Topic: My home-made ferrite antennas

[DaleReid]

Don,
After two weeks of non-lightning hell with family, work and the holiday, I'm getting nearly ready to begin.  Finally.

I have the ferrites, and am sure I have some 26 wire, found the 24 but it is a bit big.

A question on winding the cores....

Did you start at the right end, and wind over the top (spinning the top of the core away from you) or underneath (spinning the core down and 'towards' you?).

As long as you do both the same, it shouldn't make any difference, correct?

Which of the ends did you designate the 'ground' wire, or again, if you just make sure the lead from the same end of each is connected together, that is OK?  I see you loosely spiraled the one wire to the other end making a couple wraps going from the right end to the left end in the photos.  I assume that this is just to make it secure.  With the taping and final shrink wrapping, I wonder if it is OK to just go straight to the opposite end to pair up with the free end there, or is the loose wrap necessary?

I would think that there isn't much concern about the antennas being circularly polarized by phasing them differently; that is, if one took Core A and had the free ends 1a and 2a and Core B with free ends 1b and 2b, then just choose one, say the 2 wire, to be ground and do the two wire from each core to designate as ground?  Sorry if this isn't too clear.

Thanks for any further info.

Anything you've learned since the construction?

Dale

[dfroula]

Well, I wound the cores by holding the ferrite rod vertically with the spool of wire to my right. I crossed the wire from right to left over the top of the ferrite and commenced winding by rotating the rod clockwise (as viewed from the top of the vertically oriented rod).

I wound the length of the rod in this fashion until reaching about 5mm from the bottom of the rod. I taped the winding to stabilize it at the bottom end and continued winding in the same direction back to the top or starting end of the rod, in a loose spiral. This gives a "right handed" or clockwise winding, like the thread on a screw.

Following the construction of the Blitzortung-supplied ferrites, the end of the loose spiral becomes the ground connection of the antenna, and the starting end of the winding is connected to the ungrounded terminal of the amp. I don't think this is critical, though. There is supposedly some shielding benefit from doing this, but I don't think it is much. It is preferable to connect both antennas the same way to make the phasing of the antennas the same. Connecting as above is a convenient convention.

Winding and connecting as above should preserve the relative phasing of the antennas. In other words, if the two ferrite antennas were wound and connected as above and placed parallel to one another, the two traces on the signal scope would show impulses of the same amplitude and polarity in response to a lightning strike (assuming equal gain).

If one antenna were wound in the opposite direction or the connections reversed on one, the amplitudes would be the same, but the polarities would be opposite. I don't think this would really matter for the Blitzortung system, as the system triggers equally on positive or negative impulses.

Antennas for the "Lightning Radar" system DO need to be concerned about the phasing, as they use the polarity and relative amplitude of the two antennas to determine the bearing of the signal. TOA systems don't care.

I hope this helps!

Don

[dfroula]

Well, I wound the cores by holding the ferrite rod vertically with the spool of wire to my right. I crossed the wire from right to left over the top of the ferrite and commenced winding by rotating the rod clockwise (as viewed from the top of the vertically oriented rod). I think this is the same winding direction as you described in your first example.

I wound the length of the rod in this fashion until reaching about 5mm from the bottom of the rod. I taped the winding to stabilize it at the bottom end and continued winding in the same direction back to the top or starting end of the rod, in a loose spiral. This gives a "right handed" or clockwise winding, like the thread on a screw.

Following the construction of the Blitzortung-supplied ferrites, the end of the loose spiral becomes the ground connection of the antenna, and the starting end of the winding is connected to the ungrounded terminal of the amp. I don't think this is critical, though. There is supposedly some shielding benefit from doing this, but I don't think it is much. It is preferable to connect both antennas the same way to make the phasing of the antennas the same. Connecting as above is a convenient convention.

Winding and connecting as above should preserve the relative phasing of the antennas. In other words, if the two ferrite antennas were wound and connected as above and placed parallel to one another, the two traces on the signal scope would show impulses of the same amplitude and polarity in response to a lightning strike (assuming equal gain).

If one antenna were wound in the opposite direction or the connections reversed on one, the amplitudes would be the same, but the polarities would be opposite. I don't think this would really matter for the Blitzortung system, as the system triggers equally on positive or negative impulses.

Antennas for the "Lightning Radar" system DO need to be concerned about the phasing, as they use the polarity and relative amplitude of the two antennas to determine the bearing of the signal. TOA systems don't care.

