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Author Topic: A Gallery of Small Tuned Loops  (Read 11618 times)

Online jFarley

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A Gallery of Small Tuned Loops
« on: July 26, 2013, 1839 UTC »
Loop building is an addictive pastime for me, and there always seems to be some new avenue to explore.  I will never say that they are the perfect antenna for every user (what antenna is?), but they have served me well.

Here is an image gallery of a few of the Resonant Loops I have built and used.  I add electrical characteristics where I have them.  Tuning ranges expressed in kHz are typical with the standard loop amp I use, which has back-to-back tuning diodes giving an approximate 10-250pF range.  Parasitic capacitance and inductance of the windings measured via the "2 point method".



Standard Loop

The loop I use for live DXing and over-nights, and the workhorse antenna for me.  A very good performer 60 through 41 meters.

Side = 20"
N = 4 turns
L = 17uH
Cp = 11pF
Wire = 10AWG TEW (27 feet)
Range = 2400-7800kHz
Q ~ 240 @ 6925kHz



Big Blue Loop

A bigger loop for coverage of MW top end and 90M, and simply the Standard Loop upsized with some extra turns.  I need to trim this a bit to get some 75M coverage.  Blue wire used for enhanced DX from Oceania.

Side = 25"
N = 8 turns
L = 65uH
Cp = 18pF
Wire = 12AWG TEW (67 feet)
Range = 1200-3700kHz
Q ~ 250 @ 1710kHz

Edit: This loop was used to log a local Part 15 about 30 miles away from me, and I have already posted an image of the SDR reception here: http://www.hfunderground.com/board/index.php/topic,8377.0.html

This was posted with the intent that we would come back to it at some point, and I guess that time is now.  With a rough Q of 250 @ 1710kHz, the BW is about 7kHz at that frequency.  The response shape is clearly seen in the clear between 1705 and 1720, and attenuation across the WVON 1690 signal is also evident by the color rendering.  Note that the loop tuning was not peaked at the resonant peak, but in the lower slope of the response.  It was at this tuning that I got the maximum apparent S/N ratio as judged by ear.  This is an example of the type of performance I hope can ultimately be wrung out of a loop at 43M, although that will require increasing the current Q of the Standard Loop by a factor of 5.



Shielded Loop Prototype

A standard loop in a shield built from foamboard, aluminum foil, and Scotch tape, and a Standard Loop.  My entry into the "Fugly Loop" competition, created out of desperation when the Power Company wouldn't show up to fix a bad pole which was seriously crapping out my noise levels.

Side = 20"
N = 4 turns
L = 16uH
Cp = 11pF
Wire = 10AWG TEW (27 feet)
Range = memory leak
Q ~ 200 @ 6925kHz

What I learned =
    1)  Shielding a Resonant Loop seems to be effective.
    2)  The tuning range will be translated up in freq a bit
    3)  Some degradation of loop Q will be experienced

Audio clip of CFRX 6070 @ 2030UTC in the presence of extreme power pole noise.  The initial audio was captured with a standard unshielded loop, and at 42 seconds I switched over to the shielded prototype which was similarly sited.  

Link:    http://www.mediafire.com/download/4rdk48824h6tnqd/CFRX_6070AM19Oct12_2030z.mp3



Shielded Loop Working Model

A slightly smaller standard loop in a shield built from PVC sheet and solids, shielding is aluminum flashing.  Since the Power Company has fixed my noisy pole, this is on the back burner.  "If you build it, they will come".

Side = 19"
N = 4 turns
L = 15uH
Cp = 11pF
Wire = 10AWG TEW (25 feet)
Range = lost my notes
Q ~ 215 @ 6925kHz



LF NDB Loop

A Resonant Loop which is exploring some different concepts, and is still being tested.  This loop has four independent windings which can be switched into different series/parallel combinations to do band changing.  With coils in series, this loop packs about 1250uH into a relatively small volume.  This is about the biggest loop which I will be able to swing on my rotor.  This loop will be tuned by a primo silver-plated variable capacitor (15-250pF, mil surplus from an ATU) with a built in 100:1 gear ratio via a stepping motor interface.  

