I'm about to build an FM crystal radio, but the schematic calls for a
50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
if I only use the 86 pF section?

Radio page:
http://solomonsmusic.net/FM_CrystalRadio.html

On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H" <the1930s@googlemail.com> wrote:

>I'm about to build an FM crystal radio, but the schematic calls for a
>50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
>if I only use the 86 pF section?
>
>Radio page:
>http://solomonsmusic.net/FM_CrystalRadio.html

Sure, I see no reason it won't work. Assuming that the cap
you have has a terminal common to both sections, you could
leave that terminal unused and use the 2 other terminals.
That would result in about 63pf max capacitance. Stretch the
coil out a bit or make it slightly small diameter and you
should be able to get it to tune the FM band.

Mike
If there is no absolute truth then nothing can be known.

On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>I'm about to build an FM crystal radio, but the schematic calls for a
>50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
>if I only use the 86 pF section?
>
>Radio page:
>http://solomonsmusic.net/FM_CrystalRadio.html

OK, I just had to look at this circuit to see how a rectifier
(the "crystal") could demodulate FM. But it looks pretty
much like an ordinary AM circuit. So, what's really going on?

My best guess so far is that this relies somehow on the rectifier
output dropping off as the incoming carrier frequency gets farther
from the tuned frequency. But if you tuned to the nominal
carrier frequency, and the modulator was a sine wave, I'd predict
a horrible cuspy-looking mess from the output... certainly not
the "high fidelity" that the Website claims.

So, maybe you tune off-channel, to the peaks of the deviation?
Nope, just a different trashy signal, it would seem.

Anybody have the explanation?

Best regards,



Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
http://www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

On 12/22/07 6:08 AM, in article 476d1753.1464108@news.sysmatrix.net, "Bob
Masta" <NoSpam@daqarta.com> wrote:

> On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
> <the1930s@googlemail.com> wrote:
>
>> I'm about to build an FM crystal radio, but the schematic calls for a
>> 50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
>> if I only use the 86 pF section?
>>
>> Radio page:
>> http://solomonsmusic.net/FM_CrystalRadio.html
>
> OK, I just had to look at this circuit to see how a rectifier
> (the "crystal") could demodulate FM. But it looks pretty
> much like an ordinary AM circuit. So, what's really going on?
>
> My best guess so far is that this relies somehow on the rectifier
> output dropping off as the incoming carrier frequency gets farther
> from the tuned frequency. But if you tuned to the nominal
> carrier frequency, and the modulator was a sine wave, I'd predict
> a horrible cuspy-looking mess from the output... certainly not
> the "high fidelity" that the Website claims.
>
> So, maybe you tune off-channel, to the peaks of the deviation?
> Nope, just a different trashy signal, it would seem.
>
> Anybody have the explanation?
>
> Best regards,
>
>
>
> Bob Masta
>
> DAQARTA v3.50
> Data AcQuisition And Real-Time Analysis
> http://www.daqarta.com
> Scope, Spectrum, Spectrogram, FREE Signal Generator
> Science with your sound card!

I agree with you; it is a slope detector.

Bob Masta (NoSpam@daqarta.com) writes:
> On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
> <the1930s@googlemail.com> wrote:
>
>>I'm about to build an FM crystal radio, but the schematic calls for a
>>50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
>>if I only use the 86 pF section?
>>
>>Radio page:
>>http://solomonsmusic.net/FM_CrystalRadio.html
>
> OK, I just had to look at this circuit to see how a rectifier
> (the "crystal") could demodulate FM. But it looks pretty
> much like an ordinary AM circuit. So, what's really going on?
>
> My best guess so far is that this relies somehow on the rectifier
> output dropping off as the incoming carrier frequency gets farther
> from the tuned frequency. But if you tuned to the nominal
> carrier frequency, and the modulator was a sine wave, I'd predict
> a horrible cuspy-looking mess from the output... certainly not
> the "high fidelity" that the Website claims.
>
It's not a "new" thing.

The concept is commonly referred to as "slope detection". Get the
signal along the curve of the selectivity, so as the FM signal
varies, the slope of the selectivity turns that frequency variation
into amplitude variation, which the diode can then turn into audio.