I hope this helps!

Don

[DaleReid]

Thanks,

I thought as much but since you have them up and running thought I would just ask.  Once the wire is off the spool, it is hard to take off and re-wind.

Consistency is the key, I think.  And unless one is phasing something like a helical antenna for proper circular polarization, there isn't much to worry about, until the LR issue came up.  But then again doing it as you suggest takes care of the potential problem.

Dale

[Cutty Sark Sailor]

Well, Don et.al.
  I just rolled two of these and slapped 'em on the amp about 2 1/2 hrs ago.
I am blown away.
Operating under the theory that, with Scotch and a few other things, more is better,  I used 6 rods for a 300mm rod.

Didn't bother to glue them together, figuring the heat shrink would do the job just as well...  So I stacked 'em in some 3/8" clear polyvinyl heat shrink, and squeezed 'em together.
So the 'rod' sagged a bit. with no coil and no second shrink tube. So what... no biggie, we're just starting on the build

Rolled it, +/- 725 turns of 26ga enamel, total coil length of 290mm.
Heat shrunk it again with 1/2" tubing, to fix the sag and wiggle, left it unshielded, and marched out (ok, ran out  ) to the garage in anticipation.

Slapped the first one in B channel, oriented it N-S to match A (the original 120mm) cut gain in half on the 300 to get out of interference 
 set the A amp (120mm) to match, and compared signals.
The gain is approx 3 times that of the 120mm ferrite, and about half the noise floor. Much quieter than the flat panels, also. The signals seem to have better resolution.
    

Repeated the process with #2.

Now, the acid test at sunset, when we see what it takes to overcome the nearby Sodium street lights.
I may eschew shields... we'll see.

Thanks, Don! Great antennas, simple to build, and real jewels so far!

Mike
Well, there comes the first sodium, as I type this. At three times the previous level interference level  ... Now to 'speriment with shielding....

[dfroula]

Great! The extra length helped, I'm sure. I still have my flat panels mounted, but have been running the ferrites for a few months and will likely stick to them. I built up two more complete ferrite antennas in enclosures....not sure why, but I had the components, so why not? 

I found that the shielded tubes helped tremendously with power line hum. I have no identifiable noise sources when listening to the amp output, other than very low level 60 HZ stuff and slight processor noise from the controller (which I know is too close to the antennas, but doesn't affect performance at all).

Don

[Cutty Sark Sailor]

Here are my 300mm versions of Don's antenna, "cardboard-breadboarded" under testing...
No glue used, just shrink over the cores, and another layer of shrink over the winding.
These are quite rigid as they stand, and seem to work better unshielded.


Happy Winding!
Mike

[Jumpin Joe]

Nice Mike... I found my 120's from Egon work better with shielding.

Getting ready to make the "12" Ball" antenna that "scarecrow93" (Lance), made. His stat's seem to stay pretty consistent and strong.

Received all the stuff to build it today. I hope to have it done later this week. Have to finish some of my honey-dew's first.

Joe

[Cutty Sark Sailor]

My 120's were better with shielding, also... these do fine without it,... must be the magic touch.
All that bothers me are some street lights, and something new that's developed this past week, around 55Khz, that drives me a bit nuts... 55Khz is, among other things, some infrared mod freqs, and I suspect somebody's got something new in their home nearby that's leaking heavily, because of the timing of the events... ah well.

Mike

[Jumpin Joe]

Oh... I thought it was on of the Cincy radio stations ... lol

[Cutty Sark Sailor]

Oh... I thought it was on of the Cincy radio stations ... lol

Because of the typical timing, and the spouse's schedule, I've accused her of being 'too hot to handle'... as it only seemed to appear when she was home and awake.

(...and she actually thought it a compliment! Lucky me!) 

Mike

[Cutty Sark Sailor]

Let's see if we can bump this topic, since we may have new builders looking for help on Don's ferrites...

[W7DRM (old call was W3DRM)]

Okay, I'll try it. Have just ordered some shrink-wrap tubing. Have everything else so once the tubing come in I'll be ready to build my first ferrite. Have had the ferrites for quite a while now (hope I can still find 'em...). More later.

[DaleReid]

Mr. Sailor:

How appropriate for a refresh on this topic.

I was just in communication with Jim in Wisconsin and am getting the table cleared of all the tax forms and other stuff of Winter's detritus so I can get the board up and running.

With your encouragement, perhaps I'll work on the rods first, and get a feeling of starting without soldering teensy weensy surface mount thingies at the beginning.

