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40 Meter Quarter Wave Vertical/75 Meter Inverted L




 
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Author Topic: 40 Meter Quarter Wave Vertical/75 Meter Inverted L  (Read 648 times)
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AJ1G
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« on: February 10, 2020, 06:59:27 AM »

I've recently put up a 40 meter quarter wave wire vertical with an elevated (nominal 8 feet above grade) feed point and 12 elevated nominal  1/4 wave plus a little elevated radials (also nominal  8 feet above grade), will probably add a few more radials this week.  It is fed via a 24 turn 4 in diameter  RG-8X coax  "Ugly"  common mode choke positioned vertically on stand-off spacers just below the feed point.  The vertical radiator is  about 33 feet of three No. 16 twisted insulated stranded conductors - in fact it is a section of an old green outdoor extension cord, including the green jacket, which reduces its visibility.  The three conductors are parallel connected at the feed point and at the top to hopefully make it a bit more broad-banded at resonance. The vertical element is supported by a halyard hung from the crown of a very high oak tree about 20 feet out from the tree trunk.The radials are each No. 16 stranded black insulated wire, most are also made out wires taken out of removed from service outdoor extension cords. A 4x4 post supports the feed point and the inner ends of the radials. The antenna is working very well on 40 for both stateside and DXing.  

I am thinking of adding the capability to add a horizontal section at the top, another nominal 33 feet, to allow it to function as a 1/4 wave inverted L on 75/80.  The horizontal section would be connected for use on 75/80 by lowering the vertical section using its halyard, connecting the horizontal section to the halyard mechanically and to the vertical element electrically, and then hoisting away. While not in use, the horizontal section will just hang at its far end support point, it will not remain in position attached to the halyard.

I will not likely be able to add any elevated quarter wave 75/80 meter counterpoise elements due to space limitations.  Looking for opinions on how it would play on 75/80 with just the 12 to 16 40 meter nominal  1/4 wave radials.
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« Reply #1 on: February 10, 2020, 08:50:49 AM »

Assuming that you can concoct a good match into it on 75m, it should do quite well.  The 40m radial system will act as some sort of counterpoise on 75m, even though it isn't "big enough".  Heck, I regularly hear some fellow in the 80m SSB DX window working  mobile across the pond with good signal reports and all he has underneath him for "ground" is his vehicle parked down by the coast. One trick I have used on both 80m and 160m to establish a semblance of RF ground is to lay down a roll of chicken wire fence with a lead soldered onto it and that lead brought to the usual ground connection.  If your back yard is amenable to this without raising the devil with the lawnmower it's a powerful technique.  The Sherwood Engineering site  sherweng.com has an article about some good measurements he did for the old Ham Radio Magazine that show this is science and not voodoo.
Match the system on 75m and it'll work well.
73 de Norm W1ITT
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« Reply #2 on: February 10, 2020, 10:10:05 AM »

Opinion follows:
I think that twelve elevated radial is more than enough to get the most out of that antenna on 40M. You'd probably do almost as well with half as many, and wouldn't notice much difference with twice as many. More improvement might be found by tuning the radials that you have, than by adding more of them.

As for using those radials on 75M...
If you can add even one quarter-wave radial on 75M it should help with the match. Consider zig-zagging a radial for 75M or even a loaded radial to help the match. I doubt it would do very much for the pattern though. You're into a heavy compromise there, and I wouldn't expect too much low angle radiation from it. No free lunch... but it's always fun to try. Smiley


Don
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« Reply #3 on: February 10, 2020, 11:02:52 AM »

Thanks for the quick replies guys.   That "some fellow" working DX in the 75/80 meter DX window you heard most likely was me!  Have  had a lot of fun doing so since about October, with just a Hamstick and 100 watts from an IC-7100.  Haven't heard any other stateside mobiles from this side of the pond working DX down there, there are a couple a them over in the UK, I have worked mobile to mobile with one of them, Rob, M0KPD/M.  Bill, W1ZY up in Matunuck,, RI sometimes plants temporary vertical phased arrays on the beaches or at Pt.Judith Light parking lot, but only on 40 meters AFAIK.

I want to give the inverted L arrangement a try on 75 specifically for DXing in the window, I realize it will probably be a pretty poor performer for local QSOs.  Hoping it will do better than my relatively low 75 meter  (43 foot apex) shallow angle, more like a dipole, inverted vee.  Would really like to have a full quarter  wave vertical on 75 as well as 40, but getting something up that high would be tough, perhaps I could use the halyard that i hoist the 40 meter vertical with to support the middle of a 75 meter quarter wave aluminum tubing vertical at the midpoint....
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« Reply #4 on: February 10, 2020, 11:58:20 AM »

Read up on the FCP, or Folded CounterPoise for the 75 side.

