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Electronics => RF, Microwave, Ham Radio => Topic started by: metrologist on January 02, 2024, 09:41:23 pm

Title: End Fed Random Wire
Post by: metrologist on January 02, 2024, 09:41:23 pm
I haphazardly strung this up:

From MFJ antenna tuner:
Ground terminal to house electrical ground.
Antenna Wire terminal runs ~8 feet along wall, out and up ~10 with insulated wire. From here, the rest of the bare copper clad wire antenna forms an L with the short leg ~30 feet long horizontal and ~12 feet above ground, then the long leg is anchored into a tree about 100 feet away and 50 feet above ground.

I was expecting the radiation pattern to mostly shoot off in the direction of the tree, or somewhat left of there, and probably mostly up. I tried modeling just the L parts in EZNEC, a program I've never used and only spent about 5 mins using. I cannot find how to activate the 3D or elevation plots, but this is what I have.

(https://i.imgur.com/OF8fhma.png)

This seems to be showing me the main "lobe" is opposite of what I was expecting. ?

Also, I'm thinking of running a coax feed out of the shack since probably most of the RF isn't even getting out...

Any other thoughts?
Title: Re: End Fed Random Wire
Post by: Mr Simpleton on January 02, 2024, 10:30:02 pm
You find 3D plots if you point at Plot Type in main screen, select between Az El or 3D. In the Wires definition page, you set antenna height with Z... and you can do so with all wires by choosing "Change height by...." in the drop-down menu.

Operating at 3,8 MHz you will find most energy goes straight up :) Even with the wire 20 meter off ground this is just 1/4 wave lenght. But even so you will make loads of contacts, even DX!
Title: Re: End Fed Random Wire
Post by: metrologist on January 03, 2024, 01:08:42 am
Thank you. I found the plot type setting. I am specifically interested in contact between Japan and US mid-West coast.
Title: Re: End Fed Random Wire
Post by: A.Z. on January 03, 2024, 08:59:46 am
Would you be so kind to post an image of the wire geometry infos (or either to attach the .ez model file) ? I'd like to have a look at it and run some simulations

Notice that the WHOLE run of wire acts as an antenna, not just the portion outside the building, this means that part of the RF will be radiated "inside" and that when receiving the "domestic noise" will be picked up by the portion of the antenna running near/inside the house, it would be a better idea feeding the antenna using and impedance transformer (UnUn) and a run of coax, and keeping the feedpoint away from the house, check here http://vk6ysf.com/longwire_antenna.htm (http://vk6ysf.com/longwire_antenna.htm) for some ideas, notice that while the author doesn't mention it, the coax feeder will also need a good choke, otherwise you'll experience "common mode hell" :D, so it would be advisable to put something like this http://vk6ysf.com/balun_choke_balun_hf.htm (http://vk6ysf.com/balun_choke_balun_hf.htm) on the coax, either directly after the transformer or at some point along the coax before it enters the house; regarding the antenna, I suggest you to read the following

https://udel.edu/~mm/ham/randomWire/ (https://udel.edu/~mm/ham/randomWire/)

https://k7mem.com/Ant_End_Fed.html#Not_Random_Multi (https://k7mem.com/Ant_End_Fed.html#Not_Random_Multi)

as for the "counterpoise" if you have some room, a number of wires laid on ground, spread around and connected to ground stakes should do pretty well

HTH

[edit]

Just to give you an idea, you may put the feedpoint near ground at the tree, run a vertical wire up to about 50ft and then run the remainder of the wire to a rope holding it at 12ft, the total lenght of the radiator should be around 135ft (including both the horizontal and vertical portions), the antenna will be fed using a coax running from the house to the base of the tree, the 9:1 will be connected to the antenna and to a ground stake (or a system of ground stakes and wires) and the choke will be placed on the coax before it enters the house, you may try modeling it in ezNEC and see how it behaves, notice that with a 135ft radiator the antenna will allow (with the help of the ATU) to work all bands from 160 to 10 meters

