DATV-Express Project

Digital ATV - The latest generation, cutting edge ATV - Please discuss it all here.
Forum rules
This forum is run by the BATC (British Amateur Television Club), it is service made freely available to all interested parties, please do not abuse this privilege.

Thank you
G8GKQ
Site Admin
Posts: 827
Joined: Sun Mar 22, 2009 1:21 pm

Re: DATV-Express Project

Post by G8GKQ » Mon Jul 30, 2018 5:07 pm

Reference GPIO Interfaces.

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.

Dave, G8GKQ

KenW6HHC
Posts: 267
Joined: Mon Jun 01, 2009 4:20 pm

Re: DATV-Express Project

Post by KenW6HHC » Wed Aug 01, 2018 3:04 pm

Art WA8RMC reports that during July, most of his sales of MiniTiouner-Express receivers occured outside the U.S. Art also reports that there will be a pause in shipping MiniTiouner-Express units from USA from August 07 through August 18, while Art enjoys a vacation. Charles reports there are currently five units in inventory for shipments to customers in the European Union.

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:
  • EXCITER...………………………….DVB-S...……………….DVB-S2...……………….DVB-T
    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
The NOTES file can be downloaded from the www.DATV-Express.com web site on the DOWNLOADS page.

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

G4EWJ
Posts: 643
Joined: Wed Feb 17, 2010 10:11 am

Re: DATV-Express Project

Post by G4EWJ » Thu Aug 09, 2018 1:40 pm

I've just tried 1.25LP9 for the first time. Thanks Charles.

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.

Using W7PRO64.

Brian

G4GUO
Posts: 526
Joined: Tue Feb 16, 2010 12:51 pm

Re: DATV-Express Project

Post by G4GUO » Thu Aug 09, 2018 3:32 pm

Hi Brian,
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.

- Charles

G4EWJ
Posts: 643
Joined: Wed Feb 17, 2010 10:11 am

Re: DATV-Express Project

Post by G4EWJ » Thu Aug 09, 2018 6:21 pm

Thanks Charles.

I should have said that I'm using a Pluto. The carrier level after transmit off is at the same level as for transmit on.

Brian

G4GUO
Posts: 526
Joined: Tue Feb 16, 2010 12:51 pm

Re: DATV-Express Project

Post by G4GUO » Thu Aug 09, 2018 8:45 pm

OK Brian, well that is wrong :(
I am not sure when I can look at it, just too many things to do.

- Charles

KenW6HHC
Posts: 267
Joined: Mon Jun 01, 2009 4:20 pm

Re: DATV-Express Project

Post by KenW6HHC » Fri Aug 10, 2018 6:48 pm

I do not normally use cursor-keys to change the RF-power-level-slider when using DATV-Express v1.25LP9 software...so I retested what Brian G4EWJ described in his posting about using the PLUTO board as the exciter.

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

Post Reply

Return to “DATV - Digital ATV”