For some reason this info never was documented here, so for my own uses, here it iz. A few links about surplus masts, falling derricks, and IOTA.
[Updated 2016-12-23, see text on Compatibility issue]
Recently discovered an interesting, affordable, and relatively new product called Red Pitaya, designed as an open source based piece of test equipment. As a piece of test equipment the Red Pitaya has basic oscilloscope, spectrum analyzer, and signal generator apps available. The apps are designed to run as web applications with Red Pitaya board running a custom Linux and acting as a web server. Currently the apps are quite basic, but useful despite their simplicity.
Possibly more interesting for hams are the SDR receiver and transceiver apps available from Pavel Demin.
With the SDR apps, Pavel has taken this little Red Pitaya board into the areas of interest to many ham ops. The SDR receiver app has the ability to function with several currently available SDR programs. The ability to support feeding six channels into CW skimmer server is of particular interest. There are also transceiver apps which are being used by experimenters to build Red Pitaya based transceivers.
The Red Pitaya itself is a board that runs a customized linux OS(their term is ‘ecosystem’) off of an SD memory card. The board has two RF inputs and two RF outputs for use as the heart of a test system. 5V USB power supply input requires 2A. The board has a heat sink on the CPU but a small fan helps cooling. It can connect via ethernet to the network or via a wireless connection. The OS and apps are downloaded from the Red Pitaya website. SDR apps are available from both the Red Pitaya site and directly from Pavel Demin’s website. This little SDR kludge is a viable substitute for the Softrock skimmer system previously being run @W4KAZ.
SDR Uses and v0.96 Compatibility Issue
A couple of issues turned out to be a mix of hardware and software problems. The largest problem was a software incompatibility issue between the latest OS v0.96 and the SDR software. This causes problems in the SDR with interference that looks like intermod artifacts. Too much time was spent here looking for hardware problems before stumbling across the documentation on the issue. The solution was simple. It simply required building an SD card with the previous OS version v0.95, and then configuring(secure password) then re-installing the SDR app.
A couple of the SDR apps available on Pavel’s site originally included an OS that did not allow a persistent password change. To avoid that security vulnerability, the original SD card here was built with v0.96 of the OS. As of October 2016, do NOT try to use v0.96 OS with the SDR apps. V0.95 works with the SDR. Better to have several SD cards with different OS versions should you need a more recent OS for new apps as they are developed. [Update 2016-12-23. Per 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. Not yet migrated to the updates here in the W4KAZ SDR setup.]
After building the v0.95 system, the SDR app was good to go. Several different flavors of SDR are available from Pavel. The SDR app version that supports CW skimmer server also supports PowerSDR, which has a nice spectrum and waterfall display.
There is not a tremendous amount of information available, as folks are just beginning to explore the possibilities. PA0AER has an interesting post, with a few findings of his summarized in this table.
Yeah, -120db floor and 75 db of intermod suppression should work just fine in a CW skimmer application. 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. Maybe even a VNA app.
SDR Station With Red Pitaya
The time spent here going in circles chasing my non existent hardware issues was not completely wasted. The power supply was cleaned up with better filtering. Very nice. Using the AADE filter design program we also came up with a simple-to-build design for a high pass BCB filter. This filter optimizes the nulls at 680am and 850am, and drops off rapidly below the broadcast band.
This BCB filter exhibits low loss on 160m, with the modeled 3db cut off frequency being at about 1.2mhz. Ordinary C0G/NP0 capacitors are used in its construction, having had acceptable results with that type with the W3LPL design band pass filters. The result was good with testing on the base station. The difficult part was finding good leaded C0G/NP0 capacitors in proper values to use for construction. Through hole components are becoming rare. NOTE: As designed this filter is a short circuit at DC.
