Radio W4KAZ

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End Fed Half Wave-Experiment du’Jour : Part 1

Just about the only wire antenna in common use I had not experimented with is the End Fed Half Wave(EFHW).  So WTF.  May as well give it a go. 

2021 planning had me booking a stay on Cape Lookout National Seashore(CALO) for the end of June rather than the end of July.  I tried unsuccessfully to make the reservation in 2020, but could not.  Success for 2021.  So my FD 2021 will be from Cape Lookout. 

Given the layout of the cabin I prefer at CALO campground I decided to tinker with the EFHW as a possible solution for allowing multi bands with least effort.  The “least effort” factor is growing more important with each passing year.  But the EFHW itself piqued my curiosity as well, and it seems it my provide a solution to the “least effort” vs. “works well”  conundrum.   

So, here lies the experimental portion.   NUMEROUS versions of the classic 49:1 transformer are documented on WWW and in the now ubiquitous scrootoobe video.  Version guidelines exist for either 80m or 40m multi band versions.  Quite typically I chucked some of that and decided to re-invent the wheel – because what is the fun of experimenting if you are just going to follow the cookbook?  Wellll…..not quite that either.

Where to start

Looking for a 40m size and decided to try modeling out a 40m EFHW fit out with a loading coil and tag end to allow 80m or 75m.  The idea is to have an antenna that the floppy fiberglass masts would be able to support easily in the normal 20 knot winds typical on CALO.  The feed point will be at about 4 feet high as I expect to deploy it.  The mast will support the wire vertically to about 30 or 35 feet, depending on which mast is used(Spiderpole or Jackite or K4TMC).  The rest of the wire will be stretched out horizontally with the coil supported by a second mast.

This deployment will have 80m or 40m basically functioning as half wave in an L configuration.  20m will probably have a larger horizontal component than the vertical section, and if it works there 15m/10m will provide who-knows-what.  i.e., “PERFECT!” – for values of “perfect” where whatever happens is perfect.

Modeling showed best result with the wire between the feed and the load at a longer length than I expected at 70+ feet.   Using insulated wire for actual construction, I expect that to be shorter in real life.   I plan to test with a .05wave counterpoise, and use a 6 foot coax jumper at feedpoint.  The real feedpoint will be a current choke at the end of the coax jumper.  It seems likely the shield of the coax jumper will act as another counterpoise.  Maybe another choke at the radio end.

Transformer Conundrums

The item I had more questions about was the step-up transformer.  A lot of conventional wizzdom surrounding the 7:1 turns ratio versions.  I chose to give myself more options and provide multiple taps, and use the larger ft-240-43 size toroid to allow 100w.   Hopefully this will give less core heating.  Then two turns vs. three turns on the primary was considered.  Initially I favored using three turns on the primary.   I expect 80m to be more useful than 10m going forward.   Physical reality – two turns seemed more practical with the 16ga wire I used. 

The other wildcard I threw into the construction detail was about sticking to the “norms” of putting the taps on nice-and-easy turns ratios.     While waiting on my toroid order to arrive, I stumbled across N8NK’s videos.  I found the playlist on EFHW and UNUN’s interesting viewing.  The main idea I fortified was to tap the toroid in several different places.  That would have been more versatile using 3:1 windings.  Even with 2:1 windings I still liked the range of impedances available by placing “irregular” taps, i.e not on the even multiple windings.  With 3:1 I had expected to place the taps on every 4th turn.  With 2:1 windings I thought maybe every 3rd turn but with 6 taps every 2nd turn was “good enough”.

The only genuine benefit that conventional “even numbered taps” provides is ease in predicting  the transformation factor(i.e., 7:1 turns gives 49:1 step up).  To switch the flip I decided to tap the transformer at 4.5:1, 5.5:1, 6.5:1, 7.5:1, 8.5:1 and 10:1.  (FWIW, that should be stepping 50 ohms up to about: 1013, 1513, 2113, 2813, 3613 or 5000 ohms.)  Just for grins, it is easy to test with the ordinary antenna analyzers and a resistor test box(or well stocked junk box).  

