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.
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.
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 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.
By w4kaz, created on 2021.03.08 at 15:53:33 | last changed on 2021.03.12 at 22:12:18 |
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.Â
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.Â
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.  Â
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.Â
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). Â
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”.
By w4kaz, created on 2019.11.09 at 15:43:10 | last changed on 2021.05.06 at 22:39:49 |
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?Â
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.
By w4kaz, created on 2019.09.29 at 16:44:08 | last changed on 2019.10.18 at 16:56:45 |
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…
RTL-SDR BCB filter, at 3.93Mhz. SWR=2:1, RL=8.63db, IL= 1.4db
RTL-SDR BCB filter, at 3.93Mhz. SWR=2:1, RL=8.63db, IL= 1.4db
RTL-SDR BCB filter, at 1.81Mhz. SWR=16.3:1, RL=1.06db, IL= 50.5db
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.   Â
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.Â
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).
W4KAZ version of BCB filter. Built using NP0/C0G leaded capacitors, t-80-2 torroids, and a 220uh choke.
AADE predicted performance plot of the w4kaz BCB filter from DC to 10Mc. Note the nulls on 680 and 850.
BCB SWR, insertion, and return loss from 50Khz to 3Mhz
W4KAZ homebrew BCB Filter 50kc to 30M SWR scan
Band Pass Filters:Â
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.Â
10m Bandpass Filter Â
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.
10m Bandpass filter scan from 15 to 40Mhz.
10m Bandpass filter scan from 20Mhz to 35Mhz.
10m Bandpass filter scan from 20Mhz to 35Mhz.
after NanoVNA tuning, a slight improvement across 10m:
Tuned 10m band pass filter scanned from 15mhz to 40mhz
Tuned 10m band pass filter scanned from 20mhz to 35mhz, Minimum at 25.400 Mhz
Tuned 10m band pass filter scanned from 20mhz to 35mhz, on 10m band
15m Bandpass Filter
Bandpass filter scan for 15M filter
20m Bandpass Filter
Bandpass filter scan for 20M filter originaly tuned with MFJ analyzer by SWR
Bandpass filter scan for 20M filter after tuning with NanoVNA
40m Bandpass Filter
Able to tweak the 40m filter from -29.4db to -35.7 db, and filter covers 40m band easily.
Bandpass filter scan for 40M filter before re-tuning using NanoVNA
Bandpass filter scan for 40M filter after re-tuning using NanoVNA for a 6-7db return loss improvement
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”!
By w4kaz, created on 2019.09.28 at 12:41:11 | last changed on 2019.09.28 at 12:41:13 |
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.
W4KAZ IOTA 2019
W4KAZ IOTA 2019 Antennas
W4KAZ IOTA 2019 Antennas
W4KAZ IOTA 2019 Antennas
W4KAZ IOTA 2019 Antennas
W4KAZ IOTA 2019
W4KAZ IOTA 2019 station
W4KAZ IOTA 2019 station
W4KAZ IOTA 2019
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.
WX4FLY eyeball QSL
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.
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.Â
And that, a sprinkling of meteors across the Milky Way, combined with the mild weather to make the trip a winner..
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.
Sample of original 20m trap using 7 turn coil. This trap experienced SWR shifts under xmit at 100w in CW contest.
Revised traps for 20m/40m dipole. The traps use three of the TDK capacitors in series for a total value of 23pf. The 14 turn coil used resonate the traps at 12.65Mhz. Inductance calculated as approx 7uh.
Revised trap for 20m/40m dipole. The trap use three of the 2KV TDK capacitors in series for a total value of 23pf. The caps are mounted in series on a small bit of PCB for a cap value of 23pf. Joints were soldered slightly long with a bit of excess solder in the hopes of a bit of extra heat sinking.
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 :
the dipole legs being shortened,
the impedance on 20m seemed more stable,
The bandwidth on the lower band(40m) was decreased
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.
By w4kaz, created on 2019.09.15 at 15:29:37 | last changed on 2025.01.06 at 10:06:15 |
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.
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
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.
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,
I’ll probably be mostly using them on CW so maybe a tad less loss with trap rez at opposite end
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.
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.
Initial coil test data
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.
By w4kaz, created on 2019.06.08 at 12:27:11 | last changed on 2021.05.06 at 21:06:51 |
I have been using a telescoping fiberglass mast of one sort or another since 2005 or so. Most folks seem to be using these masts mostly as designed, i.e. relying on the friction fit, or using tape or hose clamps to keep the mast extended under load. None of those seemed ideal for my plans to use them with dipoles(inverted V config).
The first pole I obtained was from Henry, K4TMC (tmastco.com).(FWIW, I am acquainted with Henry via our membership in PVRC. Henry also sold me a very nice Elecraft K2 when he upgraded to the K3, and other assorted sections of surplus mast.)
This is the 32 foot pole, which results in about 29-30 foot of usable length once extended. Relying on friction fit, I ran into a couple of problems I think common to ALL of these similar type masts. The first problem is the amount of friction required to keep the poles from collapsing was also enough to make them difficult to collapse in very hot or very cold weather.(38C/98F or 0C/32F) Tape and hose clamps are usually enough to resolve that, but bring their own issues.
Tape tends to leave a lot of residue at the joint at 38C(i.e., ‘sticky mess’), which is a problem on sandy beaches. Sand does not enhance the experience of using one of these masts when it sticks to the joints. I also did not like the amount of pressure hose clamps required, nor the amount of time needed to install them in correct order(at 98F oceanside), or to fasten them without crushing the fiberglass accidentally. Because of “spontaneous collapsing” under certain types of pressure, the friction fit is not ideal for use with dipoles, my preferred antenna for portable ops.
The solution I chose was to drill the mast and use 1/8 or 3/32 cotter pins at the bottom of sections just above where they rest when extended. The pin rests on top of the next lower section, so no problems trying to align holes through two sections. Saving another 1000 words……
A section of mast extended showing position of pin, which goes through only the base of the single section.
Over the past 10 years or so I have acquired a few additional masts. Primarily to have the ability to deploy more than a single antenna, but also as redundant or spare masts. [Two is one, one is none.] These additional masts include the 12m Spiderbeam pole, both a 28 and 32 foot mast from Jackite, a 22 foot mast that was marketed as a flagpole, and several Shakespeare 20 foot Wonderpoles. The Wonderpoles are used mostly to elevate the ends of the dipole legs when it seems appropriate(mostly constricted spaces).
The mast from K4TMC has seen the most use over the last decade. It has a good combination of stiffness and flexibility for its length. I had my doubts about drilling holes for the cotter pins, but the mast has been deployed for extended periods with little signs of anything more than minor cosmetic damage. The Spiderbeam mast seems to be much more flexible, which tends to negate is useful length as a center support for dipoles. Both Jackite masts seem to be the most rigid of the group, but I have used these less than any of the others – they are relatively new buys.
The disappointment of the group for me is the Spiderbeam mast. Its flexibility requires guying to keep it from noodling with the weight of a very light weight 40m dipole made of 18ga wire. Best practice seems to be best to attach the feedline to the mast for any of these type masts, but absolutely essential with the Spiderbeam. My Spiderbeam pole also becomes difficult to extend to its full length the more it bends, although that does help keep it from spontaneous collapse. Also more difficult to deploy in heavy wind at the beach due to flexibility, common to all but more pronounced on the Spiderbeam. The other masts are more self supporting when used with the auger bases. This may indeed have more to do with their overall shorter length, and the spiderbeam masts are indeed intended to be guyed by the manufacturer. I would prefer not to use guys to save time, but in several excursions I was unable to use the full length of the Spiderbeam mast sans guy lines. Even with guys the Spiderbeam pole had excessive droop in high winds oceanside, so the additional time required did not seem worth the effort. Taken all together the Spiderbeam mast was not taking my dipole significantly higher than shorter masts.