Title: Re: End Fed Random Wire
Post by: A.Z. on January 03, 2024, 03:28:14 pm

Just in case, since I've no ezNEC around (I prefer 4NEC2) I've put together a model of the setup I described above, if you want you may try 4NEC2 and give the model a try, the comment should hopefully explain what the various lines represent :)

Code: [Select]

CM random wire antenna
CE

SY freq=3.500           ' test frequency
SY wave=(300/freq)      ' Lambda (not used)

SY wire=0.00125         ' wire radius

SY totl=45.11           ' total wire length (meters) try 32.885 too !
SY grnd=0               ' ground
SY vert=15.24           ' vertical portion
SY horz=totl-vert       ' sloping portion
SY hend=3.66            ' sloping portion height

SY segl=31
SY segs=9

SY fwir=1
SY fseg=1

' calculate the endpoint for the sloping wire
SY side=vert-hend
SY endp=sqr((horz^2)-(side^2))

' antenna geometry
GW  1 segl 0 0 grnd    0  0 vert wire
GW  2 segl 0 0 vert  endp 0 hend wire

GE  1

' ground (real, average)
GN  2  0  0  0  13  0.005

' wires, insulated copper
LD  7  0  0  0  2.1 wire
LD  5  0  0  0  58000000

EK

EX  0 fwir fseg 0 1 0 0

FR  0  1  0  0  freq  0

EN


HTH

Title: Re: End Fed Random Wire
Post by: metrologist on January 03, 2024, 04:23:26 pm
Thanks A.Z.!

There are likely many parameters that I have not set. Looks like the main lobe is going to Brazil's east coast. That's the wrong way! Unless I don't understand how EZNEC is plotting the pattern.

(https://i.imgur.com/HgvGV9N.png)
Title: Re: End Fed Random Wire
Post by: A.Z. on January 03, 2024, 05:59:31 pm
that's the VERTICAL lobe, switch to the horizontal one or to 3D, or better, take the time to RTFM and familiarize with the program; frequency, ground type and other parameters... ALL influence the radiation pattern :P

Title: Re: End Fed Random Wire
Post by: metrologist on January 03, 2024, 11:26:38 pm
OK, thank you. I started to take the car around the block. I found the manual a bit too conversational. I got a lot out of loading up some pre-packaged designs.

The Az. plot is in the first post.  :)
Title: Re: End Fed Random Wire
Post by: A.Z. on January 04, 2024, 06:29:16 am
here is some stuff you may want to check

https://www.arrl.org/antenna-modeling-for-beginners (https://www.arrl.org/antenna-modeling-for-beginners)

https://www.arrl.org/files/file/Antenna%2520Modeling%2520for%2520Beginners%2520Supplemental%2520Files/EZNEC%2520Modeling%2520Tutorial%2520by%2520W8WWV.pdf (https://www.arrl.org/files/file/Antenna%2520Modeling%2520for%2520Beginners%2520Supplemental%2520Files/EZNEC%2520Modeling%2520Tutorial%2520by%2520W8WWV.pdf)

but, again, could you please post your ".ez" model file (just attach it) ?
Title: Re: End Fed Random Wire
Post by: iMo on January 04, 2024, 08:56:01 am
The problem with above simulation is the "feed point impedance" of the wire.
What is the value of it? You are using the MFJ tuner, thus it could be almost anything after the tuning into the band. That will influence your simulation, imho.
Title: Re: End Fed Random Wire
Post by: A.Z. on January 04, 2024, 10:28:36 am
Ok, got a bit of time in my hands, picked the geometry coords from your image and remodeled the antenna in 4NEC2, configured the ground type and the wires with acceptable parameters as visible in the first picture and then ran the simulation and a full HF sweep as visible in the second image, the antenna is not exactly "exceptional", and may probably be improved a bit, on 3.8MHz as for your simulation, the antenna is almost omnidirectional with NVIS pattern, notice that I added a 5th wire (tag #9) between the feedpoint and ground and that the impedance/SWR curves may probably be improved by adjusting the total radiator length, also notice that, since part of the radiator wire runs from inside out, the real radiation pattern will be skewed by walls, I refrain my suggestion of feeding the antenna using a 9:1 transformer and placing the feedpoint far away from your home, so feeding the antenna using a run of coax

