I am interested in SDR in general, and low latency CW / SDR on portable devices while back packing in particular. I used to be active in that field around years 2007-2008, while I developed the PocketDigi application for Pocket PC platform (the Pocket PC platform has been killed by Android some five years ago), and I was hacking digital modes on an Altoids tin size transceiver http://www.kufr.cz/~ok1iak/HAM/ATS3a-digital/index.php3
I built an Omnia basic transceiver, which is a reincarnation of the Peaberry SDR, for which I modified the firmware to support low latency CW transmit generated by the SDR board directly without any host support.
https://github.com/bubnikv/omniasdrbasicfirmware
With the Omnia SDR transceiver, I was hoping to develop a lightweight back packing SDR CW setup. For CW, audio latency is important. With the help of the https://superpowered.com/latency application, I measured the following numbers on various Android devices, sorted by decreasing latency:
| Device | Android | Clock | Audio buffer size | Round trip latency |
| Onyx Boox C67ML (e-ink reader) | 4.2.2 | 44100 Hz | 1024 bytes | 325 ms |
| Samsung SM-J320FN (smartphone) | 5.1.1 | 44100 Hz | 960 bytes | 312 ms |
| Chuwi Hi8 Air (Win10/Android tablet) | 5.1 | 48200 Hz | 1152 bytes | 269 ms |
| Nexus 7 (tablet) | 4.2.2 | 44100 Hz | 512 bytes | 123 ms |
| Nexus 4 (smartphone) | 5.1.1 | 4800 Hz | 240 bytes | 51 ms |
Interestingly, the Samsung phone shows a terrible round trip latency, while otherwise I am quite in love with the device. The old Nexus 4 phone shows the lowest latency, while still not close to the 20 ms round trip latency to be considered real time from a music performance point of view.