The plot projected by the AADE filter design program above is a best-case prediction. WPTF, 50kw at 680 and WPTK, 10kw at 850 have transmitters about 3 kilometers and 12 kilometers respectively. They produced all sorts of intermod in the softrock system. The design is tailored to place the largest nulls where they might do the most work in the KAZshack. Getting the 3db cutoff at 1.2Mc was just to try to keep the losses as low as possible on 160m. To get an idea of its performance, I plugged it into the station and took S-meter readings on the Kenwood TS-590s. The BCB filter dropped WPTF at 680 from pinning the S-meter down to just another strong S9+ signal.
Skimming with Red Pitaya SDR
With the software issues corrected, let the CW skimming begin. Skimming tests seem to have spot signal levels from Red Pitaya SDR slightly better than those from the Softrock skimmer system. Full system stress test coming during 2016 SS CW. The Red Pitaya also seems to be very frequency stable, something that was a minor issue with the softrocks. When running PowerSDR, comparing Red Pitaya by ear shows it to be a bit less sensitive than the main station rig, a Kenwood ts-590s.
Does it work?
System Reconstruction – Permanent New CW Skimmer
After a good shakedown voyage through Sweepstakes CW, it will be a good time to re-arrange the test Red Pitaya SDR system into a more permanent and compact single system. One of the dead softrock CPU’s will donate a nice clam shell computer case, and all of the components should fit easily. The plan is to wall mount the completed system near the shack cable entrance. The softrock system will be raided for its discrete components, the W3LPL style band pass filters as well as the W7IUV pre amps. New splitters will be built for the new system to allow for antenna options to change in the future.
Unexplored are some more experimenting to find a proper matching transformer and Red Pitaya input jumper combinations for the best results. Some research into the transceiver experimenter comments indicate using a step up transformer is best. Some have also made mods to the front end that are supposed to boost the sensitivity by lowering the noise floor significantly, from 9 to 12 db. Currently using a 3:1 cascaded into a 4:1 transformer as step up, with the input attenuation pads bypassed via jumpering on input#1.
If you choose to experiment with Red Pitaya and the SDR apps, be sure to create your bootable SD card from a compatible OS. If you do not, you will be very disappointed at the 25db BDR and the interference and low performance you will experience. Currently, as of 2016-10-28, the 0.96 ecosystem/OS IS NOT COMPATIBLE with the SDR apps from Pavel Demin. Either use the ecosystems Pavel has or the last archived version 0.95 from Red Pitaya’s archive. Do NOT TRY SDR with v0.96 OS! Been there, done that, have a clean power supply and nice BCB filter to show for it.
The Red Piytaya ecosystems come with default root passwords. Reset your password ASAP. Also, at least one of the ecosystems Pavel provides does not allow a persistent root password change. I suggest using the 0.95 from the Red Pitaya archive and that the root password be reset to something secure if the Red Pitaya is going to be running on your home network. With the default root password, your network is open/vulnerable to having a hacked linux system behind your router’s firewall.
Other Useful Red Pitaya SDR links circa 2016-10-28:
FOSDEM 16 program by open source SDR app designer Pavel Demin (Brussels, January 2016)
After a lot of foot dragging and interruptions, all of the components required for a 100w battery operation had been acquired at casa W4KAZ in late spring 2015. The first test run was a 1E Field day operation at home. But better to put it to use afield.
So N4YDU was game for the field test on Okracoke island for 2015 IOTA. N4YDU and I operated as W4O from Okracoke Island on the NC outer banks, just south of Hatteras. Access to Okracoke is by boat, so we booked slots on the ferry out of Swan Quarter for Thursday afternoon. This worked well, allowing for set up and test operating well before the Saturday start. Also a nice break for a meal for lunch Friday down in Okracoke village. QTH of the operation was the NPS campground on Okracoke.
WX Conditions on Thursday were cool with an all day drizzle. Ugly, but no thunder and lightening, so not terrible. Set up of camp was delayed until early evening. Thursday night was warm, damp and still. Friday morning brought clear skies and an nice cooling breeze out of the north. The WX was much improved for the rest of the weekend. Thursdays rain was the harbinger of a very welcome unseasonable cool front, and WX for the bulk of the weekend were very comfortable with much lower than normal temperature and humidity – perfect for field operations.
