Author Topic: My home-made ferrite antennas  (Read 58813 times)

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Offline JonathanW

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Re: My home-made ferrite antennas
« Reply #125 on: June 03, 2014, 01:21:49 PM »
One interesting point: Mike's "stroke ratio by bearing" graph on his lightningmaps station page (#689) doesn't seem to show a whole lot of directivity--assuming he's using the 300 mm ferrites currently.

Offline Dr Obbins

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Re: My home-made ferrite antennas
« Reply #126 on: June 03, 2014, 02:14:42 PM »
One interesting point: Mike's "stroke ratio by bearing" graph on his lightningmaps station page (#689) doesn't seem to show a whole lot of directivity--assuming he's using the 300 mm ferrites currently.
This is just an empirical observation, from when I had Dave R's station running here (300 mm ferrites), comparing to my 250 mm antennas. It seemed that the longer antenna's exhibit greater directivity. I am somewhat concerned that carrying the "longer is better" philosophy too far may create some null area's in coverage at 45, 135, 225, and 315 degrees from the right-angle antennas. I know that when I have constructed tuned LF AM direction-finding ferrite antennas, "longer" usually also meant "more directional" and "sharper nulls".

Regards,

Don
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Not knowing all the  tech stuff as to why and how the antennas work, I will verify that my 2 channels behave differently. The "greater directivity" seems to fit the behavior I have seen. The one antenna seems to pick up more N-S and the other more E-W. With out having anything to compare the end results to, I can not confirm if more or less total strikes are registered.

Offline JonathanW

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Re: My home-made ferrite antennas
« Reply #127 on: June 03, 2014, 02:19:29 PM »
One interesting point: Mike's "stroke ratio by bearing" graph on his lightningmaps station page (#689) doesn't seem to show a whole lot of directivity--assuming he's using the 300 mm ferrites currently.
This is just an empirical observation, from when I had Dave R's station running here (300 mm ferrites), comparing to my 250 mm antennas. It seemed that the longer antenna's exhibit greater directivity. I am somewhat concerned that carrying the "longer is better" philosophy too far may create some null area's in coverage at 45, 135, 225, and 315 degrees from the right-angle antennas. I know that when I have constructed tuned LF AM direction-finding ferrite antennas, "longer" usually also meant "more directional" and "sharper nulls".

Regards,

Don
WD9DMP

Not knowing all the  tech stuff as to why and how the antennas work, I will verify that my 2 channels behave differently. The "greater directivity" seems to fit the behavior I have seen. The one antenna seems to pick up more N-S and the other more E-W. With out having anything to compare the end results to, I can not confirm if more or less total strikes are registered.

In theory, that's why you need two ferrites or loops at right angles to each other - one rod or loop has most of its gain in two opposite directions, with nulls at right angles.  Summing the gain patterns of both should give you relatively even coverage.

Of course, if your gain patterns are too directional, then you'd have uneven coverage, especially at 45 degrees off axis from both rods/loops.  I haven't yet seen whether I've noticed that (my station has been running jerry-rigged for about 18 hours).

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Re: My home-made ferrite antennas
« Reply #128 on: June 03, 2014, 02:23:09 PM »
One interesting point: Mike's "stroke ratio by bearing" graph on his lightningmaps station page (#689) doesn't seem to show a whole lot of directivity--assuming he's using the 300 mm ferrites currently.

Which graph are you using to see this?  I'd like to compare what I have to what now to when I put the longer antenna back in.

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Offline JonathanW

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Re: My home-made ferrite antennas
« Reply #129 on: June 03, 2014, 02:24:43 PM »
One interesting point: Mike's "stroke ratio by bearing" graph on his lightningmaps station page (#689) doesn't seem to show a whole lot of directivity--assuming he's using the 300 mm ferrites currently.

Which graph are you using to see this?  I'd like to compare what I have to what now to when I put the longer antenna back in.

