search

RPiks / pico-WSPR-tx

WSPR beacon for Raspberry Pi Pico, based on pico-hf-oscillator library. It doesn't require any hardware - Pico board itself only.
MIT License
112 stars 16 forks source link

More infos about -simple 1 transistor amplifier- #12

Open whallmann opened 8 months ago

whallmann commented 8 months ago

This is not really an issue more a question. Before trying this software, are there any informations about the mWatts that falls out of the PI? There was mentioned a simple transistor amplifier. Is there someone who tries a special one, maybe a scribble of the suroundings? Thanks, Wolf DF7PN

Jochen-bit commented 8 months ago

Roman hardcoded the WSPR message for output of the pico beacon with 12 dBm (=16mW). However, I measured almost 200 mW on a 50 ohm antenna. Personally, I think it's cool that the pico beacon does not have a PA. Of course, a good antenna is a prerequisite. However, there are many simple circuits on the web with single-transitor power amplifiers for digital signals. I myself recently reached the whole of Europe in the 40m band with a pico using my shack antenna. Give it a try, the hardware you need is less than 5€ ;-) ... and have fun trying it! Jochen, DG7JH

bradshawlupton commented 8 months ago

please explain how you measured the power on the pico.  I would like to duplicate your measurements on my device on a 17m dipole that makes it from Boston on the US east coast, all across the country to the west, and multiple spots in europe each day.

I am very pleasantly surprised.   Bradshaw K1TE

Sent with Proton Mail secure email.

On Friday, March 15th, 2024 at 6:26 AM, Jochen-bit @.***> wrote:

Roman hardcoded the output of the pico beacon with 12 dBm (=16mW). However, I measured almost 200 mW on a 50 ohm antenna. Personally, I think it's cool that the pico beacon does not have a PA. Of course, a good antenna is a prerequisite. However, there are many simple circuits on the web with single-transitor power amplifiers for digital signals. I myself recently reached the whole of Europe in the 40m band with a pico on the station antenna. Give it a try, the hardware you need is less than 5€ ;-) ... an have fun trying it! Jochen, DG7JH

— Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you are subscribed to this thread.

Jochen-bit commented 8 months ago

I used an oscilloscope to measure the output voltage (6.5Vss). On the antenna I measured reactance at 18.1 MHz (54 ohms). From this I calculated the power: 3.25V²/54Ohm=196mW Was that right ;-)?

bradshawlupton commented 8 months ago

I am a retired physics and chemistry teacher. and a ham since I was 17.  Dont know, but I will try the same.  Makes sense.  I appreciate the suggestions!

Sent with Proton Mail secure email.

On Saturday, March 16th, 2024 at 2:02 PM, Jochen-bit @.***> wrote:

I used an oscilloscope to measure the output voltage (6.5Vss). On the antenna I measured reactance at 18.1 MHz (54 ohms). From this I calculated the power: 3.5V²/54Ohm=196mW Was that right ;-)?

— Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you commented.

bradshawlupton commented 7 months ago

the gpio pins are at 3.3v so I think you are about douple the possible power. I think it is pwm which is also a power hit. I use a couple of bright 3.3 while LED bulbs, then "eyeball' it the 3.3v to gnd led is full brightness and the 18.1 mhz one is about half. Of course I dont know the power output of the led...

EngineerGuy314 commented 6 months ago

I used an oscilloscope to measure the output voltage (6.5Vss). as others have mentioned, that is unlikely since the pico IO is 3.3V max.

Also, the IO is really not suited to driving a 50ohm load at RF frequencies, so you won't get anything close to a 3.3v squarewave. I measured about 1volt RMS on the output into 50 ohms using a digital scope. The waveform wasn't a squarewave, but it was also far from a clean sinewave.

I estimate about 20mW power can be delivered (if using two outputs anti-phase). Out of that maybe 10mW of it will be on frequency, the rest will be harmonics.

Jochen-bit commented 6 months ago

Yes, you're right. I measured the difference in current consumption (tx on - tx off). This was 13 mA. I don't know what I did wrong. Probably the output was not under load. I also think the transmission power will be between 10 and 20 mW.

kholia commented 3 months ago

https://github.com/kholia/Pico-FT8-TX/tree/rig_ctrl?tab=readme-ov-file#amplifier describes the various amplification options.

Nothing-Burger-Left-Pizza commented 1 month ago

I used an oscilloscope to measure the output voltage (6.5Vss). On the antenna I measured reactance at 18.1 MHz (54 ohms). From this I calculated the power: 3.25V²/54Ohm=196mW Was that right ;-)?

Reactance does not contribute to real power, only wattless, non-productive reactive power. Would need to know the reactance and the resistance.

Also, I'm pretty sure your 6.5V measurement is peak-to-peak. RMS voltage is lower. If your antenna is resonant (reactance, X, is zero), power will be V2/(8R)