Is your opinion that these rods still work fine without a shield, or is that really going to be necessary?  I read that the ones supplied from the project assembler NEED shielding.  You said not so much for yours.  Just because they are longer?  You have a lucky location?  Isn't the E field shielding a requirement for the detector to work?

Nonetheless, I'm pleased IF they do work without shields since it is just one less putzy thing to do, and with that type of thing more often than not my work is a bit glue and rubber bands to hold everything just right without shorting the wrap around together.

Speaking of glue and rubber bands, you mentioned that your ferrites work fine without gluing them into a solid rod, but had a wee bit o' the sag in the assembly.  Would you think a tiny dab of hot glue at 12, 3, 6 and 9 oclock around the butt joint of each rod as it is assembled into a long one, would be of help or is the second heat shrink taking care of the solidity of the unit?  I'd not put the glue between the rods, just around the intersection on the outside to hold them during winding.

Dale

[Cutty Sark Sailor]

Hey, Dale..

Is your opinion that these rods still work fine without a shield, or is that really going to be necessary?  I read that the ones supplied from the project assembler NEED shielding.  You said not so much for yours.  Just because they are longer?  You have a lucky location?  Isn't the E field shielding a requirement for the detector to work?

Yes, they'll work. If I moved mine to a different location they might need shielding, but I've run them with and without, and though there is some slight decrease in my noise level, there's no appreciable effect in overall performance, at my location. Keep in mind that it appears I have high H field interference, but very little consistent E interference that I can determine, and my antennas are placed in the only 'sweet' spot I've been able to locate in my residence.

A shield can always be added later... if you have E interference this also gives you a chance to help track it down, and remedy it if necessary prior to shielding.

Nonetheless, I'm pleased IF they do work without shields since it is just one less putzy thing to do, and with that type of thing more often than not my work is a bit glue and rubber bands to hold everything just right without shorting the wrap around together.

You can use self adhesive aluminum tape from HVAC dept at Lowes. Just on a whim, last shields used this:
http://www.amazon.com/gp/product/B00ANTRRRM/ref=oh_details_o08_s01_i00?ie=UTF8&psc=1
but I did purchase it when it was priced much lower, for whatever reason....
I think it was easier to handle, and a tad faster than using the wider aluminum foil... either way it doesn't take long. Just wrap a thin piece of printer paper around the antenna (1 layer) and a couple pieces of scotch tape to hold the paper tube... then stick the shielding copper or aluminum tape to the paper... and if you don't appreciate the shielding it's easily removed. 

Speaking of glue and rubber bands, you mentioned that your ferrites work fine without gluing them into a solid rod, but had a wee bit o' the sag in the assembly.  Would you think a tiny dab of hot glue at 12, 3, 6 and 9 oclock around the butt joint of each rod as it is assembled into a long one, would be of help or is the second heat shrink taking care of the solidity of the unit?  I'd not put the glue between the rods, just around the intersection on the outside to hold them during winding.

The little sag in the first layer of shrink wrap mattered not. You're going to wind the coil over it, and use a second layer over the coil. By the time that's done they're quite rigid, no floppiness even with my 300mm length.
I wouldn't use glue of any type at all since the following method is almost foolproof:
I used a tilted shoebox lid, laid the core sections in the 'v' between the top and side, slid the wrap over the cores (should extend an inch or so beyond the core ends) and began shrinking from each end alternately --- ending in the center--- Shrinking each end first, and alternating left and right ending in the center draws the rods together and locks them as the wrap shrinks. you don't need rubber bands, glue, etc... The cores then assume the properties of one long core through magic.

Mike

[dfroula]

As I just wound Dave Robbin's antenna's, here's a comparison picture. The shorties are 5 rods, glued, wound directly onto the ferrite with a single layer of shrink tubing over the entire thing.

The longer ones used Mike's technique, except I did glue the rods with epoxy in a jig to add some extra stability during winding. I was able to use the same diameter shrink tubing (3/8") for both layers. That diameter easily accommodated the wound cores for the final wrap.

I did find that the wire was easier to wind on the core with the shrink-wrap than on the bare ferrite, due to the friction of the material.

There is a noticeable gain boost with the extra length.

As for shielding, Dave's units seem fine without it. I found that it helped mine some with the noise floor and some noise sources. It didn't seem to affect the gain at all. The shields will make any electrical noise worse if not grounded, as I (and Jim in Mauston) discovered.

