TheRadioBoard

I think there's some truth to that, Golf. In my experience with toroids, you're going to top around 500 and there's nothing else you can do. You can only go so large with wire size, litz doesn't really shine in such a short length of wire, larger cores don't seem to make much difference, spacing doesn't seem to have any effect.

Sounds right ex, my (supposed) FT240-61's were a disaster. If I was game enough I would saw them in half - at 12mm I think they are too thick (lossy).

golf
Double or triple stack the torroids if you have a few to allow the use of large Litz.

In a Chinese Radio Amateur’s Handbook (1985), I read something about the ferrite coil Q:

The inductance magnitude of a coil is related to the structure of a ferrite rod and its position on the rod.

A coil changes its position on the ferrite rod, will effect the inductance magnitude and Q value. When the coil moves out from the center of ferrite rod, the effective permeability of this ferrite rod will decrease and result in the inductance magnitude decrease, but the Q of coil will increase.

The Q value also relate to relative diameter “d/dcb” of a coil. Q can reach maximum when the ratio of coil diameter “d” and ferrite rod diameter “dcb” is 1.3. Moreover, the Q value will decrease if the coil length “a” increase.



Usually we use litz wire to make monolayer close wind coil for MW ferrite rod. Compare to normal magnet wire, its Q will be 150 ~ 200% higher.

_________________
I love crystal radio!

I'll have to look at end winding. Per the book you should have at least a coil's length of rod extending past the coil on each end. Butting another rod to the end increases the Q. Adding one to the other end increases the Q again. This works until you get to about 18 inches total length. I'll have to try butting up the additional rods all on one side.

Thanks Mac - interesting, seems to be in line with my thoughts.

Tried stacking (2) with no spacing between - inductance was about the same for the same piece of wire (less turns though, so larger litz could be used, as suggested) - no appreciable change in "Q" for the wire used.

mak1939:

That is good information and a very interesting graph - thank you for sharing it!

73, Dan

Do you have similar information on bar and toroid ferites?
Spacing on a flat bar ferite maxes out at Q around the thickness of a business card. That may compare to the spacing on your rod ferite chart?
On a couple of my rod antennas the wire is embedded in the ferite. Any info on that technology? It seems to be at odds with your chart information.

The book I copy above graph has no similar information on bar and toroid ferrite.

Today I use AWG 22 solid wire to wind a similar 240 uH coil (its sectional area is equal to 165/46 litz wire), 60 turns, 1.7" width.





Compare this coil with 175/46 litz wire coil in similar condition:

AWG 22, 60 turns, 1.7" width.
550 KHz, 349 pf, 103 Q.
800 KHz, 166 pf, 106 Q.
1700 KHz, 35 pf, 111 Q.

175/46 litz, 61 turns, 2.0" width.
550 KHz, 355 pf, 788 Q.
800 KHz, 166 pf, 840 Q.
1700 KHz, 34 pf, 699 Q.

The Qs of 175/46 litz wire coil are almost 6 -7 times better than AWG 22 coil.

_________________
I love crystal radio!

Thanks Mak - great comparison.

This coil was wound on a similar rod to my previous coil.

Solid switchboard wire - 22AWG - 0.05" OD including insulation - ~200uH.

Q = 330 @ 530kHz (min), 365 @ 1700kHz (max).

Q peaks @ around 1700kHz so spacing and separation from core might be ideal for upper part of band with this particular coil and core?.

Note that Q appears to improve when wound closer to the core (if compared to the results from Mac's solid wire sample).

I can only agree with the observations of others regarding Q's obtained
with FT240-61 toroids.This appears to be a characteristic of the toroid
configuration.I am currently experimenting with the concept of a large
ferrite rod antenna,a concept dating to the longwave antenna by
Jim Hagan a "few"years ago.I have a quantity of FT240-61 on hand ,and
am in the process to explore this.To date,I have assembled a "rod"
made up of a stack of 24 ,for a 12" hollow core rod.
To compare its performance in terms of "Q",obtainable for the same
inductance,and to be able to make a comparison to a "normal"
ferrite rod,a 7.5x.5" #61 material,also was used ,both wound to ~230uH.
The Q readings for these widely disparate coils were as follows:

kHz, 7.5 " rod , 24 core stack,

530 , 830 , 805,

790 , 860 , 850,

1000 , 830 , 760,

1500 , 700 , 600,

1700 , 650 , 540,

This appears to show a surprising consistency in Q trends,given
the vast differences in dimensions of ferrite used.
The coils were wound with 175/46 litz.

eb, that is really nice work. Thanks for sharing it.

How many turns (or total length of wire) was needed to get 230uH for each coil? Did the stacked toroids need more total wire?

And one more question -- did you glue the stacked toroids together to form the hollow "rod"?

Good stuff!

73, Dan

Hi Dan, the rods coil is on a plastic tube of 0.615" diameter and
has 51 turns,using ~10ft.The stacks coil is on a plastic bobbin
of 2.75" diameter and has 23 turns,using ~20ft.The toroid stack
is held together in two hdpe bottles I found at TAP Plastics.
The bottles are of the ideal outer diameter of 2.45",providing a
nice fit for the toroids, 2 bottles with top removed and pushed
together and taped.The result is a "rod" without any looseness,
without the commitment,and possible damage from adhesives.

Eb.