Thanks

It's at the bottom of the page here:

http://www.lightningmaps.org/blitzortung/america/index.php?bo_page=statistics&bo_show=station&bo_sid=689&bo_station_id=33&lang=en&bouser

And here is yours:
http://www.lightningmaps.org/blitzortung/america/index.php?bo_page=statistics&bo_show=station&bo_sid=1002&bo_station_id=64&lang=en&bouser

Jonathan

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Re: My home-made ferrite antennas
« Reply #130 on: June 03, 2014, 02:25:37 PM »
 Generally, two loops,  will respond with signals thus

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Re: My home-made ferrite antennas
« Reply #131 on: June 03, 2014, 02:40:16 PM »
One interesting point: Mike's "stroke ratio by bearing" graph on his lightningmaps station page (#689) doesn't seem to show a whole lot of directivity--assuming he's using the 300 mm ferrites currently.

Which graph are you using to see this?  I'd like to compare what I have to what now to when I put the longer antenna back in.

Thanks

It's at the bottom of the page here:

http://www.lightningmaps.org/blitzortung/america/index.php?bo_page=statistics&bo_show=station&bo_sid=689&bo_station_id=33&lang=en&bouser

And here is yours:
http://www.lightningmaps.org/blitzortung/america/index.php?bo_page=statistics&bo_show=station&bo_sid=1002&bo_station_id=64&lang=en&bouser

Jonathan
The BLUE lines indicate the cumulative directions,... and yes, mine are Highly directional... that's where the storms were located in relation to my station.

As far as I know, the 'green' indicates the general directivity of all stations in the network, summed together.

Of more importance is the figure up in the top: "location ratio" 24% meaning generally 24% of my signals were used to locate strikes. A network goal would be to have all stations in the 20-40% range.  (Yeah, sometimes my ratio is way down... yesterday for some time it was below 6%. I was sending a lot of signals, and had a high "efficiency" in detecting strikes on the participants chart, but the strikes were far away, and my station was not in the nearer 6 required for 'location'. Which might mean I'm sending a lot of un-necessary signals, at the expense of missing nearer ones that could be located.

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Offline JonathanW

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Re: My home-made ferrite antennas
« Reply #132 on: June 03, 2014, 02:58:10 PM »
One interesting point: Mike's "stroke ratio by bearing" graph on his lightningmaps station page (#689) doesn't seem to show a whole lot of directivity--assuming he's using the 300 mm ferrites currently.

Which graph are you using to see this?  I'd like to compare what I have to what now to when I put the longer antenna back in.

Thanks

It's at the bottom of the page here:

http://www.lightningmaps.org/blitzortung/america/index.php?bo_page=statistics&bo_show=station&bo_sid=689&bo_station_id=33&lang=en&bouser

And here is yours:
http://www.lightningmaps.org/blitzortung/america/index.php?bo_page=statistics&bo_show=station&bo_sid=1002&bo_station_id=64&lang=en&bouser

Jonathan
The BLUE lines indicate the cumulative directions,... and yes, mine are Highly directional... that's where the storms were located in relation to my station.

As far as I know, the 'green' indicates the general directivity of all stations in the network, summed together.

Of more importance is the figure up in the top: "location ratio" 24% meaning generally 24% of my signals were used to locate strikes. A network goal would be to have all stations in the 20-40% range.  (Yeah, sometimes my ratio is way down... yesterday for some time it was below 6%. I was sending a lot of signals, and had a high "efficiency" in detecting strikes on the participants chart, but the strikes were far away, and my station was not in the nearer 6 required for 'location'. Which might mean I'm sending a lot of un-necessary signals, at the expense of missing nearer ones that could be located.

Hmmm...I took it a little differently, though we might be talking about two different things.  Since the "stroke count" legend is in dark blue, the blue lines appear to be the total network stroke count by bearing in relation to the station in question...but the stroke ratio (a percentage) legend for a given station is provided in light green, and looks like it's also in terms of bearing from the station.  If green were general directivity summation of all stations, it should be the same for any station, but it's not.

In other words, it appears to me this graph provides 1) a circular graph of stroke count, indicating the bearing of the strokes detected by the network from a given station and 2) the percentage of strokes detected by the station, also in bearing.  To me, it looks like your station is pretty even in terms of stroke detection vs. bearing.