If it is important to your thought process, measure the damn unun to be sure.  To simplify, the secondary is actually tapped on turn #9,#11,#13,#15,#17, and #20.  With 2 primary turns and just 5 taps on secondary, tapping every 3 turns at #8, #11, #14, #17 and #20 should allow matching impedances of 750, 1513, 2450, 3616, or 5000 ohms.  That includes the obligatory 7:1 ratio for purists.  I only chose to use the odd taps as an appeasement to my increasingly contrarian curmudgeonly nature.

Precision Optional

 I figure to just use the antenna with the tap that provides the best SWR. I can then produce a cheat sheet for each band.  I would like to have a best choice for each band.  If it turns out the same tap works best for all bands – so much the better.   If they are NOT all the same tap I also want compromise choices that will allow one tap to allow operation on several bands without moving the tap.  Another tradeoff option – sometimes moving the tap will be easy, sometimes inconvenient.

Functionally we can call it good if some doing RBN compares to permanent dipoles prove it to perform acceptably.  The truth is I don’t care what the actual step up ratio might be.  I just want the antenna to function, and experimentally finding a good tap is “good enough”.  We are hoping that the taps provide enough options for multi-band operation with a good match.  It will be nice if a single tap is good on all bands.  It is not a deal breaker if changing bands requires moving a tap that can be reached at ground level.

Engineer the possible. Mind the trade-offs, because “best” can be the enemy of “good enough”.

Related Links(updated 2021/03)

End Fed Half Wave Experiment – Part 2
End Fed Half Wave Experiment – Part 3 Multi-Band End Fed Antenna

G0KYA, Steve Nichols.


Retroactive Filter Tuning with NanoVNA


Recently this NanoVNA product popped up on my radar, and like normal, I was a bit behind the group in discovering it. It is relatively newly available, but seems to be rapidly becoming known because it is both inexpensive and very functional. What a wonderful and useful project. There is a group devoted to the project. There is also a secondary product fork recently begun. The second fork will have a larger screen. Software will not be compatible between the two. (update….maybe more than one fork, rapidly changing).

The NanoVNA itself appears to well suited to the home hobbiest, both in price and utility. As an open source hardware design, being produced by various vendors, it is not coming out yet as a mil-spec “ruggedized” product. It is also not $50,000 USD. Also, caveat emptor. The calibration dummy load supplied with the units I obtained measured an intermittent 50K ohms instead of 50 ohms. A second unit supplied a load that measured 43ohms. [I used a known 50 ohm load for the calibrations.]

Dummy loads aside, it appears I wound up with a cheap copy of the cheap copy of the open source hardware. Yet both units appear to function, at least well enough for the 30Mhz of spectrum of interest here at W4KAZ. All images below were captured on a Samsung Galaxy S7, rather than spend a lot of time dorking around with rapidly developing beta software. Truth is – I was in too much a hurry to tinker to take the time for the software, which seems to be FB. Good enough is often “best”. Engineer the Possible. Plenty of time for software later.

Filters Tested

RTL-SDR:  The RTL-SDR 2.6Mhz high pass broadcast band filter.   This filter is quite good.  Its only drawback is that the cut off is above the 160m band.  This helped a lot in testing to find RFI problems, but I needed a filter that allowed 160m.  If 160m is not required this is an inexpensive rx only solution.   AE5X also has posted a quickie scan of this filter recently. My own scans…

W4KAZ Broadcast Band Filter:  While tracking down what I thought were RFI issues on the Red Pitaya CW skimmer, I obtained the RTL BCB filter above.  Because its cutoff is at 2.6Mhz I needed something with a lower cutoff frequency.   As a home brew experimental project I came up with a BCB filter, designed using the AADE filter design program, available from KE5FX.    

The BCB filter design is shown below, along with the projected rejection.  This design is intended to have the cutoff as near to 1 to 1.2Mhz as possible. 680Khz and 850Khz stations are respectively 1.5 and 4 miles from this QTH, and the nearest 680Khz is a 50Kw station.  The intent of the design was to null 680 and 850 as much as possible.   This filter also shows a DC short via the 100uh inductor.  It can be removed if 60hz mains noise is not an issue.