Side = 32" (outer) and 26" (inner)
N = 24 + 24 turns
L = 1250uH with all coils in series
Cp = 38pF
Wire = 10AWG THHN (464 feet)  N.B. I generally do not wind loops from THHN; it kinks, has too much memory, and is almost impossible to tension without frame distortion or breakage.  It also generally has a nylon over-jacket which tends to crack when exposed to the elements; this traps moisture which leads to Q degradation.  I had a spool lying around and used this while prototyping.  This will ultimately be wound with either TEW or Litz, depending.
Range = 265-620kHz with a mechanical variable cap (will be lowered to ~180kHz by remotely switching in
some parallel fixed cap)
Q >= 400 @ 300kHz.(design goal)

What I learned = To get down to 300kHz with the capacitor I wanted to use, a loop inductance of around 1200uH was required.  To use the typical winding layout would result in a loop which would have been too large to swing on a rotor in my siting.  This loop uses dual windings (4 individual coils) which have a hefty amount of mutual inductance which increases the apparent tuning inductance in a small package.  At least, that was my guess, and this appears to have worked.
« Last Edit: July 26, 2013, 2221 UTC by jFarley »
Joe Farley, Near Chicago
SDR-IQ / R8 / R7
Remote Resonant Loops for HF and LF / ALA 1530
Active 60" Whip / PA0RDT
QSLS appreciated to:    jfarley44@att.net

Offline BDM

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Re: A Gallery of Small Tuned Loops
« Reply #1 on: July 27, 2013, 0050 UTC »
Outstanding and very interesting, thanks for posting. It's giving me further ideas. Love those loops ;)
Radios -- Perseus SDR // Icom IC-7410 // Tecsun PL-660 // Panasonic RF-5000A --Antennas-- Pixel Pro 1B loop - 82' fan-dipole at 40' - tuned MW/BCB 40" loop and 100' receive only dipole
-Brian--North of Detroit--MI-
1710/KHz the MW Pirate Clear Channel (not so much anymore "sigh")

Offline Pigmeat

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Re: A Gallery of Small Tuned Loops
« Reply #2 on: July 28, 2013, 0229 UTC »
I could see loops one and two in my near future. I've got PVC cut to nearly the same dimensions from loops gone by and more wire than the phone company.

Joe, do have a schematic/layout of the amp/tuner circuit?

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Re: A Gallery of Small Tuned Loops
« Reply #3 on: July 28, 2013, 0508 UTC »
LOOPS! :o *drools*

Thanks for the pics! Inspirational *angelic music plays in the background of this thread* :D

Peace!

Offline Beerus Maximus

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Re: A Gallery of Small Tuned Loops
« Reply #4 on: July 28, 2013, 1423 UTC »
This is an awesome post and your loops look amazing. I'd really be interested in plans/schematics if you are ever inclined.
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Online jFarley

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Re: A Gallery of Small Tuned Loops
« Reply #5 on: July 28, 2013, 2017 UTC »
Many thanks all for the kind words; it's very encouraging.

I ment in an earlier thread that I planned on putting together a series of posts which will go up somewhere and detail the construction and setup of the Standard Loop from start to finish, and I still plan to do that.  It may take some time for me to get info together and checked, but it will happen by September.  I have also been working on a number of short write-ups on theory, calculations, etc and I will also getting around to getting that out.

I don't want to discourage eager beavers from forging ahead, so I will put something together in an "as is" form, most likely an RAR of schematics, images, and readmes.  I will include schematics in the .sch format native to the Express PCB schematic capture software package (http://expresspcb.com/index.htm).  It's free and I use it at work to order boards right out of the software.  It's a very simple and intuitive editor, and one can quickly create custom exotic components such as a 3-Terminal Assault Toilet (low dropout, of course!) if necessary.  Having the .sch file will allow anyone to easily document any changes they make to the schematics.  Will try to get this all together by the end of the week.

