Radio W4KAZ

Thanks for stopping by the virtual KazShack. Feel free to comment - I often approve them.

End Fed Half Wave Experiment – Part 2

End Fed Half Wave Experiment – Part 1

The Antenna as constructed before tuning.

The Initial cut of the antenna and the completed feedpoint enclosure.

Having looked at many of the articles available on the WWW, I wound up favoring the design well documented by G0KYA, Steve Nichols.  When modeling the antenna I started out using a coil value of 67.5uh.  Then I ran the model using the appropriate value of impedance at each given frequency.  The coil as shown above is about 63 turns of 16ga solid insulated wire on a plastic coil form of just over 2 inch diameter.  That was right at the limit of the amount of wire I could lay down on the available form.  The completed coil resonated with a handy 22pf capacitor at 3.855Mhz, which calculates out to an actual inductance of close to 77.5uh.  With the coil value known, I re-ran the model to tweak the initial guestimates with actual values of XL for the model’s load.    Then cut wire for the 40m leg as well as the 80m tag end.  BEFORE tuning wire lengths are long, 71 feet and 15 feet(about 21.6 meters and 4.5 meters). 

77.5uh inductor, ~63 turns of 16ga insulated wire wound on a 2 inch plastic form.

77.5uh inductor, ~63 turns of 16ga insulated wire wound on a 2 inch plastic form.

The coil form used seems better for RF than PVC pipe, and is a one-off that happened to be in the parts bin, original source un-remembered.  I gave it a run in the microwave, and it showed little heating.  It’s other quality is it is 1/16 wall thickness, so most of the weight is the winding.  The coil is just over 6 inches in length.  The second choice for a coil form was going to be fabricated with a few layers of fiberglass and epoxy laid up on some sort of removable former.    The measured  value is only about 2/3 of the specified 110uh from the G0KYA document(original designer-????), but it comes down to the trade-off question again.  This 77.5uh coil should provide 3400 ohms XL at 7Mhz.  Hopefully that will be sufficient to isolate the tail.  Actual testing should be interesting.  

Step-up transformer in terminal box

This is the completed transformer installed in terminal box. 

It has two ft-240-43 toroids together with a two layer cover of teflon tape to make it more slippery for winding.  It is wound with a 2 turn primary and 20 turn secondary.  Taps are placed on turns #9, #11, #13, #15, #17 and #20.  For the capacitor I used three TDK 330pf 3kV 5% ceramic caps in series.  I went that route simply because I had more of that value cap handy than either 220pf or an actual 100pf.  There are no crossover turns – that seemed counter productive for multi taps.  I would have wound the secondary turns more tightly but needed to loosen the turns up some just to fit it in the box and attach the taps.

Closed box showing tap wire.

Closed box showing tap wire on top and counterpoise on lower right.

The feed point box is an ordinary Carlon 4x4x2 terminal box. Feed thru studs are all 1/4 stainless hex bolts.  I expect to attach the antenna to the 10:1 tap(located top center) and use a jumper to short down to the lower impedance taps as needed for best match rather than have the high impedance taps float.  The stud on the bottom right is the ground/counterpoise attach point.  If nothing else, the multiple taps provide handy places for extra hardware to replace wing nuts fumbled into the sand.


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.


Skimmer Outage – Temporary

The W4KAZ CW skimmer station reporting to the RBN is down, due to work in the basement in the area of the station.  The station is going to be down for at least another two weeks, it needed to be moved to allow for replacing the water heater.  Yes, hot water is more important to XYL than CW spots.  Go figure.

Station replacement may also be delayed by migrating the skimmer software to a newer computer running Windoze 10.  That may turn into a temporary situation, just a test run to verify the backup system is good-to-go.

Been a while since any activity of any sort, website updates included.  Been paying attention to other things, have not been active with radio much.  Maybe that changes – gonna take it as it comes.

Outage began 2020-12-29.  Anticipated end of outage 2021-01-15 at earliest.