Also notice how, by setting up proper parameters, the results change, modeling in NEC isn't difficult, but one must pay care to configure all the parameters, otherwise the results will be far from being reliable, also notice that there's a mistake in the model (pic), the "source/load" tab should show  tag=1, seg=1, opt=0, real=1.0, imag=0, magn=1, phase=0, norm=0
Title: Re: End Fed Random Wire
Post by: iMo on January 04, 2024, 11:02:43 am
Quote from: A.Z. on January 04, 2024, 10:28:36 am
.. I refrain my suggestion of feeding the antenna using a 9:1 transformer and placing the feedpoint far away from your home, so feeding the antenna using a run of coax
..

I would recommend that too, even the tuning of the 50ohm coax via the antenna tuner is not optimal. Trifilar 8-10 turns on a FT43-140(240) will do the job. You may use 450ohm as the feedpoint impedance then for the sim. Also mind random length end fed antenna requires good grounding or counterpoise (best done at the 1:9 transformer).
Perhaps you may try an EFHW 80-10m band antenna, you would need aprox 22m length of wire (with the 110uH 80m resonance coil) and the 1:49 unun. No antenna tuner needed then (when the antenna is cut properly).
Title: Re: End Fed Random Wire
Post by: A.Z. on January 04, 2024, 11:27:08 am
Quote from: iMo on January 04, 2024, 11:02:43 am
Quote from: A.Z. on January 04, 2024, 10:28:36 am
.. I refrain my suggestion of feeding the antenna using a 9:1 transformer and placing the feedpoint far away from your home, so feeding the antenna using a run of coax
..

I would recommend that too, even the tuning of the 50ohm coax via the antenna tuner is not optimal. Trifilar 8-10 turns on a FT43-140(240) will do the job. You may use 450ohm as the feedpoint impedance then for the sim. Also mind random length end fed antenna requires good grounding or counterpoise (best done at the 1:9 transformer).
Perhaps you may try an EFHW 80-10m band antenna, you would need aprox 22m length of wire (with the 110uH 80m resonance coil) and the 1:49 unun. No antenna tuner needed then (when the antenna is cut properly).

Yep, and I already suggested that here

https://www.eevblog.com/forum/rf-microwave/end-fed-random-wire/msg5256861/#msg5256861 (https://www.eevblog.com/forum/rf-microwave/end-fed-random-wire/msg5256861/#msg5256861)

the ideal setup would be having a remote ATU, but willing to stay with a cheap/simple setup I believe that, using a 9:1 (and a good choke) and carefully choosing the length of the radiator, the result will be more than acceptable

Title: Re: End Fed Random Wire
Post by: iMo on January 04, 2024, 12:46:42 pm
Quote from: metrologist on January 03, 2024, 01:08:42 am
Thank you. I found the plot type setting. I am specifically interested in contact between Japan and US mid-West coast.

For that you want a ground plane (GP) vertical antenna. The radiator aprox 20m (lambda/4 for 80m band) tall and plethora of counterpoises in a star config at the ground (or beneath the ground, or similar config). The feed impedance is below 50ohm in such a case.
Such an antenna will have around 5degree main lobe elevation radiation, perfect for DXing.
With your current setup the FT8 or CW may work, an 80m SSB QSO would be rather a pretty special event..