A couple further thoughts.  I want to be sure that I make the disclaimer that anything I have done here is just footnotes to the work done by MW DXing pioneers such as Dallas Lankford, Russ Edmunds, Chuck Hutton, and Gordon Nelson.  And especially Mark Connellly.  They get the bulk of the credit, and their articles were my inspiration.  This being so, I want to make it clear that I have no commercial interest in this loop, and do not intend to manufacture it.  I would be a moron to post design data to a den of known pirates, hackers, and radio hooligans (and I say that with the highest respect for y'all) in general and expect to protect any profit motive.  If you build one and like it, feel free to make others for friends, sell them if you want, export the technology to known rogue states if that's your thing.  It's a free concert.

I have been in and out of the hobby at various times since the early 80's, and have seen the hobby community go into apesh*t feeding frenzy each and every time a "new" antenna design comes along: beverages, delta loops, T2FDs, etc.  Each and every one initially looks like the greatest thing since sliced bread, but the furor generally dies down until the next Bigger And Better Deal comes around.  This scares me that this might be yet another one of these events.  A loop such as this requires some build time, some investment of coin, and some time to get used to the quirks, and sometimes I just wonder if I'm just jerking people around.

On the other hand, there are those logs and veries I have which I feel I would not have gotten without the loop.  I have this on the wall above my desk, and this keeps me going:



This was logged on a loop similar to the Big Blue loop pictured in the gallery; it was a bridge design between MW and SW, and was one of the sequence of prototypes leading up to the loop detailed in the Proceedings article.  I got better than a half  hour of solid program detail with it, while FIBS was JBA to poor on a longwire (75 feet IIRC).   I think it is great testimony to the enormous potential of Resonant Loops.

"No brag; just fact"  --  Will Sonnett
Joe Farley, Near Chicago
SDR-IQ / R8 / R7
Remote Resonant Loops for HF and LF / ALA 1530
Active 60" Whip / PA0RDT
QSLS appreciated to:    jfarley44@att.net

Offline skeezix

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Re: A Gallery of Small Tuned Loops
« Reply #6 on: July 28, 2013, 2053 UTC »
Great post.

In the background of the picture of the Shielded Loop Prototype, is what looks like a skeleton for a gazebo or something. Would that thing be usable to make a hidden antenna?
« Last Edit: July 28, 2013, 2121 UTC by skeezix »
Minneapolis, MN

Offline outhouse radio

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Re: A Gallery of Small Tuned Loops
« Reply #7 on: July 28, 2013, 2120 UTC »
I have been in and out of the hobby at various times since the early 80's, and have seen the hobby community go into apesh*t feeding frenzy each and every time a "new" antenna design comes along: beverages, delta loops, T2FDs, etc.  Each and every one initially looks like the greatest thing since sliced bread, but the furor generally dies down until the next Bigger And Better Deal comes around.  This scares me that this might be yet another one of these events.  A loop such as this requires some build time, some investment of coin, and some time to get used to the quirks, and sometimes I just wonder if I'm just jerking people around
great post   great looking loops
i used a homemade magnetic loop   with very good results  rx was good too
a loop is worth a try  it may or may not work well for you at your location
hell guys it's just money ;)


Online jFarley

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Re: A Gallery of Small Tuned Loops
« Reply #8 on: July 29, 2013, 2142 UTC »
In the background of the picture of the Shielded Loop Prototype, is what looks like a skeleton for a gazebo or something. Would that thing be usable to make a hidden antenna?

skeezix, I think I would avoid trying either to use the structure itself as an antenna or hide an antenna in such a structure.  This is the common ornamental 10 by 10 shelter (with a fabric cover removed for the winter) which typically has a couple of dozen snap-together ill-fitting tubing joints.  All these joints tend to become rusted metal to rusted metal joints after just one season outside.  I would be afraid of all sorts of ill defined rusty joints becoming sources of low level RFI with their intermittent movement and blunting the sensitivity of any antenna within.  I have a 50kW AM only about a dozen wavelengths from me, and this would give me even more reason to fear this approach.
« Last Edit: July 29, 2013, 2330 UTC by jFarley »
Joe Farley, Near Chicago
SDR-IQ / R8 / R7
Remote Resonant Loops for HF and LF / ALA 1530
Active 60" Whip / PA0RDT
QSLS appreciated to:    jfarley44@att.net