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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jun Fri 19, 2015 1:52 am 
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This is an interesting thread for me. I just decided to try building my first
ferrite loop antenna this summer. It could be very handy for pulling ham
signals out of the noise on 160m through 30m (1.8 to 10.1 MHz).
True, solid gold is still more expensive than ferrite, but not by much.
Heh! Whenever other interest groups compete against notoriously
cheap and resourceful ham radio builders, prices quickly get bid up.
This is partly what's happened, with MF SWL's and others jumping in.
Ferrite sleeve loop antennas use 20-30-40-50- even 100 rods at a time!
Then there's the general embezzlement of the economy 'from above'
that leads to major recessions, with those not on the top rungs
economically paying the price. We see this in shipping costs and
in anything rung up at a cash register or gas pump, etc. Inflation is
real if still 'unofficial'.

I'd had my eye on a larger ferrite rod antenna designed by a G2 ham.
It's in the ARRL Antenna Compendium Number 6, dates to around 1999
I think- before this FSL thing caught on recently in the MW/BCB DXing
community. His design would be pricey indeed on today's market, as it
uses 12 of the 6in x 1/2in dia type 61 rods. The complete bundle of
ferrite is 1in max diameter and fully 18in long, made from those 12 rods
glued together with crazy clue (cyanoacrylate). He said he did a lot of
experimenting before he came up with an optimum ferrite mix and
antenna geometry overall. He says the spacing of his split, contra-
wound coils is critical for some reason. Note that he uses a center
mounted link coil in that design, but more on that later...

In a recent A vs. B shootout of the FSL types written up online, I
noticed with interest that a 3.5in dia long bundle competed neck and
neck with a 7in dia 'shorty' bundle in every category. My working
hypothesis is that the *amount* of ferrite in play is much more
determinant of antenna performance than is the exact geometries
that can be built from that particular stack of ferrite.

One big question I have right now is whether you would get any
more performance out of a completely solid ferrite rod of the same
diameter as a hollow rod made up from individual rods. The
answer to this determines whether Mikek's 'fat' bundle of pot cores
is really all that 'fat' performance wise. Can you fool Mother Nature
with a 'fat looking' bundle of ferrite, or does cross sectional area
matter? Stay tuned...

I went on the auction site and bought a bundle of 20 of the 150
permeability ferrites, sized 8mm x 160mm. It cost 28 dollars and
shipping from Eastern Europe added another 20 dollars. We
shall see. I expect to get them in a couple of weeks...

I chose Uo=150 because it was closest to the type 61 at Uo=125.
I have no idea what mix it is however. The seller is not saying.
According to the G2 ham whose article so interested me, he feels
that a nickel-zinc mix (61) is a good way to go for 160/80 meters.
Notice that the MF/BCB DXers are going with the Russian 400
permeability material a lot more, and that makes sense to me.
They want to use it over maybe 250-1500KHz, and I want to
work between 1800-10100KHz, with the best performance up
to 4000KHz. I bet that the popular Uo=40 material you see
mentioned might also work well, though it's surprising to see it
apparently being talked up by MW/BCB types. I have a lot to
learn in this new area. BTW expensive Litz wire would be worth
it to the MW boys, probably a total waste of time and money
above 1800, however. The G2 wound his coils from 24AWG
stranded PVC with a thick jacket to assure the turns were well
enough spaced (helps Q). Cheap and worked well for him.

My loop will be hollow. I'm envisioning a 12in long bundle of
10x 6in long rods x2 glued end to end. I'll probably start with the
split, contra-wound geometry. All I really have to shell out for
is the ferrite rods. I've got everything else in inventory.

I'm amazed that so many of the MW aficionados are struggling
with no coupling loop and, more important, no variable cap in
series with that to control the coupling. Both controls are included
in that G2 design, and I suspect both are extremely touchy and
deserve a good vernier under the knob- especially the main
tuning! You can pick up on this, reading over their reviews and
narratives. Someone ought to publish a better design for those
guys that will introduce them to the concept of variable coupling.
It should NOT be so super critical how far the radio and the loop
under test are spaced, if only a variable coupling and coax link
were there. BTW a Sony ICF2010 is probably a lot cheaper than
one of those ferrite monsters, commercially built. Does anyone
besides me see the asymmetry there? A better radio ought to
suffer less front end overload, as was pointed out earlier in
this thread.