PS: or better go for it in the 20m band (14MHz, best for your purpose), and with a 5m tall GP antenna or a dipole.
Title: Re: End Fed Random Wire
Post by: A.Z. on January 04, 2024, 02:00:04 pm
The alternative, if one has room, would be a doublet fed using a balanced line or, even better, a so-called "lazy loop" or "sky loop", both would allow multiband operations with an ATU but offer better performance, as for the doublet, some good references can be found here

https://ftp.unpad.ac.id/orari/library/library-sw-hw/amateur-radio/ant/docs/Introducing%20the%20All-Band%20Doublet.htm (https://ftp.unpad.ac.id/orari/library/library-sw-hw/amateur-radio/ant/docs/Introducing%20the%20All-Band%20Doublet.htm)

http://on5au.be/content/a10/wire/abd.html (http://on5au.be/content/a10/wire/abd.html)

then if ONLY the 80 meters band is of interest, there are other antennas which may fit the bill
Title: Re: End Fed Random Wire
Post by: metrologist on January 04, 2024, 08:18:11 pm
Thanks for all the info and time.

My lot is a 2:1 rectangle running E-W, and I do not have any means to add tall supports on the W side. I had also considered an inverted V fan dipole for 40M up as that is the longest leg I could accommodate in the direction I wanted.

Or I am considering https://medxr.blogspot.com/2015/02/the-tilted-terminated-folded-dipole.html
Title: Re: End Fed Random Wire
Post by: A.Z. on January 04, 2024, 08:29:36 pm
ok now you're running on a blade

http://hflink.com/antenna/Build_a_T3FD_Antenna_by_Tony_Rycko_KA2UFO.pdf (http://hflink.com/antenna/Build_a_T3FD_Antenna_by_Tony_Rycko_KA2UFO.pdf)

but I still have. some hope
Title: Re: End Fed Random Wire
Post by: metrologist on January 04, 2024, 09:08:54 pm
Yes.

I could stick with what I have strung up, feed with 75 ohm coax, and connect the braid to the house gutter that runs to about -30X, -6Y .

Title: Re: End Fed Random Wire
Post by: p.larner on January 05, 2024, 01:52:48 am
why not try a g7 fek antenna?,just use a fishing pole.
Title: Re: End Fed Random Wire
Post by: metrologist on January 05, 2024, 08:39:54 am
OMG, is that the Goldilocks of small home antennas? The article I found has the following headlines:

Ideal Replacement
Tested under the most difficult conditions
More Bands
Ideal home project

Yes!
https://www.g7fek.co.uk/blogus/newsshow.php?page=G7FEK_Limited_space_anten_29507 (https://www.g7fek.co.uk/blogus/newsshow.php?page=G7FEK_Limited_space_anten_29507)
Title: Re: End Fed Random Wire
Post by: iMo on January 05, 2024, 09:24:31 am
The g7fek antenna is still 19m+2.5m long (plus the ~12m counterpoise). Mind the ladder will radiate as well.
An EFHW80-10m antenna is 22m long, no counterpoise needed, almost always much better swr as the one depicted in the above link.
Title: Re: End Fed Random Wire
Post by: A.Z. on January 05, 2024, 10:15:02 am
Quote from: iMo on January 05, 2024, 09:24:31 am
The g7fek antenna is still 19m+2.5m long (plus the ~12m counterpoise). Mind the ladder will radiate as well.
An EFHW80-10m antenna is 22m long, no counterpoise needed, almost always much better swr as the one depicted in the above link.

Well, yes and no, the G7FEK isn't a "miracle antenna", yet with respect to an EFHW it offers pretty low radiation angles even if installed relatively low with respect to ground

https://rsars.files.wordpress.com/2013/01/g7fek-antenna-analysis-iss-1-31.pdf

on the other hand, an EFHW (or an EFRW) are easier to put together, and with a bit of care in installation, may offer good performance; given that the OP doesn't have room for large antennas, an endfed installed in "inverted L" configuration will fit and offer good performance, he wrote that the higher point is at about 50ft, now, a vertical wire going all the way up from ground to 50ft, followed by a section sloping down from the top, would represent a simple, cheap and easy (to setup) antenna, the system would then be fed at the bottom using a 9:1 transformer (UnUn) connected between the radiator and a ground stake or a number of radials laid on ground, then a choke (a Guanella) will connect the transformer to the coax running all the way to the shack, basically the antenna I'm describing will be something like the one shown in the below image, the vertical section will be hung to the tree while the sloping one will run toward the house, the coax feeder will run all the way from the shack to the bottom of the antenna (near the bottom of the tree), the antenna will be made using insulated wire, same for the radials, the latter will just lay on ground but won't be connected to ground

