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I'm not sure that we need to re-invent the wheel on this one. The DATV Express and the Portsdown both have GPIO outputs that can be driven by the transmitter software: Charles's excellent software on Windows or Linux for the DATV Express, and the Portsdown software on a Raspberry Pi which drives either the DATV EXpress GPIOs or the RPi GPIOs. Potentially either software could drive the Lime GPIOs.
The Portsdown design includes 4 channel+PTT and 8 channel+PTT switching boards with opto-isolators which have been in use for over a year now with no reported GPIO damage. Details here: https://wiki.batc.org.uk/PTT_and_band_switching and here https://wiki.batc.org.uk/8-Band_Decoder. Companion RF switches are also described; PCBs and the PIC are available from the BATC Shop.
I suggest that we standardise on this sort of interface (3v3 or 5v GPIOs, one line goes high for PTT, and 2 or 3 lines sending a binary code for band selection. The current Portsdown standard (which is also used for Portsdown driving DATV EXpress boards) is 0 for 71 MHz, 1 for 146 MHz, 2 for 437 MHz, 3 for 1255 MHz and 4 and above for transverters.
Ken W6HHC reports that the NOTES file for DATV-Express v1.25LP9 software has been updated to show a SR comparison among the four supported hardware boards.
The Symbol Rate supported by the four exciter boards varies and all rates show below are dependent on how fast is the CPU and the USB-architecture of your computer. The approximate SR maximums (or achievable channel-RFbandwidth for DVB-T protocol) are shown below:
DATV-Express (USB-2)……...100K-20M S/sec …..100K-20M S/sec...…..2 MHz-7 MHz RFbw
LimeSDR (USB-3)……………….100K-20M S/sec …..100K-20M S/sec...…..2 MHz-7 MHz RFbw
Lime SDR-mini (USB-3)……..100K-20M S/sec ....100K-20M S/sec...…..2 MHz-7 MHz RFbw
PLUTO (USB-2)…………………..100K-~2M S/sec....100K-~2M S/sec...…..2 MHz RFbw
Charles G4GUO reports that he has been spending a lot of time designing an RF amplifier for the newly opened 70.5-to-71.5 MHz DATV band in England.
Project Speed is set to slow….de Ken W6HHC
When adjusting the TX power setting with the cursor keys, the slider moves, but the power output doesn't change. Hitting ENTER at this point causes the program to exit. It's handy to have the cursor option when under adverse working conditions.
Clicking PTT to turn off a transmission leaves a carrier being emitted.
Clicking PTT to go back to transmit after changing a setting causes a re-calibration, but transmit is not activated. You have to click PTT again.
Re-calibration occurs for changes of non-frequency settings - e.g. FEC.
The problem is that when the power level is changed the the IQ
magnitude/phase balance changes so a re-calibration is required if
you want to maintain the EVM/MER. Yes it also does re-calibrate when
not necessary which is because I simplified the state table that
decides when to re-calibrate (laziness).
As far as a carrier being present on receive. I suspect it is at a low level
as I turn down the transmitter gain rather than stop the transmitter.
You will also find than when you use 16APSK and 32APSK you have to
turn back the level due to the increased peak to mean ratio of those modes.
As far as Lime is concerned, I am waiting for them to sort out their
firmware before I do much as it is a moving target, new builds of
Express are required every time they update Limesuite.
1) Brian is correct, v1.25LP9 software the RF-power-level-slider can not successfully use curser keys to move/change the power-out level. The slider moves position with the cursor-keys. but the actual RF power out does NOT change. This bug affects all the exciters: DATV-Express, LimeSDR and PLUTO. The work-around is easy, grab-and-move the slider bar with your mouse.
2) Brian is also correct that with PLUTO, clicking PTT on the GUI to turn off a transmission leaves a "same level" RF carrier being emitted. This v1.25LP9 software bug does NOT affect the DATV-Express or LimeSDR-mini boards.
Bryan G4EWJ thanks for your feedback...de Ken W6HHC
Charles G4GUO has fixed one bug for PLUTO units and has prepared a zip of v1.25LP10 software for Ken to test,
Ken W6HHC reports he has just received a v1.25LP10 zip file from Charles for the Windows DATV-Express software. This software corrects a small (code-wise) bug in the PLUTO support that allowed an RF-carrier to be produced in RECEIVE mode after the PTT button was released from TRANSMIT. Ken plans to begin testing the new software version on PLUTO, and LimeSDR-mini, and DATV-Express hardware units before uploading to the www.DATV-Express.com web site on the DOWNLOADS page.
Charles G4GUO also reports he has been spending time lately working on “pre-distortion” software for the DATV-Express software, that lower the distortion “shoulders” on the hardware RF output. The status is that he has sorted out a non-obvious math problem and is now moving in a positive direction for this new DATV feature.
Project Speed is set to slow….de Ken W6HHC
This build of software fixes the PLUTO problem where an RF carrier is sent out when clicking PTT to go back to STANDBY.
This software now supports four hardware exciter boards:
- DATV-Express (USB-2)
- LimeSDR (USB-3 or -2)
- LimeSDR-mini (USB-3 or -2)
- PLUTO (USB-2)
A stand alone NOTES file (aka README) can also be downloaded from the same DOWNLOADs page.
Many thanks to Charles G4GUO for correcting the PLUTO “unexpected carrier” bug…de Ken W6HHC
https://www.dropbox.com/s/u8irxtjz5j3qj ... 1.zip?dl=0
Thanks to John G4BAO for reporting the problem and testing it for me