Portsdown 4 HDMI Repeater TX Card Setup

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Modifications to a Standard Portsdown 4 Card for Repeater Operation

1. Set the video source. Option 1 Source, Option 3 Widescreen, down arrow to HDMI (Elgato), space bar to select, press enter. Next select 720p. Use down arrows to highlight, spacebar to select and then press enter

2. Set the Symbol Rate. Option 2 Output, Option 1 Symbol Rate, 1000 (for example), press enter.

3. Set the Output Device. Option 2 Output, Option 3 Output mode, down arrow to LIMEDVB, space bar to select, press enter.

4. Set the Transmit Frequency. Option 2 Output, Option 5 Frequency, 1310 (for example) enter. Then enter again to select Direct (no transverter).

5. Set the Modulation. Option 2 Output, Option 8 Modulation, down arrow to S2QPSK, space bar to select, press enter.

6. Set the FEC. Option 2 Output, Option 2 FEC, down arrow to 23 (DVB-S2 2/3), space bar to select, press enter. (Note that you cannot do this before you have selected the modulation).

7. Set the Station Callsign. Option 3 Station, delete BATC, enter the repeater callsign, press enter. Then enter the repeater locator if you know it. It is not used, so you can leave the existing locator by pressing enter.

8. Set the Audio Input. By default, the HDMI audio is used. However, if you want to transmit stereo analogue audio, then an EasyCap can be used. To switch to this: Option 5 System, Option 8 Audio Input, down arrow to “video”, space bar to select, press enter. Make sure that a Portsdown-compatible EasyCap is connected at this stage.

9. Set the Autoboot. Option 5 System, Option 1 Autostart, down arrow to TX_Boot or Keyed_TX_boot (as required), space bar to select, press enter. This action also sets the Raspberry Pi to reboot itself at 3 am and 3 pm (UTC) each day.

10. Load the LimeSDR firmware. Make sure that tt the LimeSDR Mini and the Elgato Camlink are connected to the USB3 (blue) ports on the Raspberry Pi 4. Configure the LimeSDR by first selecting Option 7 Lime Config.

a. First check the existing LimeSDR Firmware version: Option 7 Lime Config, Option 2 Lime FW Version. The gateware revision will be a number between 26 and 30. If it is not 30, you should upgrade your LimeSDR.

b. Upgrade to gateware revision 30. Option 7 Lime Config, Option 4 update to FW 1.30. Press enter. Then y, enter, watch progress and then press any key.

c. Next, IN ALL CASES, you must overwrite some of the Lime gateware for the LimeDVB software. Option 7 Lime Config, Option 5 Update to DVB FW. Press enter. Then y, enter, watch progress and then press any key.

There is no way of checking that the LimeDVB firmware is loaded (apart from correct operation). Subsequent Lime FW version checks will report gateware version 30.

11. If you want the hardware triggered shutdown to be operable (think carefully, as inadvertent operation by another party may require a site visit), then you should enable it now. Option 9 Shutdown, Option 8 Button Enable.

12. Now you should reboot (Option 9 Shutdown, Option 2, Reboot Now) and check that your repeater transmitter restarts and operates correctly.

13. Connect again using KiTTY. Type menu and press enter. The console menu will start.

14. You can now set the LimeSDR gain to adjust the output power. 100 is the maximum, 80 is about 20 dB down, but the steps are non-linear. Option 7 Lime Config, Option 6 Set Lime Gain, enter the number, press enter.

Typical output levels and shoulders at 1308 MHz (LimeSDR Mini with LimeDVB firmware) are:

Lime Gain 90, Output Level -2.5dBm, shoulders -48db Lime Gain 92, Output level 0dBm, shoulders -45dB Lime gain 94, Output level +2.5dBM, shoulders -40dB Lime gain 96, Output level +3.5dBm, shoulders -38dB.

That completes the configuration of your SD Card and Lime SDR.

Usage Notes

1. Repeater cards can be set to boot to transmit or boot to keyed transmit. If set to boot to keyed transmit, the keying signal is applied on GPIO Pin 12, and should be set to 3.3 volts (no more!) to demand transmit, and to 0 volts to stop transmit. When the keying signal is acknowledged, GPIO pin 7 is set to 3.3v. It goes to 0v when transmit stops.

2. Note that the key acknowledge signal is set high before the transmission has started. The PTT signal on GPIO pin 40 goes high when the transmission is valid, and this should be used to key the PA, as it will prevent any LimeSDR calibration signals from being transmitted. LimeSDR Calibration signals are many dB higher in level than the desired signal, and the PA (or at least the driver stage) should not be keyed until the signal on pin 40 goes high. It is not possible to prevent the Lime Calibration with this software version.

3. Transmit key signals need to be well behaved. The software cannot cope with brief (< 1 second) transmit de-selections and will not transmit a valid picture after such an event. However, if the key signal is then stopped for 3 seconds and restarted, valid transmissions will then restart.

4. To reduce the need for site visits, the Raspberry Pi is set to reboot every 12 hours. If the Raspberry Pi is connected to the internet, this will occur at 3 am and 3 pm GMT.

5. The repeater cards are not configured to be used with a touchscreen.

6. Power output varies with frequency according to the chart on the BATC Wiki https://wiki.batc.org.uk/LimeSDR_Mini_Output_Power_Levels and the output level at Lime Gain = 100 is about 4 dB below the level shown on the chart. Output level decreases as Lime Gain is reduced, but the relationship between Lime Gain and output level is very non-linear. Note that the output in LimeDVB mode is about 10 dB lower than the output with the standard firmware. The signal is much cleaner though.

7. The LimeSDR Mini can overheat during continuous use. For best results it should be fan-cooled.

8. The Raspberry Pi power supply voltage should be set to 5.2 volts. After installation, check that at least 5.0 volts is present on the GPIO connector (measured between GPIO pin 4 and pin 6). Lower voltages result in poor video and audio quality. Excessive voltage drop is usually caused by poor quality USB power leads. A powered USB hub should be used to connect the LimeSDR; the EasyCap can usually be directly connected to the Raspberry Pi assuming a good quality USB lead is used.

9. The Raspberry Pi 4 is known for running hot. In this application it is working reasonably hard (between 30% and 40% on all 4 cores), so a heatsink case (available from Pimoroni) is the minimum cooling that should be used.