Most of the strokes over the last 24 hours have been to the WNW of your station, Mike, but of the strokes there have been in most directions, you've picked up high percentages of them.  If your ferrites were highly directional, I'd expect to see an emphasis on stroke detection in four orthogonal directions.

Of course, the graph of stroke ratio would be influenced by ionospheric propagation, as well as stroke power and relative distance of the strokes from a given station.

Jonathan
« Last Edit: June 03, 2014, 03:55:50 PM by n0ym »

Offline Dr Obbins

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Re: My home-made ferrite antennas
« Reply #133 on: June 03, 2014, 08:43:06 PM »
Generally, two loops,  will respond with signals thus

Luckily, I happened to mount the antennas in the same basic orientation of Mike's "stroke ratio by bearing" graph. So Channel 1A is N-S and channel 1B is E-W.
North:

South:

East:

West:





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Re: My home-made ferrite antennas
« Reply #134 on: June 03, 2014, 09:19:49 PM »
Luckily, I happened to mount the antennas in the same basic orientation of Mike's "stroke ratio by bearing" graph. So Channel 1A is N-S and channel 1B is E-W.
Excellent Dave... !  Good analysis & illustration!  Dang, that's good... !

We're talking H field loops, here... not E field which is omni-directional...

Now you might see how to determine an interference source by direction,...
getting bearing on a line is simple... deciding on which half of the line is
a bit more difficult, since it can be difficult to determine exactly when the signal goes
positve or negative at the trigger,.... unless you can pull stunts like Dave did.... .

Remember that the direction and location is determined at the server,
related to time, based on curves, and intersection of those curves by
at least 5 other stations in the US, currently.

Dave. this might actually fit also on the interference thread, helping to find direction of
an interference signal,... pretty doggone good illustration of directivity of loops.
Well done, and Kudos!!!

Mike
« Last Edit: June 03, 2014, 09:44:27 PM by Cutty Sark Sailor »

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Offline Cutty Sark Sailor

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Re: My home-made ferrite antennas
« Reply #135 on: June 03, 2014, 09:35:17 PM »
Of course, the graph of stroke ratio would be influenced by ionospheric propagation, as well as stroke power and relative distance of the strokes from a given station.
Jonathan
  I strongly suspect the algorithms at the server 'image' the initial ground wave when possible, rather than a sky wave reflection. Rejection of "earth/ionosphere waveguide" signals  when enough stations detect the initial ground wave and pre-charge pulses. Egon would actually have us detecting the 'pre-charge' elements, before the stroke itself, for better location accuracy. "TOGA" as opposed to "TOA" that the net has to operate with at the present time. "TOGA", as I understand, is pretty much ready to implement once stations and networks are adequately tuned and set up. And out of a combination of the two, I suspect, will arise 'polarity' 'type' and 'strength'. Hence the need for stations to have "shorter range" as opposed to "longer range", which would be possible in a denser network.

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Offline Dr Obbins

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Re: My home-made ferrite antennas
« Reply #136 on: June 03, 2014, 09:36:25 PM »
Quote
Excellent Dave... !  Good analysis & illustration!  Dang, that's good... !
One of those "Oops! I did something right"  :lol: moments.
Quote
this might actually fit also on the interference thread, helping to find direction of
an interference signal,..
Go ahead and link the pics over there if you like. You can probably explain whats going on better than me.  ;)

Offline Cutty Sark Sailor

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Re: My home-made ferrite antennas
« Reply #137 on: June 03, 2014, 09:38:14 PM »
Quote
Excellent Dave... !  Good analysis & illustration!  Dang, that's good... !
One of those "Oops! I did something right"  :lol: moments.
Quote
this might actually fit also on the interference thread, helping to find direction of
an interference signal,..
Go ahead and link the pics over there if you like. You can probably explain whats going on better than me.  ;)
When I get some of that stuff called 'time"....

