I tested the WSPR beacon project.
This is the original idea site: http://www.vk3bq.com/2014/08/12/raspber ... -wsprrypi/
Very important below:
The expected power output is 10mW (+10dBm) in a 50 Ohm load. This looks
neglible, but when connected to a simple dipole antenna this may result in
reception reports ranging up to several thousands of kilometers.
As the Raspberry Pi does not attenuate ripple and noise components from the
5V USB power supply, it is RECOMMENDED to use a regulated supply that has
sufficient ripple supression. Supply ripple might be seen as mixing products
products centered around the transmit carrier typically at 100/120Hz.
DO NOT expose GPIO4 to voltages or currents that are above the specified
Absolute Maximum limits. GPIO4 outputs a digital clock in 3V3 logic, with a
maximum current of 16mA. As there is no current protection available and a DC
component of 1.6V, DO NOT short-circuit or place a resistive (dummy) load
straight on the GPIO4 pin, as it may draw too much current. Instead, use a
decoupling capacitor to remove DC component when connecting the output dummy
loads, transformers, antennas, etc. DO NOT expose GPIO4 to electro- static
voltages or voltages exceeding the 0 to 3.3V logic range; connecting an
antenna directly to GPIO4 may damage your RPi due to transient voltages such
as lightning or static buildup as well as RF from other transmitters
operating into nearby antennas. Therefore it is RECOMMENDED to add some form
of isolation, e.g. by using a RF transformer, a simple buffer/driver/PA
stage, two schottky small signal diodes back to back.
And more very important! Use the BPF or LPF filter!
Never connect to antenna directly your RPI.
I have built this LPF: http://www.hanssummers.com/images/stori ... ions2a.pdf
I don't have T37-6 (yellow) ferrit just T20-2 (red).
Modified the number of turns. L1/L3 12 turns, L2 15 turns.
Check the inductivity the LC meter.
Timestamp Call MHz SNR Drift Grid Pwr Reporter RGrid km az
2017-02-12 15:52 M0GLU 14.097162 -24 0 IO91vc 0.005 OE1SJS JN88ed 1236 99
2017-02-12 15:34 M0GLU 14.097110 -28 1 IO91vc 0.005 OE1SJS JN88ed 1236 99