[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.
PA0AER published test data.
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
First of all, one huge thumbs up to Pavel Demin for his open-source work on the SDR apps. Outstanding!
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.
W4KAZ version of BCB filter. Built using NP0/C0G leaded capacitors, t-80-2 torroids, and a 220uh choke.
AADE predicted performance plot of the w4kaz BCB filter from DC to 10Mc. Note the nulls on 680 and 850.
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.
S meter comparisons on the TS-590s using the W4KAZ BCB filter and built in attenuator
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?
Random selected North American spot counts from days with W4KAZ skimmer station under Red Pitaya
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.
Block diagram of likely W4KAZ Red Pitaya SDR CW skimmer system
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:
PA0AER on a comparison of Red Pitaya to Flex radio, with intermod test result(google translate to english).
FOSDEM 16 program by open source SDR app designer Pavel Demin (Brussels, January 2016)
Red Pitaya as SDR
Red Pitaya Quick Start Guide
Video 2Khz BDR 107 dbm by Yevgeni Kolganov
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”.
Si570 Programmable Oscillator board for 10m Softrock CW skimmer
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.
Photo of 10m Skimmer at W4KAZ
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.
The current Skimmer package for 20m, 15m and 10m. 20m and 15m will likely be re-worked to use Si570 Programmable Oscillator.
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 :
- W4KAZ Schematic
Schematic for W4KAZ version of Si570 Programmable Oscillator
- W4KAZ BareBones Parts List (PDF) (HTML with links)
- KB9YIG Five Dash softrock products page
- K5NWA ATTiny85 page
- PE0FKO Firmware page
Yesterday, 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 ASUS Xonar DX for a bit of putzing around.
Transmitting a cw signal(a string of dashes at about 18wpm) at 5w into a dummy load on separate radio, noting the SNR readings obtained by CW skimmer from the SoftRock center frequency(353395x) to its upper limit. With the xonar DX set to 192khz scan rate, the actual upper limit on the readings was 3629.60. SoftRock connected to normal antenna system, a NE facing K9AY with W7IUV pre-amp. In summary, a sound card test using the SoftRock system as input source.
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.
But with the WX here improving, all of that might not happen for several months. 😉
engineer the possible….
73 de w4kaz
Created a page of links and several related pages of information on the ongoing construction of the CW Skimmer station at W4KAZ.
Because of the nature of the blog package used for this website, it is easier to save this skimmer related info on ‘pages’ rather than as a “post” because it seems like a project that I’d like to have semi-permanently documented, and have the documentation easily found. Whooop…there it iz….Incomplete, but slowly growing, and probably to be frequently edited in the short term.
After some large amount of initial interest, I quit paying attention to the Softrock. As the years trickled by, the Softrock project kept moving. Lots of projects, mods, versions, and changes.
Here in the present, I had an older Softrock v6.2 sitting on the ‘ToooDooo” batting lineup since around December. It had originally been built as a 9Mhz IF kit, to be used as a panadapter. It was a gift from W3DQ. When I saw the NorCal group had a run of kits available, I ordered a pair. Wish it had been three….
But….it seemed like a good point in time too examine the IF kit, with an eye on re-working it for one of the bands of interest. As it was built, it required only four changes to put it on 40m. The Softrock Lite II kits come with components for building any band from 160m-20m, so the needed crystal was available from one of the kits. The mods took only a few minutes. That got done first.
On a roll, it was time to sift through one of the kits to see what the build was going to take. One thing leads to another….build it! The smell of solder smoke was soon wafting about. The “most difficult” surface mount parts were the first on the plate. As it turns out, these are not the smallest of surface mount parts. An ordinary 15w RatShack iron with a fine tip was sufficient for the task. The difficult part turned ot to be simply identifying the other parts. The numbers on the capacitors were difficult to read, and the color bands on the resistors all look like brown.
Lots of light and magnification? Better, but still some confusion. Most of the issue is progressive myopia, but I had not realized that color-blindness might also be progressive. Not so Fast! In order to get a second opinion, NumberTwoSon took a second look. Even with his 17 year old eyes and 20/13 vision, he also had difficulty. So, after rolling out the ToolTimeTim’s XL 2550Super’scope, the parts were sorted.