David

Edit: I located the article that's my starting point for building
a ferrite loop antenna. It's by Richard Q. Marris, G2BZQ and his
work was published in the ARRL Antenna Compendium Vol 6 in
1999. Some of these articles were never published in QST
magazine, only in the Compendium series. This looks like a very
well built and well thought out ferrite antenna. I hope mine turns
out as nice- and effective.

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Last edited by Clutter on Jul Sun 05, 2015 10:32 pm, edited 2 times in total.

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jun Mon 22, 2015 5:51 am 
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Here is the link to that FSL shootout (MW results, probably mostly Uo=400 ferrites):

http://www.am-dx.com/antennas/FSL%20Antenna%20Design%20Optimization.htm

These are indeed interesting results. It's clear that both coil diameter and ferrite length
matter, when aiming to get the most sensitive antenna. G2BZQ says in his article that
ferrite length affects both sensitivity and directivity. He says that the diameter of the
ferrite affects mainly sensitivity. Directivity is important, too. Looks to me that compromising
more towards longer ferrite rather than fatter is the better path...

David

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jun Sun 28, 2015 6:01 am 
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Quote:
I went on the auction site and bought a bundle of 20 of the 150
permeability ferrites, sized 8mm x 160mm. It cost 28 dollars and
shipping from Eastern Europe added another 20 dollars. We
shall see. I expect to get them in a couple of weeks...



My ferrite rods have arrived. Alas, 4 out of 20 were broken in shipping.
I've been in touch with the seller to see if he is going to make this right
or not. The packaging was woefully inadequate. I'm amazed that even
more weren't broken.

Some of the rods (about half) are irregular, having bends and being
less than perfect cylinders. This will make it trickier to place them
'just so' to get maximum contact between rods. I should end up with
a bundle of 6 surrounding a central 7th. That's as tight as they will
ever pack.

http://www.packomania.com/
Image

21 rods would be perfect. With 20, I'll use only 2 rods connected end
to-end at the center, all the outer rods being 3ea. end- to-end.This will
end up being pretty close to the G2BZQ design, which I'll use as my
starting point. That's over 18in of ferrite just under 1in diameter. I think
it's going to work pretty well...

Edit 05 Jul 2015: My current thinking, after a heck of a lot of
online research, is still to use the G2BZQ design as a starting point,
but in a nod to the FSL antenna type, to be OK with a hollow bundle
of ferrite rods. Longer is better, I'm thinking, also two contra-wound
coils on opposite ends of the rod may yield best nulling performance
along with decent sensitivity and good Q as well. So I'm picturing a
bundle of 21 or maybe 24 rods in groups of 3, total length just over 18in
and bundle diameter perhaps just over an inch. As with the FSL type,
the use of resilient plastic as padding under the long rods is essential
to get them to bunch together with maximum possible contact everywhere.
These surplus rods are often 'wobbly', not perfect cylinders. There will
need to be a heck of a lot of fussing and fitting and strategic gluing to
make this all come together. More later...

(Comments continued below)

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Last edited by Clutter on Jul Fri 10, 2015 1:54 am, edited 6 times in total.

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jun Sun 28, 2015 8:14 am 
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You can use crazy glue to re-attach broken Ferrite pieces, with no apparent loss of performance.

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jun Mon 29, 2015 6:43 am 
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So I have heard. I'm definitely going to pick up a fresh tube of 'crazy glue'
and try it on mine. I think it is real important to rehearse the joining
motion a few times before you put that drop of glue on. You get only one
chance and if you screw it up, you get a big gap where the glue bond is.
Not good. I've been taking a length of aluminum angle and clamping it
in the bench vise. The rods slide real easy along that 'V'. So you can
practice to your heart's content. Some breaks just want to come together
real easy, every time. Some are a bit squirrelly, though, and it's a real
pain to bring them together right.

BTW my seller got back in touch and he's being really good about the
breakage. Replacements are being sent. That seller is a 'keeper' for
sure. Now let's find out if the Russian 150 Uo material is anything like
the Ni-Zn 125 Uo stuff from the west, which has become so very over-
priced. FWIW it looks like it might be a different mix to me. 61 material
is a slate gray, this stuff I have is a reddish gray. You'd have to do
direct comparisons to be sure. I bet what I have ends up working great.
There is a p/n on each rod with "150" as part of that number. There are
similar Russian ferrite rods with "400" in the p/n and they're marketed
as such online. In fact, most of the items I saw in my searches were the
400 material, but that's better for MF/LF as far as I know, and I'm more
interested in high MF to lower HF.