Abandon All Hope Ye Who Enter THERE – i.e., Social Media Monopolies

Update, 2022/12/08

Ole Elon Musk bought hisself a crime scene when he  paid premium money for the Twitter application.  Looks like my pessimistic assessment of the evil inherent in social  media apps was  understated.   A couple of conclusions that fall out of the new info:

1) If Twitter is this bad it is a certain wager that every other social media app is doing the same shit if not worse.  Probably worse, especially in case of search engines like google.

2) Records are being destroyed right now at every other social media app.

3) We will find out much of this was directed by the government, factions within government agencies, and/or individual influential political figures.




Original follows:

Fascinating how in only a few years “don’t be evil” mindset morphed into “Embody Evil”, aina?

My original estimation was that social media was a waste of time. Then I thought it might be a viable way to communicate. Now it appears to have evolved into an information cemetery, where good ideas go to be buried, stealthily modified, or more perniciously – forever forgotten.  Then you can expect gaslighting as to whether it ever existed.

My own little circle of self flagellation here on the www-interwebzz is where I keep notes on projects. It is easy to search, and provides mechanisms to catalog and gather related items.   When required most of the content edits are dated.  All of it for my own uses, but most of it public.

Social media originally set about in a similar fashion, providing less motivated folks a method of establishing a personal web presence for whatever reasons.  The major use I found for it was reconnecting with transient friends.  Folks who are good people, who one maybe loses touch with when jobs are changed, people move, or whatever. 

As time marched on, monopoly power was aggregated without limit.  Bigg fish ate liddle fish.  Monopolists collaborate.  Options dwindle.  Sinecures established and fortified.

One of the interesting permutations is that a lot of folks who had previously set up blogs or personal websites abandoned them in favor of the “new shiny”.   Another facet is that few people understand that social media sites don’t really work the way they seem to believe they do.  Rather than proactively going to content a person wants to see,  folks passively wait for the content to be pushed to them via the application.   The applications have minds of their own, and their aims diverge from those of the “sheep” they curate.

Social media monopolies evolved and redesigned the concept of a feed.  Big Brother pushes curated content HE wants a person to see rather than what a user thought they were signing up for.  And Big Brother also HIDES content he does NOT want seen.  All via the “Holy AlGore-ithm”, whose arcane ways are mystic and adjudicated by high priests of increasingly Orwellian nature.  

These problems seem a lot more pernicious in the long run than the whole raft of probable privacy violations – an entirely huge issue of its own.  Generally, if the only source for information on a subject is going to be on a social media site, I have decided it is no longer worthy of interest.  Pass. Cashiered.  Dead Parrot. 

Printed copies of everything of sufficient interest are now necessary and worthwhile.  Otherwise the airbrushes are sure to come out and Trotsky is deleted wherever he might appear.  Keep a hard copy of favorite books and reference sources.   DVD copies of any video of interest. And multiple offline backups of all digital content, especially if it might be even slightly politikkkally inkkkerrekkktified. 

Another example of webb apps gone astray is U-toob.  Once a place for individual and start-up creators, U-toob has decided to partner with dinosaur media to try to save their bacon.  Dinosaur media video links are now pushed, while many individual content creators are suppressed or extinguished.   Any company that was once associated with a motto “don’t be evil”  is probably overcompensating for their own malign intentions.  Seems obvious in hindsight.  The only surprise is that the evil has been phased in so gradually. 

So I have come full circle, more or less.   It was bad enough when old school media was pushing propaganda.  With old school print media it was once a lot more difficult to 1984[i.e., selectively edit] articles, texts, and scientific journals.  Widespread library archives on microfiche were hard to alter.  Today the edits happen in real time, and nothing is intended to be permanent.    Now that modern Big Brother gnu media have fully embraced content modification, censorship, propaganda, and behavior modification techniques, it has become more of a roadblock than an information highway.  

Takes the sheen right off.  May as well stay here.  All social media terminated.  If they want the personal data going forward they can work for it.  Lotsa luck with that.



