Radio W4KAZ

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CW Skimmer Errors and RBN spots

After several contests, monitoring of the softrock skimmers has turned up a bit of a problem with using softrocks as the skimmer platform.  Very strong signals are producing a mirror image that is often reported as a spot to the RBN.  Certain to be annoying for the S&P packet crowd during a contest.  Annoying enough that a few flame mails have arrived.

The volume of the bad spots is relatively low on the lower bands, and more common on the higher bands.  40m is somewhere in the middle, with most of the bad spots being sent for domestic USA stations.

The problem is a combination of the hardware and software, both contributing to the problem.  A software fix could potentially be made to CW skimmer or to the RBN aggregator to correct for the problem.  Will inquire to the authors…..

In the meantime the best solution available is to throttle the RBN aggregator to allow only spots below the center frequency to be reported.  For example, the 15m skimmer is based on a softrock with a center frequency at approximately 21044.5Mc.  So for the duration of the ARRL DX CW contest, an entry in the “Notched Frequencies” will be active to not report 21044.5-21100 to the RBN.

That solution does nothing to correct for half of the possible bad spots(i.e., a strong signal above the center frequency whose mirror image is being spotted below the softrock center frequency).  But it should alleviate many/most of the actual bad spots, since most run stations prefer to operate as low in the band as they are able.

Open to other suggestions short of replacing the softrocks with better (yet unaffordable) hardware.

Update 20130217, 2140Z:  There are new versions of both skimmer and aggregator.  Perhaps upgrade will help.

More on Xonar DX Experiments

A thread over on the softrock user group list spurred the curiosity…..:

G4ZFQ has  RightMark test data for a high end Xonar D2X card, as well as several others.  An internet search found other RightMark tests of several other Xonar cards, all of whose test data show curve trends remarkably similar to those of the D2X, albeit with somewhat worse IMD, spurious, and noise figures.

The curiosity is the test data shows a roll off on the frequencies above 50khz.  The nature of the loopback test is an issue, but it also seems likely that using a sound card as the source may be having an effect on the test results at the higher edges of the sound card frequency response.  But signal generators as input to the tests shows the same general trend.  SDR at wider bandwidths pushes at these edges of a ‘sound’ card’s ability….So perhaps the SDR software is compensating for the expected performance drop-off at frequencies above audible levels?

The Test- (Pertinent Excerpt from list post):

Having not yet thought of a better way to do a meaningful real-world test on the sound card with what is available in the KazShack, I fired up the 80m softrock on the xonar DX.

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.  It would be useful to see what happens at the band edges when the best copy close to the center of the SoftRock’s scan range starts out at 20dB, 10dB, or 6dB SNR.

But with the WX here improving, all of that might not happen for several months.

Engineer the Possible…

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 Station

Added a new page to the skimmer station fun facts list.

The new page describes observations from using several different sound cards for both music and as the interface for SoftRock software defined radios and the CW Skimmer software.

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.

Skimming During WPX

“Don’t get cocky kid….”

Just when everything seems to be going smoothly, Murphy arrives.  Two days before the WPX contest, it became clear the 80m softrock had developed an issue and was useless.  It lost half of the signal, and so was useless(on 5/27) and required repairs.  Sideline that issue for now….

The 40m skimmer session kept right on chugging.  A couple of problems became clear.

  • The softrock will need better band pass filtering if they remain active during operations, or switching to shut them down during transmit
  • running CW skimmer at 192khz sample rate used a great deal of CPU time, averaged 45-50% CPU utilization.
  • Limiting the number of decoders helped somewhat
  • Reducing the scan rate to allow a 96Khz bandwidth drastically reduced the CPU usage.  Running at 96khz required an average of 15-20% of the CPU, even with the limit on the number of decoders increased.
  • The K9AY rx antenna worked well for the 40m SR skimmer.  The problem is it will need to be split and amplified for 80m and 160m as well.

All together, it looks like the skimmer posted about 8K spots while it was active during WPX.  Trying to figure out a way to check for errors.  Low priority – spot checking the spots showed most to be valid.

The 80m SR problem was resolved on Monday evening.  After having made three passes over the op-amp section, I made a fourth pass, concentrating on components in the “ring” side of the op-amp output, as well as the path back to the QSD section.  Also made a first pass over the transformer solder joints, using a higher wattage iron.  80m issue resolved.  Odds are it was in the op-amp chain(seems to be the most common cause of the symptoms), but I suspect a cold solder on the transformer was the real culprit.

Looking at the case from a dead home audio system as a permanent enclosure.  If I can fit everything in, it should be a good choice.  Time for a block diagram…



Skimming CW at W4KAZ

Note….Post dated this material to original date written…superseded by new reality…..

“All is proceeding as I have foreseen it…………..”

Been just about four years since the CW skimmer stuff really hit the contest rotary impeller. A bit of review…..