It was used when you wanted to receive FM signals, and didn't have
a receiver with an FM detector. But, of course you get no limiting
that is the norm in pretty much any real FM receiver. It's also
finicky, since you need selectivity that isn't nice and sharp, and
it's no perfect system so recovered audio will be low in amplitude.

I used to do it with an Hammarlund SP-600 shortwave receiver, that
had variable selectivity up to about 13KHz, and a converter to receiver
VHF signals. It was never a great thing, had to fuss with tuning,
low audio, noisy. A real FM receiver right next to it would meanwhile
show a nice quiet signal on the same frequency.

Michael

On Dec 23, 2:41 am, et...@FreeNet.Carleton.CA (Michael Black) wrote:
> Bob Masta (NoS...@daqarta.com) writes:
> > On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
> > <the19...@googlemail.com> wrote:
>
> >>I'm about to build an FM crystal radio, but the schematic calls for a
> >>50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
> >>if I only use the 86 pF section?
>
> >>Radio page:
> >>http://solomonsmusic.net/FM_CrystalRadio.html
>
> > OK, I just had to look at this circuit to see how a rectifier
> > (the "crystal") could demodulate FM. But it looks pretty
> > much like an ordinary AM circuit. So, what's really going on?
>
> > My best guess so far is that this relies somehow on the rectifier
> > output dropping off as the incoming carrier frequency gets farther
> > from the tuned frequency. But if you tuned to the nominal
> > carrier frequency, and the modulator was a sine wave, I'd predict
> > a horrible cuspy-looking mess from the output... certainly not
> > the "high fidelity" that the Website claims.
>
> It's not a "new" thing.
>
> The concept is commonly referred to as "slope detection". Get the
> signal along the curve of the selectivity, so as the FM signal
> varies, the slope of the selectivity turns that frequency variation
> into amplitude variation, which the diode can then turn into audio.
>
> It was used when you wanted to receive FM signals, and didn't have
> a receiver with an FM detector. But, of course you get no limiting
> that is the norm in pretty much any real FM receiver. It's also
> finicky, since you need selectivity that isn't nice and sharp, and
> it's no perfect system so recovered audio will be low in amplitude.
>
> I used to do it with an Hammarlund SP-600 shortwave receiver, that
> had variable selectivity up to about 13KHz, and a converter to receiver
> VHF signals. It was never a great thing, had to fuss with tuning,
> low audio, noisy. A real FM receiver right next to it would meanwhile
> show a nice quiet signal on the same frequency.
>
> Michael

Maybe I should just stick with AM crystal radios.

On Dec 23, 2:41 am, et...@FreeNet.Carleton.CA (Michael Black) wrote:
> Bob Masta (NoS...@daqarta.com) writes:
> > On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
> > <the19...@googlemail.com> wrote:
>
> >>I'm about to build an FM crystal radio, but the schematic calls for a
> >>50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
> >>if I only use the 86 pF section?
>
> >>Radio page:
> >>http://solomonsmusic.net/FM_CrystalRadio.html
>
> > OK, I just had to look at this circuit to see how a rectifier
> > (the "crystal") could demodulate FM. But it looks pretty
> > much like an ordinary AM circuit. So, what's really going on?
>
> > My best guess so far is that this relies somehow on the rectifier
> > output dropping off as the incoming carrier frequency gets farther
> > from the tuned frequency. But if you tuned to the nominal
> > carrier frequency, and the modulator was a sine wave, I'd predict
> > a horrible cuspy-looking mess from the output... certainly not
> > the "high fidelity" that the Website claims.
>
> It's not a "new" thing.
>
> The concept is commonly referred to as "slope detection". Get the
> signal along the curve of the selectivity, so as the FM signal
> varies, the slope of the selectivity turns that frequency variation
> into amplitude variation, which the diode can then turn into audio.
>
> It was used when you wanted to receive FM signals, and didn't have
> a receiver with an FM detector. But, of course you get no limiting
> that is the norm in pretty much any real FM receiver. It's also
> finicky, since you need selectivity that isn't nice and sharp, and
> it's no perfect system so recovered audio will be low in amplitude.
>
> I used to do it with an Hammarlund SP-600 shortwave receiver, that
> had variable selectivity up to about 13KHz, and a converter to receiver
> VHF signals. It was never a great thing, had to fuss with tuning,
> low audio, noisy. A real FM receiver right next to it would meanwhile
> show a nice quiet signal on the same frequency.
>
> Michael

Maybe I should just stick with AM crystal radios.

