Litz wire for AM Antenna Rod?
 

On Mar 26, 5:56 am, "art" wrote:
On 25 Mar, 22:07, "Bill Bowden" wrote:



On Mar 25, 9:03 pm, "Bill Bowden" wrote:

On Mar 25, 6:19 pm, "art" wrote:

On 23 Mar, 21:29, "Bill Bowden" wrote:

How much improvement can I expect using Litz wire to wind a AM ferrite
Rod antenna as opposed to using solid copper wire?

Is it worth the trouble to obtain Litz wire, or can I expect almost
the same response at say 1 MHz using regular enamaled copper wire?

-Bill

Bill, to give you a better background so the answer is more
understandable is to think about what Litz wire does for you. When are
delving into lower frequencies than AM then the skin depth required of
the wire is much deeper that at higher frequencies and if the wire
diameter is relatively small then the resistance goes up because even
if there was enough skin depth the circumference is small. If the wire
was made of many strands insulated from each other then the resistance
goes down since the wires are in parallel.
As I stated earlier Litz wire is used below AM frequencies. So now let
us examine what wire resistance does at A.M. frequencies say on your
auto, do you think that you could tell the difference on the radio if
you replace the stainless whip with say a copper wire? No I don't
think so. So for starters the Litz wire is not relavent for your
frequency of use and 2 the conductivity of the whip will not affect
your radios performance unless you took liberties with the
conductivity and replaced your whip with a wooden stick
Art

Well, according to this website, Litz wire will increase the Q factor
of a ferrite rod antenna by 6 times or more at 943Khz. The attainable
Q value is 141 with solid copper wire and 1030 using Litz wire. Quite
a significant difference. Of course the bandwidth is is only about 500
Hz with a high Q value and much wider at the lower Q, which may be
desirable. But it's much easier to start with a high Q and work down,
than the other way around.
Very easy to reduce efficiency, very hard to increase it.

Quote from website:

"Solid wire instead of litz?: Keep in mind that the work described
here used close-wound 125/46 litz wire. If one duplicates 'Coil and
Former B' in Table 2, except using 22 ga. solid copper wire (having
the same diameter) as 125/46 litz, the Q values drop to about 1/6 of
the values achieved with the litz wire. The cause is the large
proximity effect resistive losses in the solid wire. The proximity
effect, but not the skin effect loss may be much reduced if the wires
are space-wound. New trade-offs now must be considered: Same wire
diameter, and therefore a longer solenoid, or a smaller wire diameter
and the same overall length? If one wishes to use solid wire, it
should probably be wound directly on the ferrite, not on a former.
The overall Q will still be much less than when using litz, but the
loss from the high (tan δ) dielectric of the ferrite will be pretty
well swamped out because of the now higher losses from the skin and
proximity effect losses. The Q values, using a close-wound solenoid
of 22 ga. solid copper wire on a polyethylene former, as in 'Coil and
Former' B in Table 2 a 520 kHz: 130, 943 kHz: 141 and 1710 kHz: 150
when using the "best core". The Q drops only 3, 3, and 5 points
respectively if the "worst core" is used. "

-Bill

I forgot the link to the website. Here it is:

http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html

-Bill- Hide quoted text -

- Show quoted text -

Very interesting Bill but in a way the report appears to be distorted
to over emphasdise the advantages the author is declaring.To compare
the "best with the worst" is some what unusual. It would have been
better served if
average type ferrites were used and a smaller size former than that
chosen by the author. As a scientific paper it does a good job in
pointing out gains and losses between two aproaches but in real life
the differences appear to be over played. Certainly it brought up
things that had not previously thought about and I suppose the final
test of its merits depends pretty much on whether industry changes
over design for its A.M. radios and that the customer will be able to
discern advantages.. I may be wrong but it does seem to suggest that
larger ferrites are to be used
which avoids convention of small compact receivers, a much larger
negative
than any perceived advantage and the author has only emphasised
perceived advantages to enlargen the importance of his reseach.
However it was you that brought up the question in the first place and
now the supposed scientific report which begs the question what sort
of comments you were expecting from the group.
Art

I brought up the question before I found the website which was
provided by someone from another group sci.electronics.basic

Another glaring error pointed out was the bandwidth limitations using
a high Q coil. As the Q goes up, the bandwidth goes down to possibly
unusable values. At 800Khz and a Q of 1000, the bandwidth is only 400
Hz. Not very good at audio frequencies.

I think the answer is to use as high a Q as possible and then
load the antenna coil so the Q falls to the desired value. It's easy
to drop the Q, very hard to increase it.

Thanks,

-Bill