TudbuT/picoAM
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Save the FM and 2m amateur bands from harmonics

Browse source
This commit is contained in:
Daniella / Tove 2023-05-01 20:32:33 +02:00 • committed by GitHub
parent 0bcc06449a
commit 0411bbd5b8
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 18 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

18
README.md
View file

@ -15,6 +15,19 @@ My antenna for this is barely large enough for half of my room to have reception
**Also**, this project will overclock your pi. However, 200MHz is fine for 99.9% of picos and is SUPER unlikely to damage it unless you **Also**, this project will overclock your pi. However, 200MHz is fine for 99.9% of picos and is SUPER unlikely to damage it unless you
leave it running for a very long time (days or something in a closed environment). leave it running for a very long time (days or something in a closed environment).
### Most important disclaimer
Legal restrictions likely aren't enough for some people to not do this. Including me actually (tho minisenders with low power like
this are actually allowed where i live, but they have to be certified). However, there is one **EXTREMELY** importatnt thing to add:
This uses square waves, so there are GOING to be harmonics. One of those is near 99.6MHz, in the FM band. You will hear the sender there
as well in some cases as FM receivers *can usually* receive AM, its just gonna be really noisy. Your neighbors, sadly, might also hear it
there, as 99MHz FM is is in the FM radio bands. MAKE SURE YOUR ANTENNA IS SMALL!!!
There is also a MUCH STRONGER harmonic at ~155.726MHz FM, in the 2m amateur radio band. PLEASE, PLEASE, PLEASE don't use a large
enough antenna for it to be able to send that very far. And this signal will actually reach FURTHER than the AM one because it
is a shorter wavelength and therefore sends better using a short antenna. ***__PLEASE add the low pass filter I described.__***
## How it works ## How it works
The Pi generates a 1557kHz PWM signal, which will be the carrier wave. The frequency is not changed, only the pulse width. The Pi generates a 1557kHz PWM signal, which will be the carrier wave. The frequency is not changed, only the pulse width.
@ -37,6 +50,11 @@ It has the following jobs:
- **An extra resistor of about 50-100 ohms may be added from the AI+ point to the AI- point to load the signal.** This is optional, but - **An extra resistor of about 50-100 ohms may be added from the AI+ point to the AI- point to load the signal.** This is optional, but
*can* clean up a little bit of noise if you have long cables. *can* clean up a little bit of noise if you have long cables.
**ERRATA :warning:**<br>
If you aren't an asshole, ***PLEASE*** add the low pass filter as mentioned in the Disclaimer:
- Add a 100ohm resistor between pico and antenna
- Wire a 2nF (2000pF) capacitor between the new start of the antenna and ground
## How to use it ## How to use it
- Flash the ino file using the Arduino IDE - Flash the ino file using the Arduino IDE