The Muntjac SDR
The Muntjac SDR was designed by Brian G4EWJ based on the same chip as the commercially-available Caribou SDR. The Muntjac uses a RP2040 micro-controller to provide a USB interface to the Portsdown 4.
Specifications
The Muntjac SDR only operates with output frequencies in the following ranges: 390 - 510 MHz, 780 - 1020 MHz and 2400 - 2485 MHz. Individual examples may operate slightly outside these frequency ranges, but not significantly. For our use, this means that the Muntjac can only be used directly on 70 cm and the QO-100 uplink. Clearly, with external transverters it could be used on any band.
When used with the Portsdown 4, the Muntjac will transmit QPSK with symbol rates of 125 kS to 1000 kS. It will also transmit 8PSK with symbol rates of 125 kS to 500 kS. It will not transmit at higher symbol rates because the RP2040 USB 1.1 interface is limited to a bus speed of 12 Mbit/sec.
The ouput power of the Muntjac is set by a gain parameter in the range 0 - 20. The shoulders on the output spectrum are always greater than 30 dB down, and are better than that at lower output powers. Approximate output power is shown in the table below.
| Gain Setting | 437 MHz O/P | 437 MHz Shoulders | 2409 MHz O/P | 2409 MHz Shoulders |
|---|---|---|---|---|
| 20 | +5.6 dBm | -34 dB | +4.1 dBm | -30 dB |
| 19 | +4.8 dBm | +3.7 dBm | ||
| 18 | +4.0 dBm | +2.8 dBm | ||
| 17 | +3.0 dBm | +2.1 dBm | ||
| 16 | +2.1 dBm | +1.2 dBm | ||
| 15 | +0.8 dBm | -40 dB | +0.5 dBm | -40 dB |
| 14 | +0.1 dBm | -0.5 dBm | ||
| 13 | -0.9 dBm | -1.4 dBm | ||
| 12 | -1.9 dBm | -2.5 dBm | ||
| 11 | -2.6 dBm | -3.3 dBm | ||
| 10 | -3.6 dBm | -50 dB | -4.4 dBm | -43 dB |
| 9 | -4.7 dBm | -5.3 dBm | ||
| 8 | -5.7 dBm | -6.3 dBm | ||
| 7 | -6.4 dBm | -7.3 dBm | ||
| 6 | -7.4 dBm | -8.3 dBm | ||
| 5 | -8.4 dBm | < -50 dB | -9.3 dBm | < -45 dB |
| 4 | -9.4 dBm | -10.3 dBm | ||
| 3 | -10.2 dBm | -11.1 dBm | ||
| 2 | -11.2 dBm | -12.1 dBm | ||
| 1 | -12.2 dBm | -13.1 dBm | ||
| 0 | -13.2 dBm | < -50 dB | -14.1 dBm | < -45 dB |
The output power at 900 MHz is typically 3 dB less than that at 437 MHz.