I've used one of these cheap switch-mode DC-DC converters (available on eBay for a few bucks) for my WSPR U3S transmitter. Checking the transmitted signal reveals strong spurious emissions. Hints from the QRPLabs group leads me to the cause - the DC-DC converter. Replacing it with a linear LM317 one solves the problem.
I've read the PA bias study from Hans and tried to tweak the PA of my U3S for optimum harmonics suppression etc. The spectrum is measured using an SIGLENT SSA3021X analyzer. The power is measured using a 40dB tap and a cheap 20w Dummyload from Diamond: The tap is based on the work of OZ2CPU.
With the firmware version 1.8.0 I've introduce the capability to display also the input power in Watt instead of dBm. Simply tap on the unit field on the display to toggle between dBm and Watt.
I've build a simple distribution amplifier for my GPSDO.
In 2015 I've build the Frog Sounds QRP transceiver.
This little transceiver still needs improvement:
Since last weekend a new QRP transceiver joined my shack I bought her used from a German HAM via the QRPFORUM community. The transceiver is one of the older projects from the DL-QRP-AG but still a neat little transceiver. It is still offered in kit-form from QRP-Project in Berlin.
I've checked this extremly simple concept for spurious emissions and whether they're compliant with the current regulations ...
Here you can find the last spots for DL2SBA on each band within the last day and the all time farest spots.
Here some analysis of my recorded spots data with my spot data collector. As of today there are 45.000 spots recorded in my database.
I've introduced with the firmware version 1.7.1 a complexity to this project which may not be suitable to all users.
WIth the firmware version 1.7.2 I've reduced the complexity by removing the remote configuration utilities.
If you are using my powermeter software in conjunction with Maki's module and have a unstable readings or sporadic extrem value changes, this is a problem of the CS pin. It may be a grounding issue - Makis is currently analysing the problem.
I've developed a new firmware for my RF Powermeter. In this firmware, the user can now program for six calibration points the factors for the polynimial regression functions.
Therefor I've developed a JAVA GUI application for downloading these floating point values to the device.
*** CAUTION ***
All stuff described in this post is ONLY running on an Arduino which runs the OptiBoot bootloader. The EEPROM capability of the OptiBoot bootloader is needed for the features of firmware V1.7.1
Inspired from some work found on the Internet and the full functionality of my U3S I've build an automatic spot collector. The spot collector pulls every 5 minutes my spots from WSPRnet.org and puts it into a MYSQL database for later analysis. See the schematic for this setup
Measurement of the signal quality of QRP-Labs U3s with low-pass filters.Transmitter output is fed into a homemade 40dB power pad. The spectrum is measured using an SIGLENT SSA3021X analyzer.
The bias voltage was about 2.6VDC and the PA voltage was abt. 7VDC.
I made some measurements using my miniVNApro with a simple test fixture fittig the QRP labs lowpass filters.
In case you've bricked the UNO bootloader or even the USB bootloader in the ATMEGA16U2, this may help ...
The original library from Dan is not working as expected for me. So I adopted the code a little bit.
You can find the changes below. You can also download "my version" of the library here. Unzip into the Arduino's library folder.
As described here, I've build an RF Powermeter.
FlightAware ADS-B Filter measured with miniVNAtiny
My SYMMETRICOM GPSDO 090-03861-03 with firmware release 188.8.131.52-01 has a bunch of commands available: