Projects: New 20M 2x2x2 stack and 10M 12 el dipole stack - NanoVNA questions

[K1JJ]

We're moving into some new projects and questions.  Might as well retire the completed 75M delta loops thread and start a new one about the current 20M 2x2x2 Yagi stack. Also coming along are plans for a 12 el 10 dipole stack.

This is the old thread about the 75M delta loops:
http://amfone.net/Amforum/index.php?topic=47597.msg338825;topicseen#msg338825


To get the ball rolling, I took some pictures today of the 20M stack building progress, as well as some other related stuff like feeding the 20M stack with a 3:1 ferrite combiner and a very motivating EZNEC model of the 10M stack..   Also, one picture of the delta loops NE/SW switching system.

BTW, I am convinced to buy a NanoVNA.  For our limited HF use, will this $48 unit work OK?  Also, they seem to be using those tiny cables and connectors. How do you get PL-259s or simple clip leads for ham HF use?  

How about this one?  
https://www.ebay.com/itm/274706545538?hash=item3ff5c93b82:g:lxYAAOSwn1FgQJhX&amdata=enc%3AAQAHAAAA4E90boIvrgA5QuWZltZk%2BFexYRUMii2u6sfBuaL6D5gKH7jzOnbUziKWe5HTun%2Ft2bv4mzog0yECcGwLIAsZ%2BJChfVlvDTKE2LCM%2FtsOCWvNpFi0%2FON3Bd37wldk94dub%2BFAaIQj8mloviXiUbEWp0ZNYJ%2BPJ7peoTpZ3b4M5GR3VG5rXVayuZyz%2Ft34PSPksYOd2sD9IY4%2B7whb79tGFr2N%2FI30L0MddvwEKSYFQ2soXp64PPEiSWqJKcnOQUAbFNArvpGXXEJW%2BPgllvM7tQ2c%2B0D6HfKNRPhuoBh050xG%7Ctkp%3ABk9SR9rd3dTXYA


20M 2x2x2 project:

Pic # 2,3:  The elements float on fiberglass plate.       2" fiberglass solid rod for the center driven elements. Very strapping construction.


T

[K1JJ]

Pic #1:  The swing gate, one for each Yagi at 35', 70' and 105'.   They pull out and swing about 330 degrees around the tower. I have a blind spot at North.  Notice the six guy cable star triangular guying - giving additional torque strength.  Can you see where the Yagi gets bolted / mounted on the pipe?  There is a bolt-on for the boom and another for the overhead truss cable.  These swing arms and torque arms are all homebrew using an electric welder.


Pic #2:  The combiner for three 50 ohm Yagis into a single 50 ohm feedline.  Done.   I hung a 17 ohm resistor across the output and connected the MFJ-259 to the input.  Near 1:1 SWR. Works FB.  I actually used this years ago for a 6M array.  Bought from Array Solutions. Should be easy to duplicate. Three wires around a single toroid. He said it will handle QRO.

Pic #3:  The 10M  12 el dipole stack model.  Four degrees vertical elevation takeoff angle - on the horizon.  In contrast, the horizontal lobe is very broad, like a regular single bi-directional dipole.  The phasing needs to be near perfect to see such lovely lobes in the real world, thus the reason for a NanoJam for precise phasing.    Mounted like Venetian blinds, 190' high, dipole tubing elements mounted every 16' down to 16' off the ground. Each element has 1/2 wave of feedline and a 180 degree flip which gives a full wave in-phase signal to each element. Over 17 dBi gain. With reflectors, it would be over 20 dBi.  This will be a "hear everywhere at once" antenna with its broad horizontal pattern.  "Listening for far away, low angles only, please!"    When the sun spots get hot it's hard to imagine what the band will sound like with such a selective vertical lobe and a very broad horizonal at the same time.

[K1JJ]

Pic #1 is the 75M delta loops switcher for NE/SW. Very simple.  This is a temporary setup until I finalize things.   It works FB with -30  to  -35 dB front to back at times..  That RG-11 is not easy to work with.  I need to get some crimp-on connectors and tools for the aluminum shield..

Pic #2:  It's beeen real hot for Yaz with these 95++ temps.  I spray him down with the hose often. He loves it and runs back and forth for more.

Pic #3 shows the 7.5" balun support form. It will hold about 7 turns of RG-213 and six beads.  Notice it is mounted away from the elements and boom for best isolation.

[K1JJ]

Pic #1:  The staging area.  They will be mounted on the Rohn 45 tower about 40' away.  Each 2 el Yagi weighs about 60 pounds. They were modeled using YagiStress for mechanical strength... good for 1/2" of ice and 100 MPH.  The overhead cable trussing is not really needed, but I added it in anyway.   The elements are recycled from a pair of 5 el 20M Yagis I built back in 2008.   They weighed close to 200 pounds.  These 2el Yagis are quite manageable and can be lifted when needed..