After construction the filter was originally function tested by checking S-meter levels from the AM band up through HF and a few spectrum glimpses using the Red Pitaya with SDR programs.  Using the NanoVNA is a lot quicker. In lieu of computer software for trace captures I just used a field expedient solution – snapping a photo of the teeny NanoVNA screen with my phone. 

It is nice to see the real world corresponds to theory.  The filter  shows a 3db shoulder close to  design at 1300Mhz.  There is a 2:1 SWR shelf across the 160m band.  Beyond 2Mhz it rapidly improves.  Quite good for my purposes.  Also surprisingly good for hand wound coils and ordinary NP0 ceramic caps thrown together without much[i.e., none!] testing of component values.  I am not certain if I want to chance tinkering with the tuning of the 680 and 850 notches.  Both notches came out about 100 KC lower than designed(not yet shown).

Band Pass Filters: 

The following set of band pass filters are all constructed based on the K4VX article “Band Pass Filters For HF Transceivers” .  A good project, but these were originally only swept for SWR and not a lot of effort to properly tune them previously.  NanoVNA to the rescue. 

10m Bandpass Filter  

As originally built, 3:1 SWR range is from about 24Mhz to32Mhz.  Minimum is at 25.7Mhz, and its usable on the lower end of 10m.

after NanoVNA tuning, a slight improvement across 10m:

15m Bandpass Filter

20m Bandpass Filter

40m Bandpass Filter

Able to tweak the 40m filter from -29.4db to -35.7 db, and filter covers 40m band easily.

80m Bandpass Filter

????where’d it go?!?!?!?!  This one was misplaced somehow……????

160m Bandpass Filter

Very bad news on 160m filter.  Looks like a new repair project – not even close to “good enough”!

Red Pitaya SDR as Core of CW Skimmer – Part 2, Notes and Updates

Additional Red Pitaya CW skimmer notes, last update 2018-08-22
for original detailed post see:  Red Pitaya SDR as Core of CW Skimmer – Part 1
Notes and Updates

Note 4, RX Antenna:  The skimmer system is now using the 3.8 wave inverted L as its RX antenna full time.  The only anticipated interruptions will be occasional 160m contests.


Note 1:  Skimmer station outage in mid July 2018, cause appears to be rx antenna related.

Note 2, Transformer:  N6TV identified a mini circuits 14:1 transformer that is suitable for use with the Red Pitaya on RX.  Expect the transformer to be available from Red Pitaya, or occasionally N6TV.  Available from mini-circuits vendors, but may be expensive in quantity 1.

Note 3, RX antenna:  Some what by accident I discovered that the 160m L I use for transmit seems to make a fine all-band rx antenna for the Red Pitaya skimmer set up.  FWIW, the antenna is about 140 feet of wire.  About 60-70 feet vertical, with the remainder making a dog-leg turn from top of vertical section.  From there it runs horizontally  NW to second support about 40 feet away, and a second sharper turn to the east, horizontally and slightly downward for the remainder which runs west to east.  The radial system is the K2AV type folded counterpoise system described in more detail at link.

Red Pitaya SDR as Core of CW Skimmer Station Rebuild.

[Updates, 2018-08-22, also see:  Red Pitaya SDR as Core of CW Skimmer, Part2:  A link to status updates and additional notes going forward]

[Updated 2017-07-11, also see text on my own compatibility issue]

Bob, N6TV has a step by step guide on setting up a Red Pitaya posted 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.  As of this date it seems wise to follow these instructions, or know that by diverging you may encounter issues of your own.  There is also an illustrated how-to guide now available from the folks at

[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.

Red Pitaya

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 [then]latest OS v0.96 and the SDR software.  This caused 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 support 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 a waste.  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 attenuation drops off rapidly above 1Mc 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 receive only 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: Be aware – As designed this filter is a short circuit at DC via the inductor at “dipole 12”.

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 BCB design here 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, not even 10 over S9.