One FCP can work.

For the 40 side, you're already at the point of diminishing returns with 4 raised radials.

Maybe take the next 4 and make 2 for 75......?

--Shane
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« Reply #5 on: February 10, 2020, 04:03:49 PM »

Thanks for the heads up on the folded counterpoise Shane.  I saw some mention of them in my literature search but after seeing some YouTube videos on them my I interest in them has gone up quite a few dB!  Was wondering how I could put up something for 160, have been wanting to get the CE20A Multiphase Exciter and 600L amplifier going on the top band somehow and the FCP is certainly doable dimensionally.  My buddy Steve KL7JT in
Sudbury MA built one of those helical loaded antennas that were the subject of a QST article a while back, and IIRC, the total height of the vertical element is about 30 feet. May try hoisting his antenna up here in place of the 40 meter quarter wave vertical element with some FCPs for top band to see how it plays there.

For 80/75, will try to include maybe 4 elevated quarter wave counterpoise wires in the 40 meter radial mix, there are many more candidate support trees and bird houses further out in several directions, some runs can be straight, some will likely have to be dog legged.

Including a pix of the 40 meter setup feed point and common mode choke, tried to on my initial post but original file size was too large.



* F904CE97-C00F-4BD8-A2CD-CB444D93C17B.jpeg (688.54 KB, 960x1280 - viewed 46 times.)
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« Reply #6 on: February 10, 2020, 07:49:09 PM »

  Tie all of your 40 meter radials together at the feedpoint, and then put them through a single roller inductor back to the coax shield.  You will then effectively lengthen out the radials and actually can tune the antenna's response on 75. There are articles on why you don't want to use 90 degree elevated radials. "HF Antennas for all Locations" by Les Moxon G6XN where Moxon discusses radials of 45 degrees and a single common inductor. Also articles by K5IU and another by KJ6GR "Understanding Elevated Vertical Antennas" in Spring 1995
Communications Quarterly. Their conclusions is that for elevated radials,  90 degrees is probably the worst place you could be.  Ground conductivity imbalance combined with nearby metallic objects cause radial current imbalance and this messes with the antenna's radiation pattern. Their solution is 45 to 60 degree radials with this common inductor. They have data to back up their claims. I went the other way with my inverted L and went 110 degrees or so on the radials and then a series cap to bring everyone into resonance. Worked better before the people who owned the lot behind us decided to finally build a house on their property after 30 years. Lost a whole quadrant of radials! Grin

  Sounds like a fun Project to me.

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« Reply #7 on: February 10, 2020, 09:52:28 PM »

Opinion follows:
I think that twelve elevated radial is more than enough to get the most out of that antenna on 40M. You'd probably do almost as well with half as many, and wouldn't notice much difference with twice as many. More improvement might be found by tuning the radials that you have, than by adding more of them.

What method should I be using to tune the radials?  Where I am at is that all the radials are around 36 feet, a bit on the long side for a calculated quarter wavelength at the 7150 kHz band center.  I also initially made the vertical element the same length.

I initially tried to bring the antenna into resonance using four radials just laid on the ground.  Not having an antenna analyzer, just a Heathkit SWR/wattmeter. An initial sweep showed, as expected, that the SWR was least high at the low end of the band as expected, given the relatively long wire lengths. I then trimmed just the vertical element  down a foot at a time three times. The last foot appeared to overshoot things, with minimum SWR at the top of the band.  At this point with four radials on the ground and the feed point just above the ground, minimum SWR was about 1.6/1.  I then elevated both the feed point and the radials to 8 feet.  This brought the minimum SWR frequency down to about 7200 kHz and reduced the SWR at that point to 1.2/1, 1.3/1 at 7290, and 1.5/1 at 7005.  I added back about 18 inches to the vertical element (the reason for the split bolt splice above the feed point evident in the photo), which moved the 1.2/1 SWR minimum point down a bit to 7150, but did not significantly change things at the upper or lower band edges.  I also did SWR sweeps after adding each additional elevated radial 4 through 9, and then after finally adding radials 9 through 12.  The SWR measurements did not change significantly throughout the radial add on from the 4 radial condition.

I installed the common mode coax choke balun after getting to 9 radials primarily because it appeared some RF was getting into my audio, and to eliminate a flanking path to the ground from the feed line which is laid on the ground.  The RFI was very bad with the initial 4 radials on ground condition, and was greatly reduced , but not completely eliminated after elevating the feed point and radials.  The choke did appear to fully clean up the RFI issue.  No change to the SWR band sweep results were observed with the choke installed relative to those made without it.