After sorting, building was trivial.
Ran first skimmer test on both units on night of May 10th. Its interesting to see the spots a local skimmer finds versus thoses several hundred miles away. A whole project in itself….
After a lot of procrastination, the dormant Softrock v6.2 project became timely. The job was to convert a Softrock v6.2 from its intended IF usage(IF 9.001?) to something a wee more interesting fer the KazShack main op, namely a 40m Softrock v6.2. The WB5RVZ pages are the place to go for build information. A fabulous job of documentation on the many SR permutations.
Turns out, the conversion was fairly simple. As built, there were only 2 component changes, add the RX enable jumper, and add a wire for the second “ring” line output. Oh….also change the crystal. A few resistance and then voltage checks. Use the K2 as frequency meter to check the crystal oscillator frequency, and its F/4 from the divider. (28.220 and 7.055+/-).
Fired off “Rocky”, VE3NEA’s SDR program. Putz around with the settings for Rocky and the sound card….Success! Sweet.
Now the question…….What the heck is this transient!!???!!
So…..the project is not quite complete. There are two full ready to build kits waiting on the sidelines (hat tip to AE5X for noting the availability). Still need to find a suitable enclosure. It also seems like inserting isolation transformers in the line-outs will be worth the time, and maybe the cost. A search on the radio shack site comes up empty for their audio iso xfmr. Mouser or Digikey.
Job one is a nice shielded enclosure, although there are lots of warnings about being wary of creating ground loops. Probably put an isolation transformer and front end protector on the inputs. Separate power source for the SR, and isolation transformer on the lineouts(insulated) to the sound card. Perhaps extra bypass caps on the power supply.
After that is done, maybe the transients will be reduced or eliminated.
Running Rocky on a dual core Pentium D causes the CPU to sometimes spike as high as 7%. Moving the mouse causes more CPU stress than the SDR software causes. Interesting.
Gonna be a lot of fun with this toy. 🙂
Many thanks to W3DQ for the original project package.
(Updated 02/28/2012 de w4kaz)
(Updated 09/26/2016 de w4kaz, current links & match network schematic)
A saga of switching from raised radials to a version of the K2AV FCP for a 160m inverted-L.
The whole idea of operating on 160m started as curiosity. Before 2005 I had never operated on 160m. Ever. I had listened some, but never keyed the transmitter other than to experiment with arcing capacitors and high levels of SWR. But it generally seemed like it would be fun, so give it a try to find out, right?
After looking at a couple of locations in the yard, it seemed like there just wasn’t enough room to !easily! pull up an inverted-Vee, or other crooked dipole of such unusually large size. Tall trees out-the-wazooo in the yard, but spaced closely, so it is difficult for long pulls. So there is an emphasis on easy, because it is an important consideration. Any antenna that is a pain in the ass to maintain is more likely to be out of service at any given moment at the KazShack qth.
There is a great spot for a vertical rise of about 70 feet, so that seemed to be the ticket. But verticals have their own downside. Radials – bleh!…Ick!…Ptui! But any antenna is better than no antenna at all, so that’s where we get sucked into 160m madness.
The first preference was a top loaded “T”, but the useful supports are not arranged in a good pattern for that choice. There was just no way to stretch out the top-hat of the T.
The supports are arranged in such a way that an inverted-L is the logical choice. So a slightly long inverted L was the winner since it 1) fit into the yard where the trees line up, and 2) lends itself to capacitive matching if made slightly long. The result was an inv-L with the vertical section that goes up 70′, then across 40′, and across again in a different direction for another 50′. Approximately 155′(47m) of wire total length.
That leaves the radials. Buried radials just were not going to happen. Far too many tree roots and stone in the back yard, and no grass at all. What then is the nascent TopBander to do?
The Early years
The first Inv-L install circa 2005 had four elevated radials of equal length, about 37′ each. All were tied together and loaded via a coil at the base of the antenna. No chokes, and no decent matching network. In this incarnation, antenna performance was poor. Even loud stations were difficult to work. Heard no DX. No surprises there.
