Litz wire for AM ferrite Rod Antenna?
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From: John Larkin on 25 Mar 2007 23:40 On Sun, 25 Mar 2007 22:27:06 -0400, John Popelish <jpopelish(a)rica.net> wrote: >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. At 800 KHz, q=1000, the resulting audio bandwidth will be 400 Hz! John
From: John Popelish on 25 Mar 2007 22:45 John Larkin wrote: > On Sun, 25 Mar 2007 22:27:06 -0400, John Popelish <jpopelish(a)rica.net> > wrote: > >> 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. > > 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.
From: John Larkin on 26 Mar 2007 00:20 On Sun, 25 Mar 2007 22:45:35 -0400, John Popelish <jpopelish(a)rica.net> wrote: >John Larkin wrote: >> On Sun, 25 Mar 2007 22:27:06 -0400, John Popelish <jpopelish(a)rica.net> >> wrote: >> >>> 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. >> >> 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. Or maybe a bit less... 50? Again, for a superhet, the tracking problem isn't trivial. John
From: Bill Bowden on 26 Mar 2007 01:40 On Mar 25, 5:35 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...(a)att.net> > wrote: > > > > >On Mar 24, 8:22 am, John Popelish <jpopel...(a)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 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
From: MassiveProng on 26 Mar 2007 03:19
On Sun, 25 Mar 2007 17:42:10 -0500, "amdx" <amdx(a)knology.net> Gave us: > >"MassiveProng" <MassiveProng(a)thebarattheendoftheuniverse.org> wrote in >message news:il9d03tohd4u68ili8u6oa7on5q69i6lhu(a)4ax.com... >> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddress(a)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 > > 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? |