Radio W4KAZ

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About Time

2021 FD W4KAZ 1B NC from Cape Lookout

Very part-time and casual Field Day this year, mostly a vacation break at Cape Lookout National Seashore with a couple of tag-along non-ham guests. Set up of the station late Friday afternoon was pretty low key. Not a lot of work involved. Planting two auger bases into the sand and mounting two telescoping masts was very simple. The 40m EFHW went up soon after. A folded counterpoise radial for 80m was laid out along with a separate feed point box for converting the antenna into an 80m quarter wave vertical as needed. The station was fully set up and tested Friday evening.

Station

The FT-891 was used along with an MFJ external tuner, mostly for its ability to double as an antenna switch. Computer logging with N1MM was tested and ready. Very simple. The most complicated part was configuring the sound card settings to use the computer for voice keying. The station was completely battery powered, and the battery was supplemented wit 200w of solar panels. Everything tested and working early Friday evening. Just in time for bacon wrapped shrimp kabobs, supplied by tag-along companions. And the obligatory whiskey and cigar break.

Saturday, time to start

Count on Murphy to make an appearance, RIGHT at the start of FD event. Somewhere along the way the logging computer went to sleep causing N1MM to delete the logging files along with all of the settings and drivers for communicating with the radio. The first hour was blown trying to re-connect N1MM with no success. So it was time to ditch N1MM in favor of using Writelog. The only reason N1MM had been set up was that it could connect to the FT-891, which I cannot get set up in Writelog. Switching out to the Elecraft K2 was considered, but instead decided to forego computer-to-radio comms and do band changes manually. That was certain to have caused some log errors, but it was simpler than switching radios. 

It turns out there was no burning reason to rush. Saturday conditions were none too interesting, with little activity on 15m and 10m.  The relatively weak antenna for 15/10 did not help that situation. Or maybe everyone has switched to digital modes. It also became apparent from RBN spots that the antenna orientation was heavily favoring Europe instead of the US on 15m and 20m. So a bit of SSB S&P on 20 and 40. Also took the opportunity to fiddle with the antenna by removing the jumper to make it a 20m EFHW. This worked better for 20m in the short time on the air before dinner.

Being mostly casual, the folks that tagged along for vacation time pulled out the night’s meal. That was later accompanied by a bit of whiskey and cigar time. When the tag-alongs decided to turn in for the night it was time to get back to radio for a bit around 0400Z. Being 80m time, a foray out among the bloodthirsty nighttime island fauna was required to make the manual switch from 40m EFHW to 80m vertical. A nice hour on 80m proved the function on that band.  Pretty good for as last minute kludge idea.  In bed for the night by 0500Z.

Day 2 – Sunday

After a shift on breakfast duty it was back on the air at 1015Z. Worked a few more on 80m before switching the antenna back to 40m EFHW configuration. Then it was a CW run on 20m, to 40m, back to 20m for a good hour. Did a lot of band hopping after the 20m run through 1630Z and called it quits early. As always, tearing down the station and antennas went really quickly. Plenty of time to enjoy the afternoon. The FD log ended with 250 Qso’s – 25 SSB and 200 CW.

CALO wx

The weather over the entire weekend was really nice. Most of the weekend had a cool ocean breeze blowing, instead of the more normal southwest blow. Skies were overcast the first two days, but began clearing Saturday. Sunday evening produced a clear sky and a flowing Milky Way which was followed by a later moonrise just past full moon. It is interesting how brightly lit a desert island becomes under a full moon.

 

2021 WPX CW on 40m EFHW-[Extending a 40m EFHW as an 80 Vertical]

Very casual

The wpx operation was very casual.  I spent a lot of the time just tuning around the bands listening.  The beginning of a CW contest are always too fast paced for my mediocre CW skills, and taking a mental picture of band conditions was more fun.  The bands sounded “brighter” than at any time in the past couple of years.

As a quick-n-dirty mod, I used a second feedpoint to attach the efhw to an 80m folded counterpoise. This is to allow 80m operation by shifting the feedline and using a jumper to bypass the transformer.  \/expanded description below\/  This gave the antenna resonance on 3.625Mhz.  To drop the resonance into the CW segment I wound a 6 turn coil on a 1.25 inch form.  That is inserted at the bypass jumper with faston connectors.  To raise the resonance to somewhere near 3.8Mhz a 3kv capacitance of about 500pf does the trick.  80m was good-to-go. 