The first “improvement” circa 2007 was to add 12 random length radials, a 1.5:1 step down unun(W2FMI design), and a coaxial choke wound from about 70′ of rg-58 wound on a PVC garden pot. The performance improvement, while not quantifiable was immediately noticeable. Stations became easier to work on a single call, and I was now able to detect the whispers of DX stations. A new K9AY for RX was also added to the mix just before these changes to the TX antenna. It also appeared that the improved TX antenna was now hearing most of what could be heard on the K9AY, although the K9Ay has a much lower noise floor and is usually much easier on the ears.
Radials were added incrementally from 2007 through mid 2010 until there was a total of about 30. The original four 37 footers were the longest, and there were another four that were approximately 27 feet long. Everything else was a mish-mash of random lengths, added in pairs to the available trees in the area. Somewhere along the line(2008) I also added the capacitors required to get a good match at the base of the antenna, and have a nice low SWR both at the antenna base and at the shack-end of the feed line. And the nice narrow SWR bandwidth that accompanies such.
Performance of the final well-matched radial version of 2010 seemed to be quite good in comparison to the earliest version. In 2009 and 2010 it was possible to run stations(low power) in the 160m contests, and Q’s were made more often with the western US, as well as a handful of DX stations.
Before any other changes were made, I took some signal strength measurements in late 2011 using the K2 as field-strength meter, with the FT-920 as transmitter. The test configuration was 1) transmit full power from the FT-920 on the TX antenna at its lowest SWR point, 2)RX on the K2, using a dummy load at the end of a 7 foot jumper cable. dummy load hanging off edge of desk. K2 attenuator on, rf gain at max.
Using that configuration:
- 100w into the transmit antenna produces S-5 on K2 S-meter
- 100w into separate dummy load produces audible S-zero on K2 S-meter
As poor as it is, that reading is the best actual measurement available, from what in my opinion was the best of the radial configurations. Taken in early December 2011.
In 2009-2010, K2AV began discussing an idea he had for solving the small-lot-on-160m problem. Based on his modeling and studies of ground losses, he reasoned that a single counterpoise might be a solution that would work for space limited locations. He determined that a counterpoise that was 5/16th wavelengths might show useful current cancellations if it were strategically folded, to help with the problem of ground losses. So evolved the “5/16th wave folded counterpoise”, now being generally referred to as “516 FCP” or just as “an FCP” . The idea seemed to have a lot of merit, but being a serial procrastinator it took some time for me to get off my hindquarters and make the changes to try it out.
In early 2011, K2AV gave me one of his isolation transformers, as well as an inductor. Their implementations of the FCP at K2AV’s and W0UCE’s qth required additional inductance for matching(hence the inductor). They also discovered that the isolation transformer was a necessity to obtain good field strength results. The transformer design is beefy enough to handle their high power operations. The design of the FCP has gone through some evolutions/refinements, and the design K2Av is recommending was originally field tested at his own qth in the 2011 CQ160m CW contest with low power, and with excellent results.
K2AV style FCP System Installed
My own original intent was to install his isolation transformer into my original system and transition to the FCP. Curiosity compels me to wonder what sort of improvement the isolation transformer might have provided on its own in the old system. That test never happened, but it is really just a matter of curiosity. It would still be good to know if the transformer would have made an improvement in signal with the radial jumble. I expect the choking on the radial system was less than ideal, far less than what was necessary, and the system probably was subject to higher losses because of that. That transition never happened, so I missed having the new system ready for ARRL DX. Impatience won out when an opportunity to do the work came up.
In the week after ARRL DX, the radials/coil were removed and K2AV’s folded counterpoise and isolation transformer were added to the antenna. A new junction box was built to house the isolation transformer and matching network. K2AV came by with his analyzer, and we spent a morning giving the system a look-see. As it turns out, the same value of matching capacitors were suitable for use without modification, and the inductor was not required because my inv-L is long. Matching the system was as simple as adding capacitance until a match was found. A large value air variable could be used to find the required match in less than five minutes, then replaced with capacitors suitable for handling the currents.