On 12/22/07 7:41 AM, in article fkjb71$ks2$1@theodyn.ncf.ca, "Michael Black"
<et472@FreeNet.Carleton.CA> wrote:

> Bob Masta (NoSpam@daqarta.com) writes:
>> On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
>> <the1930s@googlemail.com> wrote:
>>
>>> I'm about to build an FM crystal radio, but the schematic calls for a
>>> 50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
>>> if I only use the 86 pF section?
>>>
>>> Radio page:
>>> http://solomonsmusic.net/FM_CrystalRadio.html
>>
>> OK, I just had to look at this circuit to see how a rectifier
>> (the "crystal") could demodulate FM. But it looks pretty
>> much like an ordinary AM circuit. So, what's really going on?
>>
>> My best guess so far is that this relies somehow on the rectifier
>> output dropping off as the incoming carrier frequency gets farther
>> from the tuned frequency. But if you tuned to the nominal
>> carrier frequency, and the modulator was a sine wave, I'd predict
>> a horrible cuspy-looking mess from the output... certainly not
>> the "high fidelity" that the Website claims.
>>
> It's not a "new" thing.
>
> The concept is commonly referred to as "slope detection". Get the
> signal along the curve of the selectivity, so as the FM signal
> varies, the slope of the selectivity turns that frequency variation
> into amplitude variation, which the diode can then turn into audio.
>
> It was used when you wanted to receive FM signals, and didn't have
> a receiver with an FM detector. But, of course you get no limiting
> that is the norm in pretty much any real FM receiver. It's also
> finicky, since you need selectivity that isn't nice and sharp, and
> it's no perfect system so recovered audio will be low in amplitude.
>
> I used to do it with an Hammarlund SP-600 shortwave receiver, that
> had variable selectivity up to about 13KHz, and a converter to receiver
> VHF signals. It was never a great thing, had to fuss with tuning,
> low audio, noisy. A real FM receiver right next to it would meanwhile
> show a nice quiet signal on the same frequency.
>
> Michael

In the 50s, narrow-band FM was permitted on the high freq ham bands, It was
easily listened to without a NBFM converter by doing slope detection.

On 12/22/07 7:52 AM, in article
01cfd068-e68c-4de8-b9b9-f00f626f776d@x2 ... groups.com, "Dave.H"
<the1930s@googlemail.com> wrote:

> On Dec 23, 2:41 am, et...@FreeNet.Carleton.CA (Michael Black) wrote:
>> Bob Masta (NoS...@daqarta.com) writes:
>>> On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
>>> <the19...@googlemail.com> wrote:
>>
>>>> I'm about to build an FM crystal radio, but the schematic calls for a
>>>> 50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
>>>> if I only use the 86 pF section?
>>
>>>> Radio page:
>>>> http://solomonsmusic.net/FM_CrystalRadio.html
>>
>>> OK, I just had to look at this circuit to see how a rectifier
>>> (the "crystal") could demodulate FM. But it looks pretty
>>> much like an ordinary AM circuit. So, what's really going on?
>>
>>> My best guess so far is that this relies somehow on the rectifier
>>> output dropping off as the incoming carrier frequency gets farther
>>> from the tuned frequency. But if you tuned to the nominal
>>> carrier frequency, and the modulator was a sine wave, I'd predict
>>> a horrible cuspy-looking mess from the output... certainly not
>>> the "high fidelity" that the Website claims.
>>
>> It's not a "new" thing.
>>
>> The concept is commonly referred to as "slope detection". Get the
>> signal along the curve of the selectivity, so as the FM signal
>> varies, the slope of the selectivity turns that frequency variation
>> into amplitude variation, which the diode can then turn into audio.
>>
>> It was used when you wanted to receive FM signals, and didn't have
>> a receiver with an FM detector. But, of course you get no limiting
>> that is the norm in pretty much any real FM receiver. It's also
>> finicky, since you need selectivity that isn't nice and sharp, and
>> it's no perfect system so recovered audio will be low in amplitude.
>>
>> I used to do it with an Hammarlund SP-600 shortwave receiver, that
>> had variable selectivity up to about 13KHz, and a converter to receiver
>> VHF signals. It was never a great thing, had to fuss with tuning,
>> low audio, noisy. A real FM receiver right next to it would meanwhile
>> show a nice quiet signal on the same frequency.
>>
>> Michael
>
> Maybe I should just stick with AM crystal radios.

