2MS DATV from Raspberry Pi

[G8GKQ]

I have been working on some further developments to Evariste's rpidatv build, and am publishing them on my GitHub site once I think that they are ready for others to try. There is a special install script there to install my latest version as well. See https://github.com/davecrump. EDIT: There was a bug in the download but I have just corrected it (11 am Thursday 24 Nov).

I'd be particularly interested in any bug reports or suggestions for improvements. The constraints are that you must use the March build of Jessie Lite, and you must log in over the network to run the software - not use an hdmi screen and keyboard plugged into the RPi. At first boot-up of your RPi with Jessie Lite, you can use an IP Scanner (such as Advanced IP Scanner http://filehippo.com/download_advanced_ip_scanner/, or Fing on an iPhone) to get the Pi's IP address and then log in from a PC using Putty http://www.chiark.greenend.org.uk/~sgta ... nload.html. There is no need to ever plug in an hdmi screen.

Evariste will hopefully incorporate these changes into his software once he has had time to understand and quality-check them.

Dave, G8GKQ

[VK5YYY]

Hi Folks,
This is our latest RPi effort based on the lovely little circuit from our French friends
The nice people at Ebay Store dicikey-max will make up any frequency sine wave TCXO 1MHZ ~ 225MHZ no extra cost
I chose 145mhz for the LO and used it in conjunction with Cross Technologies Up Converter also from Ebay LO 1130mhz
This unit runs at 5m/s and achieves 29 mer 1275mhz for our local repeater once amplified, successfully tested last night
Rather than build the board a SOT experimenters board on top of a proto board was used and since it is VHF it's not too fussy about RF principles
I've separated the 145mhz LO, as having right next door the I/Q modulator didn't go too well
A mini circuits 160mhz low pass filter was used after the TCXO as 3rd and 5th harmonic where present (some may want the 3rd harmonic at 70cms)
Thanks F1DJO and F5OEO for your wonderful ideas
Cheers Roger VK5YYY

[G8GKQ]

Hi Roger

Very nicely done! What modulator have you used?

I think that I can see some LC filtering on the I and Q signals. Is that correct?

Dave, G8GKQ

[VK5YYY]

Hi Dave,
The modulator is the U2790B https://media.digikey.com/pdf/Data%20Sh ... 0B-MFP.pdf
The device only goes up 1 ghz hence why we used a low LO and unconverted to 23cms
It is SO16 form factor mounted on a little development board ebay item 361703584049 (bit fiddly to make a board for SO16)
The board has a second side with TSSOP16 so drilled the plated holes with a 1.2mm drill and coated that side with copper tape for a ground plane
It's hard to beat, just a bunch of capacitors required on the main board
The original article is here http://www.vivadatv.org///download/file.php?id=956
Their filter uses a voltage divider on the input, we've used a pot in the past which makes the amplitude adjustable
There is a board made by Cimko, but veroboard did the trick at 145mhz
The constellation is not all that tight but the Mer seems fine, a cleaner local oscillator would help
I think the projects original aim was best bang for buck in a simple small form which it certainly achieves
Up to now we've experimented with mainly hardware I/Q modulators on RPi from Mini Circuits and Erie
They give a lovely result but have conversion loss, the U2790B over comes that cheaply
Evariste's software continues to evolve and your little patch to fire up an oscillator, that might come in handy, well done
Cheers Roger VK5YYY

[G8GKQ]

I've been busy making additions to the menu system for this project. New build instructions are at https://github.com/davecrump/rpidatv. Please do not use older instructions, or try to upgrade from an old build. Start a fresh install with the latest Jessie Lite (2016-11-29).

Next step is to incorporate Evariste's latest improvements to the video and transport stream encoding.

Dave, G8GKQ

[brown1]

Very informative forum thanks