My own matching network is a group of HV ceramic caps in parallel[Obsolete, probably unavailable, 2016/09/25]. These are mounted on a board that allows switching some of the capacitance out to move the resonance up the band. The switch board will also allow switching to a different vertical element, but that feature won’t be useful without also switching the FCP. The FCP is a mono-band solution.
Schematic for W4KAZ 160m inverted L with K2AV FCP
Picture of W4KAZ 160m matching network and transformer junction box in use with 155 foot long inverted L and K2AV FCP
The Present….So, What of it?
The system now up is the same/original inverted-l vertical section with the K2AV folded counterpoise and isolation transformer in place of the prior elevated radial jumble. What happened?
Using the K2 as field strength meter again, and using the exact same conditions as described above(sense antenna dummy load hanging from desk on 7 foot jumper):
- 20w into the antenna from FT-920 now registers S5 on K2 S-meter
- 40w into the antenna from FT-920 now registers S5 plus one bar on K2 S-meter
- 60w into the antenna from FT-920 now registers S5 plus two bars K2 S-meter
- 100w into the antenna from FT-920 now registers S9 (S5 plus three bars)
- 100w into separate dummy load produces audible S-zero on K2
The S-meter on this K2 is not calibrated in real world db, but even without knowing exact values the signal is obviously stronger than it was with the previous TX antenna system. Yes, that’s in the near field, but still it is encouraging.
The first field test was during 2011 Stew Perry. Anecdotally, I was very happy with antenna performance. It really seemed like I was louder, and it seemed I got fewer requests for fills. But the time for a full effort wasn’t there, so there is just a limited amount of data. Not too shabby for just three hours of operating.
A better sample was taken during the 2012 CQ 160m CW. (And here.) A total of 20 hours was operated. Terrible propagation conditions. The first 6 or so hours were very good compared to previous 160m contests. 20 total hours of operation produced 593 QSO’s. Even with terrible conditions, I was able to work a couple of EU stations. Low Power. Not as good as K2AV in 2011, but one hell of a lot better than I anticipated, especially in poor conditions. K2AV is also a much better CW op, so I doubt I’ll ever be able to hit that 925 Q milestone.
So I’m pretty happy with the current system incorporating both the FCP and isolation transformer. Many thanks to K2AV!
W4KAZ Construction Variance Notes
In implementing the FCP design at the KazShack, I made a few variances from the recommendations.
The FCP itself is constructed of stranded 14ga hardware store THHN. I like the flexibility of the wire, the sturdy insulation, and most important, I have several rolls of it already bought and paid for.
The FCP insulators were cut from an unused piece of PVC electrical conduit. That was also what happened to be at hand in the form of spreaders from an experiment with hex-beams. From the length of PVC available for the job, I cut 16 spacers of 6 inches length(~150mm). Each was drilled through three times, a hole in the center, and one about .5 inches from each end. On the leg with two wires, the spacing is about 5 inches(125mm), while on the leg with three conductors the spacing is only ~2.5 inches(~60mm). The holes are intentionally mis-aligned or drilled at offset angles. That allows the wire itself to place tension on the spreader to keep the spreaders in place. Makes it easy to do with an ordinary hand drill too, since being crooked is an advantage. 🙂 The mis-alignment alone is not enough to keep the spreaders from sliding, so they are also wrapped with vinyl cable ties as needed. The distance between each spacer works out to about 4 feet(~1.3m). Vinyl cable ties are also used as spacers at the midpoint between each PVC spacer.
Measuring and threading the wire was the most time consuming part of the FCP construction. Because all of the separators are of equal size and drilled the same, the side of the FCP with three conductors is more closely spaced than the side with two. This made mechanical construction very easy, the FCP is taut and sturdy, and did not seem to have any adverse effects on performance.
The transformer and matching network is installed in a nice hamfest/surplus telco box, about 8x8x4. This is a nice weather tight enclosure. The transformer is exact to K2AV specs(by definition – it was wound by K2AV his-self!). The matching network of switched parallel caps was pulled from the old weather enclosure(a sealed PVC pipe) and re-used in the new junction box. These components fit well enough, but there would not have been space to house the additional toroidal inductor had it been needed.
