{"id":2786,"date":"2016-10-28T21:37:30","date_gmt":"2016-10-29T01:37:30","guid":{"rendered":"http:\/\/w4kaz.com\/qth\/?p=2786"},"modified":"2021-10-24T13:37:45","modified_gmt":"2021-10-24T17:37:45","slug":"red-pitaya-sdr","status":"publish","type":"post","link":"http:\/\/w4kaz.com\/qth\/?p=2786","title":{"rendered":"Red Pitaya SDR as Core of CW Skimmer Station Rebuild."},"content":{"rendered":"\r\n

Update 2021-10-24.\u00c2\u00a0 Additional info on setup by Bjorn, SM7IUN. \u00c2\u00a0 Bjorn describes set up for running a second skimmer thread, but the forked Red Pitaya output can also be used to run a skimmer thread and an SDR with some experimentation.<\/span><\/em>
see: https:\/\/sm7iun.se\/redpitaya\/cwskimmer\/<\/a><\/p>\r\n

[Updates, 2018-08-22, also see:\u00c2\u00a0 Red Pitaya SDR as Core of CW Skimmer, Part2:\u00c2\u00a0 A link to status updates and additional notes going forward<\/em>]<\/span><\/a><\/p>\r\n\r\n\r\n\r\n

[Updated 2017-07-11, also see text on my own compatibility issue]<\/strong><\/em><\/span><\/p>\r\n\r\n\r\n\r\n

Bob, N6TV has a step by step guide on setting up a Red Pitaya<\/a>\u00c2\u00a0posted to the skimmertalk list in which he documents version compatibility issues he encountered and outlines the steps he needed to follow to get his system functional. \u00c2\u00a0As of this date it seems wise to follow these instructions, or know that by diverging you may encounter issues of your own. \u00c2\u00a0There is also an illustrated how-to guide now available from the folks at hamsci.org.<\/a><\/p>\r\n\r\n\r\n\r\n

[Updated 2016-12-23, see text on Compatibility issue]<\/strong><\/em><\/span><\/p>\r\n\r\n\r\n\r\n

Recently discovered an interesting, \u00c2\u00a0affordable, \u00c2\u00a0and relatively new product called Red Pitaya<\/a>, designed as an open source based piece of test equipment.\u00c2\u00a0 As a piece of test equipment the Red Pitaya has basic oscilloscope,\u00c2\u00a0 spectrum analyzer, and signal generator apps available.\u00c2\u00a0 The apps are designed to run as web applications with Red Pitaya board running a custom Linux and acting as a web server.\u00c2\u00a0\u00c2\u00a0 Currently the apps are quite basic, but useful despite their simplicity.<\/p>\r\n\r\n\r\n\r\n

Possibly more interesting for hams are the SDR receiver and transceiver apps available from Pavel Demin.<\/a><\/p>\r\n\r\n\r\n\r\n

With the SDR apps, Pavel has taken this little Red Pitaya board into the areas of interest to many ham ops.\u00c2\u00a0 The SDR receiver app has the ability to function with several currently available SDR programs.\u00c2\u00a0 The ability to support feeding six channels into CW skimmer server is of particular interest.\u00c2\u00a0 There are also transceiver apps which are being used by experimenters to build Red Pitaya based transceivers.<\/p>\r\n\r\n\r\n\r\n

Red Pitaya<\/strong><\/p>\r\n\r\n\r\n\r\n

The Red Pitaya itself is a board that runs a customized linux OS(their term is ‘ecosystem’) off of an SD memory card.\u00c2\u00a0 The board has two RF inputs and two RF outputs for use as the heart of a test system.\u00c2\u00a0 5V USB power supply input requires 2A.\u00c2\u00a0 The board has a heat sink on the CPU but a small fan helps cooling.\u00c2\u00a0 It can connect via ethernet to the network or via a wireless connection.\u00c2\u00a0 The OS and apps are downloaded from the Red Pitaya website. \u00c2\u00a0 SDR apps are available from both the Red Pitaya site and directly from Pavel Demin’s website. \u00c2\u00a0This little SDR kludge is a viable substitute for the Softrock skimmer system previously being run\u00c2\u00a0@W4KAZ<\/a>.<\/p>\r\n\r\n\r\n\r\n