Dirty Tricks Department

So as luck would have it, the good band conditions made testing on 80m less useful than I hoped.  20m was open until at least local midnight (0400Z), and probably was open to somewhere all night.  On Friday night few ops moved down as far as 80m with 20m and 40m providing a bottomless pit.  It did allow for gathering some info from the RBN spots, which look like either the band was open in famous fashion, or the EfHW was doing a decent job.  Maybe a bit of both, as the 80m spots looked pretty good, as well as showing up on some skimmers not normally hit with permanent inv-vee.

The antenna was also able to work most of the stations heard on 10m.  That’s a change over the few other recent outings.  15m was a bit of a mixed bag.  20m responses were comparable to other experience with dipoles.  40m seemed unusually good, but it may be more due to the very quiet sounding band conditions.  On Sunday a short 40m run coincided with the band opening to Europe, and it is shown in the RN spots.  The RBN spots started out as US only.  By the end of the 60 minute run there were several EU RBN stations showing 20-30db SNR, and a slow growth in calls from EU stations.  Too bad the contest was at its end.

The 80m Inverted-L Mod

The first attempt to use on 80m, the transformer was shorted out of the circuit and the radial attached to the ground lug.  This did not work as expected, and more testing is needed,  The first thought is the EFHW 120pf capacitor to ground needs to be removed from the circuit for the vertical.  The quick field expedient kludge was to move the coax to a feed point not sharing ground with the EFHW box.  The first test used a single radial cut for 80m. In that configuration the antenna resonated a bit below the 80m CW band segment.  Resonance could be shifted upwards by inserting a series capacitance at the base of the driven element.  SWR was very favorable at each resonance point chosen with about 150 to 200 kc of 2:1 bandwidth.

A second option was tested, using a folded counterpoise instead of the single full length radial.  In this configuration resonance was at about 3.625Mc.  A 6 turn coil inserted in series in the driven element dropped resonance to 3.54Mc, and capacitors can be used similarly to raise resonance to upper SSB band segments.  In this configuration the best SWR was about 1.8:1, and bandwidth more limited.  Easily stretched moderately with an antenna tuner.

The folded counterpoise version was used in the contest with great success.  This is going to require a lot of testing to decide if either version is a better 80m performer.  For my purposes, the FCP version is compact and easy to set up, so it will be the one used.

Potential next project: using relays to allow remote switching, both for the transformer taps when in EFHW mode, and for switching components needed to operate as a standard vertical.  Hmmmmmm

????photos coming 2021-07??????? 

Conclusions

The kludgy fix for adding 80m was an outstanding low effort method for stretching the single driven wire to use on another band.  The cost is the time used adding the FCP radial on deployment and later some manual band switching while operating.  It would not take a lot of effort to add a few relays to allow remote switching – a possible future project.  This EFHW would make an outstanding option for quick deployment by folks stuck in enemy territory where permanent antennas run up against tyrannical HOA rules.  The whole thing can be deployed or removed easily in less than 15 minutes with a bit of planning and practice.

Having a tapped transformer allows a very good match on each of the five main bands of interest in contesting.  I think using the 80m option using a folded counterpoise and 40m EFHW driven element as an inverted-L vertical the seems to be at least comparable to the version with the loading coil and 80m tail extension.  It is easy to deploy and switch, and inserting a small coil at the base was easier than tuning the 80m loaded EFHW.  An 80m FCP is 32 feet long, so it is fairly compact also.

EFHW Experiment Part5

Adding 40M

Adding a linked in tail to the 20m/30m EFHW turned out to be about as easy as you might expect.  The 40m EFHW was tuned for 7.100.  The other bands could be easily matched by selecting the best match via moving the transformer tap. 

The links at 20m and 30m will allow a lot of versatility at the cost of lowering the antenna to connect or disconnect the links.  Likewise with the transformer taps.  So a bit of footwork is the tradeoff for multi-banding.  But its not just the band changes.  Judicious configuration choices allow the possibility of multiple choices of radiation patterns.

