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Author Topic: Question regarding antenna bandwidth for coax vs: open wire line  (Read 37157 times)
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W1ITT
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« Reply #125 on: August 01, 2022, 09:22:04 PM »

One of the best and most reliable beacons out of Europe was Jan OK3BJJ.  He had a high dipole atop a multistory Eastern Bloc typical large apartment building and he was on the air most every night.  I once went 16 months of working Jan at least once a month, and usually multiple times, even in summer.  The trouble was that he had a high local noise level and could transmit much better than he could hear. Many called, thinking that the propagation ought to be reciprocal.  You had to have a decent signal to overcome the noise and work him and those who didn't make the grade heard "Veak signal. Negatif, negatif." and then he'd go back to CQing.  OK2RZ told me that Jan had died a year or so back.  I miss him.
73 de Norm W1ITT
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K9MB
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« Reply #126 on: August 02, 2022, 01:34:25 AM »

Hi Mike -

Ahhh, the flow state. I have read a few books on it and studied it closely in regards to day trading.  Really good traders do indeed enter this state and become one with the market or whatever skill they need. Intuition plays a big role too. Just like a doctor who has years of experience, he can just feel the solution.

Other than high speed CW, I've never thought of the flow state related to ham radio, however. It must be the same thing, why not? In my case I was focusing intently on the tower work to make the fear go away. I pretend I am in the shack working on a project and the fear of heights gets under control. It works for me because after a few hours the project is completed and I'm climbing down -  and   not fearful anymore. It's the anticipation that's the killer...it's sometimes harder to saddle up the horse and put on the harness than anything else.

I did some ground clearing today and positioned the loops close to perfect alignment with each other and the boom direction. The coax feed point swings on a 40' rope off the tower to distribute the weigh better.  I tuned in the 3806 Euro beacon tonight and see conditions are pretty hot. The loops are working better than even last night.  I may switch directions to the SW with clip leads and see how it does. Since everything has been matched, it should work just as well to the SW using the same parameters.

T

Notice the symmetrical flow of the repositioned loops.  (#10 THHS stranded copper)

Pic #1 and #2 show the new RG-11 coax and feedpoints at the 100' level. They will be supported on the tower legs from 70' and down.  The small 'T's   are the feedpoint PVC center insulator and the string of ferrite beads. The coax is supported by a Chinese fingergrip pipe hitch knot to better distribute stress across the coax.  I've seen the the finger grip used by commercial installers.

Mixed into the picture frames are wires from the fan dipoles and the two 40M dipoles.  The fan dipoles are end to end with the loops, no overlapping. This should maintain good isolation on 75M. They act well isolated on receive often with opposite signal strength.



Nice pictures, Tom. That is an impressive wad of wire up there! 😎
Nice to know that fine tuning the geometries is giving you measurable improvements.

Back to Flow States for a minute. The actual thing that we call Flow State is natural and present in every inventor, artist, great musician, athlete or anyone else who has achieved a level of excellence that sets them apart from all other men. This is not to say that you must be Tesla, or Shakespeare, or Leonardo DaVinci or Mozart or Steph Curry or any other individual that has set himself apart to experience Flow. I have experienced it all my life and I do not compare myself to these great individuals. Mihaly Csikszentmihalyi from Hungary first published about it and I first read about it when I read Daniel Pink’s book, DRIVE. I applied it immediately in my management style, though I had instinctively done much of it before.
Then I attended the Commencement of my youngest Daughter when she graduated from college and Jeffrey Brown, an alumnus at the school spoke about research he had done and his book called The Winners Brain. Brown interviewed hundreds of persons who were at the top of their occupation in sports, music, business, engineering, and many other fields  and he found a common thread. Every one of these individuals had reached the very pinnacle of success in their fields, but they never ever saw themselves as “arrived”, but as being on a journey. The focus was on  making measurable improvements in their performance every single day. No home runs- just a measurable incremental improvement. Every single one of them spent hours improving themselves every day. They described a state if mind where time disappeared and their focus was total and complete and it was always positive.
The fact is that almost everybody experiences flow in some activity and whatever It is, they describe it as fun and rewarding in itself.
It is why you put yourself up there straining and sweating high above the ground for hours and not only do you not want to be paid, but you pay to get to do it.
It is addictive and great fun.
I tell my grand children to choose a career not for how much they can get,paid, though getting paid well is a great thing, but choose to do a thing that you cannot help yourself from doing and be the very best at it that you can and you will also get financially rewarded and never “work” a day in your life, though it will take all your energy and passion to do it better every single day. I deeply admire tue great basketball coach John Wooden. John won 10 national championships at UCLA and he always told his players that it is essential that you “Make every day your Masterpiece”.  Yesterday’s achievements are not good enough and tomorrow will bring more challenges. That is why you are not satisfied with that great Broadband dipole and press on to greater performance for the pure joy of it.
That is what makes me continue to improve my musical instruments when many say they are the best in the world.
We will never get done, Tom and that is a great and exciting thing. I would not have it any other way…😁😎 MB
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« Reply #127 on: August 02, 2022, 06:34:07 PM »

Norm:

This should bring back memories.  OK3BJJ was a regular.  Worked him many times. Your impression is right on... Grin.
 https://www.youtube.com/watch?v=v3wTDL76Q_w


Mike: FB on the flow state.  Yes, it is a real thing and some use it very well.  Your comments are right on.

Speaking of smarts, it amazes me how some of the guys here can answer virtually any technical question.  Many have spent their lives focused on electronics professionally and as a hobby. I have consulted with quite a few over the years and you can always count on getting the right answer.  Guys like W8KHK, WA1GFZ, K1KW, K9MB, W1ITT and others are my "goto" guys.  These elite hams always surprise me with their depth of understanding.

Speaking of projects, today I climbed and dressed up the feedlines for the 75M loops..  They are supported by rope pipe hitches all the way down and do not touch the tower.   I electrically reversed the loops' direction to SW and now hear the VE1's piss weak off the back and the W4s louder on the loops than the fan dipole. Because everything is matched and balanced, I didn't have to change the  40 pF tuning capacitor that tunes the reflector!  Right now the VE1s are S1 off the back and S9 on the fan dipole.  That antenna wants to play!  I can't wait to build up the remote relays that will change directions.  That's when I can really fine tune the tuning cap for best F-B.  Having two directions really tells the story.  I'm still seeing the locals down 20-30 dB, piss weak like I expect on the loops.  I'm hoping the coiled RG-11 or closer proximity to the tower did not hurt performance.  I am still baffled why the open wire and antenna tuner did not work well, so am sensitive to watching for changes.

Looking forward to see how far down the 3806 beacon is down off the back. Later on, a remote controlled tuning cap may be a good idea to give maximum f-b across the band.

