0
$\begingroup$

How can I make a simple signal booster without introducing too much noise? My first thought was to just feed the signal into transistor base (capable of 4GHz) through a 1K resistor. I could get a 1.2W output from this, and add low/high-pass filters later. Is there a better method? I will probably end up transmitting on UHF, but frequency hasn't been decided yet.

I also need to insulate the pin sending the signal. My assumptiom is that alufoil wrapped around the wire to my breadboard, and connected to common ground will prevent leakage.

Cluebats, please.

Note: Posted in EE intentionally, it would probably take longer to get a good answer in Amateur Radio.

$\endgroup$
  • $\begingroup$ You mean an amplifier? For transmitting? 4 GHz is pushing the limits of where things are "simple" for those without microwave engineering experience. $\endgroup$ – Phil Frost - W8II Jan 17 '17 at 16:45
  • $\begingroup$ The transistor is capable of up to 4GHz. I don't need XHF. I have others which can switch at max 500MHz, and output ~80W (more than I need), and will probably use one of those when I've got my design right. $\endgroup$ – user400344 Jan 17 '17 at 16:47
  • $\begingroup$ What transistor? And you almost certainly won't get anything working at 4 GHz on a breadboard: the high contact resistance and stray inductance and capacitance will introduce too much variability. $\endgroup$ – Phil Frost - W8II Jan 17 '17 at 16:53
  • $\begingroup$ I am testing pitx at 50MHz. A transistor lile BC237 would do. $\endgroup$ – user400344 Jan 17 '17 at 17:02
  • $\begingroup$ Or a BC547 - 300MHz if I'm not mistaken... Can't find the 4GHz one, but it's irrelevant. The 500MHz one was a PNP, so can't trivially use that. Regardless, my output will supply ~5mA (I can go higher, to max 15mA. ) at 5V, to the transistor base. $\endgroup$ – user400344 Jan 17 '17 at 17:08
3
$\begingroup$

My first thought was to just feed the signal into transistor base (capable of 4GHz) through a 1K resistor.

Um, you should definitely impedance-match your amplifier. That might mean you essentially have something like a close-to-50 Ω terminated line from which you "steal" your base current through some larger base resistor, but it should definitely not simply be "signal line -> 1 kΩ -> base".

and add low/high-pass filters later.

Since a transistor used for power amplification will not operate within a linear range: Not later, now. A non-linear device is a mixer, and you're producing every product (and squares) of the harmonic signals within your input, which means components at DC, at twice your carrier frequency, three times... and if you got multiple tones inside your signal, the difference and sum and difference-of-sums frequencies of these.

In the end, neither us nor you nor the regulatory bodies involved want that you get beef with the ENS.

My assumptiom is that alufoil wrapped around the wire to my breadboard,

RF and breadboard are already a bad combination. RF, breadboard and amplification are a recipe for unexpected emissions and crosstalk. Don't use breadboard. Get a piece of copper-clad PCB material, and use a knife to "cut free" traces on that, and solder your components onto that.

If you can (that's already a bit tricky), use a trace width that implies good impedance matching (assuming you have a second copper plane on the bottom side of your board).

There's also testboards for RF transistors which you can order, or download the manufacturing files from the producers of these transistors. Also, it's not that hard to design a small board, e.g. with eagle or kicad, that has the right trace width, a ground plane, easy-to-solder holes or contact pads and contacts for edge coaxial connectors, and then order these for < 5$ from places like OSHPark.

$\endgroup$
  • $\begingroup$ This is excellent. Feel free to write more. I'll let the question wait for more answers, though. $\endgroup$ – user400344 Jan 17 '17 at 19:06
  • $\begingroup$ Could one not just use MOSFETs for signal amplifiers? $\endgroup$ – user400344 Jan 21 '17 at 10:32
  • 1
    $\begingroup$ Same Problems. MOSFETs are transistors. What would that solve? The impedance matching would get harder, instead of controlling a base current you'd adjust a gate charge, and behavior would usually be more exponential than for bijunction transistors. $\endgroup$ – Marcus Müller Jan 21 '17 at 11:38

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.