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Offline JonathanW

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Re: My home-made ferrite antennas
« Reply #138 on: June 04, 2014, 05:51:36 AM »
Of course, the graph of stroke ratio would be influenced by ionospheric propagation, as well as stroke power and relative distance of the strokes from a given station.
Jonathan
  I strongly suspect the algorithms at the server 'image' the initial ground wave when possible, rather than a sky wave reflection. Rejection of "earth/ionosphere waveguide" signals  when enough stations detect the initial ground wave and pre-charge pulses. Egon would actually have us detecting the 'pre-charge' elements, before the stroke itself, for better location accuracy. "TOGA" as opposed to "TOA" that the net has to operate with at the present time. "TOGA", as I understand, is pretty much ready to implement once stations and networks are adequately tuned and set up. And out of a combination of the two, I suspect, will arise 'polarity' 'type' and 'strength'. Hence the need for stations to have "shorter range" as opposed to "longer range", which would be possible in a denser network.

Well, I'm working with an ARRL official on the possibility of getting a writeup of the Blitzortung system and station construction in QST.  No idea on a timeframe (the guy is very busy), but I'm hoping it would help with station density in the U.S.

If it goes forward, I'll definitely put him in touch with anyone here who might want to contribute knowledge.

Also, I noticed something going through the raw data files last night...maybe others have noticed this before, too, and it's obvious...but, for strike listings in Europe, there are huge numbers of "low power" strikes (1-10 kA category), whereas in the U.S., nearly all strikes detected are above 10 kA.  I don't know how accurate the current levels calculated are (they seem low to me), but I think the point is, when people say the network in the U.S. is missing strikes, a big reason really is because lower powered strikes are simply not detectable by the minimum number of stations needed to locate them, without a more dense network.

Another reason why we need more stations in the U.S. :)
« Last Edit: June 04, 2014, 10:42:32 AM by n0ym »

Offline steel_edges

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Re: My home-made ferrite antennas
« Reply #139 on: June 28, 2014, 09:34:20 AM »
I would like to chime in with my experience building up these ferrite antennas.  I decided to make the 300mm length ferrites using the rods from Nebraska Surplus mentioned earlier in this thread.  The adhesive used was a machinable JB-weld type of epoxy that requires 24 hrs to fully cure.  After they were cured I covered them with 3/8" heat shrink, I guess I was too aggressive with the heat gun because just as the first rods heat shrink was almost complete I felt one or more if the glue joints fail. It worked out fine, once it cooled it was still very rigid and it did not cause and issue with winding.

The second rod went much better, I was more careful applying heat, taking breaks to allow things to cool, also holding the rod vertically helped keep the adhesive intact. I wound the rods with 28AWG wire because I already had a spool laying around. I then applied a final heat shrink layer of 1/2 material being careful with the heat like before.

After everything cooled down and I compare the two rods I cannot tell which one had the glue failure, they are both quite rigid.

Thanks for all the great info in this thread, it was a huge help!

George
« Last Edit: June 28, 2014, 09:36:51 AM by steel_edges »

Offline dfroula

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Re: My home-made ferrite antennas
« Reply #140 on: June 28, 2014, 09:57:45 AM »
Nice job!

I still glue mine too, although I don't think it is needed. I use a clear epoxy. I noticed that the glue introduces a very small gap between the individual ferrite slugs. It is visible if held up to a strong light source.

I think you may actually get more "intimate" contact between the ferrite slugs by not using glue, per Mike's Method of just using the shrink tubing.

I tried a half dozen different industrial glues. The joints made with every one fractured on a 1 inch drop test to the workbench. It's just the nature of the ferrite material.

Don
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Offline DaleReid

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« Reply #141 on: June 28, 2014, 10:40:59 AM »
I had the same concern about the gap in between the rods no matter how you applied it, and while not a real circuit in conductive contact rather than having a break the virtual rod with any insulating material, I figured the heat shrink would be enough.

My experience was that I didn't have to waste time (in retrospect) with the futzy and potentially ruining a set by having the glue leak down and adhere to whatever it was holding the rods in alignment, such as a piece of angle aluminum, etc.

