The tuning circuits of my xtal sets are made out of old fashioned type of coils
as seen in old magazines and photo`s, these can be Honeycomb, Basket weave,
Spiderweb and other forms of coils. In German these are: Honigwaben,
Korbspule, Spinnwebenspule. Basket weave coils are also mentioned in books
as "Lorenz" coils, and can be made in different shapes and sizes, as the
Honeycomb and Spiderweb coils.
These coils were made because of their low own capacitance,
this gives your coil a higher Q because the windings are further apart from
eachother, there is more air between the layers.
You can make your coils using enameled copper wire, or silk or cotton insulated
wire. Better if you make coils for the middlewave band using Litze wire, this
wire is made out of many insulated smaller wires, from 3 up to 1500 or more
small wires. But the more wires, the more expensive the wire.
A honeycomb coil
is not more then a one layer cilinder coil. Many variations are
made of this type of coil. After many tests and research they
came to the conclusion that the selfinduction is going through a
maximum when the cross section has a rectangular form (Thickness
is same as width) like in fig.19 is the same, and when the
average diameter is the same is 3x the thicknes of the winding.
Calculation of Spiderweb/basketweave/cilinder coils
can be done with the
"prof. coyle" programme, but I didn`t find a formule to calculate
honeycomb coils, these calculations were so complex they only published
the data to create these honeycomb coils. I have the data below as found
in old books:
Used capacitor in table 1 is 1000cm (+/-1100pF) wire
size 0,5mm. The coil form has a diameter of 5cm, thickness is 4cm.
Number of windings
180 - 430 meter
200 - 550 meter
250 - 700 meter
400 - 1000 meter
500 - 1300 meter
700 - 2000 meter
1000 - 2700 meter
1300 - 3600 meter
1600 - 4200 meter
Source : Bastelbuch fur
Coilform in table 2 is 5cm in diameter and
a width of 2,5cm. Own wavelength is the wavelength of the coil with its
Coils as in the upper tables are made on a coilform as seen
on description and photo`s below, but you can alter these by varying number of
The Honeycomb coil
Coil form with its measurements are in the following drawings. You can
use your own measurements and the number of pegs. But the above
values are for these coils here.
You can make your form out of wood, but I made it out of alluminium on a
lathe, the pegs are made out of knitting pins, bought these at the
weekly market here, if you buy these with 2 pointed sides you can make
two pegs of `m, so you need to buy half of the knitting pins you need
for the coil form.
A Honeycomb coil is getting larger in diameter the
more layers are wound on it, but the width stays the same.
You can use your own style the make your coil,...over2/under2, over2/under3,
over3/under2. Do it as you like and look at the results.
Winding method seen at the left: Over1/under 4.
If you use only one side of the coil form, you can wind
your spiderweb coil on this coilform, but you have to fix it with glue, the
needlework will not work here.
On a lathe I made two new coilforms to wind coils. Both have two rows of
15 holes in it to put in some knitting pins to wind the wire around.
The sizes are as mentioned in old books for the coils mentioned above,
one 4.5cm thick and one 2.5cm thick with a inner diam of 5cm.
Winding method: Over two, directly to other side and
again over two at the other side. (over 2/under 0)
I wound the smallest coil mentioned above (2.5cm
wide). Precisely according the description in the books with 25
windings. The value should be 50µH, but after I measured it with my AADE
meter and another LCR bridge the value was around 122µH. Same for wire
length, I took 4 meters and wound the coil till I got no wire left,..8
windings with a value of 12µH. So just wind your coil, measure and put
some more wire on it or take some windings off till you get what you
For the above honeycomb coil I made a table for
future use when I need to make some coils. I made 3 and put the value
and windings on mm-paper, I connected the points to get a rough guess of
Then I made the coils I needed and measured them and also put them
inside the table. It only goes to 162µH because I didn`t wind a bigger
Table is for honeycomb coils using the "Over2/Under0" method, wound onto
a 5cm in diameter form, 2.5cm wide with 2x15 pins.
The basket weave coil.
You can create
your basket weave coils using a piece of wood or something. I used
a piece of plexiglass with a thickness of around 1cm and drilled holes
in it, I used steel nails to put in the holes. The nails are placed in a
cicle of around 12cm. I wound the wire around the nails using the
over1/under2 methode. But this can be re-arranged by you using anothe
method,..over1/under1, over1/under3,..you name it.