Ghosts In The Machine-Red Pitaya CW Skimmer-Debugging BCB Interference

Many thanks to Guy, K2AV for tips, suggestions, and testing assistance to help resolve the following problems.

An unanticipated problem with fixing broken antenna systems is that it begins to work better.  Well – “duh”, right? 

After making repairs to the antenna switch and the 160m inv-L over the past couple of months,  the antenna systems are nearing the end of a minor overhaul.  Since about May, the CW Skimmer has been using a K9AY as the main RX antenna.  For the period of 2 years prior it has been using the 160m Inv L as the RX antenna, until problems cropped up in May 2019[a broken connection on the feedline at the switch box.]

After  correcting the broken connection and re-assembling the skimmer station, K2AV reported having spurs on harmonics when testing on 160m.  Upon a closer I found several other stations for which the SDR was also generating harmonic spurs on higher bands for signals of 40-43 DB SNR into the skimmer station SDR.   This was resulting in bad spots to the RBN, and as is sometimes noted “results may be unpredictable”.

All of the spurs appear to be caused by overload mixing from nearby BCB stations on 680, 850, 1360, and 1510.  Some of the problem was previously handled with the BCB filter constructed with notches tuned for 680 and 850.  Upon re-assemble, the BCB QRM was still sneaking in.

The bulk of the issue has been resolved by bonding the BCB filter enclosure directly to the SDR enclosure.  In a belt and suspenders approach, I constructed a second filter that has a higher cut off frequency.   It appears to function as designed, notching 1360, 850, and 680.  It adds about 20db attenuation at 1510, and rolls off at about 1650 while applying less than a db attenuation at 1800 to allow 160m into the system.  This second filter was placed at the input to the skimmer station preamplifier in the hopes of reducing the interference further.

Currently the result appears promising, as the signal SNR numbers from the skimmer seem to have benefited from the dual filtering scheme.  Perhaps the stations at 1360 and 1510 were causing more overload than I originally thought.  While neither is as strong as 680 or 850 into this QTH, both are over S-9 on the base radio using the same antenna for RX.

So now the curiosity about BCB filtering has been tweaked, and experiments modeling and building alternate filter choices are continuing.

If you are seeing bad RBN spots originating from the W4KAZ skimmer, please email the info so I can attempt to remediate the problems.


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”!

2019 IOTA de W4KAZ From Cape Lookout NC

2019 brought another solo operation for IOTA, but return to Cape Lookout for the event.  Weather was much better than 2018, the only WX challenge being the winds.  Normal for the islands on the NC coast, and very agreeable for comfort, but it caused the only bit of trouble for the antennas.

Antennas were set up on Friday.  This year two folded dipoles were used, one for 40m and the second on 20m.   A hy-gain AV-18VS vertical was set up in the unlikely event 15m or 10 would open. (Neither did for me)

Checking the tuning on the antennas had me chasing shadows for too much of Friday afternoon.  After sorting out the feedlines, there was still an SWR problem on the 40m folded dipole.  These had been tested at home before the contest, but had been tugged on quite a bit trying to straighten the mast in the high winds.  So as a fallback measure I hoisted the 40m/20m trap dipole, and tabled the folded dipole problem.  In the end it turned out to be a problem with the antenna analyzer rather than the antennas.  Since it was already in the air, I just re-positioned the trap dipole to be at right angles to the folded dipoles.   But that was after all too much walking from shack to antenna several times looking for problems.

The remainder of Friday evening was spent relaxing.  It was more of a vacation than an operation, so time for beverages and a nice cigar was available.  A nice spot for stargazing was found on the front steps to the cabin, and several nice meteor streaks crossed the Milky Way.

One of the best moments was a visit by Chris, WX4FLY. Really enjoyed meeting Chris,  learned a lot of info in our chat.  I also got an eyeball QSL card that may be one of the best custom cards I have run across.  Thanks Chris.