Or build an AM/FM crystal radio. It doesn't need to be great - have fun.

On Dec 23, 3:15 am, Don Bowey <dbo...@comcast.net> wrote:
> On 12/22/07 7:52 AM, in article
> 01cfd068-e68c-4de8-b9b9-f00f626f7...@x2 ... groups.com, "Dave.H"
>
>
>
> <the19...@googlemail.com> wrote:
> > On Dec 23, 2:41 am, et...@FreeNet.Carleton.CA (Michael Black) wrote:
> >> Bob Masta (NoS...@daqarta.com) writes:
> >>> On Sat, 22 Dec 2007 02:56:25 -0800 (PST), "Dave.H"
> >>> <the19...@googlemail.com> wrote:
>
> >>>> I'm about to build an FM crystal radio, but the schematic calls for a
> >>>> 50 pF variable capacitor, would a 2 section 233/86 pF capacitor work,
> >>>> if I only use the 86 pF section?
>
> >>>> Radio page:
> >>>>http://solomonsmusic.net/FM_CrystalRadio.html
>
> >>> OK, I just had to look at this circuit to see how a rectifier
> >>> (the "crystal") could demodulate FM. But it looks pretty
> >>> much like an ordinary AM circuit. So, what's really going on?
>
> >>> My best guess so far is that this relies somehow on the rectifier
> >>> output dropping off as the incoming carrier frequency gets farther
> >>> from the tuned frequency. But if you tuned to the nominal
> >>> carrier frequency, and the modulator was a sine wave, I'd predict
> >>> a horrible cuspy-looking mess from the output... certainly not
> >>> the "high fidelity" that the Website claims.
>
> >> It's not a "new" thing.
>
> >> The concept is commonly referred to as "slope detection". Get the
> >> signal along the curve of the selectivity, so as the FM signal
> >> varies, the slope of the selectivity turns that frequency variation
> >> into amplitude variation, which the diode can then turn into audio.
>
> >> It was used when you wanted to receive FM signals, and didn't have
> >> a receiver with an FM detector. But, of course you get no limiting
> >> that is the norm in pretty much any real FM receiver. It's also
> >> finicky, since you need selectivity that isn't nice and sharp, and
> >> it's no perfect system so recovered audio will be low in amplitude.
>
> >> I used to do it with an Hammarlund SP-600 shortwave receiver, that
> >> had variable selectivity up to about 13KHz, and a converter to receiver
> >> VHF signals. It was never a great thing, had to fuss with tuning,
> >> low audio, noisy. A real FM receiver right next to it would meanwhile
> >> show a nice quiet signal on the same frequency.
>
> >> Michael
>
> > Maybe I should just stick with AM crystal radios.
>
> Or build an AM/FM crystal radio. It doesn't need to be great - have fun.

I have an old radio that I can steal the tuning cap from, so I don't
have to look around for one of them. I couldn't even find an
Australian source for them.

<snip>
>> > Maybe I should just stick with AM crystal radios.
>>
Aww no, Play with it and hve some fun.

>> Or build an AM/FM crystal radio. It doesn't need to be great - have fun.
>
>I have an old radio that I can steal the tuning cap from, so I don't
>have to look around for one of them. I couldn't even find an
>Australian source for them.

Yeah, it's probably a 2 section cap, so use the smaller section with a series
cap to lower the capacitance range for the FM band.

Use the larger section for the AM band and switch your earphone for AM/FM.

You'll have to experimnet with the coils to get in the bands, but that's fun too.

The AM will require a million meter antenna, well maybe not quite that long and
decent ground connection. Don't forget, you need a high impedance (crystal) earphone
for it to work right.

Mike

If there is no absolute truth then nothing can be known.