Pic #3:  This is the 40M 2x2x2 Yagi stack at 190'.  The new 20M stack is an exact duplicate except scaled down by 1/2.  I used the same basic electrical and mechanical design parameters.

[W1ITT]

It looks like good manly construction practices all around.  If you get a NanoVNA of whatever model, you can check the match of the splitter, and also do a two-port measurement to check that the power division is correct .
Thinking of the 10 meter Venetian antenna, I've been pondering how to get some high angle radiation for the times that you want it.  One thing we used to do in FM arrays was to slightly detune the top and bottom elements while keeping the total array in match.  Those deep nulls you see in the elevation pattern presume that all elements are perfect and equal.  Detuning the top and bottom will create some null-fill which is just what's called for if you can't do vertical elevation slewing as we do in some of the big HF  curtain arrays.  A bit of null fill comes at the expense of a bit of gain, maybe as much as a  couple tenths of a decibel, but it will keep the fade from going right down into the noise.  I don't recall well after all these years, but it seems that FM, I was only detuning those bays by 100 khz or so, not much.  And it's cheap to do.
73 de Norm W1ITT

[W1ITT]

Tom... I meant to comment on the NanoVNAs.  Yes, the $48 unit will work well for this project.  Note that there are type SMA connectors.  They are soldered to the pc board and are not real strong.  I have bought a couple SMA to Type N short pigtails...maybe 6 inch. to connect to larger coax.  You could probably get them for other connectors of your choice but the necessity of pigtails starts adding costs..  I like the 4" screen better  on the pricier units and the N connectors mounted to the enclosure are definitely a step up for outdoor work.  When you start getting up to near $150 you can look also at the Lite-VNA which has more measurement points and sturdy construction and a 4" screen.
That said, I have been carrying one of the little $48 units in my kit overseas.  It isn't mil spec but if my real test gear got delayed I could at least get something done in the interim.  And I've left them with customers.  They like them better than tee shirts with logos.
73 de Norm W1ITT

[K1JJ]

Norm,

Tnx for the good info on the NanoJam.    I will look for pig tails with a mate to whatever unit I end up with.  That was important to me.  I just hate fooling with those tiny connectors and plugs for field work. I mean, everything isn't a lab perfect 1:1 terminated disco duck whirl out there.

You mentioned high angle for 10M.  I will leave the 10M stack as is, looking to keep it suppressing high angle and being a low angle monster.  For higher angles, I plan on a simple fan dipole for 20/10M at about 60' high using the same aluminum tubing as the 20M Yagis.  I think the two pairs of elements fed with one feedline will be quite convenient and double as reference dipoles for the two big projects.  Just like the 75M delta loops, I will use the big arrays only when low angle stuff is coming in... kinda like taking out the dragster on the street from time to time.  

T

[K1JJ]

Update: 8-28-2022:

For 10M, I decided not to do the 12el dipole stack.  Instead, I designed two wide spaced 4el stacked Yagis. The gain is almost the same, just focused more in the horizontal plane. I built two and raised each on a rope tramline up to 20' for testing. (over a half wavelength high)  Testing was quite easy....  I hooked each Yagi to a receiver and tuned in a 10M South American ham on 28.483 MHz.  I manually turned the Yagi around quickly and could see the front-back, side and forward side of the pattern.  The swr was adjusted to 1.1 : 1 using the driven element tips. The parasitic elements needed no adjustments.  The predicted computer EZNEC model was right on.

There were a few more S.A. stations, Brazil and Cuba that had similar results.  I could actually see the difference in direction between Cuba and Brazil. The pattern is quite sharp.  I estimate the f-b to be about -30dB at times and the front to side to be at least -35 to -40 dB. The swr is below 1.3 to 1 from 28 to 29 MHz; with a dip at 28.5 Mhz near 1.1 to 1.   I will be using some kind of 2:1 toroidal matching transformer between the two Yagi feeds.

So bottom line is the computer model using a 24' boom and 8' spacing between each element worked right out of the box. No need to fool with it. Next, I will be doing the same raising routine with the three 2el 20M Yagis. They are twice the weight and a little more sporting.  They will need adjustments due to the tapered telescoping tubing shortening effect.  No big deal cuz it's just one reflector to tune for max f-b  and the driven is an swr tip adjustment.

The pics below show the 10M beam with a temp coax choke and ferrite cores JS dangling. It will be mounted neatly now that I know everything works FB.

These 10M  Yagis will be in the clear with no guy wires on the self supporter. I watched the swr carefully and see no change as it passes by the tower which is about 15' away for this test.

