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Litz wire for AM ferrite Rod Antenna?

B

Bill Bowden

Jan 1, 1970
0
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 solid enamaled copper
wire?

-Bill
 
M

MassiveProng

Jan 1, 1970
0
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 solid enamaled copper
wire?


You are only talking microvolts/femtowatts here.

Loop antennas are what most stereo receivers use these days. Ferrite
rod versions are for handheld portables.

The increase is enough that those portable radio makers use it.

Hell, just buy a cheap one or grab on at a yard sale and disassemble
it. Better, just go to a military surplus store or industrial
liquidator in your town.
 
J

John Popelish

Jan 1, 1970
0
Bill said:
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 solid enamaled copper
wire?

If you would like to see some comparative experimental data,
Ben Tongue has performed some experiments and posted the
data to his web site.
http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html
 
B

Bill Bowden

Jan 1, 1970
0
If you would like to see some comparative experimental data,
Ben Tongue has performed some experiments and posted the
data to his web site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html

Thanks John,

Yes, it looks like Litz wire has a significant advantage. If I read
the results right, the unloaded Q factor at 943Khz is 141 using solid
copper wire verses a Q factor of 1030 using Litz wire.
That's quite a significant difference. Am I reading the results right?

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 are: 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
 
J

John Popelish

Jan 1, 1970
0
Bill said:
Thanks John,

Yes, it looks like Litz wire has a significant advantage. If I read
the results right, the unloaded Q factor at 943Khz is 141 using solid
copper wire verses a Q factor of 1030 using Litz wire.
That's quite a significant difference. Am I reading the results right?

I think you are interpreting this correctly. Keep in mind
that this is the Q of the coil, unloaded by any receiver
circuit. If the circuit adds a significant load, the Q
differences for a tuned antenna would be a smaller ratio
different. 22 AWG is also pretty heavy wire for a typical
antenna coil. With smaller wire, the Qs would be smaller
but closer.
 
A

amdx

Jan 1, 1970
0
If you would like to see some comparative experimental data,
Ben Tongue has performed some experiments and posted the
data to his web site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html
Thanks John,
Yes, it looks like Litz wire has a significant advantage. If I read
the results right, the unloaded Q factor at 943Khz is 141 using solid
copper wire verses a Q factor of 1030 using Litz wire.
That's quite a significant difference. Am I reading the results right?

That's the way I read it. Quite a large difference.
And according to Table 7 using a smaller wire diameter, even with the
higher
DC resistance gives better Q. I found that interesting, I new I could get
higher Q's
when I spaced turns about one wire diameter, but it seem there's a little
more to it.
Oh, and that contrawound thing is neat to. I wonder if there is any
advantage to
three or four contrawound windings.
Great article.
Thanks, Mike

Quote from website:

Table 7: Simulation of inductor BB in FEMM at 1 MHz, with various
conductor diameters (type 61 core material)
Wire dia.
in inches Inductance in uH Resistive
losses in ohms Hysteresis
losses in ohms Total losses
in ohms DC resistance
Q
0.02530 258.5 11.16 1.32 12.48 0.16 130.1
0.02320 259.6 8.04 1.33 9.36 0.18 174.2
0.02127 260.5 6.26 1.33 7.59 0.22 215.7
0.01951 261.1 5.13 1.34 6.47 0.28 253.7
0.01789 261.6 4.37 1.34 5.71 0.36 288.0
0.01265 263.4 2.91 1.35 4.26 0.64 388.1
0.008995 264.0 2.48 1.36 3.84 1.25 431.9
0.006300 264.4 3.02 1.36 4.38 2.62 379.7
0.008995* 264.5 2.57 1.40 3.97 1.00 418.6

Table 7 shows the benefits of space winding when using solid wire. All the
inductors in Table 7 use centered have solenoids of 58 turns and a length of
1.624". The only variable is the diameter of the conductor, which controls
the spacing of the turns (the winding pitch is held constant). The lesson
here is that, when using solid copper wire, there can be a great Q benefit
by space winding the solenoid, using an optimum size wire, in this case a Q
of 431.9 vs 130.1 at 1 MHz.
 
M

MassiveProng

Jan 1, 1970
0
The proximity
effect, but not the skin effect loss may be much reduced if the wires
are space-wound.

Use insulated wire, and another good sub for litz is SPC (silver
plated copper), as you get a slightly better skin, and the insulation
gives the space winding. A twisted group of smaller SPC wires can
give a slight Litz effect as well, like 7 32 ga SPC wires in teflon,
or other sheathing twisted together evenly. Not true litz, but better
than a single conductor. Particularly if the space winding effect are
the main desire.
 
A

amdx

Jan 1, 1970
0
MassiveProng said:
Use insulated wire, and another good sub for litz is SPC (silver
plated copper), as you get a slightly better skin, and the insulation
gives the space winding.