BAND TAP Best SWR SWR range to expect
40m 8.5:1 7.1(1:1) Entire band, (1.3–>1.6)
30m(j) 8.5:1 10.25(1.6:1) Entire band, 1.6:1 with wire drooping
30m(j) 8.5:1 10.1(1.3) Entire band, 1.3:1 with wire pulled taut
30m(j) 7.5:1 10.3(1.4) Alternate tap,1.4:1 with wire pulled taut
20m(40m-tail) 6.5:1 14(1.4) Entire band 1.4–>1.6)
20m(no 30m/40m tails) 8.5:1 14.025(1.4) Entire band favoring CW section
15m(40m tail) 4.5:1 21(1.1) Entire band 1.1–>1.8
15m(j) 4.5:1 21.010(1.4) Entire band under 2:1(wire drooping)
15m(j) 4.5:1 21.010(1.0) Entire band flat with wire pulled taut
10m(40m tail) 6.5:1 28.0-29 Entire band with tap 3 , 2 or 1
10m 6.5:1 28.000-29.25 28.00 thru 28.800 under 2:1(swr 1.2:1 on CW)
10m 8.5:1 28.00(1.4) 28.00 thru 28.75 < 2:1(swr 1.4:1 on CW)

*note1: “40m tail” implies both 40m and 30m links are attached, other settings are for the 20m/10m as 20m efhw or 30m/15m as 30m efhw.

note2: The transformer taps are numbered 1-5, where tap 1=4.5:1, 2=5.5:1, 3=6.5:1, 4=7.5:1, and tap 5=8.5:1 turns ratios.  corresponding impedance values would be 1013, 1513, 2113, 2813, and 3613 ohms.

note3: -right click and “view image” to see full size images below

Model Radiation patterns-10m

For the 10m images above, on the left is the modeled current and radiation patterns for the 40m EFHW when used on 10m.  The right is the current and radiation pattern for the 20m EFHW used on 10m.  Switching requires lowering the antenna to either detach or reattach the link at 20m.

Given the lengths of the wire using a 30 foot(~9 meter) support, either configuration will have a considerable vertical component.  The 40m version will add a substantial horizontal component.  The vertical components will mimic the horizontal patterns to some extent.  But the patterns will likely favor different directions.  The differences will surely be modest – maybe enough to be worth testing as options.  If nothing else, it may help reduce QRN in some circumstances.

Radiation patterns-20m

For 20m, the radiation patterns might actually be more interesting.  The full wave version(from 40m configuration) will present a compressed combination of horizontal and vertical components.  The half wave version(20m) configured with most of the antenna vertical will have a mostly vertical component with the 30ft/9m support.  This may be a fun experiment in a field day operation.  maybe worth the effort of switching the links

Addendums

HA5KDR, similar implementation.

*

End Fed Half Wave Experiment – Part 4

EFHW Experiment Part 1
EFHW Experiment Part 2
EFHW Experiment Part 3
UPDATED 2021-04-08
Transformers???

On a whim I decided to wind a transformer using two FT-140-43 cores.  I went with the same 2:1 ratio as the first transformer.  SWR testing using this second version showed that all transformers are not equal.  The SWR readings taken using the new transformer with the antenna wire as it was trimmed with the larger transformer did not have similar results.  It turns out the new transformer would require re-trimming the wire lengths to bring the 40m band into the same SWR curve.  Since I had the 80m coil&tail attached using .250 quick connects, it was easy to add wire.  Doing that allowed bringing 15m and 10m to good matches.  20m also found a sweet spot but only on the 6.5:1 tap.

New Version?

Without re-tuning the wire no good matches were obtainable on 40m.  Instead of making any permanent changes to the working 40m loaded antenna/transformer combo I am making a different wire based on a 30m wire length.  It will include a quick connect to allow the antenna to cover 20m by detaching the section of wire beyond the ~34 foot 20m wire length.  That will provide an antenna capable of 30m/20m/15m/10m.  This may become a simple way to add a permanent 30m antenna in the w4kaz antenna farm. 

Maybe I get ambitious and add a second link to include 17m, just for grins.  Does an easy tune 30m/20m/17m/15m/10m antenna sound good?  One could just as easily add quick links for each band.  Using the antenna as a full wave on the 2nd harmonic provides radiation patterns that might be more useful, but either choice provides a method to cover each band.  The initial lost opportunity cost is the need for the transformer.  For quick and dirty field construction a simple wire dipole or vertical would still be easiest – but mostly monoband, as fan dipoles can sometimes be difficult to tune.

Future ideas

Thinking about trying a different twist on using the FT-140-43 size cores by pasting three of them together for a transformer, and trying the transformers out with 3:1 turns ratios.  I have enough of the FT-140 size on hand to do this but used my last two of the FT-240 size.  My first test antenna seems to be a success, so it just need to be put on the air some to get an idea of how it fits in.  It is always good to have the option available.