So, where to next with respect to the radial tuning? I can get an analyzer involved if thatís what is needed.
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« Reply #8 on: February 11, 2020, 01:51:01 AM »

Tuning the radials was mentioned in this forum before, but I don't recall where exactly. As for a method of tuning, I would guess it could be done the same way the vertical radiator is tuned ó cut and try. Any improvement would probably be very modest if you already have a good match. I suppose the point I was trying to make is that you already have enough radials and there's little else to be done unless you want to try to squeeze the last tenth of a dB out of it. At 36 feet, your radials are already at the '5% longer' rule of thumb length so you're probably good to go.

If you could borrow an antenna analyzer I think you'd find it interesting to use. Our old friend the SWR meter doesn't tell the whole story. An analyzer can speed up the tuning process.

I built an air core choke similar to the one you made but I'm not sure how well mine worked. I've had very good success with ferrite chokes for keeping common mode noise off the line. The effect should be bi-directional. I'm sold on the ferrite chokes.

You've probably done all you need to do to have the antenna work well on 40M. Getting it to work on 75M as an inverted L is another story. I can't recall anyone using an inverted L on 75M. Dipoles and loops dominate on 75M with inverted L's being found on 160M due to the difficulty of having a quarter wave vertical of sufficient height. In the end, you're at the mercy of propagation differences between those bands. It would be interesting to see how well it works on 75M at various distances and band conditions.
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« Reply #9 on: February 11, 2020, 05:32:25 AM »

I agree with you Don that I would probably not see a lot of improvement from where I am at on 40 meters.  Better is often the enemy of good enough.  Iím going to change the 2 white radials to black, to match the rest of them, the black ones are hardly visible against the background of the yard, but the white ones really jump out visually. Picking up a spool of wire this morning to support further adventures with the vertical/inverted L project on 75 and 160. The 75 meter inverted L is being pursued for use in the DX window as a hopeful improvement over the shallow angle inverted vee for long haul work.

Itís probably time for me to pick up a good antenna analyzer.  Would appreciate any recommendations on the best bang for the buck for one these days.  Thanks again for all the help so far!
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« Reply #10 on: February 11, 2020, 12:39:34 PM »

Chris...
Best value per dollar in an antenna analyzer is the NanoVNA.  They are now under $45 shipped on Aliexpress for the 2.8" screen version.  Given the current situation in China, I'd go for an Ebay or Amazon vendor in the USA and pay a bit more.  There's also a new version for about $100 with a 4" touch screen that's better for old eyes.  Either way, you'll want a short SMA to Type UHF or N adapter pigtail.  I have a couple professional network analyzers but I still consider my NanoVNA to be FB OM for lots of ham uses.  There's a fairly long thread on NanoVNA further down into the second page of this Technical section that covers some of the software that's also available for tethering the Nano to a laptop, although the Nano gets the job done all on its own for most things.
I used mine a week ago out in the yard tweaking up my 2m mobile antenna and didn't have to drag half the lab out to do it.
73 de Norm W1ITT
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« Reply #11 on: February 11, 2020, 02:45:03 PM »

Thanks for the heads up Norm on the NanoVNA.  I think Brent W1IA has been using one to tweak up his 2 element 75 meter horizontal phases array.  I have the required adapter you mentioned, actually a couple of them, included in a very nice set of adapters UHF/BNC/N etc to micro SMA that came with my NooElec RTL SDR that my son gave me for Fathers Day a while back.
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« Reply #12 on: February 12, 2020, 07:31:52 AM »

I've recently put up a 40 meter quarter wave wire vertical with an elevated (nominal 8 feet above grade) feed point and 12 elevated nominal  1/4 wave plus a little elevated radials (also nominal  8 feet above grade)... I am thinking of adding the capability to add a horizontal section at the top, another nominal 33 feet, to allow it to function as a 1/4 wave inverted L on 75/80. ... I will not likely be able to add any elevated quarter wave 75/80 meter counterpoise elements due to space limitations.  Looking for opinions on how it would play on 75/80 with just the 12 to 16 40 meter nominal  1/4 wave radials.

Below is a NEC4.2 analysis of these configurations based on the info in the above quote.

The peak gain of the 75/80m inverted L actually is about 0.6 dB greater than that of the 40m vertical (only) configuration.

The attached PDF shows this data with better resolution.