Besides the apparent signal improvements over the rejected-random-raised-radial-rambling-razzledazzle, the FCP itself has other very practical mechanical merits and advantages over raised radials.
- The folded counterpoise is simple to build.
- The FCP is relatively small, 32′ per side(64′ total length)
- The FCP is a LOT easier to deploy than 30 elevated radials, or burying a dense radial mat
- The FCP lends itself to following contours, and models well when the FCP is not perfectly straight
- The FCP will require a lot less maintenance. The odds of falling branches breaking the FCP here at the home QTH are lower by a factor of 15. (2 legs of FCP vs 30+ radials in 30+ directions, all below branch shedding trees)
- all of the above….. !! yipeee!!
But Kaz, is it equivalent to a full size vertical with a dense mat of radials? Probably not, but there is absolutely zero chance that sort of system can ever be installed at this QTH, so the point is moot. Do I care? Nope, it “works”, and it “works” better than it’s predecessor 160m antenna systems at this QTH. Very possible that improvement is just testimony to the poor performance of the prior system. But better is “better”. Is it snake oil? Probably not, at least not according to the CW skimmer robots and the results K2AV has had with his system, and more important, my own field testing during the CQ160m contest.
At this point, my only regret is an academic point – not having run the test of inserting the isolation transformer into the old system with the radial-jumble. The sharp tuning of most 160m antennas suggests that common mode currents will often be a problem as one tunes away from the antenna’s resonance and the reactance increases. How much benefit is gained from either the isolation transformer or the FCP individually is unknown(to me), but still of both practical and academic interest. I’d really like to know if the old system would have been improved with the isolation transformer installed. Still of interest, but not enough for me to spend time hanging the radials back up again! 😉 Together, the FCP and transformer seem to do a damn fine job here. Certainly the best system that has been active in this location.
What next? FCP phased verticals…..FCP foursquares…..FCP parasitic arrays….. MANY possibilities – if only I had the room to do it!
Until such time as K2AV publishes on the subject, the available references are the basic instructions and a few message threads on the TopBand mail list on pertinent topics:
- W0UCE’s accumulation of information on K2Av’s 160m ideas, including the FCP
- Photos from W4KAZ FCP install
- K2AV discussion of the FCP
- Rolling your own FCP isolation transformer, IMPORTANT
- Topband: Where to place a preamp? Switching Beverages?
- Topband: K2AV 160m Folded Counterpoise (FCP), parts and winding for isolation transformer
- Re: Topband: K2AV 160m Folded Counterpoise Antenna (wire suggestions)
- Re: Topband: T-200 vs. T-300
- 2012-05-31, VO1HP FCP install
- DM9EE (was DL2OBO) FCP page
- W1UJ : http://w1uj.net/FCP/
- KY6R : https://ky6r.wordpress.com/2015/04/27/160m-fcp/
- IV3PRK(FCP @ HC1PF) : http://www.iv3prk.it/hc1pf-tx-antenna.htm
- DL0WH : http://dl0wh.de/80m-vertikal-mit-gefaltetem-gegengewicht-nach-k2av/
Put together a WinKeyer2 in a couple of hours two weeks before Field Day. This accessory was added as part of the plan to have the SO2R station capability operational with either USB or serial ports on the logging computer. I chose the version with a serial port, and plan to use it with a serial to USB conversion dongle. In essence, the shack will be forward or backward compatible with the computer hardware, allowing the SO2R to be feasible with whatever crappy piece of computer I have available at any given moment, from an old dos box to brand spanky new.
The keyer kit itself was built with only about 30 minutes of plugging and soldering. The kit was missing a couple of capacitors, but they are common values which I had in the parts box. It took another couple of hours to get the enclosure drilled and nibbled out – including a db9-sized hole in the wrong place. Oops. On hindsight, a simpler plastic enclosure would have been easier.
The finished product worked without any re-work. The WinKeyer2 is the newer release of the serial port version of the kit. I tested the kit out using a USB to serial converter and the “wktest” program available for download on the K1EL site. After a quick test and config with the wktest program, I brought up writelog and tested that. Flawless performance.