Radio conditions at the start of the contest were poor.  Radio conditions in the afternoon were poor.  Radio conditions in the early evening were poor.  Radio conditions overnite were poor.  Interest in operating the contest was low, so it was all done in a series of segments lasting 30 to 60 minutes.   After a decent hour or so on 40m after it opened, I received a final distraction in the form of a phone call from a long lost acquaintance.  Also a cold beverage and a nice cigar.

Call  SO2R Remote CW Qs CW Mults Ph Qs Ph Mults Op Time Score Club
W4KAZ * * 84 20 16 5 10 18,750 PVRC

I included an extra day on the end this year to allow packing up to be more relaxing, allow more relaxing, beach side relaxing, and to allow a bit of relaxed operating in an activation for Parks On The Air.  The parks hunters were a lot more plentiful than IOTA contest QSO’s, so I handed out 60 or 70 Qsos for Cape Lookout Seashore, a successful activation.  For that I used the vertical antenna on SSB, just to give it a shakedown of sorts.  All of the antennas and outdoors kit was packed before sundown, and another enjoyable evening of looking for a good fireball followed.

The island was hit pretty hard by hurricane Florence in 2018, and again by Dorian in September 2019.  It had changed since 2018 IOTA, and I imagine it will have changed again.  Hopefully damage was not as severe as the cabin area to the north, which had a new cut that ran directly through the cabin area, plus lots of other cuts and beach erosion.

The stiff breeze helped keep the islands indigenous obnoxious life forms under control until almost time to leave.  Win. Win. Win.

More interesting than the IOTA contest……The lack of decent 20m conditions had me out experimenting with the camera instead. 

And that, a sprinkling of meteors across the Milky Way,  combined with the mild weather to make the trip a winner..


Experimenting With Trap Dipoles- Part 2

see: Experimenting With Trap Dipoles – Part 1

Those coil and cap experiments described in part #1 eventually led me to the ‘best’ compromise solution for my situation. In the end I chose to build traps that were resonant below the higher band. I also chose to use cap values on the smaller end of the capacitance value range.

Sadly the Panasonic capacitors are no longer available. Possible TDK replacement are being tested. These TDK caps are physically smaller, and only 2Kv rated. I intend to use these in series/parallel groups once I determine the best values to stockpile. (TIP#x: leaning to several caps in series to extend the voltage rating) (TIP#x: Also decided to mount the caps in slivers of PCB, and use generous solder on the pads as well as not clipping the leads short, all in a hope to have that function as heat sinking).

Antenna Experiments:   In testing, these capacitors worked well on xmit for the first 20m/40m trap dipole, but I ran into problems with a 10m/15m trap. Using 33pf with an inductor of about .92uH I had failure of the capacitors while testing the antenna. 

As an alternative on 10m I used a bit larger inductance and a piece of rg8x coax as the tuning capacitor(low value approx 8-9pf). No final verdict on this solution yet, but the antenna functioned for light usage in 2019 WPX cw contest. Antennas will be used at 100w levels, so these cap variations should also prove suitable for this project. If weight is not an issue, gimmick caps from coax are viable choices, though I’d not use them with the traps resonant close to the operating frequency.

Alternatively the 20m/40m dipole has now been used in two different contests with success. A second 20m/40m dipole was constructed, using smaller coils and increased capacitance. This second experiment was less stable than the first, with the 20m SWR increasing slowly. Presumably the capacitors were heating and having the same problems as the 15m/10m model.

What Did NOT Work:  In the end, the experiments using larger values of capacitance proved to be poor choices for practical reasons. In the case of 10m, the caps failed outright. In the 20m case, the caps showed instability in the form of rising SWR, likely because they were heating. A revised 20m dipole with traps using a larger coil and smaller values of capacitance proved to be stable. Tip#1….Marginal caps can maybe stand the abuse in a trap if the coil is larger.