BTW, the 75M loops are performing amazingly well!  There's often a difference of 2-3  S units between the fan dipoles and the loops.  When I was first getting it tested, I was disappointed that the difference was much less, sometimes equal on certain nights. But conditions have changed and right now at select times the low angles are often dominant on 75M at night.  The f-b, the back to Europe, is like turning off the receiver.  Euros drop into the noise. The loops are still quieter than the fan dipole and the NE is usually quieter than SW.  

But the f-b to USA is only about -20  to -25dB or so.  Still not sure why. Same tuning in both directions.  Maybe cuz Eu is 3000 to 4000+ miles away while most USA stations I hear are within 1500 miles.  Different angles involved.

Another upcoming project:  I plan to convert the 40M low dipole at 50' high into a coax fed fan dipole to cover  40M, 20M and 10M at 45 high'.  This will be my lower height, higher angle reference antenna for these bands against the Yagis, etc.  One feedline and away from all other antennas will be a good standard.

That's it for now....

T

[K1JJ]

More:

[K9MB]

Hi Tom,
You have been busy.
The 4 element design is textbook with uniform element spacing.
You should get about 9dBd from one.
Stacking can give you an additional 3dB gain, though that requires a spacing that will add grating lobes. I always liked to use 1/2 wave spacing because it gave a very clean pattern and you still got over 2dB stacking gain. You are going to get more than 11dBd. You are right, the horizontal lobe half points are noticeable sharper than you collinear 12 element array of drivers and reflectors, but if 10 opens up- and it will- you might like being able to null out the qrm that happens.
So what boom spacing are you using? 18-22 feet seem about right if my guess is close.
BTW- was watching a video this morning on the hurricane season and the minion with the map said 80 percent of the season was still in front of us.
I suspect that you are safer than those Carolina guys, but seems like you had a pretty good blow a few years ago.
You antenna farm size reminds me of a comment one Old Timer made one time that you knew if your antenna array was big enough if it blew down within 6 months.😉😂😂
In another field of risk, I remember that it might have been Warren Buffet who said nobody long regretted selling too soon… I was that guy who failed to follow that one at times…😉😬
It all looks great now, though and whether it is a hurricane or a norther or an ice storm, you get the weather that comes and maybe your safe because it was not quite big enough and missed the curse of that Old Timer…😉😁

[K1JJ]

Hi Mike,

Yes, I prefer closer stack spacing for the 10M Yagis to get ONE main lobe at 12 degrees in this case.  I'm using 20' stack spacing (as you mentioned) with the bottom Yagi at 25' high and the top Yagi at 45'.  This may seem low, but this is the best pattern for two Yagis using average ground reflection.  If I wanted a lower angle, I would need to add another Yagi at 65', etc.  But when the sunspots are really playing, the optimum angles start to rise, thus a 12 degree take off vs: a much lower 5 degrees.  IE, five degrees  if this were a stack of four or more.  The three 20M 2el Yagis are also close spaced stacked at 35' apart, about 1/2 wave for a clean pattern, single lobe pattern.

For DX, I like to design for a single lobe and then operate when conditions favor this lobe.  The other alternative to to add a 180 degree phase shift switch to one Yagi to raise the angle up to 30 degrees when needed.

The hurricanes do come through here, maybe every five to ten years or so.  I just build my antennas and towers with careful thought to every connection, bolt and load and hope for the best.  When they break you just have to fix them.  So far since 1986, I've never lost a tower or major antenna.  I have had some ropes and wires break here and there, elements slip and feedline water  contamination, but for the most part very lucky.  I have never had a direct lightning hit in 35 years.  All of the towers are tied together using underground copper #6 cable in trenches. I am convinced that the towers bleed off the charge and actually protect the whole neighborhood from strikes.

Well, after completing these last three projects ( 10M Yagis, 20M Yagis and 10/20/40M fan reference dipole) I should be all set for the year, I hope...  and get some operating in...

What's new with you? Any recent projects?

T


EDIT:    BTW, I bit the bullet and ordered a NanoVNA unit today.  I will use it to set the parallel resonance on the 10M and 20M coax chokes at the feed points.  Maybe it will help to set up the 10/20/40M fan dipoles too.   I watched a few YouTube videos about the VNA and it is really involved!  It was mentioned here that the MFJ-259 is a 50 ohm based system and will not work for choke resonance.  But the Nano appears to have 50 ohm SMA based channel 0/1 connectors too.... or will they handle higher impedance?  

Also, there was an article somewhere about tuning the coaxial choke using the VNA. Was it DX Engineering?  I can't seem to locate it...
 

