| Description frequency doubler 19-38 GHz - DB6NT Archiwum |
| Description frequency doubler 19-38 GHz - DB6NT http://www.db6nt.de/fileadmin/userfiles/_pdf/leiterplatten/19-38ghz/19-38doppler.pdf https://drive.google.com/open?id=1MlPNvQip7asH6HTV9PdYt4kIcAezYfcN |