Title: Re: End Fed Random Wire
Post by: metrologist on January 05, 2024, 08:30:12 pm
It's not necessarily that I'm space limited, just convenient orientations don't lend well to what I want to accomplish.

The left two trees in the back are large redwood trees, over 100'tall. The trees along the back are a couple full grown oaks and a walnut to the right. The large oak in the front is technically my neighbors, so cannot use it or have any wires in the front. The right of the house is asphalt for vehicles. Main driveway is to left side of house.

(https://i.imgur.com/RTgjFNt.png)
Title: Re: End Fed Random Wire
Post by: A.Z. on January 05, 2024, 08:42:34 pm
some food for thought

https://sites.google.com/view/vk1hw/antennas/the-lazy-d (https://sites.google.com/view/vk1hw/antennas/the-lazy-d)

https://www.radiohobbyist.org/blog/?p=564 (https://www.radiohobbyist.org/blog/?p=564)

https://www.qsl.net/kc8opv/antennas/skywireloop/index.html (https://www.qsl.net/kc8opv/antennas/skywireloop/index.html)

https://vu2ppp.com/_sky-loop_antenna (https://vu2ppp.com/_sky-loop_antenna)

just ... reason a bit ;)
Title: Re: End Fed Random Wire
Post by: iMo on January 05, 2024, 10:01:05 pm
For example a 2x20m dipole for the 80m band..
Blue is a ladder or coax (the coax needs a balun in the top feed point).
Title: Re: End Fed Random Wire
Post by: iMo on January 05, 2024, 10:57:51 pm
And a dipole for the 20m band, for the azimuth 300 degrees (Japan from the mid west coast, provided the North is the top).
Title: Re: End Fed Random Wire
Post by: A.Z. on January 06, 2024, 08:00:52 am
well, if going for dipoles/doublets, given the space contraints, we may also consider something like this

https://www.m0pzt.com/80m-cobra-doublet/ (https://www.m0pzt.com/80m-cobra-doublet/)

although, sincerely, given the available space, one may consider an irregular shape "lazy loop" (see my previous post) or a multiband vertical placed on ground, for example a "gap titan dx", an "hy gain av680" or something like those
Title: Re: End Fed Random Wire
Post by: metrologist on January 08, 2024, 04:50:33 pm
I have some motivation to try a loop because the lower HF bands have ~S9 noise.

I fed my wire antenna with coax and added a second leg in the opposite direction to the front corner of the house. The wires stay about 8 feet above the house except the end of the 2nd leg, which is also a bit shorter.

(https://i.imgur.com/Db87QWB.png)
Title: Re: End Fed Random Wire
Post by: A.Z. on January 08, 2024, 04:59:44 pm
Quote from: metrologist on January 08, 2024, 04:50:33 pm
I have some motivation to try a loop because the lower HF bands have ~S9 noise.

I fed my wire antenna with coax and added a second leg in the opposite direction to the front corner of the house. The wires stay about 8 feet above the house except the end of the 2nd leg, which is also a bit shorter.

