Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Sure, I see no reason it won't work. Assuming that the capI'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 rectifierI'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
I agree with you; it is a slope detector.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
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!
Slope detection.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?
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.
In the 50s, narrow-band FM was permitted on the high freq ham bands, It wasBob 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
Or build an AM/FM crystal radio. It doesn't need to be great - have fun.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.
Maybe I should just stick with AM crystal radios.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.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
I have an old radio that I can steal the tuning cap from, so I don'tOn 12/22/07 7:52 AM, in article
01cfd068-e68c-4de8-b9b9-f00f626f7...@x29g2000prg.googlegroups.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.
Maybe I should just stick with AM crystal radios.
Aww no, Play with it and hve some fun.
Yeah, it's probably a 2 section cap, so use the smaller section with a seriesOr 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.
It does look like a 2 section cap, even though the radio has only onesnip>>> > 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.
You can figure out the size cap you need using math.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.
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.
The capacitor I just pulled from the radio (a 1960's 5 valve AM set)On 12/22/07 3:06 PM, in article
3ae5713f-e3ba-4268-a656-5eda4bafa...@e6g2000prf.googlegroups.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 (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.
The large section is the RF tuning cap and is about 365uuf fully engaged.
Thatšs 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.
From that photo it looks like both sections are identical. Usually the cap from a superhet has one sectionThe 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=IMG_6405.jpg
That's exactly the same circuit I was looking at. Uses a smallsnip
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/handouts/Superhet%20Tuning.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.
Well, let's see. 1.5" X Pi X 65 turns = 306" and 306/39.34 = 7.8M. Make it 9M toThat'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.
http://www.techlib.com/electronics/crystal.html
Roughly 8 1/2 meters. There are two ways you canThat'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.