20m/30m Constructed and Trimmed

Using the transformer built from a pair of ft-140-43 toroids sandwiched together, an antenna for 20m/10m is now built.  It includes a simple wire tail that can be attached as a link to extend for use on 30m/15m.  It should be a simple matter to prepare a wire for adding 40m use.  With the 40m wire 15m should be use-able with two configurations, either 30m or 40m.  If 15m is open that might add some interesting changes in radiation pattern when switching from a full wave to a 3/2 wave.  May as well add a jumper for 17m too(later-much later). 

TAP Cheat Sheet, 30m/20m/15m/10m

Taps 20m/30m linked EFHW (jumper to attach 30m/15m)

BAND TAP Best SWR  SWR range to expect
30m(j) 8.5:1 10.25(1.6:1) Entire band, 1.6:1 with wire drooping
30m(j) 8.5:1 10.1(1.3) Entire band, 1.3:1 with wire pulled taut
30m(j) 7.5:1 10.3(1.4) Alternate tap,1.4:1 with wire pulled taut
20m 8.5:1 14.025(1.4) Entire band favoring CW section
15m(j) 4.5:1 21.010(1.4) Entire band under 2:1(wire drooping)
15m(j) 4.5:1 21.010(1.0) Entire band flat with wire pulled taut
10m 6.5:1 28.000-29.25 28.00 thru 28.800 under 2:1(swr 1.2:1 on CW)
10m 8.5:1 28.00(1.4) 28.00 thru 28.75 < 2:1(swr 1.4:1 on CW)

*(j)= jumper attached for 30m/15m

Other ideas and observations

LINKING – Thinking about creating a “linked EFHW” out of curiosity.  If 10m were reliably open I would pursue the idea seriously.  The different patterns of radiation going from 1/2, fullwave, 3/2, 2xfullwave would be fun to work through.

Using taps on the transformer —-After testing with two different tapped transformers, using the taps makes it simple to obtain a good match.  More on the air testing is needed, but at this point trying to obtain good matches using a single transformer ratio seems futile.

Different cores = different wire  With both transformers I found that the length of wire needed was unique to each configuration.  The lesson is to build the transformer and tune the wire to the actual transformer being used.  The ft-240-43 transformer pair would not match the wire cut for the ft-140-43 transformer pair.  Need to build more transformers to see if a pair of identically built transformers(size and number) will both match the same wire.  Best guess is that will work.  But don’t expect transformers with different toroid sizes, or different number of toroids sandwiched together to all work with a set size of wire.  Be prepared to test or trim.

Wire droop not ideal   Pulling the wire as taut as possible not only shifted resonance slightly, but improved the SWR match on every band.

 

 

It Is Alive. W4KAZ Skimmer Back In Service

After a couple of months of dead air time, the W4KAZ skimmer returned to service on 2021/4/1.  The basement area housing the skimmer station required overhauling in order to replace the leaky old water heater.  After repairs, the project to return the skimmer system to service was delayed by other issues.  Foremost issue was lack of ambition to tackle the organization project spawned by tearing apart the shack.  Oiy.

Re-Organizing

Part of the re-org was to add in a new shelf rack, and put all of the shelving on casters.  The area is also used for general storage. Being able to wheel all of the shelving out into the garage will make access easier all-around.

The skimmer SDR was also found to have a dying cooling fan, so there was some delay acquiring the replacement.  Also some of the old input feedline system was replaced. 

This was also a good chance to downsize the computer system used to run the SDR.   A “new” micro form factor system was acquired, a refurbished Dell i5 in a teeny 8x10x2 box.  That’s a huge improvement over the desktop tower sized system previously in use, and the space savings  will be appreciated.  The new system has a slew of USB ports, but little else.  The desktop box will be stored and can be swapped in if needed as a backup.

Skimming System

The skimmer as currently being run still consists of the Red Pitaya used as an SDR, with the 160m inv-L over FCP antenna system.  The new Dell system is a Dell Optiplex 3020 micro form factor equipped with a 4th generation i5-4590T processor, 12gb ram, on a win8.1 pro OS platform.   This processor is 4-core/4-threads and runs somewhat faster than the previous platform.  On a lightly used band the skimmer is humming along using about 5% of capacity.  On a heavy contest this will probably max out at about 20% CPU.  Good enough for CW skimming, but probably not too hot for RTTY.  Other SDR software has not yet been migrated to the new CPU.