[K9MB]

Hi Mike,

Yes, I prefer closer stack spacing for the 10M Yagis to get ONE main lobe at 12 degrees in this case.  I'm using 20' stack spacing (as you mentioned) with the bottom Yagi at 25' high and the top Yagi at 45'.  This may seem low, but this is the best pattern for two Yagis using average ground reflection.  If I wanted a lower angle, I would need to add another Yagi at 65', etc.  But when the sunspots are really playing, the optimum angles start to rise, thus a 12 degree take off vs: a much lower 5 degrees.  IE, five degrees  if this were a stack of four or more.  The three 20M 2el Yagis are also close spaced stacked at 35' apart, about 1/2 wave for a clean pattern, single lobe pattern.

For DX, I like to design for a single lobe and then operate when conditions favor this lobe.  The other alternative to to add a 180 degree phase shift switch to one Yagi to raise the angle up to 30 degrees when needed.

The hurricanes do come through here, maybe every five to ten years or so.  I just build my antennas and towers with careful thought to every connection, bolt and load and hope for the best.  When they break you just have to fix them.  So far since 1986, I've never lost a tower or major antenna.  I have had some ropes and wires break here and there, elements slip and feedline water  contamination, but for the most part very lucky.  I have never had a direct lightning hit in 35 years.  All of the towers are tied together using underground copper #6 cable in trenches. I am convinced that the towers bleed off the charge and actually protect the whole neighborhood from strikes.

Well, after completing these last three projects ( 10M Yagis, 20M Yagis and 10/20/40M fan reference dipole) I should be all set for the year, I hope...  and get some operating in...

What's new with you? Any recent projects?

T


EDIT:    BTW, I bit the bullet and ordered a NanoVNA unit today.  I will use it to set the parallel resonance on the 10M and 20M coax chokes at the feed points.  Maybe it will help to set up the 10/20/40M fan dipoles too.   I watched a few YouTube videos about the VNA and it is really involved!  It was mentioned here that the MFJ-259 is a 50 ohm based system and will not work for choke resonance.  But the Nano appears to have 50 ohm channel 0/1 connectors too....?  

Also, there was a  article somewhere about tuning the coaxial choke using the VNA. Was it DX Engineering?  I can't seem to locate it...
 

Hi Tom,
I was kidding you a little-cannot help it…😉😂😂😁
Seriously-
I like your approach. At 25ft, you are 3/4 wavelength above ground and at 45 feet, you are closer to 3/2 waves. That is not going to burn out the overhead angles at all…😉

Ground reflection gain is a real thing. When I used to go to the Central States VHF conferences, ther measured antenna gain an the receiving standard antenna was placed close to the ground to eliminate ground reflection gain, but in real operations, it can give you up to 2dB more. We always tried to hear moon echoes back then at moonrise to get that edge…😎
Obviously, it is much more efficient when the horizon is seawater or in your case, maybe below the horizon.
Your half wave stacking will give a very focused clean polar graph plot and the E-plane plot will enjoy your positioning. I am assuming here that you are not that far from the sea and that your ling horizon is blow horizontal.
Only horrible ground losses could make this not a great idea.
As for more vertical stacking, that can be a bad thing with paths providing differenr optimal takeoff angles.
I had an elevation motor for my big array on 2M and even with tropo, the angle does matter at times to hit ducts, etc..
You will get at least a 12vtimes ERP multiplier with that rig and with ground relection it might reach over 20x.
If 10 is open, you can work the world in 10 watts, so 20-35+ KW ERP should be almost enough…😉😁😂😂
Very exciting work, Tom. You have thought this through very well IMO. 73, Mike

[K9MB]

Tom,
You are likely buried in the actual work of putting up your 2x 4el yagi array for 10 meters.
I was reading an old Eimac bulletin today and ran across this interesting article that was part of my research in the mid-70s Moonbounce work that I did with W9UWL.

This article begins with a description of the Stanford University project to see what was required to accomplish moonbounce with HF transmitters.

This is an array of 40ft boom Vee Logs with 40 elements per Log and the phased array was 75 feet wide and 1200 feet long. The gain was 27dBDand the polar plot was 1.5 degrees by 30 degrees with the azimuth getting the 30 degrees for maximum window of time.
Since it was linear polarized, they whistled into the mic until they got maximum reflection from the phase rotation inherent in this mode, and then they sent their identification. 600kw was the output of the transmitter….
😂😂😂 Tom, I hate to tell you, but there were guys ahead if you with bigger arrays on 10 Meters…😉😁

What is so funny about this is that it could be done at 144 or 432 with far less power with passive parabolic reflectors….
However, if you really want to cook the E and F layer over the pond, the design is out there and all you need to do is make it into a quarter mile curtain about 150 feet tall.  Thus was for amusement, however, not a suggested design…😉 73, Mike

[K1JJ]

Yo Mike,

Yep, men and their toys....  it's amazing what motivation we have in our youth...