On Dec 23, 6:18 am, Mike <nomtrxs...@comcast.net> wrote:
> <snip>>> > Maybe I should just stick with AM crystal radios.
>
> Aww no, Play with it and hve some fun.
>
> >> Or build an AM/FM crystal radio. It doesn't need to be great - have fun.
>
> >I have an old radio that I can steal the tuning cap from, so I don't
> >have to look around for one of them. I couldn't even find an
> >Australian source for them.
>
> Yeah, it's probably a 2 section cap, so use the smaller section with a series
> cap to lower the capacitance range for the FM band.
>
> Use the larger section for the AM band and switch your earphone for AM/FM.
>
> You'll have to experimnet with the coils to get in the bands, but that's fun too.
>
> The AM will require a million meter antenna, well maybe not quite that long and
> decent ground connection. Don't forget, you need a high impedance (crystal) earphone
> for it to work right.
>
> Mike
>
> If there is no absolute truth then nothing can be known.

It does look like a 2 section cap, even though the radio has only one
band. What value capacitor do I need? It already has a ceramic disk
connected that reads 82 or 8.2.

Dave.H wrote:
> On Dec 23, 6:18 am, Mike <nomtrxs...@comcast.net> wrote:
>
>><snip>>> > Maybe I should just stick with AM crystal radios.
>>
>>Aww no, Play with it and hve some fun.
>>
>>
>>>>Or build an AM/FM crystal radio. It doesn't need to be great - have fun.
>>
>>>I have an old radio that I can steal the tuning cap from, so I don't
>>>have to look around for one of them. I couldn't even find an
>>>Australian source for them.
>>
>>Yeah, it's probably a 2 section cap, so use the smaller section with a series
>>cap to lower the capacitance range for the FM band.
>>
>>Use the larger section for the AM band and switch your earphone for AM/FM.
>>
>>You'll have to experimnet with the coils to get in the bands, but that's fun too.
>>
>>The AM will require a million meter antenna, well maybe not quite that long and
>>decent ground connection. Don't forget, you need a high impedance (crystal) earphone
>>for it to work right.
>>
>>Mike
>>
>>If there is no absolute truth then nothing can be known.
>
>
> It does look like a 2 section cap, even though the radio has only one
> band. What value capacitor do I need? It already has a ceramic disk
> connected that reads 82 or 8.2.

You can figure out the size cap you need using math.
For capacitors in series you can use either

1/Ct = 1/C1 + 1/C2
or
Ct = (C1*C2)/(C1+C2)

where Ct is the total capacitance you want.
You know Ct = 50 and your C1 is 86, so you
can stuff estimated values for C2 into the
equation until you find the value you need.

When you put capacitors in series, the total
will always be lower than the smallest cap.
So if you put 86 pF in series with say 63 pF,
the value *must* be lower than 63 pF. As it
turns out, those two in series would give you
about 36 pF.

Ed

On Dec 23, 5:14 pm, Don Bowey <dbo...@comcast.net> wrote:
> On 12/22/07 3:06 PM, in article
> 3ae5713f-e3ba-4268-a656-5eda4bafa...@e6 ... groups.com, "Dave.H"=

>
>
>
> <the19...@googlemail.com> wrote:
> > On Dec 23, 6:18 am, Mike <nomtrxs...@comcast.net> wrote:
> >> <snip>>> > Maybe I should just stick with AM crystal radios.
>
> >> Aww no, Play with it and hve some fun.
>
> >>>> Or build an AM/FM crystal radio. It doesn't need to be great - have =
fun.
>
> >>> I have an old radio that I can steal the tuning cap from, so I don't
> >>> have to look around for one of them. I couldn't even find an
> >>> Australian source for them.
>
> >> Yeah, it's probably a 2 section cap, so use the smaller section with a =
series
> >> cap to lower the capacitance range for the FM band.
>
> >> Use the larger section for the AM band and switch your earphone for AM/=
FM.
>
> >> You'll have to experimnet with the coils to get in the bands, but that'=
s fun
> >> too.
>
> >> The AM will require a million meter antenna, well maybe not quite that =
long
> >> and
> >> decent ground connection. Don't forget, you need a high impedance (crys=
tal)
> >> earphone
> >> for it to work right.
>
> >> Mike
>
> >> If there is no absolute truth then nothing can be known.
>
> > It does look like a 2 section cap, even though the radio has only one
> > band. What value capacitor do I need? It already has a ceramic disk
> > connected that reads 82 or 8.2.
>
> The large section is the RF tuning cap and is about 365uuf fully engaged.
> That=B9s good for the AM band.
>
> The smaller section is used for the AM oscillator tuning; I don't recall
> it's value. It is too large for the FM band unless you remove all but one=

> rotor plate, then it should be usable.

