| Author |
Message |
Jerry Avins
Guest
|
 Posted:
Wed Nov 30, 2005 1:16 am Post subject:
Re: Building a (cheap) software radio |
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Michel Rouzic wrote:
| Quote: | Christen Fihl wrote:
I'm considering acquiring a BT878 based TV tuner, it's supposed to have an
input of 448 ksps (but from what I understood, due to "aperture
You need 2 A/D's, to make both I and Q signals!! Makes it comples to use
BT878 I guess.
Oh, yeah, I think it only inputs mono. So, will my 44.1 ksps sound card
will be enough to do the job anyways?
|
You need two inputs. Look at the block diagram at
http://www.amqrp.org/kits/softrock40/
| Quote: | The signal from SoftRock is no demodulated yet. That is where the software
sets in.
You get I and Q from the quadrature part of SoftRock.
In analog world: quadrature demodulator:
http://n.ethz.ch/student/rodonil/da/bericht/node52.html
Digital, then you feed I and Q into FFT functions as real and complex parts,
as far as I understand it (not studied much yet). And then do some more
magic ;-)
Wait, if you feed I and Q into FFT functions as real and complex parts,
it means that I and Q are in the frequency domain?
|
Thee I and Q from softrock are plain audio signals; time-varying voltages.
| Quote: | In SoftRock you get I and Q by opening and closing 4 switches, to get
signales delayed 0, 90, 180 or 270 degree.
A simple wire can pass under a closed wooden window without killing the
signal.
The problem is that it won't work with my aluminium window
|
It might. The aluminum window frame itself might be a good enough
antenna. At worst, you can glue a piece of heavy aluminum foil to each
side of the glass and attach wires to them. The RF rill go right through
the glass. It becomes the dielectric of a capacitor and the foils are
the plates. You need only a few tens of picofarads.
| Quote: | Any wire is good for a start. Always straight or big zigzag somehow,
not in a big pile.
Ok, I guess I'll zigzag my 50 meter cable (it's rigid so it should do
it) and put it somewhere in my bedroom. If I zigzag it flat, I guess
the reception of a station will depend on its orientation right? By the
way, does it work better if you connect your wire to some big metallic
thing like the doors of a closet or a gutter?
A wire is like putting your finger on a screwdriver in the antenna socket on
your radio ;-)
How high in receiving frequencies can you get with SoftRock?
300 divided my meter makes MHz. 40Meter is about 7MHz.
--
Christen Fihl
http://oz1aab.Fihl.net/
|
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Christen Fihl
Guest
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Christen Fihl
Guest
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| Posted:
Wed Nov 30, 2005 1:16 am Post subject:
Re: Building a (cheap) software radio |
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| Quote: | Oh, yeah, I think it only inputs mono. So, will my 44.1 ksps sound
card will be enough to do the job anyways?
Yes, for max 20KHz demodulation. Fx for AM, FM (narrowband like |
walkie-talkie), SSB,... Not for wideband FM/TV.
| Quote: | Wait, if you feed I and Q into FFT functions as real and complex
parts, it means that I and Q are in the frequency domain?
I am at that stage right now in my own testing. I like the technic |
behind it all, not so much the talking on the ham bands.
I need to read more of Chapter 8, "Quadratur Signals" of following book
;-)
See the book: "Understanding Digital Signal Processing" by Lyons
See http://tinyurl.com/bxbuh (amazon link)
Also see comment in this group by November-15 "Shameless...."
Very good.
--
Christen Fihl
http://oz1aab.Fihl.net/ |
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Christen Fihl
Guest
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| Posted:
Wed Nov 30, 2005 1:16 am Post subject:
Re: Building a (cheap) software radio |
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| Quote: | ... does it mean that a softrock with a lowband kit will only receive
signals between 3.75 and 10 Mhz,
Should be between 3 and 30MHz! |
Yes, and not only between, but also only on fixed frequencies,
controlled by a crystal.
| Quote: | And what will the DDS-60 change to it?
It will make you tune anything between 0 and 60MHz, commercial, fax, |
anything, not just amateurs.
The crystal is then replaced by the frequency oscillator.