At this time I also chose to move the resonant frequency of traps a bit farther away(lower) from the operating frequency on new construction. This resulted in :

  1. the dipole legs being shortened,
  2. the impedance on 20m seemed more stable,
  3. The bandwidth on the lower band(40m) was decreased
  4. Precision in component selection becomes less critical

That set of compromises suit me, as the capacitance values are readily available, and the overall antenna length is reduced slightly, without any serious performance compromises as compared to an ordinary single band inverted V.  The antennas will be tuned to favor the CW segments, and if needed I will use the radio internal antenna tuner(at the home station) to find a match for SSB if required for 40m.  The tuner would likely only be required at the upper band edge if at all.

What worked well enough – Final Versions Constructed:  RBN testing of the trap dipole versus a normal 20m dipole showed enough uniformity in results that I am not concerned with trap losses.  The end result was a set of dipoles both for permanent use at home and several variations made as light weight as possible for portable operating.  The final 20m/40m dipole for the home station was constructed with the traps resonant at 12.650Mhz.  A coil with 14 turns close wound on the 1.5″ form was used with a capacitor constructed of several ceramics in series giving a value of 23pf. 

A 40m/80m antenna was also constructed.  These traps used a coil of 12 turns on the 1.5″ form and capacitors in series parallel for a value of 100pf.  Resonant frequency was 6.65Mhz.  For future construction this design will likely be modified to move the trap resonant frequency down to the 6Mhz range by increasing the number of turns on the coils while using the same 100pf capacitance value.

A practical benefit of having the resonant frequency away from the operating frequency is that component selection becomes less critical.  By selecting a resonant point below the band rather than on or near the band, it is not required to have values to resonate at an exact frequency.  Instead, it is only required that each trap resonates at close to the same frequency.   This is easier to tweak by adjusting the coil, and it becomes fairly simple to have traps that can be adjusted to within 100hz of one another.  The caveat here is that the dipole legs are different based on the trap frequency – but these need to be trimmed to length anyway.  [It is possible to easily replicate antennas if the traps are easy to replicate. ]  So for a 20m/40m dipole, it makes little difference whether the trap is resonant at 12.5Mhz, 12Mhz, or 13Mhz, so long as the antenna legs are trimmed properly for each.

My experiments show that having the capacitive reactance at the higher operating frequency be in the order of 400-750 ohms seems to reduce the current flow through the caps.   Probably this is enough to allow otherwise marginal caps to survive without heating and/or exhibiting SWR variations on xmit.  The voltage rating needs to be sufficient, and this can be aided by using several caps in series.  The caps in use here are all 2kv or 3kv, and used in series to increase voltage ratings.  This is sufficient for 100w levels, but unlikely to survive at 1kw or 1.5kw.   I have also mounted them on bits of circuit board to keep the leads short and provide a tiny bit of additional heat sinking.  Again, good enough for 100w, but QRO – probably not.

Experimenting With Trap Dipoles- Part Numero Uno

The Project and Situation: After quite a bit of trying over the past 15 years to find the best way to pull dipoles up into the closely packed trees in the yard it is clear the options are limited. Having the dipoles favor the NE/SW directions are the goal, but the arrangement of the best supports make this difficult. To beat this problem a combination of single band and multi band fan dipoles were used. [No, the “chainsaw solution” is not an option – yet.]

The primary supports are now occupied with supporting a 160m inverted L and another with a vee dipole for 80m. These are not high enough for direction to make much difference, but are in convenient locations. So everything else needs to fit around those two primary constraints.

The current problem is that there is really only one support that easily allows stretching out the legs of a 40m dipole in the desired directions while also achieving a good height for 40m(almost 50′). The other high supports will only allow the antenna to be deployed favoring a N/S direction(i.e., legs are stretched out E/W).

Using fan dipoles has come with its own practical problems. The dense tree branch coverage tends to tangle in the multiple wires of the legs. Then the fan legs have become entangled in heavy winds. So it is both a problem deploying the antennas, but also the SWR issues when legs are entangled after bad WX. An ongoing maintenance issue.

Alternate solution: trap dipoles. With dual band trap dipoles, it seems like it may be easier to arrange the antennas in favorable directions AND at good heights. The traps are relatively small compared to the mess of multiple wires on a fan, so also maybe it will be a bit easier to navigate dense branch cover of the biological deciduous antenna support structures. The downside is in the extra effort required in constructing the traps, tuning them to desired frequencies, and tuning the antenna legs for each desired band.