(https://i.imgur.com/Db87QWB.png)

The curve doesn't seem so good, my suggestion is to use this tool

https://k7mem.com/Ant_End_Fed.html#Not_Random_Multi (https://k7mem.com/Ant_End_Fed.html#Not_Random_Multi)

to obtain an antenna length which will offer you a better match on the desired bands, that being said, since you've a bit of garden, a "tried and true" method to improve your reception on the HF bands is the installation of this antenna

http://www.kk5jy.net/LoG/ (http://www.kk5jy.net/LoG/)

it's really easy to put together and install and will greatly improve your reception by eliminating a lot of the QRM, as an example, have a look at this

https://www.youtube.com/watch?v=wMb8i5QajW0 (https://www.youtube.com/watch?v=wMb8i5QajW0)

and judge it by yourself, the idea is to use the endfed to transmit and the LoG to receive

HTH

Oh and forgot, a lot of the noise your endfed is picking up comes from the fact that the antenna runs all the way inside your home and that is also connected to your mains ground, as I already suggested to you, move the feedpoint AWAY from home, use a 9:1 to feed the antenna, use a ground stake or some radials and then a run of coax, with a good choke from the 9:1 to your station, that will definitely improve things (for both RX and TX), then by the way, the LoG will improve things even more

Title: Re: End Fed Random Wire
Post by: metrologist on January 08, 2024, 06:41:06 pm
I can tune every band with the MFJ tuner, but like I said, I did change the configuration. It's fed with coax and it looks like an unbalanced dipole. I don't recall if the center leg is 130, 132, or 135 feet long. The braid side is ~68 feet long.
Title: Re: End Fed Random Wire
Post by: A.Z. on January 08, 2024, 08:01:09 pm
Quote from: metrologist on January 08, 2024, 06:41:06 pm
I can tune every band with the MFJ tuner, but like I said, I did change the configuration. It's fed with coax and it looks like an unbalanced dipole. I don't recall if the center leg is 130, 132, or 135 feet long. The braid side is ~68 feet long.

ok I'm giving up, good luck
Title: Re: End Fed Random Wire
Post by: metrologist on January 09, 2024, 12:51:41 am
Quote from: A.Z. on January 08, 2024, 08:01:09 pm
ok I'm giving up, good luck

Already? In earlier posts, it was suggested to feed the antenna with coax (done), and skip the 9:1 balun (done), and to run counterpoise. I can't run ground wires around and especially cannot lay a loop antenna on the grass as the landlord staffs groundskeepers who have been an unending source of frustration with their meddling into my stuff outside. For sure there will be an issue with antenna wire sucked up into lawn trimming equipment.

I do find it interesting to fabricate a 1:1 balun and/or choke.

Anyway, just trying one thing at a time and all I can do is measure the antenna s parameters and model its radiation performance.
Title: Re: End Fed Random Wire
Post by: A.Z. on January 09, 2024, 06:50:10 am
not to skip the 9:1 but to use it, followed by a choke, the idea is to use a length of wire far away from 1/4 and 1/2 Lambda (and multiples) to avoid too low/high impedance, so that there will be an acceptable "match" to the coax and then to move the antenna feedpoint as far away from the house as possible; you may try 84ft for the radiator and 17ft for the counterpoise wire as a starting point and then, if needed, add more counterpoise wires of different lengths, the coax should run more or less perpendicular or in any case at an angle from both the radiator and counterpoise to avoid coupling

As for the 9:1 and the 1:1 choke, willing to build them, refer to these

http://vk6ysf.com/unun_9-1_v3.htm (http://vk6ysf.com/unun_9-1_v3.htm)

http://vk6ysf.com/balun_choke_balun_hf.htm (http://vk6ysf.com/balun_choke_balun_hf.htm)

if instead you prefer going for commercial stuff, these may fit

https://www.dxengineering.com/parts/ldg-ru-9-1 (https://www.dxengineering.com/parts/ldg-ru-9-1)

https://www.dxengineering.com/parts/ldg-ru-1-1 (https://www.dxengineering.com/parts/ldg-ru-1-1)

and won't break the bank

Title: Re: End Fed Random Wire
Post by: A.Z. on January 09, 2024, 08:26:37 pm
just to be clear, when it comes to the so-called "random wire" antenna, as of today there are some "rules" to follow

