Difference between revisions of "The Muntjac SDR"
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| − | The Muntjac SDR was designed by Brian G4EWJ based on the same dual band AT86RF215 RF chip as the commercially | + | The Muntjac SDR was designed by Brian G4EWJ based on the same dual band AT86RF215 RF chip as the commercially available CaribouLite SDR. |
It is a transmit-only SDR for DVB-S2 DATV on 13cm (QO-100) and 70cm, which uses an RP2040 micro-controller, as used on the Raspberry Pi Pico, to provide a USB interface to the Portsdown 4. | It is a transmit-only SDR for DVB-S2 DATV on 13cm (QO-100) and 70cm, which uses an RP2040 micro-controller, as used on the Raspberry Pi Pico, to provide a USB interface to the Portsdown 4. | ||
| − | The 75 x 30mm board will come without SMA connectors, so that it can optionally be wired into a system for maximum flexibility. Long thread types are recommended. | + | The 75 x 30mm board will come without SMA connectors, so that it can optionally be wired into a system for maximum flexibility. Long thread SMA types are recommended. |
The optional user-fitted mixer is shown, which can be used for experiments on other bands. DATV is generated on the high band and mixed with the harmonic of a carrier on the low band. | The optional user-fitted mixer is shown, which can be used for experiments on other bands. DATV is generated on the high band and mixed with the harmonic of a carrier on the low band. | ||
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The Muntjac connects to the Portsdown by USB. No other power supply is required. | The Muntjac connects to the Portsdown by USB. No other power supply is required. | ||
| − | + | The first time you use each Muntjac device, it needs to be registered so that the Raspberry Pi recognises it at the next reboot. | |
| + | |||
| + | After connecting the Muntjac to the Portsdown 4, select "Output to" and then "Muntjac". If "Output to" is already set to "Muntjac", change it to something else and then back to "Muntjac". | ||
| + | |||
| + | A message will pop up saying "System will reboot now to register new Muntjac. Touch screen to continue". Touch the screen, and after the reboot, your Muntjac is ready for use. | ||
| + | |||
| + | You will not need to repeat this process unless you connect a different Muntjac, or you use a different Portsdown. | ||
Next, set the Muntjac gain with reference to the table above. | Next, set the Muntjac gain with reference to the table above. | ||
| − | Connect the correct output to your transmit amplifier; the | + | Connect the correct output to your transmit amplifier; the low band output is used for 437 MHz (and 900MHz) and the high band output is used for 2400MHz. The high band output is to the north of the "Muntjac-4" legend. |
Within the limitations above, the Muntjac behaves similarly to a LimeSDR Mini. | Within the limitations above, the Muntjac behaves similarly to a LimeSDR Mini. | ||
Revision as of 15:49, 26 March 2026
The Muntjac SDR was designed by Brian G4EWJ based on the same dual band AT86RF215 RF chip as the commercially available CaribouLite SDR.
It is a transmit-only SDR for DVB-S2 DATV on 13cm (QO-100) and 70cm, which uses an RP2040 micro-controller, as used on the Raspberry Pi Pico, to provide a USB interface to the Portsdown 4.
The 75 x 30mm board will come without SMA connectors, so that it can optionally be wired into a system for maximum flexibility. Long thread SMA types are recommended.
The optional user-fitted mixer is shown, which can be used for experiments on other bands. DATV is generated on the high band and mixed with the harmonic of a carrier on the low band.
Muntjac-4 was meant to be intermediate development version, but it is working well enough to make it available as part of an extended beta trial. Some configuration in Linux may be necessary, so if you don't consider yourself to be an 'early-adopter' it may be worth waiting until it has matured.
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 DVB-S2 QPSK with symbol rates of 125, 250, 333.333, 500 and 1000 kS. It will also transmit DVB-S2 8PSK with symbol rates of 125, 250, 333.333 and 500 kS. Transmit data is sent to the AT chip at 128M bits/s on an LVDS bus. This is 4M x 13bit IQ samples/s, with 4 times oversampling, which limits the symbol rate to 1000k symbols/s.
The ouput power of the Muntjac is set by a gain parameter in the range 0 - 20, with each step being nominally 1dB and power zero being -15dBm. 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.
Preparing for Use
The Muntjac is supplied as a kit with the final assembly step of soldering the output connectors to the PCB required for completion. If the SDR is to be mounted in a box (it does fit a small die-cast box) right-angle SMAs with long shafts should be used to allow sufficient clearance between the SMA plug and the box.
An example of the Muntjac mounted in a box (with short SMA Conectors) is shown here.
Another Boxing Idea
As Muntjac-4 was meant to be an intermediate development version, not much thought was given to fitting it into a box.
The Hammond 1550P can be used by cutting slots into the top edges of the box and dropping in the Muntjac-4 board vertically.
The 1550P is about £6 in bare metal and about double that as the 1550PBK with a black finish.
Using Muntjac with the Portsdown 4
The Muntjac connects to the Portsdown by USB. No other power supply is required.
The first time you use each Muntjac device, it needs to be registered so that the Raspberry Pi recognises it at the next reboot.
After connecting the Muntjac to the Portsdown 4, select "Output to" and then "Muntjac". If "Output to" is already set to "Muntjac", change it to something else and then back to "Muntjac".
A message will pop up saying "System will reboot now to register new Muntjac. Touch screen to continue". Touch the screen, and after the reboot, your Muntjac is ready for use.
You will not need to repeat this process unless you connect a different Muntjac, or you use a different Portsdown.
Next, set the Muntjac gain with reference to the table above.
Connect the correct output to your transmit amplifier; the low band output is used for 437 MHz (and 900MHz) and the high band output is used for 2400MHz. The high band output is to the north of the "Muntjac-4" legend.
Within the limitations above, the Muntjac behaves similarly to a LimeSDR Mini.
Muntjac LEDs
There is a main LED near the button and an LED near each SMA socket.
The main LED blinks HI in morse (.... ..) at power up. This is for software version 1v0b. Later versions will blink 'MJ' and the last letter of the software version.
The LED near each SMA socket is normally off and lights when that band (low or high) is in use.
The main LED is normally on and blinks off 1 / 2 / 3 times depending on whether low / high / both bands are active.
The main LED output is also available on the J4 socket position, for mounting on a box. Pin 11 is ground and pin 12 is for the +ve end of an LED, through a suitable resistor.
Pin 1 of J4 is the square one and odd numbered pins are along the edge of the board.
Monitoring Muntjac Operation
To see the live log output from the Muntjac driver on the Portsdown (muntjacsdr_dvb) log into the Portsdown with ssh and type:
nc -kluv 9979
IQ Calibration of the Muntjac
Poor IQ balance in an SDR can cause a carrier to be transmitted at the centre frequency of a DATV transmission.
This causes a reduction in MER. The reduction is most noticeable at high MER, but it will not affect reception, because the MER is already high.
It seems to have less effect when the MER is comparatively low, as on QO-100. It just looks wrong to see a spike in the middle of your signal.
The plan is to generate a calibration file at the factory for each Muntjac, which will be available for download and incorporation into the Portsdown software.
A tool is under development to enable the Muntjac calibration file to be generated by the user.