Question:  I have an extra 60' of RG-11 left over on each loop. I coiled it up in a hank for now and hung it on a pvc pipe at ground level.  This is also a 1/2 wave point so I added 5 ferrite cores there, next to the coiled cable.  I realize that the coiled hank of coax may have problems with inter coupling, etc.  How should I route this extra cable?  Should I pick up two 5-gallon plastic pails and wind  the RG-11 excess on each in an orderly fashion to improve the CM?  Or should I keep the coax straight.. or make a BIG 3' coiled hank?   I'm thinking that it could add a small amount of CM rejection.

T
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« Reply #128 on: August 02, 2022, 07:24:33 PM »

Tom..Knowing what to do with that 60 feet of "excess" coax calls for measurements.  I can't recall if you said you have one of those MFJ clamp-on RF current probes, but you can make one cheap if you don't.  Fire some RF into the system, set the sensitivity for "some" deflection on the meter and walk along the line (perhaps set up on saw horses} and look for a periodic variation that would match 80 meters.  You have about a quarter wave of real estate to look at so you should find something if there is enough common mode to worry about. Or it might be flat.  ( I believe the habit of calling a low SWR line "flat" comes from the old days when fellows would run RF ammeters shunted along their open wire lines, or neon bulbs in the case of the less financially fortified, to test the match.)  At least in this iteration you are walking along the ground, not hanging on a lanyard.  The spirits of the buzzards of old will be walking with you.
73 de Norm W1ITT
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K9MB
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« Reply #129 on: August 02, 2022, 10:42:48 PM »

Norm:

This should bring back memories.  OK3BJJ was a regular.  Worked him many times. Your impression is right on... Grin.
 https://www.youtube.com/watch?v=v3wTDL76Q_w


Mike: FB on the flow state.  Yes, it is a real thing and some use it very well.  Your comments are right on.

Speaking of smarts, it amazes me how some of the guys here can answer virtually any technical question.  Many have spent their lives focused on electronics professionally and as a hobby. I have consulted with quite a few over the years and you can always count on getting the right answer.  Guys like W8KHK, WA1GFZ, K1KW, K9MB, W1ITT and others are my "goto" guys.  These elite hams always surprise me with their depth of understanding.

Speaking of projects, today I climbed and dressed up the feedlines for the 75M loops..  They are supported by rope pipe hitches all the way down and do not touch the tower.   I electrically reversed the loops' direction to SW and now hear the VE1's piss weak off the back and the W4s louder on the loops than the fan dipole. Because everything is matched and balanced, I didn't have to change the  40 pF tuning capacitor that tunes the reflector!  Right now the VE1s are S1 off the back and S9 on the fan dipole.  That antenna wants to play!  I can't wait to build up the remote relays that will change directions.  That's when I can really fine tune the tuning cap for best F-B.  Having two directions really tells the story.  I'm still seeing the locals down 20-30 dB, piss weak like I expect on the loops.  I'm hoping the coiled RG-11 or closer proximity to the tower did not hurt performance.  I am still baffled why the open wire and antenna tuner did not work well, so am sensitive to watching for changes.

Looking forward to see how far down the 3806 beacon is down off the back. Later on, a remote controlled tuning cap may be a good idea to give maximum f-b across the band.

Question:  I have an extra 60' of RG-11 left over on each loop. I coiled it up in a hank for now and hung it on a pvc pipe at ground level.  This is also a 1/2 wave point so I added 5 ferrite cores there, next to the coiled cable.  I realize that the coiled hank of coax may have problems with inter coupling, etc.  How should I route this extra cable?  Should I pick up two 5-gallon plastic pails and wind  the RG-11 excess on each in an orderly fashion to improve the CM?  Or should I keep the coax straight.. or make a BIG 3' coiled hank?   I'm thinking that it could add a small amount of CM rejection.

T

Tom,
My experience with full wave Delta arrays phased with coax cable is close to zero.
However, I have a couple of fake Socratic questions so I avoid making a complete ass of myself by asserting something wrong:

It seems to me that you have different impedance loops on the differential and common mode feedline lengths.
The differential path is the one that you are tuning for the necessary 90 degree phase shift to get the unidirectional cardioid polar plot you want, is that right?
Seems like that is an odd number of quarterwaves electricallly, allowing for the rg11 velocity factor of 80%?

However, the common mode resonator is a 100% velocity factor because it is in the air- or close to that.

So, of you have an effective common mode choke at the top, why does it matter if the feedline touches the tower or gets close to it? That is a real question-by the way- not a Socratic mind game.

Also, if you have a decent choke at the top, a coil close to 125 feet from the top- 1/2 wavelength in air can only increase the choking impedance and not affect the differential path phasing , so why not?

I do not have answers on this, but those things make me want to ask what might,be stupid questions about these matters.
Norm and Chuck may have direct experience here…

One thing seems clear to me- the use of the rg11 must be isolating the differential path very effectively, given the high  F-B and the lack of need to retune when you switch in your phasing line to reverse.
You are obviously wearing blinders for the locals, exactly what you need to keep RFI and qrm from interfereing with your DX paths.


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« Reply #130 on: August 02, 2022, 11:00:28 PM »

Norm,

OK on the common mode test.   I will look into it and let you know what I find.  Tnx!


[Mike we posted at the same time - see below...]  

Now for another question... I am stuck and cannot proceed with the relay switching and parasitic reflector f-b tuning until this next calculation is done.

Normally to tune a stub for a PARASITIC reflector, I would put a capacitor or inductor across the reflector stub/feedline and try it. If neither worked, I would cut some feedline off and try again until I had a cap or inductor that cleanly covered the range and provided a sharp null of front to back.  I am presently getting a null, but it is very broad... no sharp dip -  and seems far to the edge of the tuning range to be effective.  I think I need to cut some feedline and try again. I would like to stay with a cap if possible. Not sure.

I understand that a 1/4 wave reflects back the opposite value. IE a cap becomes inductive. And, 1/2 wave reflects back the same value, IE a cap is still a cap.

In my case now, randomly cutting the feedline will make a major hardship because of the difficulty of putting on new connectors for RG-11.  I want to calculate the length of the stub, determine the approximate cap or inductor value, THEN cut the feedline.  So far I have some numbers but am not sure before cutting anything.

RG-11 is 0.84 velocity factor.   1/2 wave = 109'.    1/4 wave is 54.5'.     The present feedline length = 176.3' for each loop.   162.5' = 3/4 wave  - it is presently 13.8' longer than 1/4 wave.  This makes it inductive and a cap should work, right?   Each loop was resonated to 3.790 MHz as measured at its feedpoint on the tower, no feedline attached.   Each feedline was measured alone and the low impedance freq was found to resonate at 3.517 MHz using the MFJ meter.