The shrink wrap sizes given were perfect, and using a true heat shrink gun (cheap as anything I've gotten lately, from Harbour Freight) made the shrinking fast, fun and nearly foolproof, vs. trying to use my wife's hair drier.

The worst part of winding the rods was the initial piece of wire that had to stick out a foot or two and go round and round while I wound it, but the second one went better when I realized I could roll the extended lead up in a circle and gently tape it to the end of the rod after I got the first inch or two wound on.  And winding for a bit and applying a little bit of Scotch 3M electrical tape to keep it from unwinding if I had to take a break or maybe a sip of something, was helpful.

I used the smaller gauge diameter enamel, too.  One thing that some of the initial stuff from the development team was cautioning that proper spacing between the winds was necessary, even implying that a dummy cord or something to specifically separate the winds a little bit was needed.  I don't see anyone doing home brew doing anything except nestling each rotation up next to the one that was just laid down, forming a relatively solid wind, almost like a hose on a reel or line on a fishing reel.

I don't have a rod from the kit so I can't comment as to how the ones that are sold with the kit are rolled. 

Has anyone taken a look at what Egon, et.al. are sending out?  Are the winds next to one another, or is there some spacing material wound along with it to separate them a bit?

Nonetheless, the proof is in the pudding, and these home built ones, no matter what size wire used, and whether or not glued or just heat shrunk, seem to be spectacular.

Considering the rods are first shrunk, then wound which actually does give a teeny bit of stiffness in its own right, then again heat shrunk, then placed in some sort of support like cotton batting or live rubber or the stuff I used, low density foam rubber strip used as a window door sealer that is adhesive on one side, and then stuffed in PVC means that they'll withstand a 12.7 on the Richter scale and still stretch and yawn and shake it off.

I think the glue is not needed.

I think there are many factors on the size of enamel wire used, including more wraps means more magnetic line crossings as the wave moves by, there are resistance changes, there is the impedance which affects the filter resonance and Q, etc. which I'm sure technically makes a difference.  But again, if the engine starts and runs, who cares if it is 87 octane or 91?

On the other hand, I'm sure if NASA was doing it, they'd test glues vs. no glue, and length of rod and size of wire and spacing of wraps and so on, and find some differences that might make a difference if the probe were going to the heliosphere or a person's life depended upon it.  But if it works and is close to optimal, it probably isn't worth anyone's time doing those experiments.

I have an interest in antennas, so if there are those who know the answers to some of the questions being raised, I'd love to hear the comments.  I love the impetus to learn and look stuff up that this movement has generated.

Dale
« Last Edit: June 28, 2014, 10:44:09 AM by DaleReid »
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Offline Cutty Sark Sailor

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Re: My home-made ferrite antennas
« Reply #142 on: June 28, 2014, 11:17:26 AM »
Electrically, bonding the rods is not necessary other than if you desire some piece of mind or temporary rigidity... the bonds likely won't hold anyway, unless you can obtain some of the very expensive chemically active epoxy designed expressly for ferrite material.
All that's really necessary for a flux, magnetic, 'connection' is that they be touching with no gap. They then behave as one "longer" ferrite. We'd desire magnetic coupling not capacitive which gaps introduce, and then all them damn Q's and gausses and stuff really get diddled with.
Thinner wire means more turns, more 'sensitivity" and fits inside the 2nd suggested shrink tubing. Thicker, fewer turns, and may not fit. So, get bigger tubing, and have less gain... doesn't matter a lot overall. But we've got a bunch of stations using the 26ga multiple core 50mm X 7.5mm ferrites... and if have any questions about whether Don's innovation, glued or unglued, works, just go check the 'participant's page, and forget all the fancy electrical theory... just follow the cookbook.

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Offline Cutty Sark Sailor

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Re: My home-made ferrite antennas
« Reply #143 on: June 28, 2014, 11:20:39 AM »
The cookbook... remember that if you truly want to make a cake from scratch, first you have to create a "Big Bang" and all that goes with it.