* AJ1G NEC Plots.pdf (376.02 KB - downloaded 16 times.)
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« Reply #13 on: February 12, 2020, 03:39:03 PM »

Thank you for running those models for me!  Canít say itís deployed over perfect ground, but it is smack dab over our septic system leach field, so itís obviously well watered!  Topsoil goes down many feet, the neighborhood was built on farm fields. 

One question about the inverted L plot, is there any azimuth directivity associated with  which way the horizontal L section is pointed, I think what the plot is showing is better radiation on the side of the pattern away from where the L section lies above the radials.

Another question, it looks like the inverted L model for 75 uses only the 12 nominal 36 foot 40 meter quarter wave plus elevated radials, correct?

Of course the proof of the pudding will be A to B comparisons against the shallow angle inverted vee.

One thing Iíve noticed that is contrary to a common observation for verticals vs horizontal antennas is that it is not any noisier on recieve.  Was expecting the worst in that the closest neighborís house sports a 32 panel grid tied solar array.  I can see on my SDR waterfall and hear some low level EMI harmonics during the daytime
that are not detected at night that I suspect is coming from the grid tied system which is somewhat annoying but not horrible, not anything to complain about, similar signal levels on the shallow angle inverted V and the vertical on 40.  Hope Iím as lucky on 75.

For info, enclosing a pix of  the inverters that have been installed in the grid tied solar systems in the neighborhood.





* FAB748CA-F23E-49E5-912C-8917E7212C8C.jpeg (220.22 KB, 1280x958 - viewed 22 times.)
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« Reply #14 on: February 12, 2020, 08:11:04 PM »

The HD Wave inverters are OK for noise production.  They tie in with the panel mounted optimizer....  Surprised youre jot getting worse noise than you are.

480 three Phase.  Must be nice out there!

--Shane
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« Reply #15 on: February 13, 2020, 03:30:27 AM »

The HD Wave inverters are OK for noise production.  They tie in with the panel mounted optimizer....  Surprised youre jot getting worse noise than you are.

480 three Phase.  Must be nice out there!

--Shane
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If the HD Wave inverters are OK for noise production, why are you surprised I am not getting worse noise than I am?   Also, where are  you coming from re 480V three phase comment?  We donít have that in our immediate neighborhood, although Eversource our local electrical utility, has over the last few months brought 3 phase 7200 volt feeders down into our area from two different directions to improve continuity of power to the sewerage plant about a mile away from here. They just the new feeders in service within the last few weeks.  Our immediate neighborhood has about 26 subscribers fed off a single phase 7200 high line tapped off  the three phase feeders about a quarter mile from the house.  I may have mentioned the 3 phase upgrade on another discussion topic.  Eversource has done a lot of work on the upgrade, significant clearing back of trees, and all new much higher poles to carry the new 3 phase feeders, which appear to use much larger circular mil conductors than the old single phase high line feeder.  Hopefully the upgrade will cut down the number of outages we suffer during storms in this area.  We did not have an outage last week when 74 mph gusts/ 60 mph 
sustained wind came through, although there were many outages elsewhere in town.

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« Reply #16 on: February 13, 2020, 05:27:01 AM »

The HD Wave inverters are OK for noise production. 
480 three Phase.  Must be nice out there!

--Shane
KD6VXI

Were you referring to the 480V label on the HD Wave inverter pix?  I think that's the maximum DC output voltage of my neighbor's (to the north, not the one closest to the antennas) solar panel array...
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« Reply #17 on: February 13, 2020, 05:31:55 AM »

Thank you for running those models for me!  Canít say itís deployed over perfect ground, ...

You're welcome. The top section of my graphics page shows the results of an Average Gain Test on the NEC wire model.  The AGT calculation needs to be done using perfect ground conditions.  This model showed an AGT result of 0.02 dB,  meaning the model has almost zero error, and test results are highly reliable ó including for non-perfect conductivity of the ground plane.

Earth conductivity was set to 2 mS/m, d.c. 5 for the other two plots on that page; to be close to its values at/near a transmit site in Connecticut, USA.

Quote
One question about the inverted L plot, is there any azimuth directivity associated with  which way the horizontal L section is pointed, I think what the plot is showing is better radiation on the side of the pattern away from where the L section lies above the radials.

The horizontal wire of the ~80m inverted L is oriented along the +Y axis shown in the wire model section at the bottom of the page.  Maximum radiation for this configuration occurs near the bearing of the -Y axis, as shown in the h-plane and v-plane patterns in that section.

Quote
... it looks like the inverted L model for 75 uses only the 12 nominal 36 foot 40 meter quarter wave plus elevated radials, correct? ...