The loops perform decently with NO reflector termination, an open, on the end of the 176.3' stub.  This tells me it is too close to the range border. I see little difference when I tune a 100 pF variable cap or inductor.    What is the proper feedline length to resonate the reflector to about 3.725 Mhz when using a variable cap of 30 - 300 pF?  I have a vacuum cap available I could use. My instinct tells me to cut some feedline, but I'd rather have a calculation guide me first.

Thanks.

T
 

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« Reply #131 on: August 02, 2022, 11:13:16 PM »

Mike,

OK on all.

The loops are using a tuned parasitic reflector.  The 90 degree phasing section is out for now. Maybe later.

As for the RG-11 isolated from the tower... I figured just in case it has some CM, it may be better to let it float. It probably couples to the tower anyway, being only 1' away.
I definitely don't want the two feedlines to see each other. Maybe being overly cautious due to the openwire test failure..

The calculation I need probably uses a Smith chart, though I have figured it out on paper in the past. I have tuned a lot of Yagis and loops using stubs in the past, but I do not like the way this feedline/ stub is acting.  I am usually able to get a sharp null of -30 dB, but tuning the cap anywhere from 0 - 250 pF gives me roughly the same f-b null with this particular 176.3' feedline length.  Maybe the reflector is resonating down around 3550 when I have found it best in the past to be up around 3725 to work well on 3790.

The antenna works "OK" as is, but I think there is a better optimization for tuning in there somewhere.


I hope this is enuff info.

T

BTW, tonight, beaming SW, the Eur beacon on 3806 is down -15 dB off the back. That f-b is "OK" but not quite what I have seen in the past with this array.  The W4s are definitely louder on the loops SW, [vs: fan dipole] which is a good thing.
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« Reply #132 on: August 03, 2022, 10:52:14 AM »

Mike,

OK on all.

The loops are using a tuned parasitic reflector.  The 90 degree phasing section is out for now. Maybe later.

As for the RG-11 isolated from the tower... I figured just in case it has some CM, it may be better to let it float. It probably couples to the tower anyway, being only 1' away.
I definitely don't want the two feedlines to see each other. Maybe being overly cautious due to the openwire test failure..

The calculation I need probably uses a Smith chart, though I have figured it out on paper in the past. I have tuned a lot of Yagis and loops using stubs in the past, but I do not like the way this feedline/ stub is acting.  I am usually able to get a sharp null of -30 dB, but tuning the cap anywhere from 0 - 250 pF gives me roughly the same f-b null with this particular 176.3' feedline length.  Maybe the reflector is resonating down around 3550 when I have found it best in the past to be up around 3725 to work well on 3790.

The antenna works "OK" as is, but I think there is a better optimization for tuning in there somewhere.


I hope this is enuff info.

T

BTW, tonight, beaming SW, the Eur beacon on 3806 is down -15 dB off the back. That f-b is "OK" but not quite what I have seen in the past with this array.  The W4s are definitely louder on the loops SW, [vs: fan dipole] which is a good thing.


Tom,
Again- my experience is nil on this, but a couple of observations:

1- if you put a capacitor across a small loop, the capacitor will be a very high impedance at resonance, so the capacitor is very critical in value to reach resonance.
Putting a 250pF cap across a resonant full loop means that it is across an impedance of  75-200 ohms depending on the geometry of the loop with 100 ohms being common.
Shunting a 250pF cap across a slightly inductively reactive resonamt loop means that it can have almost no effect at all, IMO. Now, if you were to put a capacitor in series with the feed on the loop, you would be injecting a capacitive reactance in series with the inductive reactance and that would tune the loop higher or lower.
However, we are talking about a very small amount of reactance here, so any capacitor will necessarily be very large to effect any change as a series tuning element, IMO.
I am speaking out of general,experience, not specific knowledge here-again…

2- I watched a YouTube video about 2 element yagi modeling and ot includes plots of the frequency vs gain,and F-B functions and it is interesting to see that there is a sharp inflection point in the gain and F-B curves aroumf resonance as a parasitic elemet passes from resonant up t0 be a,director and down to be a reflector.
Above that inflection point, there is a small broad peak,and,then the curve trails off at a low slope function.
This tells me that the tuning of reflectors an directirs are only,very critical,just above and below resonance and then they do not cha ge much for wide frequency shifts.
The thing that is more critical is the match, however and that should be adjusted for maximum power transfer efficiency.
See the screen shot of one of his graphs and the limk to themYoutube video,below:
73, Mike


https://youtu.be/2DcvmGPLdT0


* BF157799-A2F4-426C-86F9-442314129092.jpeg (207.23 KB, 1235x1255 - viewed 169 times.)
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« Reply #133 on: August 03, 2022, 08:40:02 PM »

Hi Mike -

Thanks again for the info.  Yes, a parasitic element will greatly influence the driven element (swr) when its resonant frequency approaches the driven ele. I know where the parasitic element is tuned when the swr soars. In the case of the loops the reflector is down around 3650.  I'd like to pull that up somewhat by trimming the RG-11 stub coax soon.

Did some more testing today.  Got the force feed system [90 degree phase shift section] to work pretty well, but not as good as the parasitically tuned reflector.  So back to the tuned reflector.

The open 176' stub RG-11 feedline is pretty well optimized just as it was cut, by sheer coincidence.  To verify, I added a few feet to it as well as larger sections and the f-b just got poorer. I am convinced that by shaving OFF a few feet of RG-11 it will find the sweet spot of max f-b.

I checked both directions on the band tonight and can see times when there is 20-30 dB f-b both ways.  I think it's time to cut/trim the coax and go for the -30 to -35 dB null.

The reflector tuning seems broader, much broader than the open wire version. The original question, the subject of this thread, was about bandwidth of open wire vs: coax.  The tuner was very hi-Q thus I was never satisfied until I found a sharp dip with the coax. But it's just not there.  I tried adding a bunch of random lengths today with caps and inductors, but there was no super sharp f-b null, just a broad area.  That's OK, cuz I see decent f-b performance from about 3600 up to 3900. Maybe the extra coax loss is causing it.  But the loops are 2-3 S units louder at times than the fan dipole into Eu, so WTF.

So I  designed up a simple relay switching system for NE/SW.  Ordered the relay on eBay, $13.  It's just one DPDT 25A  open frame Potter/Brumfield relay.  The stubs have no coax or L/C components to switch around... just an open stub of the proper length and the driven element.

I'm pretty happy with the present performance and feel like a few fine tuning cuts of the RG-11 will be all that's needed to finish up.  