1. keep the feedpoint as far away from the "domestic electrosmog" as possible

2. choose an antenna length which is
 a. longer than 1/4 wave at the lowest desired frequency
 b. not an odd multiple of 1/4 wave at any frequency we want to use
 c. not a multiple of 1/2 lambda at any frequency we want to use

3. if #2 is respected, use a 9:1 to feed the antenna using coax cable, the mismatch between the impedance presented at the transformer output and the coax will be tolerable

4. since no current can flow on the antenna without an equal and opposite current flowing "elsewhere", and since the coax braid (see common mode currents) isn't meant to be a radiator, add something to let the "return current" flow, it may be a ground stake or one or more wires acting as "counterpoise" and offering a low impedance path at the various frequencies we want to use

5. since no counterpoise system is perfect and since we may still have common mode currents along the coax, even with a good counterpoise system, add a good wideband choke (a "guanella" will do, an air choke or "ugly balun" won't), place the choke at a point where the coax runs "away" from the radiating system so that its purpose won't be defeated by (undesired) coupling, if in doubt, add more chokes at different spots, they won't hurt

6. at or near the point where the coax enters the building, or in any case at a suitable spot, add a gas discharger device to the coax, not mandatory, but will help avoiding issues with static charges and lightnings

7. always remember that electrical ground and RF ground are NOT the same

HTH

edit:

as for the radiator length, if ones doesn't want to calculate the "good" ones, this tool

https://k7mem.com/Ant_End_Fed.html#Not_Random_Multi

may be of help
Title: Re: End Fed Random Wire
Post by: A.Z. on January 10, 2024, 07:09:51 am
oh and as for measuring

https://owenduffy.net/blog/?p=458 (https://owenduffy.net/blog/?p=458)

https://www.owenduffy.net/module/icm/index.htm (https://www.owenduffy.net/module/icm/index.htm)

that will tell you if your choke is working and can also help you finding the best spot along the coax to place a choke (just slide the ammeter along the coax until you find a current minimum and that's the place where to insert the choke), the device is pretty simple and may probably be built using stuff found in the "junkbox"


Title: Re: End Fed Random Wire
Post by: metrologist on January 11, 2024, 01:51:33 am
Thanks! I like that Duffy quotes Lord Kelvin as my favorite is "To measure is to know"
Title: Re: End Fed Random Wire
Post by: A.Z. on January 11, 2024, 09:54:25 am

Just as an alternative idea, consider the setup in the image below, the blue line is a "lazy loop" (aka "sky loop") with a total length of about 457ft, you may model it in NEC and then move the feedpoint position around to find the best one for your purpose, that is the one offering more gain toward the desired direction, let aside the overall gain and the impedance match for the moment, just put together a coarse model to check "how it does", then it may be adjusted and refined later on

Title: Re: End Fed Random Wire
Post by: iMo on January 11, 2024, 10:25:17 am
Quote from: metrologist on January 09, 2024, 12:51:41 am
I do find it interesting to fabricate a 1:1 balun and/or choke.

When messing with dipole/doublet (symmetrical or asymmetrical) fed by a coax, you have to use a balun in the feedpoint in order to isolate the outer coax shielding from the dipole's legs. When the coax shield is wired to a leg directly the leg gets grounded (as the coax' outer shield is "grounded" at your TRX). Many hams do not use the balun in the feedpoint of a dipole when fed with a coax (especially at portable), hoping their dipole "works just fine"..