Auger Bases? Why didn’t I think of that? : The other divergence from the norm is my use of these auger bases. These auger bases are items I have scrounged from different sources. The first pair of them I obtained from Harbor Freight in the early 2000’s, where they were being marketed as beach umbrella stands. That source disappeared soon after my purchase. A second group of smaller augers[NOT pictured below] are marketed as “Aussie Augers”, but needed modification to use with the fiberglass masts(unless you don’t mind removing the end caps from the bottom).
These augers pictured below were available via Amazon in the US in 2019. They work extremely well in sand. They are heavier gauge material than the Harbor Freight versions. The larger tapered base is my first choice for sand and seems to be the strongest. It would also work anywhere with a deep layer of loam or sandy topsoil. The base with the narrow welded on auger is more useful where the soil is less friendly, with stone or tree roots. I use the narrow base in my home yard, which is chock full of quartz stones and tree roots. It sometimes requires multiple placement attempts, but seldom takes more than a few minutes to install. For areas with no topsoil, shallow stone, or mountains, this solution might be less than ideal. The other caveat is leaving a hole in the deployment area.
Both bases are about 60cm in length(22 inches) and have a 60-61mm throat width(approx 2-3/8 inches). This is just barely wide enough for the Spiderbeam mast to fit without removing the base cap. All of the other masts are a bit smaller at the base and fit in easily. The large base has a depth about 178mm(7 inches) and the larger a depth of 127mm(5 inches). FWIW, with the smaller diameter masts I often insert a section of 2″ PVC into the base as a bushing sleeve, and the mast into the PVC bushing section. Large tapered base at Amazon [American Ground Screw Model 2] Narrow welded base at Amazon [American Ground Screw Model 1 with Cap ]
Two different types of auger bases for use with telescoping masts by W4KAZ
Two different types of auger bases primary difference is size. The auger on the left has threads down a tapered shaft. On the right, the auger shaft is a uniform width of tube welded onto the top section. The usable depth on the left auger is also about 2 inches more than the one of the right.
I don’t expect I have been the first to go down this less traveled path but have not seen it documented elsewhere. So some photos above for reference. I drilled 9/64 holes in the bottom of each nested section, just ABOVE the joints, and use 1/8 cotter pins.
My 10+ year old mast from K4TMC has been deployed numerous times. There is still only minor wear to the drilled holes, and zero cracking or vertical splits. YMMV. Caveat Emptor. An additional tip would be to have spare pins, and pins in at least two lengths. The bits of wire are used to keep the pins from vibrating loose in the ocean breeze. The also are used with coax to keep the feedline close to the mast. Generally I tape the feedline when using twinlead.
The choice of feedline is made on deployment depending on the distance from the antenna to the operating position. I use LMR240/RFC240 for the feedline drops when the operating position is close to the antenna, and 300 ohm ladderline from DX engineering for long runs.
Note 4, RX Antenna: The skimmer system is now using the 3.8 wave inverted L as its RX antenna full time. The only anticipated interruptions will be occasional 160m contests.
2018-08-22:
Note 1: Skimmer station outage in mid July 2018, cause appears to be rx antenna related.
Note 2, Transformer: N6TV identified a mini circuits 14:1 transformer that is suitable for use with the Red Pitaya on RX. Expect the transformer to be available from Red Pitaya, or occasionally N6TV. Available from mini-circuits vendors, but may be expensive in quantity 1.
Note 3, RX antenna: Some what by accident I discovered that the 160m L I use for transmit seems to make a fine all-band rx antenna for the Red Pitaya skimmer set up. FWIW, the antenna is about 140 feet of wire. About 60-70 feet vertical, with the remainder making a dog-leg turn from top of vertical section. From there it runs horizontally NW to second support about 40 feet away, and a second sharper turn to the east, horizontally and slightly downward for the remainder which runs west to east. The radial system is the K2AV type folded counterpoise system described in more detail at link.
By w4kaz, created on 2018.07.22 at 11:58:16 | last changed on 2018.08.27 at 17:39:43 |
The normal group of Field Day scalawags were in the wind for 2018. N4GU was uncertain if the QTH from 2016 and 2017 would be available. N4YDU took up N9NB’s offer for FD at Ted’s QTH in VA foothills. I was also kindly invited, but decided that I didn’t want to drive quite that far, despite the nearly ideal location. I do love me some VA mountains.
