Forums

Litz wire for AM ferrite Rod Antenna?

Started by Bill Bowden March 24, 2007
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

On 23 Mar 2007 21:50:54 -0700, "Bill Bowden" <wrongaddress@att.net>
Gave us:

>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.
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 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
On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote:
> 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 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
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 =CE=B4) 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
Bill Bowden wrote:
> On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote: >> Bill Bowden wrote: >>> How much improvement can I expect using Litz wire to wind a AM ferrit=
e
>>> 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
>=20 > Thanks John, >=20 > 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=20 that this is the Q of the coil, unloaded by any receiver=20 circuit. If the circuit adds a significant load, the Q=20 differences for a tuned antenna would be a smaller ratio=20 different. 22 AWG is also pretty heavy wire for a typical=20 antenna coil. With smaller wire, the Qs would be smaller=20 but closer.
> Quote from website: >=20 > " 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 =CE=B4) dielectric of the ferrite will be prett=
y
> 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. " >=20 > -Bill >=20
"Bill Bowden" <wrongaddress@att.net> wrote in message 
news:1174787636.562038.124710@e65g2000hsc.googlegroups.com...
On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote:
> 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 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
>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.
On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddress@att.net>
Gave us:

> 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.
"MassiveProng" <MassiveProng@thebarattheendoftheuniverse.org> wrote in 
message news:il9d03tohd4u68ili8u6oa7on5q69i6lhu@4ax.com...
> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddress@att.net> > Gave us: > >> 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.
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.
On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddress@att.net>
wrote:

>On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote: >> 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 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 > >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
John Larkin wrote:

> 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.