Early tonight there were a few W3 nets on that I tested with.  Usually they are too close to see much difference, but tonight the W3s were much louder on the loops.  The VE1s were pissweak off the back and loud on the front.  I heard a few Euro hams talking locally come up out of the noise tonight at sunset. It was quite dramatic to hear on the loops - then they dropped down again into the noise minutes later. And the old trusty 3806 Eu beacon was louder than the fan and weaker than the fan in the correct directions.  This is now a few nights of repeatable results.  75M is not an easy band to get decent gain.  F-B is easy - even a loopstick has directivity. But meaningful gain over a high reference dipole is a bitch at times.

When the relays arrive I'll have some more updates.  Switching directions really adds data cuz there is gain in both directions now. Before it was the fan against the loops. Now it will be the added gain of another direction to make it more dramatic.

I'm still seeing a ~6 dB better S/N in favor of the loops. The noise is simply lower. This is not T-storm noise, but ambient background noise.  Not sure why, but the difference is there day or night.  Huge advantage in hearing the weak ones.

T


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« Reply #134 on: August 06, 2022, 08:35:03 PM »

75M Delta Loops UPDATE:  8-6-2022

Hi Mike and all,

I've got some very interesting test results.  Using the tuned reflector technique with an RG-11 coaxial stub. SPST relay for directional switching.

Band conditions certainly have a big effect on the f-b and gain of the delta loops.  Tonight between 4PM and 7PM I saw the best performance so far.  I was listening to 3760 - to a group of VE1s to the NE, about 500 miles away. This is in the same direction as Europe for me.  They were running a net so I had a large sample of stations.  When listening to the NE, there were several stations that were S9 +20 over.  Most were below S9, but all easy copy.   When I switched to the SW off the back, I could not copy any of them!  They dropped into the noise as much as -30 to -45 dB.  I've not seen that deep of a null off the back of this antenna before.  It just took the perfect conditions to show itself.

Now here's the kicker:  There was a group of W4s to the SW centered in Tennessee on the same frequency having a QSO.  Neither group could hear each other. When I listened to the SW, I could hear the W4s S9 +10.   The VE1s  were gone.   When I switched to the NE, the W4s were gone and the VE1s were strong again as before.   This is the ultimate set of rare test conditions - to have two QSOs on the same freq and being able to hear either one clearly - by selecting directions.

I've not tried to trim/ fine tune  the RG-11 stubs feedlines yet. But I would like to raise the sweet spot from 3760 up to around 3800. I notice that the f-b tuning is rather broad, so I think I can get good performance up on 3885 too.  I'm hoping that a trim of about 1' to 2' per leg oughta do it.  

Over the last few nights I've heard a few foreign hams from Europe on 3795 calling CQ with no response. The loops appear to do their job when switching on them.  DX activity on 75M has been dead due to the summer and static. I hope to change that soon... :-)

I've not done any field strength coax measurements yet, but to see deep f-b nulls like this must mean the common mode stray radiation is very low.  The loops always beat the fan dipole when over 300 miles away in the proper direction. Locally, (<100 miles)  the fan dipole is usually about 20 dB louder than the loops. I can usually tell where a signal is from, distance and direction -  in a few seconds. The delta loops have good SWR bandwidth as well as performance bandwidth, so I'm pretty happy with the system so far.

T
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« Reply #135 on: August 07, 2022, 08:00:29 PM »

75M Delta Loops UPDATE:  8-6-2022

Hi Mike and all,

I've got some very interesting test results.  Using the tuned reflector technique with an RG-11 coaxial stub. SPST relay for directional switching.

Band conditions certainly have a big effect on the f-b and gain of the delta loops.  Tonight between 4PM and 7PM I saw the best performance so far.  I was listening to 3760 - to a group of VE1s to the NE, about 500 miles away. This is in the same direction as Europe for me.  They were running a net so I had a large sample of stations.  When listening to the NE, there were several stations that were S9 +20 over.  Most were below S9, but all easy copy.   When I switched to the SW off the back, I could not copy any of them!  They dropped into the noise as much as -30 to -45 dB.  I've not seen that deep of a null off the back of this antenna before.  It just took the perfect conditions to show itself.

Now here's the kicker:  There was a group of W4s to the SW centered in Tennessee on the same frequency having a QSO.  Neither group could hear each other. When I listened to the SW, I could hear the W4s S9 +10.   The VE1s  were gone.   When I switched to the NE, the W4s were gone and the VE1s were strong again as before.   This is the ultimate set of rare test conditions - to have two QSOs on the same freq and being able to hear either one clearly - by selecting directions.

I've not tried to trim/ fine tune  the RG-11 stubs feedlines yet. But I would like to raise the sweet spot from 3760 up to around 3800. I notice that the f-b tuning is rather broad, so I think I can get good performance up on 3885 too.  I'm hoping that a trim of about 1' to 2' per leg oughta do it.  

Over the last few nights I've heard a few foreign hams from Europe on 3795 calling CQ with no response. The loops appear to do their job when switching on them.  DX activity on 75M has been dead due to the summer and static. I hope to change that soon... :-)

I've not done any field strength coax measurements yet, but to see deep f-b nulls like this must mean the common mode stray radiation is very low.  The loops always beat the fan dipole when over 300 miles away in the proper direction. Locally, (<100 miles)  the fan dipole is usually about 20 dB louder than the loops. I can usually tell where a signal is from, distance and direction -  in a few seconds. The delta loops have good SWR bandwidth as well as performance bandwidth, so I'm pretty happy with the system so far.

T


Tom,
I expected the side F-B performance from the graphs I posted last week and that is a great thing.
You have excellent performance on both antennas IMO.

I think that you need to look at all the mechanical design
To see if any improvements can be made and the common mode choke(s). The chokes are the weakest part of your system , IMO, though I am an overkill fruitcake so maybe ignore me…🤪😉😂
Good work. Please, keep posting on sir data.
I have learned a lot from it already.. 73, Mike
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« Reply #136 on: August 07, 2022, 09:44:31 PM »

FB, Mike -

Let's see, mechanical design of the chokes...  How would you improve them?     I sealed them off for water / ice as suggested.  They are supported with rope by the center insulator taking the strain off the coax.  Do you mean the potential lightning pulse problem?


The thing I am concerned about is an ice storm putting a heavy load on the RG-11.  I have no problem with RG-213, but RG-11 is pretty light stuff.  If I had to bet, I would say everything should be OK. The movement will be minimal since supported by towers.

Interesting 75M conditions lately. A few days ago conditions and f-b tests were normal.  Yesterday they peaked and gave outstanding performance. But tonight the loops are about the same strength as the fan dipole and the f-b is less than yesterday.   So tests need to be averaged out for changing conditions.

Tomorrow I will bite the bullet and cut the RG-11 stubs shorter to pull the loops up in freq..  Frank gave a good suggestion to add a relay to switch back in the cut stub - to allow the sweet spot on 3770 to remain as well as covering 3885.  I may do that to broaden the performance range.