Radio propagation did not live up to the WX, so there were periods of slow conditions. A nice breakfast is always good.
The solar set up included two 30w solar cells sending power to the charge controller and two deep cycle batteries. Our solar cells were augmented by the temporary loan of an 85w solar panel by WB8YJF, Jon. WB8YJF vacations at Okracoke every year at this time, and with his help we had a strong 8A charge current throughout the day Saturday.
Having the battery fully charged going into the evening hours was nice. Rates slowed fairly early, so two days of beachside life had us leaving a few possible qso’s on the table. Sleep was the better option.
The station consisted of the batteries, feeding power to the Elecraft K2. Antenna supports consisted of several fiberglass masts. All of the masts have been modified by drilling holes at the base of each mast section for pins. Hitch pins are used for the smallest sections, and 2 inch cotter pins are used in the larger sections. This was faster and more secure than using hose clamps, but it may ultimately weaken the masts over the long term. That trade-off seems worthwhile for the time saved on deployment and take down.
The 33 foot fiberglass pole from TheMastCo was used as the center support for a lightweight fan dipole for constructed from 300 ohm twin lead and surplus field wire, covering 40m/20m. A 22foot fiberglass flag pole combined with most of a 20 ft. Shakespeare wonder pole was used to support an inverted-L for 80m. Thirteen foot crappie poles were used to get the ends of the dipoles and vertical as high as possible in the limited space offered by two spaces in the campground. We also deployed a 2 element triband yagi on five sections of surplus military camo mast, at a height of about 18 feet.
Radio conditions were poor, but the WX was unusually good for the NC coast at the end of July. Great trip and another successful field test of something different.
Life’s swirl of events led me to be non-committal about FD with the usual suspects this year. Probably a good thing, given the way brown stuff keeps making sudden contact with the rotary impeller. Even the minimal home operation in lieu of a real event was in question as days grew shorter.
So 2015 FD was flying solo in the KazShack. [Some photos here] The twist to make it FD was to run the station on emergency power, class 1E. With enough ’round-too-its’ having been previously cashed in to assemble a portion of the battery set up desired, the battery op seemed feasible. Accumulated over the past year are a couple of 30w solar panels, a pair of well-matched deep cycle marine batteries, a decent charge controller, and assorted minor peripherals(cables, connections, etc). The original plan was to be ready for NC-QSOP earlier in the year. Brown Stuff vs Rotary Impeller. Brown Stuff won, no Qso party.
In field day spirit, I also hoisted an “emergency” field portable 40m/20m inv-V off of a fiberglass telescoping mast obtained from “The Mast Company” several years back. After collecting dust for these years, it occurred to me that it could fill a big unused space on the edge of the ‘wire-farm’, backed up very nicely by the 20m/40m reflectors in their permanent positions. This worked very well on both bands during FD, showing four or five S-units difference depending on conditions and the direction of the signals.
The 2015 FD Station:
For the event, I relocated the solar panels to be within reach of the feeder cables to the shack. The batteries had been connected to the solar panels for over a month, so they were nicely topped off. The batteries were brought into the shack, and connections were set up to power the K2 as the load off the controller. Not willing to go whole-hog QRP, all transmitting was done at intermediate-low power levels, 45w overnight, 75w during daylight. (Based on actual current draws by the K2 as measured in place). Add a laptop and ready to go. The antennas were the normal wire farm plus the hasty-install dipole on the fiberglass mast.
The Solar Problem:
Expected to have poor results from the solar panels, as their default location for the shack is only in full sun in the afternoon. Hoped for a sunny afternoon on Saturday. No. Such. Luck. In fact, the WX really sucked. When the WX didn’t suck, there was lightning and rain. Zero sunlight. The panels only produced about .3amps in shade under clouds, instead of their full-sun 2.8amps. 90% reduction.