Update:  I figgered out how to use the nano VNA for antennas and coaxial choke optimization.   Definitely alien technology. The YouTube videos were invaluable.  

Using a 6" PVC form, I was able to duplicate  5K - 15K ohm parallel resonant coaxial chokes (no ferrite) on 14 MHz and below.  Yes, the VNA goes nuts when the impedance gets above 5K or so. Roughly 5T = 11 MHz.  7T = 7 mHz.  16T = 5.8 MHz. The closely wound solenoid winding is very important to generate the inter-capacitance to create a resonate circuit.  And, too many windings will kill the impedance.  Without resonace, the choke (without ferrite)  is about useless in most situations, sometimes less than 50 ohms..  For 20M I found only 2.5 coaxial turns were needed to make a 4K choke.   On 10M a different approach will be needed cuz we are down to a single turn.  Those turns numbers may change in real use - I did a rough wrestling match with the coax...  The toroidal  approach for 10M may be needed as we discussed before, I don't know yet.   Note:  The coaxial coil is very sensitive to surroundings. Even a close hand can have a big effect.  IE, watch when mounting them. It's like mounting a tank coil in a rig, especially when resonant and high impedance like this..

The new 10,15, 20, 40M  FAN dipole combo is working very FB.  I needed to use PVC tubing spacers for the first 18' of the 10 and 20M sections cuz the leg spacing greatly affects the swr tuning on these bands.  40M is pretty stable.  It's best to get a stable physical spacing and then adjust the leg length for swr.  I raised the FAN to 50' high and find the swr to be under 1.5:1 on most bands.  On the air A/B tests shows gain performance to be the same as a regular single dipole, as you'd expect. The 50' height above ground is a good higher angle "fill in." Nice efficient use of feed line and space.  The use of rope and pulleys is important for rapid adjustments.  I'll post some pics in a week or so.    ** I supported the feedpoint /feedline, heavy ferrite donuts and PVC spacers in the middle -  on the tower. VERY important for this heavy antenna, especially for ice.  Use a big 4" diameter metal pulley and 3/8" rope for the feedpoint hoist halyard. Smooth and strong.

For what it's worth, using the 10-40M FAN, I can change bands in about one second using the 20W Hi-Fi ricebox. On AM, I can go "hello 40M, hello 20M, hello 15M, hello 10M" all using ricebox presets. Yipppppe!   75M and 160M  takes one extra antenna toggle. Now I need a BIG autotune solid state linear to make it really count.  

The 20M 2x2x2 Yagi stack is coming along. I was just waiting for the coaxial choke design to be ironed out for it including the 10M 4 el stack. Now I can proceed once the rain stops.  The drought – we really needed the rain and got a few inches – more the next day or so.   I still climb almost every day.  

The 75M loops are really performing well - including the 75M broadband fan.  I'm looking to put it all to bed within this month to move on to some operating.  I hear a lot of talk on the air about the solar cycle activity and the low band intentions of 75M and 40M Dxers. I'll be ready.

T

[K9MB]

Yo Mike,

Yep, men and their toys....  it's amazing what motivation we have in our youth...


Update:  I figgered out how to use the nano VNA for antennas and coaxial choke optimization.   Definitely alien technology. The YouTube videos were invaluable.  

Using a 6" PVC form, I was able to duplicate  5K - 15K ohm parallel resonant coaxial chokes (no ferrite) on 14 MHz and below.  Yes, the VNA goes nuts when the impedance gets above 5K or so. Roughly 5T = 11 MHz.  7T = 7 mHz.  16T = 5.8 MHz. The closely wound solenoid winding is very important to generate the inter-capacitance to create a resonate circuit.  And, too many windings will kill the impedance.  Without resonace, the choke (without ferrite)  is about useless in most situations, sometimes less than 50 ohms..  For 20M I found only 2.5 coaxial turns were needed to make a 4K choke.   On 10M a different approach will be needed cuz we are down to a single turn.  Those turns numbers may change in real use - I did a rough wrestling match with the coax...  The toroidal  approach for 10M may be needed as we discussed before, I don't know yet.   Note:  The coaxial coil is very sensitive to surroundings. Even a close hand can have a big effect.  IE, watch when mounting them. It's like mounting a tank coil in a rig, especially when resonant and high impedance like this..