For 2018 I took exit ramp #3, and went with the backup backup plan. Operated 1B at a campground near Wilmington NC. A nice easy drive, with a couple of easy on/off stops along the way to stretch out the body parts complaining loudest. That made the drive tolerable.  Also made it into a mini-escape, leaving home QTH on Thursday with a return on Monday morning.
Weather conditions[i.e., heat] soon had me thinking I’d have been better off in the VA mountains, but after acclimatizing to “swamp butt” conditions, it was fine. When I sweat enough to remind me of living on the South coast – its pretty darn sticky. Usually not quite so bad in NC, but it happens enough to know to be prepared. Lots of water and gatorade. Thursday afternoon was the worst of it though.
Friday morning was spent doing a bit of unrelated recon. Friday afternoon I laid out the antennas and supports, and some more unrelated area wide explorations. WX on Saturday dryed out some, and there was a nice breeze that picked up from the start of operations though early evening. Never a drop of rain, just temps and humidity in the 90’s. Just like being back in good ole Bigg Swampy(SE Louisiana).
Antennas:
2018 was a time to test some antenna ideas. I built a 2 band triangular yagi for 20m/15m, based on article by Herb,N4HA as published in June 2018 QST. I kept to the published dimensions(mostly) but fashioned the driven element(s) from 300ohm ladder line. For supports I used a mast from Henry, K4TMC as the support for the drive element/apex. The tails sloped down to connect to the reflectors, and those ends were supported by 2 masts cobbled together by combining a Shakespeare Wonderpole on top of a section of 4 foot mil surplus mast.  Simple, and easier than I expected. This antenna was fed with 300 ohm ladder line run to a tuner rather than coax.
40m was a simple inverted Vee supported by a Spiderbeam 12m telescoping mast. Note: Simple does not mean “easy”.
10m was an afterthought. After struggling with the 40m dipole-that-wouldn’t, I had a relaxing breakfast and gave some thought to 10m. Had plenty of time, so may as well. To get on 10m I made a dipole by cutting a couple of equal 8.5 foot lengths of wire and constructed a “FD style” center insulator from a pair of cable ties taped together. Used a “composite” feedline – a ladderline drop to a 1:1 unun and a short coax run into the tent. I had a length of ladder line about 25 feet long so the 10m dipole was up about 23 feet.  At the end of the ladder line at ground level I plugged the ladder line into a 1:1 unun, and ran the last 30 feet or so into the station with coax. From start to finish this antenna took about 30 minutes to put up, including cutting legs and twisting it all together.
No antenna at all on 80m. Decided I’d have enough business on 20m & 40m to keep occupied, and figured on sleep rather than a night of 80m T-storm QRN. 😮
Now, about that 40m Vee. The antenna that would NOT. Still not certain where the problem was, but it had an issue in one of the feedlines somewhere[update-think one of the legs has broken wire]. Far too much time was wasted raising and lowering the antenna trying to debug the issue. Lesson1: Always have an alternative.  Lesson2: Don’t dick around debugging when you have the alternative at hand ready to go. Lesson3: Save debugging for down time. Lesson4: Read Lesson1 and Lesson2 until they really sink in.
Operating:
Once the CQ’s started, there were plenty of QSO’s to log. Saturday was a bit slow at first, but I got a better rhythm in the evening. Was tired though, and sacked early, including a 45 minute nap at 5pm in the nice cool breeze that came up. Also got up early Sunday, 5am-ish.  Sunday morning was quite a bit of fun, right up until my keyer interface died around 11am. So I finished the event with a bit of lackadaisical SSB, mostly S&P.
Camp:
The Cabelas tent goes up easily. My only regret is not getting one of the larger sizes. It has room for setting up a table for the station and also for a cot along the opposite side. But it is a bit cramped. Next time I do this I think I will use a screen tent for the station and the tent just for snoozing/bad wx. Also, the ideal site would allow for the tent to use an overhead spike support and avoid the need for the center pole.
Overall a big win. Keeping the ants away…..the real challenge!