If you use shields, ground 'em! 

Don F.
WD9DMP

[DaleReid]

I'll take the hot glue gun back out to the shed (which I can now access with the snow finally melting and a whole 44 degrees today) and proceed with lining up some ferrittes and shrinking.

Thanks for the tip on doing ends first and alternating back in towards middle.  Luckily I ordered a spool of the heat shrink when this thread first started and was pleased with it, both quality appearance and price.

I have some extra rods, and will indeed stack another one or two on.  Greg, how many did you use for the longer assembly?

Will this alter the electrical appearance to the preamplifier?  More wraps, more length of wire, more resistance, change in inductance, etc. 

You obviously have the test setup and the previous experience to do this, and from your comments you did not hesitate a bit.  I think there was some lengthy discussion earlier, but if it works, if there is more gain, better to do it now.  I have some 28 and 24 wire, no 26 to wind.  Can I get a better antenna by taking the time and extra effort to wind the smaller gauge and therefore get more turns on the same length of rod?  Or again, having something is better than trying to tweak?

I remember spending hours with a Bird meter and peaking the 2 meter antenna on one of my first mobile installs, very proud of myself for a minimal SWR.  Then a guy who is chief engineer for a radio company pulls up with his truck and, I kid you not, a piece of insulated wire just soldered to a button that was in the top of the old Motorola mount he had and it worked as well as mine...  I guess if I were listening for earth moon earth signals I'd be more worried. 

Thanks again.  Getting the stuff out now.  Dale.

[DaleReid]

Even though the Scotch is still in the bottle, I went back to re-read and found the answer to number of cores.  5 for the original wrap and one more, total 6, for the longer one.  Thanks.
Dale
Just being a nervous nellie.

[Cutty Sark Sailor]

I'll take the hot glue gun back out to the shed (which I can now access with the snow finally melting and a whole 44 degrees today) and proceed with lining up some ferrittes and shrinking.

Good!

Thanks for the tip on doing ends first and alternating back in towards middle.  Luckily I ordered a spool of the heat shrink when this thread first started and was pleased with it, both quality appearance and price.


I have some extra rods, and will indeed stack another one or two on.  Greg, how many did you use for the longer assembly?

Will this alter the electrical appearance to the preamplifier?  More wraps, more length of wire, more resistance, change in inductance, etc. 

no problem

You obviously have the test setup and the previous experience to do this, and from your comments you did not hesitate a bit.  I think there was some lengthy discussion earlier, but if it works, if there is more gain, better to do it now.  I have some 28 and 24 wire, no 26 to wind.  Can I get a better antenna by taking the time and extra effort to wind the smaller gauge and therefore get more turns on the same length of rod?  Or again, having something is better than trying to tweak?

Really recommend good quality enameled 26 gauge.... here's what I used:
http://www.amazon.com/gp/product/B0082CUNVE/ref=oh_details_o04_s00_i00?ie=UTF8&psc=1

Relax... this isn't that complex...

Mike

[DaleReid]

I just heat shrunk six cores together.

The nice tubing that was recommended is so tight that by the time I got to the middle, there was trapped hot air.  I fussed until I thought about it a bit and made a tiny cut across the middle of the bubble and it came down nicely.

Now, where's that wire....

[DaleReid]

Antennae are done!

I got brave and decided to try a wrap.

I used #28 wire since it was the only magnet wire I had other than 24 and I figured that was too course and would not allow enough turns.  I anchored the free end with a wrap of tape, leaving about 2' sticking out and put the spool of wire on an empty blank CD spindle, which worked great for keeping the wire spool in place, and provided just the right amount of un-wind tension to keep the wire coming.  It didn't take long to notice two things.  First, it was pretty easy to get the right amount of pressure between my thumb and forefinger to get the wrap tight, and the angle that the wire coming off the spool was easy to adjust and keep as it made a tight wrap with no gaps.  Secondly I found that the free 2' end of wire was almost as snarly as most fishing lines when unrestrained.  I finally settled on trying to gently straighten out the rat's nest that had formed, and to keep the wire extended directly along the same axis as the cores, which were turned.  I'm sure some torsion of the wire occurred, but despite flopping around a bit and keeping the end from catching on stray stuff on the work bench, worked pretty well.

Needless to say, the second core went much faster and was neater and less twisting on the free end.  After taping the final end wrap, I did a gentle spiral up (thanks for the pictures!) and then secured it at the top, leaving another two feet to use for connections.  I did mark the start end and the final end for phasing later.