The capacitor I just pulled from the radio (a 1960's 5 valve AM set)
has two sections about the same size.
Looking at it now it has 21215 stamped on the back (sounds like a
serial number) and J C4 on the front
Not sure if this is suitable for FM (probably not) but I'm looking
towards building an AM set instead.
Does anyone know of a good AM crystal set that would use this cap?
Has to be easy to build, with no hard to get parts (well I've already
got the tuning cap, that was the only hard to get part)
Picture of the cap: http://s222.photobucket.com/albums/dd23 ... 9/?action=
=3Dview&current=3DIMG_6405.jpg

<snip>
>The capacitor I just pulled from the radio (a 1960's 5 valve AM set)
>has two sections about the same size.
>Looking at it now it has 21215 stamped on the back (sounds like a
>serial number) and J C4 on the front
>Not sure if this is suitable for FM (probably not) but I'm looking
>towards building an AM set instead.
>Does anyone know of a good AM crystal set that would use this cap?
>Has to be easy to build, with no hard to get parts (well I've already
>got the tuning cap, that was the only hard to get part)
>Picture of the cap: http://s222.photobucket.com/albums/dd23 ... G_6405.jpg

From that photo it looks like both sections are identical. Usually the cap from a superhet has one section
with smaller and/or fewer plates. The smaller section was used for the "local oscillator" and since it almost
always ran at 455KHz higher than the station being received, it had a lower value.
See http://www.ittc.ku.edu/~jstiles/622/han ... Tuning.pdf if you care.

Just about any germanium diode will work just fine. In a pinch even a schottky diode will work ok if you have
a good long antenna. The only difference the variable cap will make with any crystal set is the tuning range,
so you'll have to experiment with the coil to tune AM broadcast band.
I would start with this simple crystal radio. http://www.techlib.com/electronics/crystal.html
Note how much smaller the unused section of the tuning cap is in the photo. The author gives lots of good info
& tips the beginner. The improvments later on the page might be fun to play with after you get it working.

Mike
If there is no absolute truth then nothing can be known.

On Dec 24, 12:39 am, Mike <nomtrxs...@comcast.net> wrote:
> <snip>
>
> >The capacitor I just pulled from the radio (a 1960's 5 valve AM set)
> >has two sections about the same size.
> >Looking at it now it has 21215 stamped on the back (sounds like a
> >serial number) and J C4 on the front
> >Not sure if this is suitable for FM (probably not) but I'm looking
> >towards building an AM set instead.
> >Does anyone know of a good AM crystal set that would use this cap?
> >Has to be easy to build, with no hard to get parts (well I've already
> >got the tuning cap, that was the only hard to get part)
> >Picture of the cap:http://s222.photobucket.com/albums/dd237/ozguy89/?action=view&current...
>
> From that photo it looks like both sections are identical. Usually the cap from a superhet has one section
> with smaller and/or fewer plates. The smaller section was used for the "local oscillator" and since it almost
> always ran at 455KHz higher than the station being received, it had a lower value.
> See http://www.ittc.ku.edu/~jstiles/622/han ... ning.pdfif you care.
>
> Just about any germanium diode will work just fine. In a pinch even a schottky diode will work ok if you have
> a good long antenna. The only difference the variable cap will make with any crystal set is the tuning range,
> so you'll have to experiment with the coil to tune AM broadcast band.
> I would start with this simple crystal radio.http://www.techlib.com/electronics/crystal.html
> Note how much smaller the unused section of the tuning cap is in the photo. The author gives lots of good info
> & tips the beginner. The improvments later on the page might be fun to play with after you get it working.
>
> Mike
> If there is no absolute truth then nothing can be known.

That's exactly the same circuit I was looking at. Uses a small
diameter coil so I can build a set into a plastic project box. How
many meters of wire would a need for the coil? I plan on winding it on
a 4 inch long PVC pipe.

<snip>
>
>That's exactly the same circuit I was looking at. Uses a small
>diameter coil so I can build a set into a plastic project box. How
>many meters of wire would a need for the coil? I plan on winding it on
>a 4 inch long PVC pipe.

Well, let's see. 1.5" X Pi X 65 turns = 306" and 306/39.34 = 7.8M. Make it 9M to
allow for the taps and lead wires.
You'll have to plug in the actual OD of your PVC.