The new 10,15, 20, 40M  FAN dipole combo is working very FB.  I needed to use PVC tubing spacers for the first 18' of the 10 and 20M sections cuz the leg spacing greatly affects the swr tuning on these bands.  40M is pretty stable.  It's best to get a stable physical spacing and then adjust the leg length for swr.  I raised the FAN to 50' high and find the swr to be under 1.5:1 on most bands.  On the air A/B tests shows gain performance to be the same as a regular single dipole, as you'd expect. The 50' height above ground is a good higher angle "fill in." Nice efficient use of feed line and space.  The use of rope and pulleys is important for rapid adjustments.  I'll post some pics in a week or so.    ** I supported the feedpoint /feedline with heavy ferrite donuts and PVC spacers in the middle -  on the tower. VERY important for this heavy antenna, especially for ice.  Use a big 4" diameter metal pulley and 3/8" rope for the feedpoint hoist halyard. Smooth and strong.

For what it's worth, using the 10-40M FAN, I can change bands in about one second using the 20W Hi-Fi ricebox. On AM, I can go "hello 40M, hello 20M, hello 15M, hello 10M" all using ricebox presets. Yipppppe!   75M and 160M  takes one extra antenna toggle. Now I need a BIG autotune solid state linear to make it really count.  

The 20M 2x2x2 Yagi stack is coming along. I was just waiting for the coaxial choke design to be ironed out for it including the 10M 4 el stack. Now I can proceed once the rain stops.  The drought – we really needed the rain and got a few inches – more the next day or so.   I still climb almost every day.  

The 75M loops are really performing well - including the 75M broadband fan.  I'm looking to put it all to bed within this month to move on to some operating.  I hear a lot of talk on the air about the solar cycle activity and the low band intentions of 75M and 40M Dxers. I'll be ready.

T

Hi Tom,
I am skeptical of the wisdom of resonant chokes in antennas. Maybe There is a lot I do not understand, but just knowing that the imaginary component inverts at resonance makes me worry about anything above that point. Also, tje sensitivity you observe is real-of course. One wonders what happens with water and ice entering the dialectric function?  Seems like distributed capacitance could rise?
Rising capacitance would shift it lower in frequency.

I hope that I am mistaken, but the ferrites- properly designed provide a broad-highly resistive choking function.

If inductive resonance is good, then why not use the old school 1/4 wave stub to suppress current on the shield?
It is inherently a narrow band device, but has very high impedance at the design band.

For multiband chokes, the 31 or 43 material provides a high loss resistance across a wide range.
I used a pair of FT240-52 Toroids with 13 turns of rg400 for 10-30mHz.
52 Ferrite performs very well above about 10mHz. Stable at high temperatures (high Curie Temperature).
Joe Risert used it a lot I think in his chokes.
I know- I beat the same drum on this. Looking forward to being mistaken. 😉😁

[K1JJ]

UPDATE  9-8-2022:

I took a break from the 10 and 20M Yagi stacks to finish up the reference 10-40M FAN Dipole. The FAN was a tough job to get optimized right, both phsically and electrically. The tuning was challenging because all legs had some effect on the others.  At one point the 20M legs resonated at 14.5 MHz but later were at 13.4 MHz.  The 10M legs were at 25 MHz.  I actually had to TRIM some legs to get them to go down in frequency. Weird.   Very much like optimizing an interlaced Yagi.

Anyway, the end result is now a very strapping, electrically stable and frequency agile antenna.  It uses a tower at 50' as a center support and the ends are anchored to other towers. The SWR is near 1:1 on some frequencies but usually under 1.5:1 on most.  The Fan seems to perform well as a higher angle 50' high dipole compared to other antennas.  I am hearing strong stations on 20M as well as some on 15 and 10M.   The swr is rock solid now that I got the inter-leg spacing tied down.

It is important to get the legs spaced and solid; no movement between them. Then trim the legs to get resonance on each band. I did not need to use a pair of legs for 15M because 40M has 15M as a third harmonic.  Thus, just 10, 20 and 40M legs are needed to cover the four bands.

I find myself using it a lot to compare existing antennas. It will get more use once the new 10 and 20M Yagi stacks go up. Flipping back and forth A/B reconfirms that everything is working well... and suggests the take off angles we are working with at the time.

Mike:  FB on your 1/4 wave stub suggestions for the choke.  For the 10 and 20M Yagis I have decided to use a combination of RG-213 coax turns wound on a big ferrite core as well as a few cores slid over the coax... and even a close approximation of a resonant choke. I'll only need 2-3 turns  for the resonant choke, so might as add it in series with the others.  Being 14Mhz and 28 MHz, shouldn't take too much.

T


Pics:  At 50' high, that's #10 THHS wire with 2" PVC insulators, spaced about 5" apart.  Using 3/8"  Dacron rope and a 4" pulley.  It is easy to raise and lower in seconds for tuning. Just lower the center - the ends stay fixed to access the whole antenna. Imagine that - no tower climbing.   If there is an ice storm threat, I intend to lower it somewhat.  I keep it slack most of the time anyway.

Well waterproofed coax and straight vertical coax drop to the ground.