I found the process fun and strangely calming, similar to when Nurse Chambers helped us with basket weaving at the Happy Thoughts Farm and Sanitarium, but this time no doors were locked and I didn't see any nice young men in white coats.

I will heat shrink the second coat over the assembly tomorrow, and get the necessary plastic parts to hold the diagonal angles as needed and secure the delicate wires.


Now, however, the tough part begins with sorting the numerous resisters, capacitors and start on the board assembly, which probably won't go as quickly and I may see some white jackets called in.

[DaleReid]

Don,
While studying your pictures of the PVC pipe 90 degree holder with the L box you used, there is a red wire with periodic blue stripes on it.  I assume, but need to ask, if this the ground wire for the tape shield you have made, since the magnet wires seem to be run into the box independently and it isn't just one of them spliced to the heavier duty wire for a more robust wire to handle?

Dale

[dfroula]

Yes, that's the ground wire. I have enough 24 AWG telephone patch panel interconnect cable with the colored-band coding for several lifetimes, so I used that. The colored wire connects to the aluminum foil shields.

I used aluminum foil tape designed for sealing sheet-metal air ducting for the shields as it was cheap and available. One width of the widest tape I could find was not sufficient to wrap completely around the PVC tubing that I used as enclosures for the ferrite antennas. I had to overlap two strips, leaving the narrow gap in the shield.

Doing this presents two problems.

The first is that the two layers of tape have no electrical conductivity to one another because of the adhesive.

The second is that (as most of us are aware), one simply cannot solder copper to an aluminum surface, at least not without special flux and techniques.

I solved both issues by drilling a small hole through one of the foil layers at one end of the tube. I strip a few inches of insulation from the wire and pass the bare end through the hole from the inside of the tube. I then bend the bare wire into a tight "S" shape and bend it to overlap the two layers of foil. I secure the "S" with a short length of foil tape directly across the wire "S", covering the hole as well. I burnish this strip down tightly with a small dental tool to give better contact.

I got the idea when constructing a few of Gerry's flat panel antennas from aluminum-clad foam board. It has worked fine in both applications.

I solder the shield ground wire and the ground side of the antenna (the loosely wound wire from the end of the winding) together with the shield braid and black wire from the shielded pair microphone cabling I use for the interconnect between the amp and antenna. I solder the other end of the antenna winding to the red wire of the cable.

It is really important not to reverse the ground and hot sides of the antenna connections to the amp. One side of each amp connection is at ground potential. The shielded braid of the cable and grounded end of the antenna wire MUST connect to the grounded side of the amp input. You won't blow the amp if you reverse them, but if you do, the shield becomes part of your antenna and you will find all sorts of strange noise pickup.

Don

[Silversword]

Hi All,

Thanks for all the info in wiring the ferrite antenna wrapping.  I am still waiting for the shrink wrap that should be here this coming week.  Got the ferrite cores yesterday.  Also got the electrical conduit and the "L" coupling and end caps. Almost ready to go.

Also got the Bud cases, shielded CAT cable a 3' for testing and a 25' for placing the amplifier/antenna somewhere outside.

I still have to do the boards but got the parts separated.  I am old school in resistor reading (4 band) and not versed in the 5 band configuration.  Here is a good link for using the color scheme http://www.hobby-hour.com/electronics/resistor_color_code.php. or you can just the VOM to find out what they are. Some colors on the resistors are hard to see what they are.

Anyway, looks like I am on my way to get this project done between keeping up with mowing my yard because of the rains we have been getting the last few weeks. We are almost doubled for this years average at this time of year.  Some flooding in the area.

Regards,

--Stan Y.
   KH6HHG
   Maui, Hawaii

[DaleReid]

Don,

In your lengthy post with the great pictures on winding and then shrink wrapping the rods, plus inserting them into the PVC with the L box for a mount, you seemed to run the wires inside and connect them there, but not really tie them down.  Not that they'll need a lot, but my first impulse was to perhaps glue a terminal strip to the back of the L box, and then use that to join the delicate wires from the antenna windings to the outgoing, more substantial, shielded cables.  Was there a reason for doing it as you did vs. putting a six terminal strip back there, other than expense?  I assume once connected all is fine and a couple wraps of wire around the shielded stuff and a hit of shrink wrap to insure nothing moves or touches is a lot cheaper, but are you aware of any problem with trying a strip?

Just curious.

Dale