I'm trying to find the best place to put up a 20M array. It could be real aluminum Yagis or a wire array of Lazy H's with reflectors.  Everything I've considered has issues with interaction, span distance, wrong direction, weight, etc.  

T

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« Reply #137 on: August 08, 2022, 09:03:24 AM »

FB, Mike -

Let's see, mechanical design of the chokes...  How would you improve them?     I sealed them off for water / ice as suggested.  They are supported with rope by the center insulator taking the strain off the coax.  Do you mean the potential lightning pulse problem?


The thing I am concerned about is an ice storm putting a heavy load on the RG-11.  I have no problem with RG-213, but RG-11 is pretty light stuff.  If I had to bet, I would say everything should be OK. The movement will be minimal since supported by towers.

Interesting 75M conditions lately. A few days ago conditions and f-b tests were normal.  Yesterday they peaked and gave outstanding performance. But tonight the loops are about the same strength as the fan dipole and the f-b is less than yesterday.   So tests need to be averaged out for changing conditions.

Tomorrow I will bite the bullet and cut the RG-11 stubs shorter to pull the loops up in freq..  Frank gave a good suggestion to add a relay to switch back in the cut stub - to allow the sweet spot on 3770 to remain as well as covering 3885.  I may do that to broaden the performance range.

I'm trying to find the best place to put up a 20M array. It could be real aluminum Yagis or a wire array of Lazy H's with reflectors.  Everything I've considered has issues with interaction, span distance, wrong direction, weight, etc.  


T



Tom,
I should have said :
1- Mechanical issues
2- Common Mode choke design

Mechanical-
You already have recognized these challenges and have addressed some of them.
Your sealing system looks very good and leaks are unlikely if you have eliminated internal gaps to prevent anything from “breathing”.
Even small amounts of air moving in and out of an enclosed space will inhale wet air but never exhale all the moisture so it accumulates.

I am uneasy about the RG-11 hanging unsupported.
True-it is light and the skin is tough, but take a trained gymnast and let him hang from the bar for 10 minutes and he will not notice it, raise that to an hour and he rises to the occasion. Make that a week uninterrupted and he goes down.
Like any antenna we put up on a calm sunny day, it looks like it can go on forever, but the it rains and then the rain freezes and the light coax can weigh 75-109 lbs or more and then the strength becomes critical.
This SAT and CATv stuff has low density foam, 50% per- week braid and worse- an aluminum inner shield that bears nothing and will not stretch much.
Ok- the stuff does stretch you get Chinese handcuff action in the braid snd the foil fractures so it is no longer continuous, perhaps.
Can you depend on the feedline to keep the same performance?
That is an empirical question and the experiment will answer it.
As an obsessive over designer, I am impatient to get past the failures and destruction by avoiding all recognizable and preventable failure modes and suffer the jibes and guffaws of my neighbors who consider me an obsessive fruitcake…😉

I have considered it a the easiest thin is to attach a 1/4 inch Dacron braided line to each hanging rg-11 feedline and add knitted a knotted small loop half way down and then tie the top to your 3/8 Dacron line and two 1/4 lines upward to each supporting tower at the half way point as supplemental support and dampers to prevent wagging in the middle.
The downside is that it will be more likely to accumulate more ice, but 1/4 Dacron is good for about 900-1000 lbs, so as long as the top snd middle supports hood, you are good.

Or you could ignore this old obsessive compulsive freak and finish the experiment this winter…😉😂😂😂

Finally- I am still uncomfortable with your California KW cooking you bead skewers at an inconvenient moment..
Of course the most inconvenient moment may be that February I’ve storm snd I’ve is s great cooling substance, so probably not an issue.
73, Mike
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« Reply #138 on: August 08, 2022, 11:37:17 AM »

Mike,

I appreciate the suggestions.

The RG-11 is supported at the feed point at 100' and again at 60' using the Chinese finger grip pipe hitch rope knots.  So there is presently two hanging feeders with 60' and 40' unsupported drops.   When it cools down later in the week I'll climb up there and tape all the unsupported legs to the tower rails.  I'll tape them at 5' intervals.  That should make a big difference in support and also keep the swinging-in-the-wind at bay.   I kinda knew I would eventually have to do this, but wanted to take it a step at a time.

Good point about the internal stress that's put on the foil and braid. Hopefully the light weight of the RG-11 will cancel out the stress vs: using RG-213 that is stronger but much heavier. Maybe it's a wash.

Back in 1988 I had a 120' free hanging vertical drop of RG-213 attached to a 75M dipole. It broke its internal shield braid.  Boy, was that a hard intermittent to find!  Turns out that the coax got stretched out because it was moving up and down in the wind until the braid simply broke and pulled apart at about 8' above ground level.  It was anchored to the ground with too little slack. It would fix itself for a while then rinse and repeat.  I never really found the problem until one day I finally lost patience and ripped the dipole down. It took a VOM braid end to end test to find it. IE, the last thang you wud expect...  So this sorta stuff does happen.



T
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« Reply #139 on: August 08, 2022, 11:02:01 PM »

Mike,

I appreciate the suggestions.

The RG-11 is supported at the feed point at 100' and again at 60' using the Chinese finger grip pipe hitch rope knots.  So there is presently two hanging feeders with 60' and 40' unsupported drops.   When it cools down later in the week I'll climb up there and tape all the unsupported legs to the tower rails.  I'll tape them at 5' intervals.  That should make a big difference in support and also keep the swinging-in-the-wind at bay.   I kinda knew I would eventually have to do this, but wanted to take it a step at a time.

Good point about the internal stress that's put on the foil and braid. Hopefully the light weight of the RG-11 will cancel out the stress vs: using RG-213 that is stronger but much heavier. Maybe it's a wash.

Back in 1988 I had a 120' free hanging vertical drop of RG-213 attached to a 75M dipole. It broke its internal shield braid.  Boy, was that a hard intermittent to find!  Turns out that the coax got stretched out because it was moving up and down in the wind until the braid simply broke and pulled apart at about 8' above ground level.  It was anchored to the ground with too little slack. It would fix itself for a while then rinse and repeat.  I never really found the problem until one day I finally lost patience and ripped the dipole down. It took a VOM braid end to end test to find it. IE, the last thang you wud expect...  So this sorta stuff does happen.



T

I believe that your plan to take unsupported lines to the towers every 5 feet will do it. I see no negatives at all in this and it will prevent the tortuous wind from destroying it.
Time and the elements tell a true story about our decisions in designing antennas.
You have done much to defeat Murphy…😎
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« Reply #140 on: August 16, 2022, 10:32:38 AM »

Tom,
I found this article in a 1984 73 Magazine issue.
The guy built a 75 meter fan and only spread the ends 3 feet and got less than 1.6 vswr from 3760 to 4.0mHz.