The main reason for the CPU  parallel “upgrade” was the micro form factor of the acquired system.  Having the computer be the size of a SMALL cigar box is a huge convenience for a cramped shack location.  It also sports a solid state drive, which has been the single most likely point of failure for previous CPU’s installed in a somewhat humid non-climate-controlled location.  But the size is most important.  (That’s what SHE said….)

Whazzup Wit All Dat?

So now that the system is up and running, more shack clean-up and resurrection is coming.  Organizing mediocrity out of the mayhem is the plan.  But can the plan survive contact with the mayhem?  heh – probably not.

Update-20210406

  • Unexpected crash of CW skimmer ~0800Z 20210406
  • Unexected crash of skimmrsrv `0800z 20210407 (???)

 

End Fed Half Wave Experiment – Part 3

 End Fed Half Wave Experiment – Part 1End Fed Half Wave Experiment – Part 2 
The “Tune-up-ening”

The first attempts to tune up the real antenna did not go well.  I found from the trap dipole project attaching the wires beyond the trap was needed to get the higher bands tuned properly.  This worked against me here.  With the high impedance on the end fed I was better off tuning the 40m antenna segment without the coil and 80m tail attached.  Unfortunately, I wasted a lot of time experimenting/snipping before I decided to detach the inner antenna from the coil.

Once taking that step, I found I had probably trimmed too much off.  Tuning for 40m without the coil proved simple enough.  After that the other bands were easier too.  I was also able to re-attach the coil and 80m tail, and find tap settings and tail lengths to allow operation with good matches on 80m and 20m.  With the 20m tails attached 40m operation on the upper edge is possible.  With tails 40m SWR was a bit high on CW segment, although possible with a tuner.  10m seemed unaffected by the coil and tail.  15m provided low SWR only with the coil and tail detached, but SWR of 2:1 up to 3:1 with 80m coil and tail.

Antenna Stuff

The coil as wound measured out to 77.5uh, resonant at 3.85Mhz with 22pf of capacitance.  It is ~63 close-wound turns on a mystery plastic coil form of ~2 inch diameter, wound with 16ga solid insulated wire.  The final wire length in the 40m section is xxft(zz.zm).  The 80m tail is xxft(zz.zzm) in length and the portion for ssb(75m) is xxft(zz.zm).  To make the choices more flexible for POTA or other portable uses, I have a series of jumpers in several key places.

The first of the jumpers is installed near the feed point.  The antenna was trimmed at the feed point for ease-of-access reasons.  Since I ultimately decided I had over-trimmed before detaching the 80m coil&tail, it seemed easier to insert a jumper there.  This will also allow  having an easy method of re-tuning on the fly if it seems necessary in different deployment configurations. 

The next set of jumpers comes at the junction between the 40m antenna and the 80m coil&tail.  There are two more jumpers on the 80m tail itself, positioned to allow choosing between a mid-band SSB section centered at around 3.8Mhz or a CW section centered at about 3.575Mhz.  The lower section will allow use on both CW and in the lower 3.600Mhz SSB segment.

The antenna can be deployed with or without the 80m coil&tail.  I found that the matches in the 40m and higher segments are much with the tail removed/detached. 

All Taps NOT Ideal

As described in previous posts, the transformer brewed up for this project has multiple taps, not the fashionable 49:1 single solution.  It turned out having the choices of taps gave better SWR matches than any single tap.  In fact, only one of the taps worked well for the 15m/10m bands, the lowest impedance 4.5:1 tap.  For 40m and 80m, the 8.5:1 tap proved the best choice.  20m SWR curves favored the 7.5:1 tap, although the 6.5:1 tap proved useful with the 80m cw configuration.  When configured for 80m CW the 6.5:1 tap provides better than a 1.5:1 SWR across all of 20m.  

TAP Cheat Sheet

Taps 40m and up, bare wire,  NO 80m coil&tail

BAND TAP Best SWR  SWR range to expect
40m 8.5:1 7.15Mhz@ 1.2:1swr Entire band, 1.8:1 up to 2:1  centered on 7.15
20m_1 7.5:1 14.15 Entire band good favoring CW section
20m_2 6.5:1 14.275 Entire band good favoring SSB section
15m 4.5:1 21.3 Entire band under 2:1
10m 4.5:1 28.2 28.00 thru 28.800 under 2:1