PS: a search for an "optimal antenna setup" is definitely not a Sunday afternoon exercise. It is a long way to go.. Be warned   >:D
Title: Re: End Fed Random Wire
Post by: metrologist on January 11, 2024, 01:23:56 pm
A.Z., the east side is like a short alley, so the SE corner needed to be pulled in to the roof peak. Modeled radiation pattern was OK at that roof peak, but could not find resonance on any band of course. I also worked up a leaning delta loop, keeping my existing long leg and feed point, then running the short leg to the back fence and connecting the ends. I modeled it with the appropriate wire length so it tunes nicely on 80M and up. This seems like a worthy candidate.

iMO, the ham club at work have been thinking of better antenna setups for years, ultimately wanting a large SeppIR Yagi.
Title: Re: End Fed Random Wire
Post by: A.Z. on January 11, 2024, 04:21:58 pm

Here's another idea for you, the image below shows it, it's a "random" but installed in inverted-L configuration, fed at bottom between the radiator and some radials laid on ground, the top of the vertical section can be hung to one of your tall trees branches using a rope (and eventually a pulley), while the horizontal (ok sloping) section will be hung to your rooftop using another rope, check the radiation pattern on 80 meters, I think it may fit your need
Title: Re: End Fed Random Wire
Post by: A.Z. on January 11, 2024, 06:31:22 pm
further stuff about the inverted L

http://on5au.be/Cebik-2/StraighteningOutTheInverted-l.pdf (http://on5au.be/Cebik-2/StraighteningOutTheInverted-l.pdf)

Title: Re: End Fed Random Wire
Post by: A.Z. on January 12, 2024, 11:49:26 am
@metrologist

Here's another idea for you, if you are only interested in the 80 meters band and in contacts with Japan, given that you have some tall trees available, you may consider the vertical rectangular loop you can see in the attached image, to calculate the starting size of the loop, beging by obtaining the Lambda in meters (300/MHz e.g. 300/3.6) obtaining the total loop perimeter; add some length to be able to "prune" the antenna when tuning, then go on and calculate Lambda/2 to obtain the length for "half loop" and then calculate the short side as 1/3 of that length and from that calculate the long side, install the antenna with the bottom side at 2m or more from ground, then "prune" it by cutting the wire at the feedpoint and so raising the bottom side a bit at a time, the resulting antenna will give you a bidirectional pattern with almost 5dBi of gain and a nice low radiation lobe, the drawback, if we want to call it this way, is the "bandwidth" (SWR < 2) which is quite narrow; if you want, model it in NEC, it shouldn't be difficult and will allow you to "explore" the idea a bit more
Title: Re: End Fed Random Wire
Post by: passedpawn on February 01, 2024, 02:06:14 am
I find the best JP contacts to be on 12m - lots of JP on there at night.  I operate 6m to 80m on two antennas, a 40m EFHW and an 80m off-center fed wire (OCF).  Both have baluns and are 120' from my shack.  I can get on most nights and make contacts all the way to Australia from FL here, with 100W. 

I got the EFHW from ARRL (matching transformer came as a kit, build it yourself, which was not hard for me).  Second, the 80m, I bought here (https://myantennas.com/wp/product/ocf-8010e-3k-windom/). 

I have a VNA and use it to tune the wire length to optimize SWR at the bands I like. 
Title: Re: End Fed Random Wire
Post by: metrologist on February 01, 2024, 02:41:57 pm
Quote from: passedpawn on February 01, 2024, 02:06:14 am
I find the best JP contacts to be on 12m - lots of JP on there at night.  I operate 6m to 80m on two antennas, a 40m EFHW and an 80m off-center fed wire (OCF).  Both have baluns and are 120' from my shack.  I can get on most nights and make contacts all the way to Australia from FL here, with 100W. 

I got the EFHW from ARRL (matching transformer came as a kit, build it yourself, which was not hard for me).  Second, the 80m, I bought here (https://myantennas.com/wp/product/ocf-8010e-3k-windom/). 

I have a VNA and use it to tune the wire length to optimize SWR at the bands I like.

Sadly, my HF rig does not have 12M, but I'll give it a listen on my SW receiver.

https://siglentna.com/operating-tip/how-to-configure-the-sva1x-for-complex-impedance-measurements/
Title: Re: End Fed Random Wire
Post by: p.larner on February 02, 2024, 02:58:09 pm
just get as many feet of wire in the air as you can,windowline fed and use an atu,it does not need to be ressonant to radiate!