The good news is the batteries seemed up to the challenge on their own. Battery voltage dropped to 12.3v at its lowest. The K2 drew only about 11 amps in transmit, and just over 1/3 amp when in receive. If the panels had been in a good full-sun location the charging would probably have kept up with the demands during daylight operating. Success. The charger says that 24ah were drawn over 12 hours of operating, with transmitter power at 50w for the 6 hours on Saturday, and 75w for the 6 hours on Sunday. In full sun the solar cells would probably have kept the batteries topped off until sundown.
The current draw at full transmit power on the K2 is in the 15A ballpark. Rolling the transmit power back to 65 or 75 watts is a good compromise between output power and current demands, as the current draw is closer to 11amps at 70W.
Actual Operating Condx:
WX conditions cut outs a large chunk of Saturday prime time in the late afternoon/early evening. So after putzing around for the 1800Z-2000Z hours, did not return to the chair until 0150Z. Then a decent three hour stretch, alternating between 40m and a few sweeps of the other bands. A nice long nap and the back in the chair well after sunup Sunday morning. Not terrible Sunday morning, but not fantastic.
Finished with 532 CW contacts logged and 2128 QSO points. Not terrible for only about 10 hours of butt-in-chair time.
So the emergency power and emergency antenna set up worked well enough. A bulk of the QSOs were made on the portable antenna. In the shack the charge controller indicated the station drew a total of 24 amp hours. The solar cell charging put 9 amp hours back in, not bad given the clouds and shade trees. That was with the solar cells providing only about half an amp. In full daylight the charging would have been sufficient, and closer to 3 amps. The power draw had been conservatively estimated/ball-parked/WildAssedGuessed at a need of about 40 amp hours.
The Renogy charge controller is well worth the minor additional expense. It senses the voltages from both battery and solar panel, and can charge 12v batteries from 24v solar cells if needed. It also monitors both load and input currents, as well as the battery charge state. (Seems to be sold under several different name plates, all seem identical based on advertising specs.)
Overall, very happy with the experiment.
Note: More links at bottom of page: This is a simple-to-build Si570 oscillator for use with the Softrock Lite kits for CW skimmer and input to the Reverse Beacon Network. It uses the Si570 chip and an AtTiny85-20 programmed with the PE0FKO firmware used for the Softrock Ensemble kits.
Currently a programmed ATTiny chip is available separately from K5NWA. The firmware is available for download, so programming the AtTiny is also an option. The PE0FKO site also provides the required USB device driver, software, and guidance on using them. (links) The Si570 is available from Digikey(digikey part#:336-2518-ND, manufacturer part:570CAC000141DG).(SiLabs 570CAC000141DG part )
The oscillator itself is pretty simple, and is the bare essential hardware required for re-programming the oscillator for a needed single frequency to use with a Softrock Lite II rx. It is based on what I saw in the the schematic of the Softrock Ensemble RX, nothing original, just pared down and hijacked from the original Ensemble design. The Si570 part itself is the bulk of the expense of the oscillator, and the cost of the Si570 chip is almost as much as the Softrock Lite kit itself. The oscillator signal is fed into the divider through a 10K voltage divider as in the Softrock RX.
So why an Si570 Programmable Oscillator ?
The RX Ensemble kit is a viable alternative expense wise. It really depends on the intended usage. Using separate Softrock Lites as single band CW skimmers leads to the choice of a programmable oscillator for customizing the center frequencies, especially for the high bands. The method used for 20m using the third harmonic seems to result in a decrease in dynamic range. That results in an increase in false mirror images being reported to RBN by the CW skimmer as actual spots.