Taps with 80m SSB section

BAND TAP Best SWR  SWR range to expect
80m 8.5:1 3.825Mhz@ 1.2:1swr 3.7 thru 3.9Mhz , ?tuner at edges?
40m 8.5:1 7.3Mhz, 2:1 7.2 to 7.3Mhz, tuner needed
20m_1 7.5:1 14.1 14 to 14.35 under 2:1
20m_2 6.5:1 14.225 Best choice, entire band good favoring SSB section
15m 4.5:1 21.05 @ 2:1 21.0 to 21.35, SWR over 3:1 above 21.35
10m 4.5:1 28.2 28.00 thru 28.800 under 2:1

Taps with 80m CW section

BAND TAP Best SWR SWR Range to expect
80m 8.5:1   3.525 to 3.75 <2:1
40m 8.5:1   7.2 up under 2:1
40m_2 8.5:1 1.3:1@7.3 40m jumper ins, useable on cw
20m 7.5:1 14.0 14 up to 14.275 < 2:1
20m_2 6.5:1 1.5 40m jumper ins, all band
15m 4.5:1 21.245 @ 2:1  
10m 4.5:1 28.1 28.0 to 28.7 < 2:1

 Test Deploy

All tuning was done with the antenna strung up using two Jackite telescoping poles as supports.  A 31 footer is used for the vertical portion, and the feed point is at about 4 feet off the ground.  The horizontal runs out about 40 feet to the second mast, a 28 footer.  The second mast supports the weight of the wire and the loading coil, probably the heaviest portion of the antenna if used.   I ran a 7 foot long counterpoise wire, and a six foot long coax jumper angles down to ground level from the feedpoint to the first choke, eight turns of coax wound on a ft-240-31 ferrite(another 6 foot jumper for that). 

The short section of straight coax jumper will likely be a second counterpoise for the antenna.  The first choke plugs into a second choke constructed of 10 turns of a 14ga wire pair wound on a second ft-240-31 ferrite and mounted in an enclosure.  From the chokes a fifty foot long lmr 240 feedline is attached, and all testing was done at the end of the feedline.  That simulates the most likely portable deployment.

FWIW, SWR results did not change when the fifty foot section of coax was removed.  Will be a curiosity to find out if altering the shape of the deployed antenna changes SWR. 

Additionally, I toyed around with inserting pieces of wire as jumpers to lengthen the 40m section.  These jumpers are inserted close to the feedpoint on the vertical section.  I inserted them to try to improve 40m SWR when the 80m loading coil&tail were linked in, as 40m SWR was too high for CW operation without tuner with tail attached.  This turns out to be a useful compromise solution.  It will allow using either 40m or 80m without adjustment, and 20m/10m can be used with tap change.  15m is the odd man out in this configuration, but could maybe be used with a tuner.

Stress Test Awaiting

Following are some key down stress tests to gauge how well the RBN can hear and to see if there will be any heating in the ferrite cores when at 100w levels.  Perhaps a POTA operation would be better.   No “SWR creep” was found when I did 60 second key down tests on the dead bands at 1800Z.  Both extreme ends were tested at 60 second key down, 80m and 10m.  Then a series of test transmissions that consisted of three repetitions of the test string: “V V V TEST W4KAZ W4KAZ W4KAZ V V V”. 

RBN Spots from 40m EFHW at 1800Z on 2021-03-11

RBN Spots from 40m EFHW at 1800Z on 2021-03-11

The RBN spots from 1800Z show decent results, not too dissimilar from what I am accustomed to seeing from the permanent wire dipole antennas.  The test antenna is deployed in a much-less-than-ideal location.  The test EFHW horizontal section is running parallel to the horizontal tail of my permanent 160m inverted L, and it is only about 20 feet away.  So I’m not too concerned with the locations of spotting stations.  I expect to try a POTA activation soon, which will maybe be more interesting.

RBN Spots from 40m EFHW at 2345Z on 2021-03-11

RBN Spots from 40m EFHW at 2345Z on 2021-03-11 

Likewise the above set of RBN tests run later, near to and just after local sunset  @2330Z, show fairly typical results. 

80m RBN Spots from 40m EFHW at 2345Z on 2021-03-11

RBN Spots from 40m EFHW at 2345Z on 2021-03-11   *

I expected 80m results to be poor but they were maybe better than my low expectations.  Nothing great, but certainly good enough for an easy to deploy portable antenna.  Better to have some 80m capability than zero capability. 

Next Question:  What happens if I use a different transformer?

see part4   EFHW Experiment – Part 4

*

End Fed Half Wave Experiment – Part 2

End Fed Half Wave Experiment – Part 1

Construction
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). 

Inductor
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.

References:

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

nonstopsystems.com 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.