--
Christen Fihl
http://oz1aab.Fihl.net/ |
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Jerry Avins
Guest
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| Posted:
Wed Nov 30, 2005 5:16 pm Post subject:
Re: Building a (cheap) software radio |
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Michel Rouzic wrote:
...
| Quote: | Wow! a capacitor out of a glass? but won't it, as a capacitor, produce
some unwanted effect to the signal?
|
As long as the impedance of the capacitor is much less than the
impedance of the antenna, it won't have any practical effect. Even if
the two are the same, you'll still get half the signal power.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Yves
Guest
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| Posted:
Wed Nov 30, 2005 5:16 pm Post subject:
Re: Building a (cheap) software radio |
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In article <v_idnVtgxpDTFRbeRVn-gg@rcn.net>, Jerry Avins says...
| Quote: | What you're looking at
isn't "software radio", but "software defined radio". Big difference!
|
I always tought that "software defined radio" and "software radio" were
about the same thing. Could you please add some more details? thx
Yves |
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Michel Rouzic
Guest
|
| Posted:
Wed Nov 30, 2005 5:17 pm Post subject:
Re: Building a (cheap) software radio |
|
|
Christen Fihl wrote:
| Quote: | ... does it mean that a softrock with a lowband kit will only receive
signals between 3.75 and 10 Mhz,
Should be between 3 and 30MHz!
Yes, and not only between, but also only on fixed frequencies,
controlled by a crystal.
And what will the DDS-60 change to it?
It will make you tune anything between 0 and 60MHz, commercial, fax,
anything, not just amateurs.
The crystal is then replaced by the frequency oscillator.
|
Cool, so, with a SoftRock and a DDS-60, I guess a LowBand or HighBand
kit would be quite useless, right? |
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Michel Rouzic
Guest
|
| Posted:
Wed Nov 30, 2005 5:17 pm Post subject:
Re: Building a (cheap) software radio |
|
|
Jerry Avins wrote:
| Quote: | Michel Rouzic wrote:
Christen Fihl wrote:
I'm considering acquiring a BT878 based TV tuner, it's supposed to have an
input of 448 ksps (but from what I understood, due to "aperture
You need 2 A/D's, to make both I and Q signals!! Makes it comples to use
BT878 I guess.
Oh, yeah, I think it only inputs mono. So, will my 44.1 ksps sound card
will be enough to do the job anyways?
You need two inputs. Look at the block diagram at
http://www.amqrp.org/kits/softrock40/
|
Yeah, that's why I was saying that a BT878 wouldn't do it and that my
sound card may be fine since it's stereo
| Quote: | The signal from SoftRock is no demodulated yet. That is where the software
sets in.
You get I and Q from the quadrature part of SoftRock.
In analog world: quadrature demodulator:
http://n.ethz.ch/student/rodonil/da/bericht/node52.html
Digital, then you feed I and Q into FFT functions as real and complex parts,
as far as I understand it (not studied much yet). And then do some more
magic ;-)
Wait, if you feed I and Q into FFT functions as real and complex parts,
it means that I and Q are in the frequency domain?
Thee I and Q from softrock are plain audio signals; time-varying voltages.
In SoftRock you get I and Q by opening and closing 4 switches, to get
signales delayed 0, 90, 180 or 270 degree.
A simple wire can pass under a closed wooden window without killing the
signal.
The problem is that it won't work with my aluminium window
It might. The aluminum window frame itself might be a good enough
antenna. At worst, you can glue a piece of heavy aluminum foil to each
side of the glass and attach wires to them. The RF rill go right through
the glass. It becomes the dielectric of a capacitor and the foils are
the plates. You need only a few tens of picofarads.
|
Wow! a capacitor out of a glass? but won't it, as a capacitor, produce
some unwanted effect to the signal? |
|
| Back to top |
|
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Michel Rouzic
Guest
|
| Posted:
Wed Nov 30, 2005 5:17 pm Post subject:
Re: Building a (cheap) software radio |
|
|
Christen Fihl wrote:
| Quote: | Oh, yeah, I think it only inputs mono. So, will my 44.1 ksps sound
card will be enough to do the job anyways?
Yes, for max 20KHz demodulation. Fx for AM, FM (narrowband like
walkie-talkie), SSB,... Not for wideband FM/TV.
Wait, if you feed I and Q into FFT functions as real and complex
parts, it means that I and Q are in the frequency domain?