Using the Si570, the oscillators can be set at the frequencies needed by the Softrocks, i.e. 4 times the center frequency. (for 96Khz bandwidth the oscillator would need to be: 20m=56.188, 15m=84.188, and 10m=112.16). A programmable oscillator also allows switching from 96Khz to 192 Khz bandwidth(20m=56.38,15m=84.38, and 10m=112.38). Keeping just the bottom half of a 192Khz bandwidth CW skimmer would at a minimum eliminate at least 50% of bad mirror image spots. There are also likely to be fewer stations CQ’ing below the “.096” section of a band(e.g., most often there is not so much regular CWactivity above 28.096 as there is below). That is the idea anyway.
The Si570 Programmable Oscillator Prototype:
The first version is deadbugged on a bit of board scrounged from the parts bin. Not many parts, but a bit more PCB real estate would have been better. Functional rather than esthetic. The USB connection is via the usb cable end clipped from an old computer mouse in the parts bin(unlabeled black coil in left of photo). “Engineer the possible”.
Testing the original prototype board pictured resulted in three build mistakes to debug: a missing 5v connection to the ATTiny and the reversal in polarity on both zener diodes across the USB data pins. These mistakes prevented function without damage to the components. After correction of the build errors the software was able to function with the Si570 as needed for both programming the oscillator(‘startup’) frequency and running as a stand-alone oscillator.
The Si570 when programmed for 112.36Mc was found to have an actual oscillation at close to 28.090 exactly from the Softrock divider, as measured with TS-590 and Elecraft K2. This was with the oscillator inserted in-circuit as the Softrock Lite oscillator via a transformer(5 bifilar turns on a type 43 torroid core) and a 2.2k resistor. The frequency is very consistent and stable when the power is cycled on/off.
Setting the frequency is accomplished using either the USB-Sync program by DG8SAQ or via the test program Si570_USB_test from the QRP2000 project from www.sdr-kits.net. DGF8SAQ’s program is easiest.
Easy measurement of the actual frequency in place is good enough for initial setting up of the skimmer software. A few KC either way will make little difference in a CW skimmer set-up, as final adjustments were done in CW skimmer software to put the skimmer signals ‘on frequency’. In this case the CW skimmer center frequency is nearly identical to the Si570 programmed frequency. That has not been the case with the versions using ordinary crystal oscillators, those having a bit more drift off their nominal value.
A new Softrock Lite II is the 10m test bed, with 15m revision to follow. These two bands suffer the most from poor dynamic range and false mirror images. The 15m oscillator also has a nasty tendency to drift with temperature changes. If the modified softrocks perform as desired it will be time to pair these two bands with the best of the sound cards available. That will be a separate game of trial and error. The 20m softrock skimmer may also be retrofit, as using the third harmonic for the softrock center frequencies seems to adversely impact the dynamic range.
As an aside, the first 10m center frequency chosen was 28.060 into a 192Kc bandwidth sound card. Horrible choice, as it was close enough to the 15m harmonic that interference spikes were present on both bands every 900hz. Resetting the Si570 oscillator to place the center Fo for 10m at 28.080 greatly reduced(but not eliminate) the problem. Currently set on 28.090 as of 20150414. More tinkering required, and migrating the 15m Softrock over to an Si570 oscillator may help.
Si570 Programmable Oscillator UPDATE, 2016-11-08
The Si570 oscillator as described was perfectly usable in this application. However 10m and 15m performance was was poor on the softrocks, the primary difficulty being a low dynamic range. This is indicated by mirror images that appear when SNR values on the actual signals were higher than 35dbSNR.
The most useful work around for this problem is to scan at 192Khz sample rate, and only use the lower half of the sample for the CW skimmer. Using the upper 96kc might be easier, as the center frequency could be set at 28.0Mc and 21.0Mc. The latter may ulimately be the best approach. There are unlikely to be any useful signals below the bottom of the bands, and those could be readily discarded as false or otherwise unusable(i.e., out of band).
LINK LIST, Si570 Programmable Oscillator :
Some repairs to the skimmer station set up have been made after losing the 20m and 10m softrocks. Both were probably damaged due to modifications I made to the voltage regulation circuits. That appeared to eventually fry the QSD chip, which is the heart of a softrock.