SDR Uses and v0.96 Compatibility Issue<\/strong><\/p>\r\n\r\n\r\n\r\n

A couple of issues turned out to be a mix of hardware and software problems.\u00c2\u00a0 The largest problem was a software incompatibility issue between the [then]latest OS v0.96 and the SDR software<\/a>.\u00c2\u00a0 This caused problems in the SDR with interference that looks like intermod artifacts.\u00c2\u00a0 Too much time was spent here looking for hardware problems before stumbling across the documentation on the issue<\/a>.\u00c2\u00a0 The solution was simple.\u00c2\u00a0 It simply required building an SD card with the previous OS version v0.95, and \u00c2\u00a0then configuring(secure password) then re-installing the SDR app.<\/p>\r\n\r\n\r\n\r\n

A couple of the\u00c2\u00a0SDR apps available on Pavel’s site originally included an OS that did not allow a persistent password change.\u00c2\u00a0 To avoid that security vulnerability, the original SD card here was built with v0.96 of the OS.\u00c2\u00a0 As of October 2016, do NOT try to use v0.96 OS with the SDR apps.\u00c2\u00a0 V0.95 works with the SDR<\/a>.\u00c2\u00a0 Better to have several SD cards with different OS versions should you need a more recent OS for new apps as they are developed. \u00c2\u00a0[Update 2016-12-23. \u00c2\u00a0Per comment from Pave Demin, the SDR applications have been updated and should now work with v0.96 and v0.97 of the Red Pitaya ecosystem. \u00c2\u00a0Not yet migrated to the updates here in the W4KAZ SDR setup.]<\/strong><\/em><\/span><\/p>\r\n\r\n\r\n\r\n

After building the v0.95 system, the SDR app was good to go.\u00c2\u00a0\u00c2\u00a0 Several different flavors of SDR support are available from Pavel<\/a>.\u00c2\u00a0 The SDR app version that supports CW skimmer server also supports PowerSDR<\/a>, which has a nice spectrum and waterfall display.<\/p>\r\n\r\n\r\n\r\n

There is not a tremendous amount of information available, as folks are just beginning to explore the possibilities.\u00c2\u00a0 PA0AER has an interesting post,<\/a>\u00c2\u00a0with a few findings of his summarized in this table.<\/p>\r\n\r\n\r\n\r\n

\r\n
\"PA0AER<\/figure>\r\n
\r\n

Yeah, -120db floor and 75 db of intermod suppression should work just fine in a CW skimmer application. \u00c2\u00a0<\/p>\r\n<\/div>\r\n<\/div>\r\n\r\n\r\n\r\n

Keep in mind, the softrock system being replaced has about 45db of useful dynamic range as implemented here. Plus we get the bonus of using Red Pitaya as a minimal spectrum analyzer and oscilloscope.\u00c2\u00a0 Maybe even a VNA app.<\/p>\r\n\r\n\r\n\r\n

SDR Station With Red Pitaya<\/strong><\/p>\r\n\r\n\r\n\r\n

First of all, one huge thumbs up to Pavel Demin<\/a> for his open-source work on the SDR apps<\/a>. \u00c2\u00a0Outstanding!<\/p>\r\n\r\n\r\n\r\n

The time spent here going in circles chasing my non existent hardware issues was not a waste.\u00c2\u00a0 The power supply\u00c2\u00a0 was cleaned up with better filtering. \u00c2\u00a0Very nice. \u00c2\u00a0Using the AADE filter design program we also came up with a simple-to-build design for a high pass BCB filter. \u00c2\u00a0This filter optimizes the nulls at 680am and 850am,\u00c2\u00a0 and attenuation drops off rapidly above 1Mc the broadcast band.<\/p>\r\n\r\n\r\n\r\n

This BCB filter exhibits low loss on 160m, with the modeled 3db cut off frequency being at about 1.2mhz. \u00c2\u00a0Ordinary C0G\/NP0 capacitors are used in its construction, having had acceptable results with that type with the W3LPL design receive only band pass filters. \u00c2\u00a0The result was good with testing on the base station. \u00c2\u00a0The difficult part was finding good leaded C0G\/NP0 capacitors in proper values to use for construction.\u00c2\u00a0 Through hole components are becoming rare. \u00c2\u00a0NOTE: Be aware – As designed this filter is a short circuit at DC via the inductor at “dipole 12”.<\/span><\/p>\r\n\r\n\r\n\r\n