Yes, correct.  All three sections of that graphic show performance using the same set of elevated horizontal radials (each one ~1/4-wave long on 40 meters), plus the elevated radiator.
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« Reply #18 on: February 13, 2020, 07:32:24 AM »

Thanks again for all the help, looking forward to getting the 75 meter  inverted L configuration in place once this day after day of gloomy cold rainy weather  breaks, seems more like SE Alaska than SE Connecticut winter weather lately.
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« Reply #19 on: February 13, 2020, 08:30:00 AM »

You're correct, that's the DC operating points on the inverter.  Was a long day yesterday....  Pulse hit 186 at the docs, had other things in my mind.

As I said, the HD Wave are OK at noise suppression.  They do nothing for the panel mounted or panel integrated optimizers......  Which are a staple of the solar edge system.

OK doesn't mean great.  Plenty of people have had problems with them, you're lucky.  Having installed quite a few, I can tell you count your lucky stars.

--Shane
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« Reply #20 on: February 13, 2020, 12:24:31 PM »

Whoa!  Thatís one hell of a case of White Coat Syndrome!  Hope all is well..
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« Reply #21 on: February 13, 2020, 04:01:44 PM »

Just got the OK from my neighbor to put a halyard in one of his trees just past my property line for the far end of the 80 meter flat top section, so it will be running to the southwest, putting the better side of the pattern towards Europe.  Now to see if I can  get an OK to send a Beverage wire  through his woods back there on the same axis, and maybe extend the flat top section for 160.  He probably will be OK with both, I fed him power for years from our genset during outages until he got his own generator.
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« Reply #22 on: February 13, 2020, 04:14:07 PM »

Just got the OK from my neighbor to put a halyard in one of his trees just past my property line for the far end of the 80 meter flat top section, so it will be running to the southwest, putting the better side of the pattern towards Europe.  Now to see if I can  get an OK to send a Beverage wire  through his woods back there on the same axis, and maybe extend the flat top section for 160.  He probably will be OK with both, I fed him power for years from our genset during outages until he got his own generator.
AJ1G's neighbor grants him a favor. But there's a catch...
https://www.youtube.com/watch?v=x50KRCdjZX0
 Wink
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« Reply #23 on: February 13, 2020, 11:12:37 PM »

Whoa!  Thatís one hell of a case of White Coat Syndrome!  Hope all is well..

I'll know more next Thursday, that's when I have my follow up for the tests.

Had a zio patch for two weeks.  First weekend I was jn the presence of some serious rf.  Hope it survived.

Blood pressure is high, pulse even higher.

When I was hit with 6 kvdc, I was told it could take a year for the aftershocks (pun intended).  It was a year Dec 18, '19.

Good deal on your neighbor being good w an attachment point.  I've always had a saying, "It's your neighbors that decide how Q5 you'll really be".

--Shane
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« Reply #24 on: Yesterday at 11:10:57 AM »

The 75/80 meter inverted L is up a running.  Did it all yesterday in the sub-freezing cod snap so was confident it would work well.  Final configuration ended up being a sloping inverted L with the extension off the top of the 40 meter vertical running down at about a 45 degree angle to the west.  The original plan to run horizontally to the southwest supported by the neighborís tree has been put in hold for the time being,  will reguire a significant effort clearing tree branches over the run.  Did some researching into using a sloped L section and figured it was worth a try.

Initially tested using just the 12 elevated 40 meter radials.  Got it resonated mid- band near the DX window with a minimum SWR of about 2:1, expected it would be somewhat high due to probable feed point impedance around 30 ohms at resonance.  Saw that I had room to extend at least 3 of the forty meter radials to 1/4 wave plus for 75 meters, did that and left the remaining 40 meter radials still part of the elevated counterpoise.

Resulting SWR after extending the 3 radials actually went up slightly.  Figured that was likely due to further reduction of the feed point impedance.  Tried to improve match at the feed point with a shunt cap of 500 pf, what I use for matching my mobile Hamsticks on 80 and 40 meters.  The shunt cap brought in a near 1:1 match at around 3700 kHz.  Pruned off about 20 inches and brought the 1:1 match point up to 3790 kHz in the DX window. Will do more tweaking and will end up with segments and jumpers  at the end of the L section for best matches at the AM window, DX window, and CW end of band.

Initial results working across the pond early this morning encouraging many ďboy are you loud vs normalĒ?what did you? comments. 😁😁😁 Havenít done any Antenna A Antenna B comparisons vs the inverted V, but significant improvement apparent in received DX signal levels.
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