The 20m skimmer was replaced completely with a new softrock lite. 10m is pending re-work, but replacement would probably be the best bet.
So for WPX 2013 there are five bands available, 160m through 15m. These will be active during WPX intermittently. I intend to bring them up and down based upon my own operating. The skimmer will be down when I am operating.
Other changes made to the skimmer station include loading windows XP onto the Optiplex 360 that had been running windows vista. Vista was able to run one instance of CW skimmer, but was not able to support two instances simultaneously due to sound card conflicts. Windows XP does not seem to have a problem with the two sound cards, and is an OS supported by CWSkimmer(Vista is NOT supported by skimmer).
After several contests, monitoring of the softrock skimmers has turned up a bit of a problem with using softrocks as the skimmer platform. Very strong signals are producing a mirror image that is often reported as a spot to the RBN. Certain to be annoying for the S&P packet crowd during a contest. Annoying enough that a few flame mails have arrived.
The volume of the bad spots is relatively low on the lower bands, and more common on the higher bands. 40m is somewhere in the middle, with most of the bad spots being sent for domestic USA stations.
The problem is a combination of the hardware and software, both contributing to the problem. A software fix could potentially be made to CW skimmer or to the RBN aggregator to correct for the problem. Will inquire to the authors…..
In the meantime the best solution available is to throttle the RBN aggregator to allow only spots below the center frequency to be reported. For example, the 15m skimmer is based on a softrock with a center frequency at approximately 21044.5Mc. So for the duration of the ARRL DX CW contest, an entry in the “Notched Frequencies” will be active to not report 21044.5-21100 to the RBN.
That solution does nothing to correct for half of the possible bad spots(i.e., a strong signal above the center frequency whose mirror image is being spotted below the softrock center frequency). But it should alleviate many/most of the actual bad spots, since most run stations prefer to operate as low in the band as they are able.
Open to other suggestions short of replacing the softrocks with better (yet unaffordable) hardware.
Update 20130217, 2140Z: There are new versions of both skimmer and aggregator. Perhaps upgrade will help.
A thread over on the softrock user group list spurred the curiosity…..: http://groups.yahoo.com/group/softrock40/message/68324
G4ZFQ has RightMark test data for a high end Xonar D2X card, as well as several others. An internet search found other RightMark tests of several other Xonar cards, all of whose test data show curve trends remarkably similar to those of the D2X, albeit with somewhat worse IMD, spurious, and noise figures.
The curiosity is the test data shows a roll off on the frequencies above 50khz. The nature of the loopback test is an issue, but it also seems likely that using a sound card as the source may be having an effect on the test results at the higher edges of the sound card frequency response. But signal generators as input to the tests shows the same general trend. SDR at wider bandwidths pushes at these edges of a ‘sound’ card’s ability….So perhaps the SDR software is compensating for the expected performance drop-off at frequencies above audible levels?
The Test- (Pertinent Excerpt from list post):
Having not yet thought of a better way to do a meaningful real-world test on the sound card with what is available in the KazShack, I fired up the 80m softrock on the xonar DX.
After CW skimmer collected a bit of data, the SNR readings above 3600 improved to 37-39.
So the worst case for CW skimmer(as currently configured) using a Xonar DX is being 6db less sensitive at the upper edge of the 192khz bandwidth than it is at the center. That is actually a lot better than I expected for an audio device pressed into service outside normal audio ranges (and I already liked the Xonar DX).
My curiosity is now nagging me to run the same tests on all of the other in-shack cards more methodically at their maximum scan rates(mostly 96khz), and to find a lower level outside signal source. I’ll try to recruit a fellow in the near field who will better be able to generate a low level test signal. It would be useful to see what happens at the band edges when the best copy close to the center of the SoftRock’s scan range starts out at 20dB, 10dB, or 6dB SNR.
But with the WX here improving, all of that might not happen for several months.
Engineer the Possible…