, for example) for satellite dish motors and ...


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