David

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jul Fri 10, 2015 3:08 am 
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It turns out it is rather complicated to make slender 8mm rods fit together, joined
in strings of three and also joined side to side. What makes it so challenging is
that the Russian rods are often wavy/'out of round', they are not perfect cylinders.
It is perhaps not surprising that these rods would find their way into FSL style
antennas, where all you need to do is arrange bunches of them around a common
circle. The FSL antennas sort of resemble a Gattling gun, in that regard.

I'm going to stick to my plan and try to duplicate the G2BZQ design. That antenna
is long and slender, with a ferrite core only about 1 inch diameter but fully 18 inches
long. I believe it has advantages so far as better nulling, being a balanced
arrangement- not to mention that having adjustable coupling is an important
feature not seen with FSL's. I'm going to use mine with a communications receiver;
the FSL guys are mostly using small portable SWL radios with internal loopstick
antennas. Modifying one of those inexpensive receivers is rarely done. Google
"ultralight radio" for sites devoted to this branch of SWLing.

It looks like what will work for me is a square arrangement with a hollow core,
i.e. a 3x3x3 arrangement but with the innermost ferrite rod missing (8 rods total).
These Russian rods also vary a bit in length. I believe it must be important to
keep any and all gaps as minimal as humanly possible- especially the two joints
in each 18in long string of 3 rods. How I'll deal with the waviness/out of round
is to use the more irregular rods in the center of each bundle (horizontally) and
try to use the straightest rods on the outside. Each irregular rod can be
rotated next to its neighbor to find configurations that expose the smallest gaps.
It all looks doable, so far. I'll have to select rods of the same length for the center
rod of each 18in trio. The idea is to assemble groups of 3 rods horizontally,
one at a time, using a little crazy glue to hold them together. All the ends must
match precisely and squarely so that 3 of these bundles can then be joined
end-to-end for the 18in 3x3 trios. I will no doubt have to use file and sandpaper
to clean up the rod ends quite a lot. All that needs to be square is the inner joints
where the bundles join. A wood fixture will be built to help in the assembly. The
outer rod ends can be irregular in length, falling wherever they may. I hope to
end up with a square bundle 18in long, made from 3 of the 6in bundles glued
end-to-end, hollow in the middle. That puts its average diameter in the
neighborhood of 1in as with the G2BZQ loop. Fit that whole assembly into a
varnished cardboard tube and wind your three coils on it.

It all sounds complicated and it is complicated but is doable in my judgement.
With a little fiddling and tweaking it will come together. Having researched
current ferrite rod prices, I'd suggest that for upper MF/lower HF, the #61 rods
from Fair Rite, 0.5 x 4in size are currently a best buy because they are a lot
straighter and should be pretty effortless to glue together if one wants to go
for length rather than girth (FSL). Buy from Amidon, Bytemark, etc. I did save
a good bit by going with Russian surplus rods, but the FSL guys have bid even
these up a good bit, it appears. For a FSL antenna, they will probably be fine.

Edit 19 Jul 2015: I put a 220 grit disc on my sander and have been playing
with squaring up the ends of those 150 mu Russian ferrite rods. Looks like I can
put a nice, flat, square surface on the ends. It's a slow process, but doable.
Flat faces should be best to get all the rods in the bundle most fully in play.
I'm trying for very small gaps bonded with crazy glue at every joint.

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Last edited by Clutter on Jul Sun 19, 2015 8:04 pm, edited 1 time in total.

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jul Fri 10, 2015 6:27 pm 
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Location: Vincennes Indiana
Can't recall if I brought it up but in an issue of Fine Tuning (94/95 issue) they did a shootout of ferrite antennas and there was a definite point of diminishing returns. They made one that you almost rode like a gun mount in ww2.
http://www.universal-radio.com/used/sold586.html


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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jul Sat 11, 2015 3:06 am 
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db gain wrote:
Can't recall if I brought it up but in an issue of Fine Tuning (94/95 issue) they did a shootout
of ferrite antennas and there was a definite point of diminishing returns. They made one that
you almost rode like a gun mount in ww2.
http://www.universal-radio.com/used/sold586.html


Wow- that would be most interesting to hear about. Can you remember any details from
that article? Even if it's only generalities, any info about the various sizes that were
compared and a summary of their results and judgements would be fascinating.
"Rode like a gun mount"? That sounds like one big mass of ferrite, to hear you
describe it that way.