What’s the frequency, Kenneth?!? Using EzNEC 6 I ran models with trap data. Based on those results I initially decided to use traps tuned for just above the top frequencies of any given band(e.g., on 20m tuned for 14.400). I’m willing to live with the trap losses for the advantage of maintenance simplicity. Models showed tuning traps for the top end resulted in wire lengths that are the same as a single band dipole, or slightly longer. I then chose to build antennas with traps above the high end of the band based on the following.

  1. A trap resonant frequency above the band results in the dipole wires being the same length or slightly longer than the single band dipole at the trap frequency
  2. A trap resonant frequency below the band requires the dipole wires to be shorter than a dipole for that band. This might be worth pursuing if trying to reduce the antenna length.
  3. there were already a few spare dipoles laying about, and if the traps project flopped they would still be usable mostly intact if traps designed above band,
  4. I’ll probably be mostly using them on CW so maybe a tad less loss with trap rez at opposite end
  5. the gut feeling that a 20m trap resonated at 13.900 would maybe have more loss than the trap at 14.4 when used at 14.025.
  6. NOTE: SEE Part 2 for notes on how these initial assumptions changed!

Research: The traps will inevitably add unwanted weight to the antennas, and I wished to keep them as lightweight as possible. The reasoning for light weight was to extend the project to portable dipoles deployable on telescoping fiberglass masts. So I ruled out using one of the many coaxial trap designs simply to save weight where possible. For coil forms I chose to use small pieces of 1.5″ plumbing waste pipe cut from small sections of what is sold in the US as a “drain tail piece”. This is thin wall pipe, and much lighter than ordinary schedule 40 PVC. The second form material tried AND ABANDONED is 3.4 inch PVC sched 40.

Excluding the coax trap articles, there are relatively few trap dipole projects written up or documented in places accessible via internet searches. The best[most relevant] source is an ARRL antenna book article on a 2 band trap dipole. W8JI also has some interesting trap info published. Although it does not cover the specifics on the options I chose, it led me to the final result. My choices were made based on materials already on hand(wire, capacitors, and coil form material). Engineer the possible.

Initial Trap Construction: The available values of capacitors also drove the selection of trap resonant frequencies. On this point I made an effort to follow W8JI’s information and make the traps resonant off of the desired operating frequencies to minimize trap losses. Beyond this guideline I could locate nowhere any info to indicate if certain values of inductance vs capacitance were better or worse. A larger inductor will allow the antenna to be shorter overall, but the length of the dipole legs was not a restricting parameter for my project. This was merely about having the dipole resonant on 2 bands. Also, the capacitors are 2KV and 3KV 5% tolerance ceramics from Panasonic that I have used previously in band pass filter projects with great success. (NOTE: MORE ON THIS LATER!!!)

Coil Guidelines????: Guidelines for winding the coils are also a bit of guesswork, beyond W8JI’s testing results that show the highest losses occur on the resonant frequency of the trap. I simply started with the inductors, targeting a value of 6uh, initial turns counts generated by a random calculator found via internet search. Then trial and error on actual coil winding. Calculated inductances are based on trap resonant frequency measurements recorded and on the assumption the 5% caps were the most accurate component. Inductances are then calculated from cap face values and resonant frequency.

Test coils for the traps were close wound with #14 THHN stranded housing wire. They were close wound by hand as tightly as possible onto the forms. Coil Q is probably lower than it could be, but the close winding was a compromise accepted for ease of construction and ease of replication. Four inch lengths of 1.5″ waste pipe and three inch lengths of 3/4 inch PVC were tried. The latter were discarded as unsuitable.

Experimenting With the Coils and Caps: The 5% Panasonic caps on hand typically measure very close to the marked nominal values, much better than any 5% or 10% silver mica caps I have used in similar projects. I found that coils wound with similar technique and the same number of turns would reliably resonate within a range of +/-100 to 200hz. Generally the accuracy and reproducibility is better at 7 and 14 Mhz than at 28Mhz. The coils at the higher frequencies have fewer turns, and smaller differences in inductance and capacitance have a larger effect on resonance.