The center insulator is a big guy cable "Johnny Ball."

Barely moves in the wind.... no trees.

[K1JJ]

Pic 3:  The coax is supported by a pipe hitch, hangman's noose of rope at the center insulator.  You can see the string of ferrite cores on the coax. RG-11 75 ohm connects to the 75 ohm hardline underground. IE, all 75 ohm to the shack.

**Like the GREEN wire?   

[K1JJ]

Pic 2:  Notice that all legs are supported at the ends with rope and insulators.  I did not depend on the spacers for support. Each leg hauls its own freight.

Pic 3:  Tommorrow time to install the coax chokes and get the Yagis operational.  They are already tuned. I'm getting some custom aluminum support arms TIG welded to hold up the 10M Yagis. Once working, on to the triple 20M stack.  I'm hoping to finish the major work by Sept 30.

[K9MB]

UPDATE  9-8-2022:

I took a break from the 10 and 20M Yagi stacks to finish up the 10-40M FAN Dipole. The FAN was a tough job to get optimized right, both phsically and electrically. The tuning was challenging because all legs had some effect on the others.  At one point the 20M legs resonated at 14.5 MHz but later were at 13.4 MHz.  The 10M legs were at 25 MHz.  I actually had to TRIM some legs to get them to go down in frequency. Weird.   Very much like optimizing an interlaced Yagi.

Anyway, the end result is now a very strapping, electrically stable and frequency agile antenna.  It uses a tower at 50' as a center support and the ends are anchored to other towers. The SWR is near 1:1 on some frequencies but usually under 1.5:1 on most.  The Fan seems to perform well as a higher angle 50' high dipole compared to other antennas.  I am hearing strong stations on 20M as well as some on 15 and 10M.   The swr is rock solid now that I got the inter-leg spacing tied down.

It is important to get the legs spaced and solid; no movement between them. Then trim the legs to get resonance on each band. I did not need to use a pair of legs for 15M because 40M has 15M as a third harmonic.  Thus, just 10, 20 and 40M legs are needed to cover the four bands.

I find myself using it a lot to compare existing antennas. It will get bigger use once the new 10 and 20M Yagi stacks go up. Flipping back and forth A/B reconfirms that everything is working well... and suggests the take off angles we are working with at the time.

Mike:  FB on your 1/4 wave stub suggestions for the choke.  For the 10 and 20M Yagis I have decided to use a combination of RG-213 coax turns wound on a big ferrite core as well as a few cores slid over the coax... and even a close approximation of a resonant choke. I'll only need 2-3 turns  for the resonant choke, so might as add it in series with the others.  Being 14Mhz and 28 MHz, shouldn't take too much.

T


Pics:  At 50' high, that's #10 THHS wire with 2" PVC insulators, spaced about 5" apart.  Using 3/8"  Dacron rope and a 4" pulley.  It is easy to raise and lower in seconds for tuning. Just lower the center - the ends stay fixed to access the whole antenna. Imagine that - no tower climbing.   If there is an ice storm threat, I intend to lower it somewhat.  I keep it slack most of the time anyway.

Well waterproofed coax and straight vertical coax drop to the ground.

The center insulator is a big guy cable "Johnny Ball."

Barely moves in the wind.... no trees.

This looks pretty good. I like your eclectic approach on the baluns. Those small coax loops will have pretty high impedance at 28mHz but self resonance will be well out of tue HF bands and the loops through the ferrite cores will provide the necessary wide frequency range for 7-28mHz easily.
You are right about stabilizing spacing. Once you find the right trim, it will be very stable. My only concern might be icing on those large PVC pipe spreaders, though your using center supports make it very strong, IMO.
Very nice work.
These Fans are excellent standards and provide a way to see the effects of MUF on angle of takeoff for multiple hops. Multipaths are going to be there and maybe the best one is not the lowest angle for a give. Path and MUF at each layer providing the reflections.
Keeping notes cam be valuable to others. Not many of us have your resources, but it is quite fascinating to think about all the interactions.
73, Mike

[K1JJ]

Question:

I have the first of three 2el  20M Yagis suspended about 10' off the ground for tuning. I adjusted the driven element for 1:1 at 14.2 MHz.  I roughly calculated a reflector based on 7% longer than the driven element.  Turning it with ropes and listening to a live receiver outside shows it has the usual 15 dB or so of f-b on USA and Eu signals.  All good.

When I slowly shorten the reflector, I see the swr go from 2:1  to 1:1 as the EZNEC model  says it should. The input impedance changes from 80 ohms (as a dipole alone) down to 40 ohms j0 with the reflector in place.  It is behaving as it should. I was using the MFJ-259B.