I always bear in mind that mostly these guys are MW SWL's. In that region, Litz
wire does make a difference and can be worthwhile. For the range I'm building,
1.5 to 4 MHz and even on up to 7 or 10MHz, Litz would offer no benefit. It makes
less sense that a ferrite rod antenna be huge to cover those frequencies. As it is,
I was impressed that G2BZQ ended up with such a big ferrite rod as he did
(1in x 18in)- but he said that was the end result of a lot of experimentation on his
part. He wanted 1.8 to 4MHz, mostly the lower end, but he said that the antenna
he designed was actually pretty good at 4MHz as well, To me, 1 x 18in is
indeed 'large'. BTW I plan to use silver plated stranded copper wire with teflon
insulation for my coils. I think it ought to do fine. FWIW it turns out that for
convenience in construction with the wobbly Russian ferrite rods, hollow is
better. That's the only way I can come up with a reasonably tight square 'tube'
of ferrite with minimal gaps. No way I could pack them tightly in 3x3x3. They
are too wobbly.

Gary DeBock has demonstrated larger (8in) FSL antennas doing just as well
as a 4ft, multi turn traditional loop antenna on the broadcast band. I think 'big'
may be of more benefit in the MW region. I may try a FSL later, but only if I
can come up with one that is balanced (parallel, contra-wound coils) and with
a link winding and coupling cap. That better fits the big, heavy communications
receiver (transceiver) I'm using. I cant pick that thing up and wave it around
to find the 'sweet spot' for coupling. 'Ultra light' radios are a whole different
ball game, in that regard.

David

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jul Sat 11, 2015 6:29 pm 
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Sadly I gave the issue away, if you're really interested in these kinds of antennas it will be worthwhile to find a copy as it had pics and schems as well as the test results. Oddly I have yet to find an online repository of the ft proceedings.


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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Mar Wed 27, 2019 3:55 am 
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Joined: Nov Tue 29, 2016 6:05 am
Posts: 51
Location: Burnaby BC Cda. V5E 4A6
Hi

Seeking advice, comment assistance with some FSL projects.

1) Remotely locating small commercial loops, Select A Tenna 541m, Terk AM Advantage, and/or Kaito AN 100/200's to a Window Sliding Glass Patio Door and/or weather protected Balcony

2) Retrofitting small commercial loops, Select A Tenna 541m, Terk AM Advantage, and/or Kaito AN1 00/200's into an FSL Antenna

3) Remotely locating a conventional FSL Antenna. A wideband low noise Antenna Preamplifier or a Radio Control Model Servo

Thanx
73 de Jordan ve7jjd


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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Mar Wed 27, 2019 4:23 am 
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The tunable loops have to be in close proximity to the radio to do any good. Remotely locating them wouldn't seem to be worthwhile.

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Mar Wed 27, 2019 4:35 am 
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Location: Saskatoon
Check out this loop antenna built by Jim Kearman KR1S (admin of TheRadioBoard forums):
http://kr1s.kearman.com/html/hooploop.html

The loop can be located remotely because the tuning capacitor and matching transformer don't need to be located at the loop. For Jim's application, he didn't need a tuning capacitor at all, because he connected it directly to his Tecsun receiver which automatically applies the correct capacitance to tune the antenna. However for a receiver that doesn't do this, you would need to add a tuning capacitor at the receiver location, in order to peak the antenna.


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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Dec Mon 16, 2019 1:38 pm 
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My 6" FSL consists of 45 ferrite loop sticks ( 15cm length x 1cm diameter ) wrapped around an aqua foam core dumbell. The ferrite loop sticks came with bubble wraps and I kept them to add extra protection. It took me half an hour to put it togethor. Total cost is £45. The aqua dumbbell and aqua foam blocks were old junks. All I needed were masking tape and cable ties.