Mike



"The scientist is possessed by the sense of universal
causation...His religious feeling takes the form of
rapturous amazement at the harmony of natural law,
which reveals the intelligence of such superiority
that, compared with it, systematic thinking and acting
of human beings is an utterly insignificant reflection."
Albert Einstein (theoretical physicist)

Dave.H wrote:

<snip>

>>http://www.techlib.com/electronics/crystal.html


> That's exactly the same circuit I was looking at. Uses a small
> diameter coil so I can build a set into a plastic project box. How
> many meters of wire would a need for the coil? I plan on winding it on
> a 4 inch long PVC pipe.

Roughly 8 1/2 meters. There are two ways you can
figure out how much:

1) Wrap 1 turn around the former. Then lay that turn
out in a straight line and measure it. Multiply by the
number of turns to get the total. Then add a bit more,
as there are taps on the coil which use up some length,
and the lead length at the ends of the coil.

2) Math - multiply the circumferance (pi*d) of the former
by the number of turns. Then you add a bit for lead length,
the fact that each turn will be slightly longer than the
circumference since it is wound at a slight angle, length
needed for the taps etc.

At the cited url, the former is 1 1/2 inches, so don't forget
to convert from inches to meters.

Ed

On Sun, 23 Dec 2007 20:31:05 -0500, Mike <nomtrxspam@comcast.net>
wrote:
>
>"The scientist is possessed by the sense of universal
>causation...His religious feeling takes the form of
>rapturous amazement at the harmony of natural law,
>which reveals the intelligence of such superiority
>that, compared with it, systematic thinking and acting
>of human beings is an utterly insignificant reflection."
>Albert Einstein (theoretical physicist)

Lest anyone be mislead into thinking that the above
edited quote indicates that Einstein was a believer,
check out:

http://www.celebatheists.com/?title=Albert_Einstein

The full passage containing the quote is at:

http://religion.beloblog.com/archives/2 ... ein_a.html


Best regards,




Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
http://www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

On Sat, 22 Dec 2007 07:52:13 -0800, Dave.H wrote:
>
> Maybe I should just stick with AM crystal radios.

Actually, you already have one with the slope detector -
the thing is, FM broadcast is 88-108 MHz, and AM broadcast
is 530-1650 Khz, so you'd have to change your tuned circuit
to change from AM to FM, just so there'll be signals to
receive.

But go ahead and build it anyway - that's a terrific way
to learn about this kind of stuff.

Have Fun!
Rich

Rich Grise (rich@example.net) writes:
> On Sat, 22 Dec 2007 07:52:13 -0800, Dave.H wrote:
>>
>> Maybe I should just stick with AM crystal radios.
>
> Actually, you already have one with the slope detector -
> the thing is, FM broadcast is 88-108 MHz, and AM broadcast
> is 530-1650 Khz, so you'd have to change your tuned circuit
> to change from AM to FM, just so there'll be signals to
> receive.
>
> But go ahead and build it anyway - that's a terrific way
> to learn about this kind of stuff.
>
Of course, there was a wave when "crystal radios" were common
for VHF. But they were specific to the aircraft band, 108 to 136MHz,
since of course that band uses AM. I remember one in Elementary Electronics
in 1971 or 72 where it built on flexible circuit board, so you could
wear it without anyone noticing. I thought that was novel, but I've
seen similar circuits in older magazines.

Michael

On Mon, 24 Dec 2007 13:38:04 GMT, NoSpam@daqarta.com (Bob Masta)
wrote:

>On Sun, 23 Dec 2007 20:31:05 -0500, Mike <nomtrxspam@comcast.net>
>wrote:
>>
>>"The scientist is possessed by the sense of universal
>>causation...His religious feeling takes the form of
>>rapturous amazement at the harmony of natural law,
>>which reveals the intelligence of such superiority
>>that, compared with it, systematic thinking and acting
>>of human beings is an utterly insignificant reflection."
>>Albert Einstein (theoretical physicist)
>
>Lest anyone be mislead into thinking that the above
>edited quote indicates that Einstein was a believer,
>check out:
>
> http://www.celebatheists.com/?title=Albert_Einstein
>
>The full passage containing the quote is at:
>
>http://religion.beloblog.com/archives/2007/04/religion_sneak_peek_einstein_a.html

Thanks, Bob. I read the page. It gets the idea across pretty well
and accurately enough, though it is shy on quotes. Einstein had a
personal meaning for 'religious,' quite different from the use most
carry for it.