BUT, here's the problem... when I hook the NanoVNA  to the Yagi and sweep it from 10 MHz to 16 MHz, I see only a single dip for the 14.0 to 14.3 MHz spectrum. It looks as it should with a 1.3:1 or less SWR and 40 ohm impedance. BUT except for a deeper impedance and swr dip on the driven element at 14.2 MHz, I do not see the reflector on the nanoVNA.   Shouldn't there be a second dip or broadening down around 13.70 MHz indicating the reflector coupling?  I tried lengthening and shortening (and detuning) the reflector and there is no sign of its influence on the VNA.   I wanted to use this as a double check for the three Yagis' tuning. Since the reflector tuning allowed me to approximate the model's input impedance of 40 ohms, I'm not worried, but am puzzled why it does not show.  In contrast, I see a big broadening dip from the reflectors at 6.2 MHz on my 2el 40 M Yagis....

Or, does the reflector just show up as an influence on the driven element swr and impedance, but not as a separate component on the resonant frequency it is tuned to?  


Before I finish the tuning and raise them, any ideas?

T

BTW, 20M was really hopping today.  Europe, Russia and other areas were heard big time.  15M has been opening too.  Perfect timing to test the 20M f-b.

[W1ITT]

Tom....Just thinking out loud....  but the reflector and driven element are closely coupled, and they are essentially one resultant impedance at the feedpoint as a result of the mutual impedance that exists between them.  They essentially form a circuit and I wouldn't expect them to show individuality.
I think you're on the right track.  Don't ya love having a swept display with the NanoVNA as opposed to having to take spot measurements.  I still have my old GR916 impedance bridge where it was necessary to adjust the R and X dials to get a null, then read and normalize the dial and log it on paper.  I admit that I haven't used it in years.
It looks like there are a couple of nice crisp fall days upcoming in New England, fine for antenna work.
73 de Norm W1ITT

[K1JJ]

Hi Norm,

I'm hoping you are correct.   I read some articles about tuning a Yagi with a NanoVNA and got the impression that the reflector could be seen.  But I think it was referring to the broading out of the swr and impedance curve...

It talked about tuning the reflector to achieve the final Yagi impedance as the NEC model shows.  This supposedly makes the f-b and gain peak out at the proper input impedance and swr curve.  Maybe this is what I have already done.

I also noticed a single dip on the 75M 2el loop array.   The 40M Yagi's reflectors are tuned at 13% longer, which may be why the curve is so broad.  Maybe the same effect as a 75M fan dipole.  I notice a fat swr and impedane curve on mine.

The VNA sure is an interesting device. Having a few different methods of tuning an antenna gives confidence. It was kind cool rotating the Yagi by hand and hearing the dips and sometimes the aurora sound on DX signals when beaming in various directions. That's another way of knowing it is tuned right.

I tried some experiments bringing the reflector up to 4% longer but find the best overall length is 7% longer for my partiular 20M 2el Yagis using 12' spacing.  I have an old Array Solutions  ferrite transformer combiner.   50,50,50 to 75 ohms.  The easy way out.

Tnx for the answer, OM!

T

[K9MB]

Hi Tom,
I think that Norm has the right idea.
The thing that parasitic elements tuning affects is feed impedance and  the phase shift that deflects the driven element fields back toward the driven element or focuses it away from the driven element in the case of directors.
I have built a lot of yagis and never did the analysis of why it works, but Norm’s idea that it is not two things, but one thing that focuses antenna fields in one direction and away from the other.
The phase of the current causes the directional characteristics, but it is not individual antennas, but one system.
Yagis are a special case, but LPDA antennas use this same characteristic and the phase shifts are caused by length and distance between the active drive system.
End Fire arrays also use this concept, as well.

I can tell you that tuning the reflector even 10-12% lower may not have a huge effect on F-B and the bandwidth will improve. Gain may also be slightly lower at best F-B, but who cares?
Fortunately, 2 element beams work great over a wide range of chosen criteria, unlike the 15 element long yagi I built once for 2meters, which tuned to 144.1 was useless at 145.5mHz because the directors were approaching resonance too close

VNAs are great for measuring impedance and figuring out the reactance needed to effect a match, but may provide more doubt than performance in this case.
I have a dial caliper that I use a lot for precision work, but when cutting a 2x4, a steel tape is all that is needed.
VNAs are, however great for getting you matching and phasing harness right.

7% is fine, IMO and if the match is better at 9%, it will still give good F-B in my experience because the F-B curve is quite flat in slope in that direction, though going too high will hit an inflection point as one approaches resonance- no man’s land! 😬😉

You have excellent performance obviously and only a broadband match and good
F-B across your used band are going to matter, IMO.
73, Mike

[K1JJ]

For the continuation and completion of this antenna project go here:


http://amfone.net/Amforum/index.php?topic=47823.0