Another type of coil is the basket
weave coil made using two rings of nails to wind your wire through.
At the right you see 2x11 steel nails. The methode of winding here
is over2/under2, but you also can use over1/under2 or something
Note: Of you follow the wire in the
over2/under2 methode, you get to the starting point after 3
circulations of the wire. Now you layed down just one layer. This
also includes the coils mentioned above.
This is what they mean by the windings do not see eachother, there
is lots of air between every layer, this gives you a coil with a
This way I made several basket weave
coils and some of these had one layer after 8 windings.
In table 1 they used 25 windings and 4meters of wire on a coilform
of 5cm in diameter. These 25 windings are the windings,..not the
layers. You have to watch out not lay down 25 layers.
A basket weave coil stays the same diameter while the width is
Below some pictures of coils I made and on their
form. (this is my first and old coilform)
My homebrew coilform.
Coil being made using the form with knitting pins
Close-up of the coil
This coil is not glued, but I did some needlework.
3D coil made on a 1mm thick
piece of "trespa"
Side view of the 3D coil
10 layer Honeycomb coil, made
of 0,75mm thick enameled wire. Fixed
using shellac and zapon laquer.
Fixation of the coils so they do not fall apart can be done using some
needlework, another used methode from the beginning of the 20th century
is to fix the coil using "zapon-laquer". This a laquer on a
nitrocellulose basis. Long time ago you could make this yourself by
dissolving celluloid film negatives into ethanol. Beware: film negatives
these days are not made out of celluloid. Now you submurge the coil into
the solution you get and after that you get it out of the solution and
let it dry. You also can use "shellac" to fixate the coils, this is
available plentyfull on Ebay,..a kilo for 8 Euro`s or so.
Self resonance of coils
I made a cilinder aircoil with a value of 15µH. Without a capacitor
connected I measured the resonance of this coil. It was resonant at
11.110Mhz. -3dB point was at 11.220 and 10.930, this makes a bandwidth
So this is the frequency where the coil is resonant with it`s own
capacitance. The Q of this coil is 11.110mhz/0.29mhz=38
Not really a good choise to use for a chort wave crystal receiver.
Its own capacitance is approx.
If I use this coil on shortwave, the selectivity would go any better
then this 290khz. Q is only getting better at a lower frequency.
I also measured the self resonance of my 440x46 spiderweb coil of my
2006 BTTF receiver.
Resonant at 2.523Mhz, -3dB point at 2.539 and 2.505Mhz, this makes a
bandwidth of 34Khz.
The Q of the coil at this frequency is 2.523/0.034=74.
Here I see that the Q is much better at lower frequency as i measured in
another chapter on my site.
Self capacitance is around 16pF
If I wanted to make myself a 10-15Mhz shortwave crystal receiver with a
bandwidth of around 9Khz, then I
would have to use a coil with a Q of around 1300, this means a self
resonance point that is at a much higher level, and
a even lower capacity,..even lower as 5pF,..I still want to seperate the
I also made a aircoil out of 6mm copper brake piping, 11cm in diameter,
8 windings, space between winding is 6mm.
These type of coils were used very often in old radio equipment.
Self resonance at 17.690Mhz, -3db point at 17.980 and 17.350, makes a
bandwidth of 630Khz.
Q of this coil at 17.690Mhz is 17.690/0.63=28
How do I
get I veeery high Q at shortwave,..I think never, even a aircoil I made
with a diameter of 25cm
had a low Q.
I also made myself a coil winder according to the Gingery Coil Winder
manual. With this type of winder you can make yourself some nice small
radio coils for your project. Below a small movie I found on the
internet on how the coil winder works.
The coil winder in the above links are in principle the same as the
Gingery winder, only the cam has been changed into a heart shaped one.
This type of cam has the advantage that the wire does go around the
circumference of the coilform in a triangle shaped fashion, instead of a
sinus with the round excentric cam. The heart shaped cam gives the coil
a much higher stability when winding the coil. Below a scan from WM.
Querfurth`s book of the heart shaped cam with the round excentric cam in
red to compare the two cams.