TheRadioBoard

was interested in ferrite coil q that one could obtain

article on subject by Ben Tongue confused me a bit ( quite a bit )

When all else fails , make relative asessment

Board member Mak1939 agreed to wind coils and measure q . Cannot speak of equipment , but same instrument used to measure q of each coil

thought i'd share results ( mak1939 agreed )

same person made each coil ( he makes a very good basket coil, too )

litz wire used ( I suspect xizi litz , thats what he sells ).. end of free advertisements

all coils used the same amidon-61 4" by 0.5" rod that i sent him, randomly selected , nothing special about it as far as i know

All coils centered radially into 20 ml. injection tube, Diameter are 0.8" and 3.5" long. Will send pictures of setup once i figure out how , or will send pictures to member willing to post 4 me. dont know what a photo bucket is , dont want to know

Coils are not centered on rod in axial direction . All start about 0.4" from one end of rod

setup makes nifty way to compare coils , if you have the equipment to measure. Or ears good enough to tell the difference.

Coil #1 240 uH:

40/44 litz, 58 turns, 1.2" width.
550 KHz, 353 pf, 520 Q.
800 KHz, 166 pf, 610 Q.
1700 KHz, 34 pf, 596 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.

330/46 litz, 67 turns, 3.0" width.
550 KHz, 350 pf, 803 Q.
800 KHz, 165 pf, 808 Q.
1700 KHz, 33 pf, 610 Q.
_________________________________

Coil #2 110 uH:

40/44 litz, 40 turns, 0.8" width.
695 KHz, 470 pf, 475 Q.
800 KHz, 358 pf, 500 Q.
1700 KHz, 76 pf, 585 Q.

175/46 litz, 40 turns, 1.3" width.
700 KHz, 470 pf, 775 Q.
800 KHz, 363 pf, 795 Q.
1700 KHz, 78 pf, 766 Q.

330/46 litz, 41 turns, 1.9" width.
700 KHz, 468 pf, 808 Q.
800 KHz, 360 pf, 810 Q.
1700 KHz, 76 pf, 693 Q.

660/46 litz, 43 turns, 2.8" width (this coil only has 105 uH)
720 KHz, 467 pf, 802 Q.
800 KHz, 383 pf, 780 Q.
1700 KHz, 81 pf, 620 Q.
________________________________

Coil #3 440 uH:

175/46 litz, 89 turns, 3.0" width.
550 KHz, 195 pf, 785 Q.
800 KHz, 91 pf, 788 Q.
1420 KHz, 25 pf, 656 Q.
________________________________

anybody have results to post for their ferrite coils? , centered or not ?
run of the mill ferrite results would be appreciated , but would also like to know what get from "special" rods

ANDY

Ferrite rod and coil:

For this amidon-61 4" by 0.5" rod that we test, looks like 175/46 litz wire can get very good Q. 330/46 only little better but in 1700 KHz is worse than 175/46. 660/46 is waste here.





All coils for test:




40/44 litz coils: 240uH, 110uH




175/46 litz coils: 440 uH, 240uH, 110uH




330/46 litz coils: 240uH, 110uH




660/46 litz coils: 105uH

_________________
I love crystal radio!

There have been several forum entries on coil Q but they are hard to find in searches.
This one covers several experiments and links to other forum entries.
http://theradioboard.com/rb/viewtopic.p ... f991862596

thnans for the post a goldmine of info

I went thru a spell of measuring the Q of toroid coils. Mainly -61 material from cwsbytemark on the web. I found them to be all over the block for Q. The AL value was fine and I could count on the inductance calculations to work but the Q varied greatly, over 2:1 difference in some cases. What I took away from that exercise is that there is no guarantee that one ferrite coil can be reproduced by the next guy with the same results unless he has the same luck of the draw.

I think the same applies to the ferrite rods. I recall someone saying that they got great Q measurements from a certain type of rod salvaged from a certain brand of German radio. That doesn't surprise me.

These exercises are good. Although the ferrite formula may differ greatly its a good directional pointer to which winding may be best.

Thanks for the great pics and results mak1939.

exray - you are right - some rods are disappointing, as are some "-61" toroids (grrrr....).