Thought you might like to see the article.
My only co cern with his design is that he was using awg 18 galvanized steel electric fence wire for the antenna….😳😬😬😉😂😂.

One cannot help but wonder if part of the broadband characteristics have to do with the extra resistance of the antenna wire.
I bet that he could have achieved 1.00 swr across the entire band if he switched to nichrome wire….😉😂😂😂

Anyhow- assuming that the wire material was not the biggest factor, one might conclude that good results could be had at even smaller end spacings than the 20’ you and others have used. 73, Mike


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« Reply #141 on: August 16, 2022, 11:02:35 AM »

Hi Mike,

Makes sense.  In my case, the difference between a single #12 wire and a 20' spacing effective thickness is X  a few thousand.  So the swr can make stellar improvements over a single wire like <1.5:1  from 3.5 to 4.0  - what I see here.


The difference between  20' and 2' spacing is only about X10, thus the 1.5:1  between 3.760 to 4.0.    But ANY spacing is better than a single wire. [though, in this example it does appear to be non-linear, in favor of using the widest spacing]

I would use copper wire.  

My fan dipole continues to do VERY well for both DX and local work. Best local "compromise" antenna  I have tried.


The 75M delta loops:  I buttoned everything up [project finished] and do a nightly A/B test on the 75M signals. Interesting that the DX window Euro ham stations show the biggest forward gain difference between the fan and loops  - just as I had hoped for.  Also, the loops are much quieter for background noise hiss. I'm still not sure why. It can be 6 dB most of the time and often the difference between hearing the DX or not.  The front-back is amazing on the Euros.  They go from +20 over to into the noise.  However, the f-b to the USA is about 15 dB less. Maybe it has to do with ocean to the NE and land mass to the SW.  It has always been that way over the years.


20M array:
Right now I am about to start a new thread about building up a 10 element 20M array.  I have ten  ~35' long aluminum elements sitting on the ground. They are 2" diameter at the centers, strapping.  I want to build either a 2X2X2X2 array at 35', 70', 105', 140'    OR a 3X3X3.  I'm also considering a common reflector with both a NE and SW driven element to have instant switching NE or SW.   I was listening last night to the 20M EUROS and ZL/VK stations coming in at the same time, around 10 PM.  

Also considering a pair of 4 el Yagis, hanging on gates, using ropes to manually rotate them. I have done that before, but find I am too lazy to go out and rotate them very often...

Will start a new thread in a week or so once I settle in on a design and take some beginning pics.   This has been one of the hardest decisions to make.  There are many options with so many good and bad points to work around. The work load is significant too, based on design.   I plan to tune them individually for gain, f-b and swr by raising and lowering them on a temporary halyard using a beacon and receiver, etc.

I don't plan on any 15M or 10M antennas until I see solid proof of a robust solar cycle. 20M is always a FB band, but when 10 and 15M are hopping, 20M becomes a ghost town.  I have considered a stack of eight dipoles fed with open wire for 10-20M. This would solve the problem, but the system would be bi-directional, thus compromised.  Log periodics are a solution, but mucho work too.  It all depends on the sunspots, which are really unpredictable.  Either way, there should be enough solar activity to provide SOME fun on 10-15M for a few years at worst.   Decisions, decisions.


T
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« Reply #142 on: August 17, 2022, 01:30:32 AM »

Hi Mike,

Makes sense.  In my case, the difference between a single #12 wire and a 20' spacing effective thickness is X  a few thousand.  So the swr can make stellar improvements over a single wire like <1.5:1  from 3.5 to 4.0  - what I see here.


The difference between  20' and 2' spacing is only about X10, thus the 1.5:1  between 3.760 to 4.0.    But ANY spacing is better than a single wire. [though, in this example it does appear to be non-linear, in favor of using the widest spacing]

I would use copper wire.  

My fan dipole continues to do VERY well for both DX and local work. Best local "compromise" antenna  I have tried.


The 75M delta loops:  I buttoned everything up [project finished] and do a nightly A/B test on the 75M signals. Interesting that the DX window Euro ham stations show the biggest forward gain difference between the fan and loops  - just as I had hoped for.  Also, the loops are much quieter for background noise hiss. I'm still not sure why. It can be 6 dB most of the time and often the difference between hearing the DX or not.  The front-back is amazing on the Euros.  They go from +20 over to into the noise.  However, the f-b to the USA is about 15 dB less. Maybe it has to do with ocean to the NE and land mass to the SW.  It has always been that way over the years.


20M array:
Right now I am about to start a new thread about building up a 10 element 20M array.  I have ten  ~35' long aluminum elements sitting on the ground. They are 2" diameter at the centers, strapping.  I want to build either a 2X2X2X2 array at 35', 70', 105', 140'    OR a 3X3X3.  I'm also considering a common reflector with both a NE and SW driven element to have instant switching NE or SW.   I was listening last night to the 20M EUROS and ZL/VK stations coming in at the same time, around 10 PM.  That would be a good reason to have instant switching.

Also considering a pair of 4 el Yagis, hanging on gates, using ropes to manually rotate them. I have done that before, but find I am too lazy to go out and rotate them very often...

Will start a new thread in a week or so once I settle in on a design and take some beginning pics.   This has been one of the hardest decisions to make.  There are many options with so many good and bad points to work around. The work load is significant too, based on design.   I plan to tune them individually for gain, f-b and swr by raising and lowering them on a temporary halyard using a beacon and receiver, etc.

I don't plan on any 15M or 10M antennas until I see solid proof of a robust solar cycle. 20M is always a FB band, but when 10 and 15M are hopping, 20M becomes a ghost town.  I have considered a stack of eight dipoles fed with open wire for 10-20M. This would solve the problem, but the system would be bi-directional, thus compromised.  Log periodics are a solution, but mucho work too.  It all depends on the sunspots, which are really unpredictable.  Either way, there should be enough solar activity to provide SOME fun on 10-15M for a few years at worst.   Decisions, decisions.


T

Hi Tom,
On the fan dipole article above, it is different than the W4xxx antenna that you used that stagger tuned the dipoles in that the elements are equal at 110 feet total.
The K7MEM.com that presents the fat dipole from the Antenna Anthology vol 2 also has equal sides with a 3 ft spacing, so the only difference is that this 73 Magazine article has a fan shape while the fat dipole quickly goes to a 3 ft spacing.

The thing this last guy said was that he gained little more by spacing more, but the wider spaced one stagger tuned, so they are different and may have different optimum spacing when equal or unequal.