A twisted group of smaller SPC wires can
give a slight Litz effect as well, like 7 32 ga SPC wires in teflon,
or other sheathing twisted together evenly. Not true litz, but better
than a single conductor. Particularly if the space winding effect are
the main desire.

I'd be interested in seeing the results of that experiment. Ben's best
Q is 431 using a single #31 wire. The results shown in Table 7 suggest
that, getting the wires close to each other reduces Q. Twisting 7-#32
wires (with teflon) together and winding with that bundle would probably
end up with no space between turns.
Mike






Let the name calling begin, but try to use something new.
 
J

John Larkin

Jan 1, 1970
0
Thanks John,

Yes, it looks like Litz wire has a significant advantage. If I read
the results right, the unloaded Q factor at 943Khz is 141 using solid
copper wire verses a Q factor of 1030 using Litz wire.
That's quite a significant difference. Am I reading the results right?


In a superhet, high Q will make it that much harder to track the LO,
so you may well lose signal with a q=1000 rod. Why do you want a high
antenna Q? In the AM band, gain is cheap and s/n is dominated by
ambient noise, so it won't matter much.

John
 
J

John Popelish

Jan 1, 1970
0
John said:
In a superhet, high Q will make it that much harder to track the LO,
so you may well lose signal with a q=1000 rod. Why do you want a high
antenna Q? In the AM band, gain is cheap and s/n is dominated by
ambient noise, so it won't matter much.

I think the main point to keep in mind is that it is easy to
throw Q away, but hard to make it if the L and C don't have
it, to start with. You might want to calculate the ideal Q,
and then use an antenna coil construction technique that is
pretty sure to exceed that requirement.
 
J

John Popelish

Jan 1, 1970
0
John said:
At 800 KHz, q=1000, the resulting audio bandwidth will be 400 Hz!

So what would be a reasonable Q for the tuned antenna?
Something close to 100, I suspect.
 
J

John Larkin

Jan 1, 1970
0
I think the main point to keep in mind is that it is easy to
throw Q away, but hard to make it if the L and C don't have
it, to start with. You might want to calculate the ideal Q,
and then use an antenna coil construction technique that is
pretty sure to exceed that requirement.

At 800 KHz, q=1000, the resulting audio bandwidth will be 400 Hz!

John
 
J

John Larkin

Jan 1, 1970
0
So what would be a reasonable Q for the tuned antenna?
Something close to 100, I suspect.

Or maybe a bit less... 50? Again, for a superhet, the tracking problem
isn't trivial.

John
 
B

Bill Bowden

Jan 1, 1970
0
In a superhet, high Q will make it that much harder to track the LO,
so you may well lose signal with a q=1000 rod. Why do you want a high
antenna Q? In the AM band, gain is cheap and s/n is dominated by
ambient noise, so it won't matter much.

John

It's just a little portable AM radio I've been wanting to build for
years. I took a radio class in 7th grade 50 years ago and never got
around to finishing the superhet design. But I got an A anyway. We
used tubes in those days.

I'm using the Signetics NE602 balanced modulator IC that produces
about 13dB gain. The antenna rod is buffered with a JFET so there is
minimal load on the antenna rod yielding another 12 to 18 dB. The
front end is pretty hot.

But as you say, the bandwidth is narrow with a high Q coil, so I'm
using a switch to short a couple turns on the antenna rod to load the
antenna for local strong stations. Local/DX select.

The biggest problem is separating a distant station 40KHz away from a
strong local 50KW station 5 miles up the road.

-Bill
 
M

MassiveProng

Jan 1, 1970
0
I'd be interested in seeing the results of that experiment. Ben's best
Q is 431 using a single #31 wire. The results shown in Table 7 suggest
that, getting the wires close to each other reduces Q. Twisting 7-#32
wires (with teflon) together and winding with that bundle would probably
end up with no space between turns.
Mike
Of course there would be space between the turns. The insulation
alone edicts it. Can you really be that thick? The solid wire nests
right next to itself from turn to turn because it is mag wire,
dipshit.
Let the name calling begin, but try to use something new.

Like your 8 blank line dumbshit, followed by yet another retarded
remark after your reply?
 
A

amdx

Jan 1, 1970
0
MassiveProng said:
Of course there would be space between the turns. The insulation
alone edicts it. Can you really be that thick? The solid wire nests
right next to itself from turn to turn because it is mag wire,
dipshit.
Oh, I thought you might have read the article. The length of the windings
of all coils in Table 7 is 1.624". His High Q coil has about .019" between
each turn.
I doubt you could even duplicate his experiment with your suggested wire.
But as I said, "I'd be interested in seeing the results of that experiment."
Like your 8 blank line dumbshit, followed by yet another retarded
remark after your reply?

Come on Massive, dipshit, dumbshit and retarded, is that the best you can
do?
Entertain us with something original. You use the same old tired names over
and over. They've lost their oomph, their punch, their pizzazz.


