Litz wire for AM ferrite Rod Antenna?
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From: YD on 27 Mar 2007 12:01 Late at night, by candle light, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal opus: >On Mon, 26 Mar 2007 22:27:55 GMT, Rich Grise <rich(a)example.net> wrote: > >>On Sun, 25 Mar 2007 22:40:34 -0700, Bill Bowden wrote: >>> On Mar 25, 5:35 pm, John Larkin >>>> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...(a)att.net> >>>> >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 >>>> >>>> >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. >>> >>> 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. >> > >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 > Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away. Great for RFI immunity testing. - YD. -- Remove HAT if replying by mail.
From: John Larkin on 27 Mar 2007 18:33 On Tue, 27 Mar 2007 13:01:12 -0300, YD <ydtechHAT(a)techie.com> wrote: >Late at night, by candle light, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal >opus: > >>On Mon, 26 Mar 2007 22:27:55 GMT, Rich Grise <rich(a)example.net> wrote: >> >>>On Sun, 25 Mar 2007 22:40:34 -0700, Bill Bowden wrote: >>>> On Mar 25, 5:35 pm, John Larkin >>>>> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...(a)att.net> >>>>> >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 >>>>> >>>>> >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. >>>> >>>> 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. >>> >> >>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 >> > >Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away. >Great for RFI immunity testing. > >- YD. We look up at this beast from our back window. Something like 22 megawatts of AM, FM, TV, and HDTV... http://en.wikipedia.org/wiki/Sutro_Tower and we're in a wooden building... no shielding at all. All the scope traces are fuzzy. John
From: john jardine on 27 Mar 2007 20:11 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:oc6j03hprt40skqs7ohh0gns5i1uvjf6e5(a)4ax.com... > On Tue, 27 Mar 2007 13:01:12 -0300, YD <ydtechHAT(a)techie.com> wrote: [...] > >Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away. > >Great for RFI immunity testing. > > > >- YD. > > > We look up at this beast from our back window. Something like 22 > megawatts of AM, FM, TV, and HDTV... > > http://en.wikipedia.org/wiki/Sutro_Tower > > > and we're in a wooden building... no shielding at all. All the scope > traces are fuzzy. > > John Ugh!. Thought I had it bad with an interfering 10uV of line scan noise from the PC monitor a few feet away. Even considered seeing if the LCD types were any better. Clearly I'm living on easy street. How on earth do you cope when designing low level stuff stuff, a screened room any worth?. -- Posted via a free Usenet account from http://www.teranews.com
From: John Larkin on 27 Mar 2007 23:33 On Wed, 28 Mar 2007 01:11:49 +0100, "john jardine" <john(a)jjdesigns.fsnet.co.uk> wrote: > >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:oc6j03hprt40skqs7ohh0gns5i1uvjf6e5(a)4ax.com... >> On Tue, 27 Mar 2007 13:01:12 -0300, YD <ydtechHAT(a)techie.com> wrote: >[...] >> >Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away. >> >Great for RFI immunity testing. >> > >> >- YD. >> >> >> We look up at this beast from our back window. Something like 22 >> megawatts of AM, FM, TV, and HDTV... >> >> http://en.wikipedia.org/wiki/Sutro_Tower >> >> >> and we're in a wooden building... no shielding at all. All the scope >> traces are fuzzy. >> >> John > >Ugh!. >Thought I had it bad with an interfering 10uV of line scan noise from the PC >monitor a few feet away. Even considered seeing if the LCD types were any >better. Clearly I'm living on easy street. > >How on earth do you cope when designing low level stuff stuff, a screened >room any worth?. We design it to be EMI hard, which you may as well do anyhow. Multilayer boards, solid ground planes, signal bypass caps and ferrite beads, and no low-level opamp type things directly exposed to the outside world. The RF is terrible here, but less intense than a CE suceptability test or a cell phone nearby. And an EMI hard design tends to have better ESD resistance and, actually, just be more reliable. We do occasionally use an old analog, even tube-type scope, to see low-level stuff. The digital scopes fuzz up seriously and there's not much you can do about it. Interestingly, the 12 and 20 GHz sampling scopes are very clean, probably because they are all 50 ohm coax and SMA connectors. We do have an old unused bathroom we may convert to a screen room so we can do crude radiated emissions tests. That would be an interesting project. John
From: Bill Bowden on 28 Mar 2007 00:44
On Mar 27, 8:01 am, YD <ydtech...(a)techie.com> wrote: > Late at night, by candle light, John Larkin > <jjlar...(a)highNOTlandTHIStechnologyPART.com> penned this immortal > opus: > > > > >On Mon, 26 Mar 2007 22:27:55 GMT, Rich Grise <r...(a)example.net> wrote: > > >>On Sun, 25 Mar 2007 22:40:34 -0700, Bill Bowden wrote: > >>> On Mar 25, 5:35 pm, John Larkin > >>>> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...(a)att.net> > >>>> >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 > > >>>> >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. > > >>> 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. > > >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 > > Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away. > Great for RFI immunity testing. > Is that KOGO clear channel (600Khz) in San Diego? Up here in LA area, we have clear channel KFI on 640KHz. They both carry Coast to Coast with Art Bell, George Noory, etc. Some of the stuff is pretty good, but I stay away from the remote viewing, flying saucers, "out of body experiences" and shadow people stuff. Some of the callers ghost stories are very original. I like good story tellers, even if it's BS. -Bill > - YD. > > -- > Remove HAT if replying by mail. |