S meter comparisons on the TS-590s using the W4KAZ BCB filter and built in attenuator
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
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
Block diagram of likely W4KAZ Red Pitaya SDR CW skimmer system

Important Notation[see update]:

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.  [Update 2018-12-23.  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.  Migrated to the updates 2017-11-15 here in the W4KAZ SDR setup.]

The Red Pitaya ecosystems come with default root passwords.  Suggest resetting your password ASAP.  Also, at least one of the pre-built ecosystems Pavel provides does not allow a persistent root password change.  I suggest using the 0.95 the current ecosystem from 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


W4KAZ Softrock Based CW Skimmer Station – 05) Si570 Programmable Oscillator for Softrock CWSkimmers – or for “Whatevah”

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

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  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

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 Oscillators.

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 :

  1. W4KAZ Schematic

    Schematic for W4KAZ version of Si570 Programmable Oscillator

    Schematic for W4KAZ version of Si570 Programmable Oscillator

  2. W4KAZ BareBones Parts List (PDF) (HTML with links)
  3. KB9YIG Five Dash softrock products page
  4. K5NWA ATTiny85 page
  5. PE0FKO Firmware page
  6. Document:


Xonar DX es SoftRock CW Skimmer

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.

Test condx:
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

Skimmer Notes

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.

Softrock Lite II

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….

Rocky rocks softly

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.

The Evolution of a 160m Inverted-L with FCP(K2AV FCP long version)

Saga of transitioning to K2AV’s FCP(folded counterpoise)

(Updated 03/13/2021 de w4kaz, add/edit links and link to newer K2AV FCP page)   NOTE: Please use this K2AV link for most current construction info

TopBand?  Wazzat?

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. 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.

Where O where does a 160m antenna fit?

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.

The Intermediate

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.

Decision Time

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.  [NEW link: K2AV FCP home page]  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

Schematic for W4KAZ 160m inverted L with K2AV FCP

Picture of W4KAZ 160m junction box

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.  This method makes it easy to do with an ordinary hand drill – 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 does not seem to have any adverse effects on basic function.

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 is scavenged 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!!
Bottom Line…..

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/likely that improvement is just a 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,  the results K2AV has had with his system, and more important, my own field testing during the CQ160m contest.  W8JI has done some comparisons of models.  But since they are comparisons to antennas that will not be practical at W4KAZ location, it is academic info.  For use here it is about the footprint and 80 foot radials are simply not practical HERE.

2021-03-14 Notation….Nothing Changed

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.


The K2AV reference page should be used for the most current work by K2AV.
* * *USE DATA FROM HERE:–> * * *

Historical references, related opinions, original subject matter posts, and a few older message threads on the TopBand mail list on pertinent topics:

  1. Original K2AV NCJ article “The FCP: A 160 Meter Counterpoise for a Postage-Stamp Lot “
  2. W0UCE’s accumulation of information on K2AV’s 160m ideas, including the FCP
  3. Photos from W4KAZ FCP install
  4. Older K2AV discussion of the FCP
  5. K9YC: “Working 160M From a Small Lot (and Larger Ones Too)”,
  6. W8JI on FCP, a comparison to antennas that I cannot have.
  7. Rolling your own FCP isolation transformer, IMPORTANT
  8. Topband: Where to place a preamp? Switching Beverages?
  9. Topband: K2AV 160m Folded Counterpoise (FCP), parts and winding for isolation transformer
  10. Re: Topband: K2AV 160m Folded Counterpoise Antenna (wire suggestions)
  11. Re: Topband: T-200 vs. T-300
  12. 2012-05-31, VO1HP FCP install
  13. Balun Designs commercially available FCP transformer

Other links:

  1. W1UJ :
  2. KY6R :
  3. IV3PRK(FCP @ HC1PF) :
  4. DL0WH :
  5. DM9EE:, and
  6. W8TN :
  7. WB5NHL :
  8. LA9XGA FCP :
  9. M0KWR:
  10. AC2RL article in RDXA Fall 2018 (see page 16)
  11. ?
  12. ?