I do imagine that Einstein may have felt that the shared positive
aspects of science and of religion might be a: "free and responsible
development of the individual, so that he may place his powers freely
and gladly in the service of all mankind." And perhaps on that point
Eintein placed his hopes.

Probably the best part of one of his monologues on science and
religion is this one. I'll quote it more fully because it covers this
idea of a personal god and provides enough context to get the main
idea he was trying to discuss.

"The main source of the present-day conflicts between the
spheres of religion and of science lies in this concept
of a personal God. It is the aim of science to establish
general rules which determine the reciprocal connection
of objects and events in time and space. For these rules,
or laws of nature, absolutely general validity is required
-- not proven. It is mainly a program, and faith in the
possibility of its accomplishment in principle is only
founded on partial successes. But hardly anyone could be
found who would deny these partial successes and ascribe
them to human self-deception. The fact that on the basis
of such laws we are able to predict the temporal behavior
of phenomena in certain domains with great precision and
certainty is deeply embedded in the consciousness of the
modern man, even though he may have grasped very little
of the contents of those laws. He need only consider that
planetary courses within the solar system may be calculated
in advance with great exactitude on the basis of a limited
number of simple laws. In a similar way, though not with the
same precision, it is possible to calculate in advance the
mode of operation of an electric motor, a transmission system,
or of a wireless apparatus, even when dealing with a novel
development.

"To be sure, when the number of factors coming into play in a
phenomenological complex is too large the scientific method
in most cases fails us. One need only think of the weather,
in which case prediction even for a few days ahead is
impossible. Nevertheless no one doubts that we are confronted
with a causal connection whose causal components are in the
main known to us. Occurrences in this domain are beyond the
reach of exact prediction because of the variety of factors
in operation, not because of any lack of order in nature.

"We have penetrated far less deeply in the regularities
obtaining within the realm of living things, but deeply
enough nevertheless to sense at least the rule of fixed
necessity. One need only think of the systematic order in
heredity, and in the effect of poisons, as for instance
alcohol, on the behavior of organic beings. What is still
lacking here is a grasp of connections of profound
generality, but not a knowledge of order in itself.

"The more a man is imbued with the ordered regularity of
all events the firmer becomes his conviction that there is
no room left by the side of this ordered regularity for
causes of a different nature. For him neither the rule of
human nor the rule of divine will exist as an independent
cause of natural events. To be sure, the doctrine of a
personal God interfering with natural events could never
be refuted, in the real sense, by science, for this doctrine
can always take refuge in those domains in which scientific
knowledge has not yet been able to set foot.

"But I am persuaded that such behavior on the part of
representatives of religion would not only be unworthy but
also fatal. For a doctrine which is able to maintain itself
not in the clear light but only in the dark, will of
necessity lose its effect on mankind, with incalculable harm
to human progress. In their struggle for the ethical good,
teachers of religion must have the stature to give up the
doctrine of a personal God, that is, give up that source of
fear and hope which in the past placed such vase power in the
hands of priests. In their labors they will have to avail
themselves of those forces which are capable of cultivating
the Good, the True, and the Beautiful in humanity itself.
This is, to be sure, a more difficult but an incomparably
more worth task. After religious teachers accomplish the
refining process indicated they will surely recognize with
joy that true religion has been ennobled and made more
profound by scientific knowledge."

But to be clear, Einstein also pointed out the anthropomorphic
derivations of religious ritual and response to mystery, as well as
the overriding role science plays in improving the quality of it, in a
single sentence: ".. so it seems to me that science not only purifies
the religious impulse of the dross of its anthropomorphism but also
contributes to a religious spiritualization of our understanding of
life."

Most folks, using the word 'religion' do not often mean it the way
Einstein did -- neither by way of his earlier nor later writings. To
understand his responses and his evolution, one must actually
carefully read what he wrote and not just my quotes or anyone else's.
He writes enough, though, that most of us reading all of them will
arrive at a similar understanding. Certainly, those with much science
training, anyway. I'm an atheist, didn't read Einstein on this
subject until my own mid-life, and I find his comments completely
congruent with my own long-developed views. That doesn't make him an
atheist, but he certainly isn't 'religious' in the usual meaning.

Jon