.................

I agree! I've had a batch of toroids from the same source range from ~180 to above 400. My personal record for toroids is 400+ on a random pick of FT50 size scatter-wound. Go figure?

"Don't try this at home".

How about a solid wire coil with about the same diameter as one of the Litz wires for comparison?
It has been suggested several times on the forums that Litz does not gain you much over solid wire on ferrite but my experience has been that I see a noticable increase in volume and selectivity.
Maybe copy the highest and lowest Q coils?

I will find some solid wire to compare later. Thanks!

_________________
I love crystal radio!

I have noticed the same benefits. I've never double checked with a "Q" meter, but I have ALWAYS found a noticable difference in volume and selectivity on ferrite core coils of ALL kinds, when using a good quality Litz wire instead of single conductor copper. This has held true for me across the board, whatever way the coil was wound - directly on the ferrite rod, or with a small, thin teflon spacing former, or even on a larger polypropylene coil former twice the diameter of the ferrite when building a "ferrite enhanced" type coil. This has held especially true when the coils were 'close' wound, rather than 'space' wound. I have never tried to wind a ferrite core coil with a single conductor 'pure silver' wire (due to cost considerations,) but I may try one in the future, just to see how the 5% higher conductivity of the silver over simple plain copper affects the overall Q. (Of course, bare pure silver wire would have to be enameled first before using close-wound, just as copper would.) I suppose the litz would still have the Q advantage on a close wound coil due to eddy current factors, but it might be interesting to see what would occur on a space-wound ferrite core coil where that wouldn't be quite as much of a factor - Jim.

Good Q results (HP 4243A meter) using an antenna ferrite and low count litz of "non-preferred" gauge. Windings held in place using teflon plumbers tape. Rod is one of my "better" ones.

Rod specs. = 130mm x 8.6mm (5.1" x 0.34")
Winding L. = 90mm (3.65")
Wire = 40/44 litz (not /46)
Turns = ~90
Spacing = Single
Induct. = ~340uH
Q = 800 @ 530kHz / 700 @ 1700kHz (min.)
Qmax. = 850

The first batch of coils are close wound served Litz taped at the ends and golf's coil is spaced unserved Litz taped with teflon tape the whole length?

solid wire with insulation , or no insulation ( other than coating on wire )

member mak1939 (ming) made comment in email to me that got better q when coil not centered on rod ( if i uderstood it correctly , i may not have ) any comments ? I'm glad to see that this has stirred up some more interest. I have been pleasantly surprised with ferrite coils. Maybe get better q with basketweave or spider coil , but they dont even come close to fitting into altoids can

ming gets all the credit for the work. It was just my silly idea to re-stir the pot

andy

and another note

if mak1939 can wind some solid wore coils and use the same core as used for all the rest of coils . have a pretty good relative asessment of what is going on.

same "Q" meter , assuming same measurement technique , same piece of ferrie , etc. Hopefully what is measured better is beter for all cores of same size ( 61 ferrite ) regadless if instrumentation

Mine is served but maybe with thinner layer.
Mac's might be double served (or cotton?, silk?).

Jim G. might know better (and I would trust his take on it) but I am leaning towards thinking that the closer the wire is wound to the core, the higher the inductance for the same length of wire, which seems to result in better "Q". I think it is a case of finding the best "Q" at the minimum distance from the core. It may even be as low as one conductor diameter (eg. 46AWG) or maybe one "bundle" diameter? Mine was wound on a single layer of the thin teflon tape (there are several grades over here - white, pink & yellow). If you think of the core as being lossy, and wanting to suck up the RF, then the closer the coil is to the core, the better the coil may perform (closer to the available field)?

I am not even sure that spacing windings is overly beneficial. I have a feeling that the fields are so strong with ferrite that normal "high Q air-coil" techniques might have minimal effects (at least with "Q"s less than [say] 1000).

This might be heresy, but, I am also wondering if ferrite toroids are so unwilling to share their fields, that high Q's might be harder to achieve with them, than with rods?

As always, these are just my thoughts and I defer to those with more experience.
..............................