Space intentionally left blank for new improved original name calling.
Mike
 
A

Anthony Fremont

Jan 1, 1970
0
Bill said:
On Mar 25, 5:35 pm, John Larkin

It's just a little portable AM radio I've been wanting to build for
years. I took a radio class in 7th grade 50 years ago and never got
around to finishing the superhet design. But I got an A anyway. We
used tubes in those days.

I'm using the Signetics NE602 balanced modulator IC that produces
about 13dB gain. The antenna rod is buffered with a JFET so there is
minimal load on the antenna rod yielding another 12 to 18 dB. The
front end is pretty hot.

I take it this is connected to pins 1 and 2? How did you do your oscillator
on 6 and 7?
But as you say, the bandwidth is narrow with a high Q coil, so I'm
using a switch to short a couple turns on the antenna rod to load the
antenna for local strong stations. Local/DX select.

The biggest problem is separating a distant station 40KHz away from a
strong local 50KW station 5 miles up the road.


What are you using as an IF filter and AM detector? I've been tinkering
around trying to build a 10MHz WWV receiver and I have an NE602 that I'm
injecting my "PIC locked" 9.545MHz LO into (pin 6) and using a 10MHz tank
circuit ( 2.8uH and ~100pF) as a preselector with the antenna coupled to the
coil. I only have that much done so far, but it's time to do some filtering
and detection and I'm not sure what direction to take on that. Just playing
around, nothing critical.

I always wanted to build a crystal set using an oatmeal box sized coil form
with a sliding tap. Maybe when my daughter gets a little older she'll wind
it for me. ;-)
 
R

Rich Grise

Jan 1, 1970
0
On Mar 25, 5:35 pm, John Larkin

It's just a little portable AM radio I've been wanting to build for
years. I took a radio class in 7th grade 50 years ago and never got
around to finishing the superhet design. But I got an A anyway. We
used tubes in those days.

I'm using the Signetics NE602 balanced modulator IC that produces
about 13dB gain. The antenna rod is buffered with a JFET so there is
minimal load on the antenna rod yielding another 12 to 18 dB. The
front end is pretty hot.

But as you say, the bandwidth is narrow with a high Q coil, so I'm
using a switch to short a couple turns on the antenna rod to load the
antenna for local strong stations. Local/DX select.

The biggest problem is separating a distant station 40KHz away from a
strong local 50KW station 5 miles up the road.

I've read somewhere that the idea is to build the selectivity into the
IF part.

Have Fun!
Rich
 
J

John Larkin

Jan 1, 1970
0
I've read somewhere that the idea is to build the selectivity into the
IF part.

Yes, but you have to be careful that nothing overloads in the
front-end, or in the first IF stage, from that 50 KW monster. A decent
antanna Q helps some. Fets are really good for avoiding nonlinearity.

So, low-gain jfets or mosfets in the front end and maybe the first IF,
and pile up selectivity and gain in later IF stages. Manual stage gain
pots, rather than AGC, would be fun.

John
 
B

Bill Bowden

Jan 1, 1970
0
I take it this is connected to pins 1 and 2? How did you do your oscillator
on 6 and 7?

The oscillator is the Hartly version with a tapped coil. Pin 7 goes to
the tap through a 0.1uF cap. Pin 6 goes to the high side of the coil
through another 0.1uF cap. Low side of coil goes to ground and tuning
cap goes across the coil.

But, I had to rewind the oscillator coil because the tap on the
regular (red slug) coils is too close to one end for good oscillation.
I put the tap about 1/3 the way up and used a resistor (1K) in series
to get it about right.
What are you using as an IF filter and AM detector?

I have 2 IF stages planned, but just using one right now. It just uses
the normal (black slug) coil with a 2K secondary to drive the
detector. The detector is a Schottky diode that feeds the gate of a
JFET. There is a 2 Meg resistor from gate to +V to bias the diode at a
few microamps and a 1000pF cap from gate to ground to filter out the
RF. Audio comes off the source of the JFET.

I'm not sure exactly how this works, but it does the best job of all
the other configurations I tried. The audio is good from a weak
station. I have an article about using a zero bias JFET so that no
diode is needed, but I haven't tried that one.
I've been tinkering
around trying to build a 10MHz WWV receiver and I have an NE602 that I'm
injecting my "PIC locked" 9.545MHz LO into (pin 6) and using a 10MHz tank
circuit ( 2.8uH and ~100pF) as a preselector with the antenna coupled to the
coil. I only have that much done so far, but it's time to do some filtering
and detection and I'm not sure what direction to take on that. Just playing
around, nothing critical.

I always wanted to build a crystal set using an oatmeal box sized coil form
with a sliding tap. Maybe when my daughter gets a little older she'll wind
it for me. ;-)

-Bill
 

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