Hooking up the paddles was a bit less satisfying. I’m not terribly proficient using paddles and a keyer, and the WinKeyer2 seemed a bit temperamental with my shaky fist. Maybe after more practice it will become easier. But for now, the paddles will be routed through the logikeyer CMOS4, and the paddles will be combined with the computer generated CW from the WinKeyer via a “Y” connector going into the CW input.
I also have the same problem using an MFJ keyer I have on hand. I’m not sure why that is, but so far the Logikeyer and the keyer built into the K2 are the easiest to use of those available.
One quirk I found with the winkeyer(or my understanding thereof) was related to the pot setting for the keyer speed. Starting the programs(either logging program or “wktest”) while the speed pot was set to maximum caused a bit of confusion. To allow computer control of the speed setting, it seemed necessary to disable the speed pot via the software.
Part of the learning curve.
This home brew SO2R controller project follows the “old-n-busted” theory, and is based on the design by N6BV in the ARRL Handbook, as well as some input from K4QPL. In summary, it is built around the use of an LPT port for computer control of the CW, PTT, Radio A/B, and band data. As previously outlined, the LPT port is less expensive and easier to accommodate – even if obsolete. Hence “old-n-busted”. I expect to be able to bridge the gap to USB at some point by adding a K1EL WinKeyer, and the Piexx SO2Rxlat dongle.
The rig control is still accomplished via a serial port for each radio. The LPT parallel port is used for PTT, CW, transmit focus, and band data for one radio. The K2 band data is a separate option not installed in my K2[another void the Piexx SO2Rxlat dongle will solve].
As it stands now the only parts missing for a conversion to USB device control are the WinKeyer and SO2Rxlat devices. Everything else in the SO2R control chain is home brew.
There are several resources available that block diagram the components needed inside the shack for SO2R[e.g.,see DL1IAO, for the W5XD SO2r Box]. For ease of use and construction, the heart of the SO2R box breaks down into four logical units which were built into three separate boxes.
Band Decoder: One of the peripheral boxes will provide automated band switching driven by the logging program[or directly from a radio] by acting as the band decoder. Most logging programs provide band data in the “BCD” format, and Yaesu radios provide that format via their hardware dedicated band data outputs. The binary coded band data make the design of the decoder relatively simple. In hindsight, it seems like a good idea to expand this component’s abilities by using a set of relays to provide for either positive or sinking switching. This is a consideration for driving band pass switches or antenna switches, and is also a design factor for home brewing those components.
The internal view of the band decoder
More band decoder photos.
Band decoder schematic. PNG Image, PDF file
For those looking for an inexpensive band decoder solution, the Unified Microsystems band decoder looks like a real bargain and could easily be incorporated into a home brew design. To build a band decoder, it is probably better to start off with the Unified Micro unit and build the support hardware around it.
Audio Switch: The second is a simple peripheral to the main SO2R box is a simple remote switch. This device itself is simple, yet it really makes the SO2R a lot easier. This device was subdivided into two physical component parts. The actual relay board that switches the audio was built on its own small pc board and mounted within the SO2R box. The user controls are mounted in a small project box. The small box sits just above the keyboard on the desktop.
For my own preferences, it seemed better to have one small “remote” user control box for switching in the heat of battle. The remote has a rotary switch to control the headphone audio, and it can choose either radio individually, stereo with one in each ear, stereo with left and right reversed, or it can be set to have the audio follow the transmit focus. It also has a momentary contact switch for each channel, which can be used in stereo mode to listen to either channel for as long as the switch is depressed. The remote switch control is connected via a Cat-5 cable to the SO2R control box. The control box and its rats nest of wiring can be placed away from the station controls.
Remote: The momentary contact switch feature will soon be enhanced to correct an original construction oversight. Parallel connections for the momentary contact switches will be added to allow using a footswitch. That will provide hands-free audio switching when in stereo mode. That is important, as I need the hands free to type and deal with CW and radio tuning. Hat tip to K4QPL for the idea.