My next question, however, is- what would happen if you added a third elements half way between? Could the bandwidth be spaced even more?
I know you are on a different track right now, but it is an interesting question only answerable by empirical testing.

On the 20 meter beam, it made me think of the 6 element wire beam I built by adding reflectors and directors to an extended double Zepp wire antenna.
I wondered at that time what would happen if I could have stacked two of those arrays (8 elements)
My 80 element 2 meter antenna was actually based on 8-10 element beams designed by Russ Farnsworth. It began with an extended double zepp driven element and added a pair of reflectors, and two pairs of directors.
I used coax phasing lines fed by power dividers made from square aluminum tube with copper tube center conductors.
All you need to do is scale it up 10 times to go from 144mHz to 14mHz…😉😂😂😂

Seriously, sounds interesting. I am wondering, though, why you are not making a 5 element Delta beam?
73, MB
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« Reply #143 on: August 17, 2022, 08:40:39 AM »

Tom,

This is a really long thread with lots of iterations. Can you go over your final measurements on loop lengths, spacing and anything else relevant to reproducing this antenna? Perhaps a synopsis article in the Antenna section for posterity?

Thanks,
John
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« Reply #144 on: August 17, 2022, 09:26:51 AM »

Tom,

This is a really long thread with lots of iterations. Can you go over your final measurements on loop lengths, spacing and anything else relevant to reproducing this antenna? Perhaps a synopsis article in the Antenna section for posterity?

Thanks,
John

Hi John,
I second that. Tom has published a lot of length, spacing and other data within the thread, but if compressed, it would make a fantastic article for others to build this excellent design. Do not forget the pics either, Tom. As a technical problem(s), I have felt that belonged here as an engineering problem to be solved.
It would, however, then clearly be an antenna article as a complete design and reside in Antennas. 73, Mike
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« Reply #145 on: August 18, 2022, 11:00:07 AM »

Hi Mike, John -

Making condensed articles is a good idea, though in this case I will leave it as an "experimenter's delight." These threads [blogs at times] are more to inspire and show the various trials and tribulations of constructing an antenna system that is out of the ordinary for performance. This is also a great way of keeping archive notes for future maintenance.  I have many times gone back and referred to things I've built but had long forgotten.  

It is difficult to get more specific with plans to duplicate what I am doing, other than what I have already written. The problem is that for both the fan dipole and especially the loops,  wire lengths are greatly affected by height above ground, shape, spacing, coax velocity factor, other antennas, etc.  The best way is to start with the published formulas and expect to change  dipole/loop lengths until you get resonance on the driven loop or dipole.  Then adjust the reflector stub for each direction to give the best front to back based on real signals on the band.

Delta Loop info:  Each loop is resonant at 3790 (with no feedline).  The two RG-11 open stubs (84% velocity factor) are about 170' long each after final trimming.  Your mileage will vary.


Another thing - unless you can get the bottom of the loops to be at least 1/2 wavelength above ground, it is best to stick with dipoles. (Yagi style)   For effective loops, it would take a 190' tower on 75M and a 95'er for 40M.  So 10-20M loops would be a better way for amateurs with towers of 60' or less.   Inverted Vees will work better than low loops, though flat dipoles should always be the goal for best performance.

There should be enough info within these threads for an intermediate to advanced antenna builder to pull it off.  Or if any questions, just ask away and we will try to help. We help each other as shown by the many, many good ideas that have modified my plans over time.


BTW, 20M array Update:

I settled on a 2X2X2  array.   Three, two-element Yagis at 35', 70' and 105'.   They will be mounted on steel swing gates for manual rope rotation from the ground.  I ordered RG-213 coax, ferrite beads and 2" diameter fiberglass rods for the driven element centers. There will be a combination of coaxial choke and ferrite beads at the three feedpoints.  Now in the drilling and blasting mode.  

The 40M 2x2x2 stacked Yagi array is probably the best performing antenna I have, so why argue with success? I will duplicate it for 20M scaled down by 1/2.   The overall f-b is always greater than a single 2el Yagi due to the "curtain array" effect. My 40M 2x2x2 has a 20 to 25dB f-b.  Also the horizontal main lobe is quite broad compared to a 3el Yagi. This is an advantage when using a manual rotation system as I have.

As a reference dipole, I will add a single aluminum tubing dipole at 65' high, about 150' away from the 20M array.  Notice that 65' is about the average height (center point) of the 20M array.

T
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« Reply #146 on: August 18, 2022, 05:52:26 PM »

Hi Mike, John -

Making condensed articles is a good idea, though in this case I will leave it as an "experimenter's delight." These threads [blogs at times] are more to inspire and show the various trials and tribulations of constructing an antenna system that is out of the ordinary for performance. This is also a great way of keeping archive notes for future maintenance.  I have many times gone back and referred to things I've built but had long forgotten.  

It is difficult to get more specific with plans to duplicate what I am doing, other than what I have already written. The problem is that for both the fan dipole and especially the loops,  wire lengths are greatly affected by height above ground, shape, spacing, coax velocity factor, other antennas, etc.  The best way is to start with the published formulas and expect to change  dipole/loop lengths until you get resonance on the driven loop or dipole.  Then adjust the reflector stub for each direction to give the best front to back based on real signals on the band.

Delta Loop info:  Each loop is resonant at 3790 (with no feedline).  The two RG-11 open stubs (84% velocity factor) are about 170' long each after final trimming.  Your mileage will vary.


Another thing - unless you can get the bottom of the loops to be at least 1/2 wavelength above ground, it is best to stick with dipoles. (Yagi style)   For effective loops, it would take a 190' tower on 75M and a 95'er for 40M.  So 10-20M loops would be a better way for amateurs with towers of 60' or less.   Inverted Vees will work better than low loops, though flat dipoles should always be the goal for best performance.

There should be enough info within these threads for an intermediate to advanced antenna builder to pull it off.  Or if any questions, just ask away and we will try to help. We help each other as shown by the many, many good ideas that have modified my plans over time.


BTW, 20M array Update:

I settled on a 2X2X2  array.   Three, two-element Yagis at 35', 70' and 105'.   They will be mounted on steel swing gates for manual rope rotation from the ground.  I ordered RG-213 coax, ferrite beads and 2" diameter fiberglass rods for the driven element centers. There will be a combination of coaxial choke and ferrite beads at the three feedpoints.  Now in the drilling and blasting mode.  

The 40M 2x2x2 stacked Yagi array is probably the best performing antenna I have, so why argue with success? I will duplicate it for 20M scaled down by 1/2.   The overall f-b is always greater than a single 2el Yagi due to the "curtain array" effect. My 40M 2x2x2 has a 20 to 25dB f-b.  Also the horizontal main lobe is quite broad compared to a 3el Yagi. This is an advantage when using a manual rotation system as I have.