So in hindsight – I’m glad contest sponsors read my blog.  😉

Since the rule-parsing panned out to my immense satisfaction, it is easier to concentrate on the toy itself.  Since then, skimmer stations sprouted, and the Reverse Beacon Network was born.  That is a really interesting project.  Its a great tool for checking propagation, comparing station signals, and getting impartial signal reports.  Outstanding resource.

Unfortunately there is not a local skimmer station that is feeding the RBN.  Spots from MD are not always useful in Central NC.

So it with the moon in phase and the planets approaching the grand alignment, it seemed like time to look into the subject of skimming.


The Skimmer software comes with a component that is designed to work with the QS1R SDR.  That combination is likely the ideal solution.  So all I need is a fast Pentium i7 Quad core, and a thousand samolies……  Great idea, just not possible.

Much more possible….Combine a few Softrocks with some cast off circa 2008 computers.  Yup, that’s the ticket.  Rather than sit on my thumbs….Engineer the Possible.  O’course, the possible is not always completely practical.  Everything is relative.  What tradeoffs are reasonable?  Engineer the Possible.

It has been done before…AC0C has documented the challenges and his solutions.  Despite the validity of his conclusions, it is now possible to cobble together a scaled down version using scrounged computer hardware.  Using softrocks, it is now very practical to put together a skimmer package for 160/80/40/20 meter bands with obsolescent computer hardware.  The price/performance ratio of the softrock is a huge factor.  If they were a mass production commodity, they would probably cost under $10.

15m and 10m may be more of a challenge, so that has been shelved for the moment.  So the softrock solution is not perfect.  But there are solutions to that too.  Future project….

The current project direction

So the game plan is to skim on 160m thru 20m using softrocks.  40m and 80m softrocks are done.  Its not going to be as professional a finished product as AC0C’s, but it should function.  Reclaimed from the off-lease refuse stream are an Dell Optiplex 745sff and a Dell optiplex 360 SDT.  Both of these boxes require low-form-factor cards.  The on-board sound of the 745 leaves something to be desired, but the 360 has an on-board sound card capable of 192khz bandwidth.  So small form factor add-in cards are needed to run skimmer on multiple bands.  Four bands on two computers.

Other Naughty Tidbits….

The Asus Xonar DG is a small form factor sound card that turned out to be a fabulous bargain. It allows only 96khz bandwidth, but has excellent dynamic range for its cost.  Sounds great with music too.  Also had an Asus Xonar DX, which is higher fidelity than the Xonar Dg, and offers 192khz bandwidth with a softrock.  The sound card issue is the real sticking point in this design, but the Xonar cards are able to coexist with the onboard SoundMax devices in the Dell boxes.

Not so much luck with a Soundblaster Live 24.  Experiments installing and using the Soundblaster were problematic.  Compatibility issues with the other sound devices and SDR software crashes. The Asus cards are much higher quality, but attempts to pair either with the soundblaster caused problems.  Attempts to install both Xonar cards in the same system were also buggy.  So the Soundblaster is sidelined for later rainy day experimentation,  the ASUS cards are each on a different host system, and it is fortunate that the onboard sound cards are useable.

The final compromise chosen was to install the 192khz Xonar DX in the Optiplex 745 that has 48khz onboard SoundMax.  The Xonar DG is installed in the Optiplex 360 that has 192khz SoundMax onboard sound.  In testing the Xonar cards work very well with all of the SDR software tested.  The SoundMax cards are noticeably less capable, but not terrible.

Mix and Match

The skimmer sessions sound card pairings in daily usage are likely to be:

  • 160m…48khz on Optiplex 745 onboard sound
  • ……………..Center@????????,Covers ?
  • 80m…..96khz on Optiplex 360 Asus Xonar DG
  • …………….Center@3533950, covers ~3485 thru 3581
  • 40m…..192 or 96khz on Optiplex 745  Asus Xonar DX
  • …………….Center@7055015, covers ~6959 thru 7151@192Khz, 7007 thru 7103@96Khz
  • 20m…..192 or 96 Khz on Optiplex 360 onboard sound
  • ……………..Center@????????,Covers ?

Those pairings should spread the CPU load somewhat.  A live test on 40m and 80m during CQ WPX should give me a benchmark for CPU loading.  CW Skimmer allows the definition of the maximum number of active decoders, and I expect to get some insight on setting those values to help moderate the load.  Currently, allowing 500-600 decoders seems workable.

During 160m contests, the 160m skimmer will likely switch to a wider bandwidth card, at least 96Khz.  The fall contest season will allow more testing to determine if the 192khz skimmers will need to be narrowed during contests or throttled by limiting the max number of decoders – maybe both.  Also, the nature of any given contest may also make temporary changes to the line-up appropriate.  But that’s the basic setup.