Instead of using it for DXing and coupling it inductively, I use it as the RF tank coil of a Frankenstein three-tube superhet lash-up (tube line-up: 6SB7Y, 6SQ7GT and 1Q5GT) with one IF stage and AVC. Without an IF amp stage , a 3 tube superhet would be rather deaf but the SFL turbocharges it. The RF coil is wounded with SGW22 enamel wire on a foam sheet. The tuning dial is connected to a vernier reduction gear drive. The FSL RF coil is fully tracked across the whole MW band with a hand wounded oscillator coil. Their inductance values are based on the superhet three point tracking solutions. It is as sensitive as an AA5 but it is overloaded; very loud sound on a 2k ohms 1920s' Brown type F headphones that i have to turn the volume all the way down. I dont know its Q because I dont have a proper Q meter.

I have 60 ferrite loops and these are enough for a 8" FSL future project. I can easily convert the above 6" into 8" FSL in no time. I dont get hung up with using the most expensive high threads count Litz wire. But I am more interested it applying SFL directly to the RF tank of a homebrew superhet in an indoor environment where the reception is very poor and an external aerial is not permitted, e.g. my flat with thick concrete walls and ceilings. My first experimental super ferrite was 20 loop sticks stuffed ( including its shipping bubble wraps) inside a 3" cardboard postal tube and it was again used directly in a RF tank circuit. It increased the sensitivity of the homebrew superhet greatly. I was sold, full stop. I dont buy into the pseudo science behind it and I question the claims made by the original author about the effects of length of ferrite rods,and solid mutli-cores vs sleeve cores in his discredited article.


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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Dec Thu 19, 2019 8:16 pm 
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fifties wrote:
The tunable loops have to be in close proximity to the radio to do any good. Remotely locating them wouldn't seem to be worthwhile.


I've had pretty good luck with my outdoor loop. Sadly it has succumbed to a wind storm and needs to be rebuilt... again...

http://www.antiqueradios.com/forums/vie ... 1&t=208459
http://www.antiqueradios.com/forums/vie ... 6&start=40

These FSL antennas sound intriguing! I would love to try building one if cost wasn't so high.

-Steve


Attachments:
outdoorloop1.jpg
outdoorloop1.jpg [ 111.71 KiB | Viewed 1456 times ]

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Dec Thu 19, 2019 9:06 pm 
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azenithnut wrote:
fifties wrote:
The tunable loops have to be in close proximity to the radio to do any good. Remotely locating them wouldn't seem to be worthwhile.


I've had pretty good luck with my outdoor loop.

To be clear, I meant that a tunable loop inductively couples it's stronger RF signal to the air or ferrite loop in a radio, and wouldn't work if placed too far away.

Your outdoor creation looks great, BTW!

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Dec Thu 19, 2019 10:09 pm 
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Thanks Fifties!

Yeah, I used a single turn coupling loop inside the main loop, which is then connected to RG-11 coax to feed the radio connected to it.
The remote tuning is done with a stepper motor.

-Steve

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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Jul Thu 30, 2020 11:47 pm 
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Location: Seattle, WA 98122 (from Hungary)
Has anyone here compared the performance of a ferrite sleeve loop of X diameter vs. the same diameter of a ferrite bundle? Does a ferrite bundle have any better performace? What is the significance of the 'sleeve' construction?


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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Aug Wed 05, 2020 8:07 pm 
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This is the 12 inches version that i upgraded from the 6" version a few months ago. It uses 300 strands 0.04mm Litz. Litz wires are expensive in the UK. I cannot remember the exact number of loop sticks, maybe around 75.

I bought a Heathkit Q meter but it has a broken movement coil. I have not been able to measure the Q of the FSL. I would measure Q versus different number of loop sticks. I put the project aside as I am busy at homebrewing FM receivers.


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12 inches.jpg
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 Post subject: Re: Ferrite Sleeve Loop antennas: Are they for real?
PostPosted: Aug Sat 29, 2020 5:20 pm 
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Location: Morristown, N.J.
Attached are pics of my FSL project, soon to be a xtal set. It uses 42 ferrites between machined plexiglass; the coil is 660/46 Litz; typical Q is around 500 going up to 550 at some point that I failed to record. It resonates with a General Radio precision cap; the inductance was set so that most of the cap range 50-1100uuF is used to resonate. I expect to increase the Q much further. Information will be forthcoming.

There is large intermediate ferrite rod located in the middle and the resonating cap from a Boonton 260 Q meter. Its not complete so I can't give any operational results.


Attachments:
FSL 1.jpg
FSL 1.jpg [ 145.64 KiB | Viewed 390 times ]
FSL 2.jpg
FSL 2.jpg [ 141.99 KiB | Viewed 390 times ]

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