Remote locating allows both the main SO2R box and the band decoder to be located away from the other major components in the station. That highlights the single caveat I experienced – RFI on SSB. After experiencing RFI problems during ARRL SS SSB, both of these units still need some attention paid to choking RF on the interconnects. Re-locating them a bit further from the RF hot spots and coax connections should also help with the RFI. Judicious and liberal use of clamp on RFI chokes seems to abate the problem.
For some reason, the K2 seemed more susceptible to RFI than the Yaesu FT-920. The RFI source there turned out to be on the PTT line. A combination of ferrites and a diode in the PTT line finally tamed that hotspot. Note: in the PTT line, the PTT hot is at the radio’s mike connector, and it really didn’t sink into the thick head right away.
W4KAZ SO2R control box
More SO2R box photos
SO2R box schematic PNG Image, PDF file
Audio switching schematic PNG Image, PDF file
SO2R Box: The guts of the system all reside in the main SO2R box. It has inputs for headphone audio from each radio, CW inputs, PTT inputs, and microphone audio inputs. There is also an LPT Db-25 input for connection to the computer. The set up is designed to receive control input from the computer LPT port to drive some of the switching and provide band data.
The main box contains two separate components. Two small perf boards were used to simplify construction. One board contains switching for the headphone audio. The other board handles switching for the CW, PTT, focus control, and microphone audio. The audio is normally switched via the switch remote, but it can also be slaved to follow the logging program’s transmit focus and be controlled from the main SO2R board.
Future Migration to USB:
In order to migrate to a logging computer with USB ports, it should be a minor change to replace the LPT cable with a USB connection via the Piexx SO2Rxlat device. By making the components LPT port compliant, the SO2R capability can also remain backward compatible with an older computer that has no USB support, running Writelog. Just in case the only option is an ancient junker from someones junk bin. The SO2RXlat will also provide band data for both radios via a single LPT DB-25 connector.
The total cost in parts was not large. The 4401 NPN transistors, relays, connectors, bypass caps and diodes were all generic ‘project part’ items I have been accumulating over the past several years. I have gravitated towards using RCA connectors because of the availability of inexpensive sheilded RCA cables and the low cost of the connectors. The CD2048 IC for the band decoder was a dedicated purchase, and were around $1.98 USD. The amount of time put into construction, the biggest real expense, amounted to about 15 total hours, spread over a long period in several hour long increments. I spent more time debugging the RFI issues.
The RFI is probably partly due to using plastic enclosures, but these enclosures were easy to come by. In hindsight I would add ferrite beads on to all interconnects inside the boxes. The ferrites on the interconnect cables create a bit of additional clutter and impede quick wire pulls. Kludgy.
The remote switch has since been modified to add a jack for an external switch to concentrate both channels on either the left or right radio. This will allow for use of a foot switch and will allow hands-free audio switching.
After building the 80m/160m splitter, it seemed like the signal levels from the K9AY were down a bit, probably from losses in the filters. So after looking around at pre-amps, and procrastinating on buying the Ar2 preamp, I again landed on the W7IUV site.
W7IUV has updated his preamp schematic, and it looked easy enough. Building the project was simple after gathering some suitable parts.
Trying the pre-amp out seemed to show that it was more or less filling the desired role quite well. With the preamp engaged, levels from the K9AY were now on par with signal levels from the transmit antennas on both 160m and 80m. The preamp is installed in the shack just ahead of the band splitter. Noise levels on the RX system were down about two to three S units from the TX antenna in these moderate noise conditions.
During the 160m contest this weekend, the RX system got its chance to proove itself. Noise levels here were moderate – not as quiet as good winter conditions, but not S9+ summertime noise either. The RX antenna with the preamp turned on was always the best choice on weak signals in these conditions. It also necessary to switch the K9AY around a lot – signals were not always best in the expected direction because of higher noise to the north. The southeast direction was dead quiet, but from here in central NC there isn’t much to listen to on 160m to the SSE. The actual compass direction on the SE leg is about 10 degrees south of southeast.
So the short version is that the preamp is an improvement when splitting the RX antenna for two radios.
- Try moving the preamp out to the base of the K9AY, probably in a new K9AY switch box
- Test the RX with the splitter removed, preamp on/off.