A group of several capacitor values were used along with an MFJ-259C as a grid dip meter to find the resonant frequencies. Pickup coupling coil was a coax jumper terminated on the business end with gator clips and a short length of #14 wire formed into an adjustable sized loop.

Some initial experimenting with the number of turns on the inductors was based on these available values of fixed capacitors. The first inductor was 12 turns on the 1.5″ forms, then resonance was tested with the values of capacitance that were on hand, or able to be easily derived using series and parallel pairs. It was then relatively simple to find the number of turns needed to be able to produce a trap resonant at a given frequency. I also wound coils on the same form material using 7 and 9 turns, and measured resonance for these.

Experimenting With Trap Dipoles- Part 2


Field Day 2019 – 1B NC de W4KAZ

2019 Field Day was once again a solo effort vacation camping at Carolina Beach. 

WX: 2019 WX was for the most part much better than 2018’s trip to the same location.  Temps were cooler, but the rain played a game of cat-n-mouse for the duration Saturday and Sunday.  Lessons learned in 2018 led me to use a picnic table and a tarp cover for the station, and limit the tent to sleeping and dry storage.  This worked very well, and is the plan for all future outings of this nature.

CAMP: Arriving on site Thursday afternoon, setting up the camp was not rushed by anything besides the chance of rain.  So the tent went in first, and the shade tarp was set up over the table for a rain refuge.  The shade tarp/screen tent is the NoBugZone, an idea I got from a vid by youtube channel “Outdoors On the Air”,   ordered from a sporting goods company in Canada. 

It turns out the NoBugZone was very nearly ideal for the way I chose to use it  in “spike camp” manner over a campsite picnic table.  That turned out to be useful soon after setup, as the rain came in about 5pm.   Friday was clear and warm, but the clear WX gave way to scattered storms on Saturday.  Set up Friday afternoon went well enough, deploying three telescoping masts for the antennas.

Antennas, Station, and Operating Condx.:  Decided to play with alternative antenna ideas this go around.  The recent projects at home prior to FD were some experiments with trap dipoles (in-progress-post coming late August 2019) in an effort to get a physically easier and more reliable method of multiband antennas than the previous fan dipoles.  So for this FD I chose to us an 80m/40m dipole and a 40m/20m dipole at 90 degrees to each other.  For 10m/15m I went with a fan dipole as a quick solution.

The station was once again battery powered, this year augmented by an extra solar cell to help with the mostly-shaded location charging.  The rig was an Elecraft K2.  Station & antenna set up Friday afternoon was fairly smooth, with the only problem being the fan dipole, which was difficult to trim to resonance.  

20m gave up the most Q’s.  40m would have been good were it not for high local QRN which was a tremendous problem, limiting 40m to S&P.  80m condx were better than expected given the local storms.  Operating was interrupted at least three times Saturday by passing storms tossing lightning around.  One of the breaks was prolonged by prolonged rumbles in the distance.  Not a big believer in staying on the air in bad wx, so erred on side of caution.  O’course, more cigar breaks that way was not a problem. 

Lessons?   The biggest lesson was probably related to tuning the 15m/10m fan.  Should have had that task handled before showing up on site.  10m didn’t show itself, so the time wasted was pointless.  The next lesson was finding out a cigar lighter makes an excellent pocket sized soldering torch if and when the connections are arranged for torch work.  The screw-in mast bases are champs.  The Spiderbeam 12m mast is too flexible for most of my intended uses.  The NoBugZone was really simple to set up using a tree support on one end and a pole on the second end, and not much more difficult to set up using two poles and guy lines.  It was also easy to adjust the sides for inclement wx.  Suited my intended uses perfectly.  The antenna plan was valid, as the two 40m antennas showed good results in different directions, but that was restricted by the QRN and the storms.