Fortunately for us that's been done already... all we need are ingredients and directions... mess much with either one, and you won't get cake.

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Offline dfroula

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Re: ,
« Reply #144 on: June 28, 2014, 11:22:56 AM »
The worst part of winding the rods was the initial piece of wire that had to stick out a foot or two and go round and round while I wound it....

Cat toy!

Offline Jumpin Joe

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Re: ,
« Reply #145 on: June 28, 2014, 01:13:52 PM »
The worst part of winding the rods was the initial piece of wire that had to stick out a foot or two and go round and round while I wound it....

Cat toy!

You guys should have seen me trying to wrap my 12" ball.... should have videoed it. It was hilarious.  At the time is was... shall I say fustrating?!?!?!? :lol:

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Re: My home-made ferrite antennas
« Reply #146 on: June 28, 2014, 01:51:03 PM »
The shrink wrap I used was pretty thick.  I had left some wrap hanging off the end.  I hand drilled a small hole through the wrap at the starting end.  I then strung the wire through the hole and left a good foot out the end.  But that way the hole helped with the first few wraps of wire.  Once I had probably a dozen tight turns around, I used some black tape to hold that.

Once I got a bit further down, I pulled that piece off so the black tape would fully cover the end.  But the whole trick works nicely.  I put a knot at the starting end of my wire so I know which end is which.  But even without the knot, you could see the difference where one wire was more centered than the other.
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Offline JonathanW

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Re: My home-made ferrite antennas
« Reply #147 on: June 28, 2014, 02:23:14 PM »
Electrically, bonding the rods is not necessary other than if you desire some piece of mind or temporary rigidity... the bonds likely won't hold anyway, unless you can obtain some of the very expensive chemically active epoxy designed expressly for ferrite material.
All that's really necessary for a flux, magnetic, 'connection' is that they be touching with no gap. They then behave as one "longer" ferrite. We'd desire magnetic coupling not capacitive which gaps introduce, and then all them damn Q's and gausses and stuff really get diddled with.
Thinner wire means more turns, more 'sensitivity" and fits inside the 2nd suggested shrink tubing. Thicker, fewer turns, and may not fit. So, get bigger tubing, and have less gain... doesn't matter a lot overall. But we've got a bunch of stations using the 26ga multiple core 50mm X 7.5mm ferrites... and if have any questions about whether Don's innovation, glued or unglued, works, just go check the 'participant's page, and forget all the fancy electrical theory... just follow the cookbook.

I agree--in fact, one point in favor of the "heatshrink the cores first" method, aside from helping with rigidity, is that it provides some elastic force holding the cores together.  With high-permeability cores such as these, air gaps can have a significant effect.

Offline JonathanW

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Re: My home-made ferrite antennas
« Reply #148 on: June 28, 2014, 02:54:35 PM »
For the curious, here's what my LCR meter says on the two ferrites I rolled...

Ferrite 1:
1 kHz:
1 kHz 10 kHz 100 kHz
Q 27.1 7.08 3.77
Inductance (mH) 20.840 19.562 13.799

Ferrite 2:
1 kHz 10 kHz 100 kHz
Q 26.3 6.27 3.46
Inductance (mH) 22.090 20.590 13.787

Also, my kill-a-watt meter has pegged system power usage, including power lost to the power supply, consistently at 2.5 watts.
« Last Edit: June 28, 2014, 02:57:50 PM by n0ym »

Offline 92merc

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Re: My home-made ferrite antennas
« Reply #149 on: June 28, 2014, 02:56:12 PM »
When I started making my second set of antennas, I decided to peel one of Egon's covers back to see what he did on the wire at the "done" end and how he brought it back.  I noticed he brought his straight back.  Not winding back like some of the others had done.

It got me to thinking, if that wire wrap on the way back is the opposite winding, could that negate some of the existing windings?  Basically counter effecting what was done?  Its only 10 or so wraps, but still.

So I figured if it's good enough for Egon to go straight back, that's what I did.  Plus I can feel the wire though my black tape and tell which is which, if for some reason I lost a knot and didn't know which end was which.
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