Using the spots

The Reverse Beacon Network Blog has info on connecting to the RBN telnet server.  Highly recommend taking their advice on filtering!  The RBN server uses DXSpider documented on DXSpider Wiki.

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.


When I upgraded the dead computer a couple of years back, I stuffed the current machine(Dell Inspiron 545S w/Pentium Dual-core E5300 @ 2.6ghz) with 8GB of RAM, expecting to do some experimentation with running VMware or some such to tinker with PC based VM’s.  After looking around a bit, other shiny objects attracted more attention.  So, being easily distractable…..VM’s slipped down the memory hole.

Fast forward to present.  Looking over at the Oracle VirtualBox website, a bit of light reading showed that a lot of work has been done on their VM software in the last 18months.  More robust USB support, and a lot of bug fixes.  Its free for personal use, so give it a shot.

The VirtualBox software itself installed on Windows 7  easily.  Within a few minutes after that, A VM for an Ubuntu Linux partition was ready for the OS install.  Virtualbox is able to install an OS from an ISO disk image.  So after a few minutes waiting for the latest Ubuntu 11.10 version to download, the VM was ready to install.  It took longer to download the ISO than it took VirtualBox to install the OS(unusually slow day for the internet connection to blame there).

The quick summary is that Ubuntu runs well inside the VM sitting on a Windows7 host.  I expect that the opposite is likely to be a more desirable arrangement, but living in the real world, there it is.  I expect to use the Ubuntu partition to allow tunneling over to the Linux server box using VNC to control the desktop on the remote server.  Its possible to set that up using something like TightVNC under windows, but the whole thing is a lot simpler to configure in a Linux to Linux environment.  The VM runs on the windows desktop just like another windows application.  Nice and simple.

More complicated hardware interfaces are probably a lot more difficult to configure(if they are possible at all), but outside of some radio control software, I don’t expect to need to delve that deeply.  I suppose there will be latency issues based on some comments from N4AF, but curiosity may eventually point me in that direction anyway.

Unrelated sidenote, but after installing the 11.10 version of Ubuntu, I immediately ditched the “unity” desktop and reverted to “gnome”.  Another “Unity = new coke” example? ? ?  [Comments appreciated on this topic]

A second VM is now set up with a small Windows XP partition using the Windows XP license from the dead desktop.  It turns out that XP was a bit more difficult to install.  The problems were probably due to hardware conflict issues between VirtualBox and the host over the CD-DVD drive.  After ripping  XP to an on-disk ISO, installation made much better progress.

It turns out the XP partition will be handy for running the version of EZNec I have.  Later versions of EZNec have a 32 bit installer, but the last edition I have is using a 16 bit installer which will not work with 64 bit Windows 7.  So now EZNec has a home on the desktop again, even if its inside a shell running on top of the shell.  In fact, the EZNec install on an XP VM runs quite a lot better than I expected – much faster than on a P4 with 1 GB of ram.

So for some select older applications, an XP VM in the VirtualBox world is a viable option.  It’s a kludge, but potentially a very useful kludge.  Another very useful aspect is that the VM’s can be very easily copied.  Useful for backups and migration.  And always having a pristine version saved could be handy.  I’m tempted to start saving pennies for a multicore processor machine with the latest/greatest fast CPU’s and memory, and use a VM for everyday usages.   Also curious if running the VM’s over a Linux host OS ultimately makes more sense.

Latest-n-greatest is wonderful, but I just hate leaving behind programs that work perfectly well.  CT anyone?  OK, maybe not….

O’course the bleeding edge crowd will still descend into hysterics over the concept of “continuing to drive the 1984 Honda Civic”, but I figure they have enough cash in their pocket to not be concerned with the trivial expenses involved in their upgrades to all new replacement software.  If it were not just for a  hobby tinkering project, maybe I’d agree.

“Better” is such a subjective concept, aina?


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

(Updated 02/28/2012 de w4kaz)

(Updated 09/26/2016 de w4kaz, current links & match network schematic)

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. 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.

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.  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.  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!!
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 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:

  1. W0UCE’s accumulation of information on K2Av’s 160m ideas, including the FCP
  2. Photos from W4KAZ FCP install
  3. K2AV discussion of the FCP
  4. Rolling your own FCP isolation transformer, IMPORTANT
  5. Topband: Where to place a preamp? Switching Beverages?
  6. Topband: K2AV 160m Folded Counterpoise (FCP), parts and winding for isolation transformer
  7. Re: Topband: K2AV 160m Folded Counterpoise Antenna (wire suggestions)
  8. Re: Topband: T-200 vs. T-300
  9. 2012-05-31, VO1HP FCP install
  10. DM9EE (was DL2OBO) FCP page

Other links:

  1. W1UJ :
  2. KY6R :
  3. IV3PRK(FCP @ HC1PF) :
  4. DL0WH :
  5. ?