As a reference dipole, I will add a single aluminum tubing dipole at 65' high, about 150' away from the 20M array.  Notice that 65' is about the average height (center point) of the 20M array.

T
Nice summary Tom and I get it, there is a lot of information in the give and take and experimental iterations found in the thread, so keeping it metaphorically placer mining for gold nuggets in these pages as opposed to gold jewelry ready to wear leaves a bit of fun for the next guy to “pan out”.
Also, the reason I will not build a delta loop for  75 meters is precisely because I do not have the requisite150-200 ft towers that allow the performance you are seeing.
However, I am inspired to put some of my own cache of CATV-SAT rg-11 to work for a 60’  high fat dipole or fan dipole myself. It will serve for shorter range hops and my 80’ monopole will rise next year for 160-80 meter longer range work to come.
I have been eyeing a conical monopole setup for that tower with 8-10 wires around the floating insulated 25g center support. Looking at covering 1.5-4.0mHz on that.
This is a fun thread for so many reasons, even as an armchair exercise.
So many ways to do everything!😉 73,MB
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« Reply #147 on: August 18, 2022, 06:45:09 PM »

Tom...
The triple stack of 20m Yagis sounds swell.  I have a question  to axe regarding feeding the stack.  Perhaps it was covered in previous discussion of the 40m stack but it's rather voluminous to peruse at this point.
How do you combine the three Yagis and get things at 50 ohms?  Ages ago when I was building FM transmit arrays, if I had a 3-bay, I'd tune each bay to 150 ohms, j0 and combine them with a wavelength (electrical) of line between them.  As it was air dielectric coax, that gave me one lambda spacing and all was hunky dory.  The middle bay had slightly different mutual impedance to its neighbors than an end bay, but that generated just a bit of null fill in the elevation plane which we did not begrudge.
How is it done at JJ Worldwide?
73 de Norm W1ITT
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« Reply #148 on: August 18, 2022, 08:55:56 PM »

Mike,

Yes, the fan dipole is really a worthwhile project.  When using it, it feels like a dummyload... :-)  I can go anywhere on the whole 75/80M band and see a great match.  75/80M is an especially large band to cover. (%-wise)  

For a DX antenna, if you have limited tower height, like say under 80', then the best antenna for 75M and possibly 40M is a pair of phased dipoles. Space them 1/4 wave and feed them 90-120 degrees out, make them switchable directions and you gots it all.    They work better than a parasitic Yagi when at low heights around 1/4 wave above ground.


Norm,

I was just thinking of how to match the three 20M Yagis...  In the past I usually tune stacked 2 el Yagis for as high an impedance as I can get away with. 75 ohms is possible for each Yagi and still have good broadband gain. When combined and fed with a 1:2 unun or just tied together and fed with 50 ohm coax usually works well. I usually experiment and find the best solution by trial and error.  Sometimes a short 75 Ohm RG-11 insert can help.

I also have a 3 way combiner from Array Solutions... 50 ohms in with three 50 ohm ports out. Gotta see if I can find that somewhere around here.

Also considering a 180 degree flip for the center Yagi which will give a nice higher angle 35 degree takeoff. The three Yagis in phase are about 13 degrees TO.

I was listening to a guy on 20M last night with a 5el Yagi at 140'.  He was having trouble hearing stations and blamed it on the low angles and sharp nulls on his high Yagi. You had commented on this earlier concerning corntest stations. I do not want to get caught with a low angle cigar pattern that works only 3% of the time at best. Especially when angles start going higher later on with active sunspots.


BTW, thinking ahead, I'm considering a fixed NE/SW 10M stacked dipole array.  Wanna hedge my solar bets.  Imagine  TWELVE 10M aluminum elements hung from 190', like venetian blinds, spaced every 16', all the way to the ground.  (190' down to 16')    Or, make the elements full wave and have a bunch of stacked lazy H's.    Each 10M element would connect to the single open wire feedline  fed starting at the bottom, that is flipped over 180 degrees at each element.  The vertical pattern would be clean with ONE lobe at <3? degrees.  The horizontal pattern would be a bi-directional  figure eight, broad like a dipole.  This would be a "listening everywhere" DX array and probably quite fun considering how crazy and unpredictable 10M can get during the hot sunspot times.  Signals coming in from many directions... the times when we burn out rotators trying to keep up with propagation.

The question I have:  Rather than calculate the feedline placement spacing on each element to get a perfect 1/2 wave  0-180-0-180.... phase relationship with cumulative errors, how would you experimentally find the proper feedline connections?   What if you stretched out the feedline horizontally 5' above the ground, terminated it at the other end and put 100 watts into it and used a florescent light or FS meter to find each perfect 1/2 wave point. Then tie on the element and go to the next position based on the brightness, etc.?  I imagine adding each element would drag the phase a little off, but not sure.  I don't want to build one of these and "hope" the calculated phasing is correct; rather have it right on the money since a small error on 10M can really add up over a twelve element run.  Maybe after doing a few element placements, the spacing distance will be the same and not require further placement effort...  

I will be using  #10 THHS insulated wire for the OWL.  I don't want to go with equal multiple OWL feedlines due to complexity and the fact that it is only for 10M, thus I can get away with the 0-180-0 flip..  

Any ideas?   I figgered you've had a lot of experience here with the many SW BC station arrays you've set up.


T
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« Reply #149 on: August 18, 2022, 10:11:54 PM »

Tom...
I don't think the fluorescent light will give you the precision that you want and need for the 10 meter Venetian.  Do you have one of the NanoVNAs ?  If not, get one.  The new VNA-lite or whatever they call it has a 4" screen and goes for around $150.  They go up to 6 ghz but we HF guys don't care.  Or you can even do this for $50 with the original Nano.
What you do is connect the Nano to the feedline via a balun.  Set a marker for whatever 10 meter frequency you want to play at.  Then take a reference point by putting a shorting bar across the feedline.  A bolt or a butter knife will work.. Obviously, enameled wire complicates this.   Looking at a Smith Chart ,note the position of the marker on the perimeter of the Smith Chart.  Every trip around the chart is a half wavelength.  You can take this from there if you use a tape measure to get you into the ballpark and the VNA to get some precision.  I can't recall if the Nano can change the phase reference position like the expensive analyzers, but it doesn't matter.  Just memorize the starting point. Or start your butter knife at a point that's easy to recall (i.e. the right end of the axis of reals)  If you can enlist a helper, you can take the smart end (the VNA) or the dumb end (the butter knife) and mark the points on the line for precise placement of your dipoles.   Remember the Lecher Lines we used to read about in the old buzzard radio books?  This is in the same vein but now we have great instruments for chump change.  We can now locate half waves and multiples with great precision.
73 de Norm W1ITT
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