I am at that stage right now in my own testing. I like the technic
behind it all, not so much the talking on the ham bands.
I need to read more of Chapter 8, "Quadratur Signals" of following book
;-)
See the book: "Understanding Digital Signal Processing" by Lyons
See http://tinyurl.com/bxbuh (amazon link)
Also see comment in this group by November-15 "Shameless...."
|
Oh yeah, I've been wanting to buy that book for a while, but I ain't
really got the money. Maybe I should ask it for xmas, that'd be a good
idea (since i'm lackin ideas for xmas). Got a link to that comment? |
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Michel Rouzic
Guest
|
| Posted:
Wed Nov 30, 2005 11:29 pm Post subject:
Re: Building a (cheap) software radio |
|
|
Jerry Avins wrote:
| Quote: | Michel Rouzic wrote:
...
Wow! a capacitor out of a glass? but won't it, as a capacitor, produce
some unwanted effect to the signal?
As long as the impedance of the capacitor is much less than the
impedance of the antenna, it won't have any practical effect. Even if
the two are the same, you'll still get half the signal power.
|
OK, but since my window frame is in aluminium, I could as well stick
the wire to the window, and on the other side, stick the wire to it
too, so the aluminium would conduct the signal.
But I think i'm not going to bother a probably just stick it to the
window frame without anything outside, unless I feel that it's not
giving me something good enough |
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Jerry Avins
Guest
|
| Posted:
Thu Dec 01, 2005 12:43 am Post subject:
Re: Building a (cheap) software radio |
|
|
Michel Rouzic wrote:
| Quote: | Jerry Avins wrote:
Michel Rouzic wrote:
...
Wow! a capacitor out of a glass? but won't it, as a capacitor, produce
some unwanted effect to the signal?
As long as the impedance of the capacitor is much less than the
impedance of the antenna, it won't have any practical effect. Even if
the two are the same, you'll still get half the signal power.
OK, but since my window frame is in aluminium, I could as well stick
the wire to the window, and on the other side, stick the wire to it
too, so the aluminium would conduct the signal.
|
If the window frame is grounded, that will short out the signal. If not,
you can close the window on the wire, just as if it were wood.
| Quote: | But I think i'm not going to bother a probably just stick it to the
window frame without anything outside, unless I feel that it's not
giving me something good enough
|
If the window frame is grounded, that will short out the signal.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Michel Rouzic
Guest
|
| Posted:
Thu Dec 01, 2005 1:17 am Post subject:
Re: Building a (cheap) software radio |
|
|
Jerry Avins wrote:
| Quote: | Michel Rouzic wrote:
Jerry Avins wrote:
Michel Rouzic wrote:
...
Wow! a capacitor out of a glass? but won't it, as a capacitor, produce
some unwanted effect to the signal?
As long as the impedance of the capacitor is much less than the
impedance of the antenna, it won't have any practical effect. Even if
the two are the same, you'll still get half the signal power.
OK, but since my window frame is in aluminium, I could as well stick
the wire to the window, and on the other side, stick the wire to it
too, so the aluminium would conduct the signal.
If the window frame is grounded, that will short out the signal. If not,
you can close the window on the wire, just as if it were wood.
|
grounded? as in electrically connected to the ground? if so then no,
i'm on the first floor (or maybe in your country you would call that
the second floor). and i can't really close the window on the wire
anyways, due to the shape of the window thing.
| Quote: | But I think i'm not going to bother a probably just stick it to the
window frame without anything outside, unless I feel that it's not
giving me something good enough
If the window frame is grounded, that will short out the signal.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Jerry Avins
Guest
|
| Posted:
Thu Dec 01, 2005 9:16 am Post subject:
Re: Building a (cheap) software radio |
|
|
Michel Rouzic wrote:
...
| Quote: | grounded? as in electrically connected to the ground? if so then no,
i'm on the first floor (or maybe in your country you would call that
the second floor). and i can't really close the window on the wire
anyways, due to the shape of the window thing.
|
The window frame could be connected to earth in some way. A #30 enameled
wire is less than 1/64th of an inch in diameter. Surely, you have room
for that! A bare #22 wire (a pretty standard size for radio work) is
about 1/40th of an inch, also no problem if the frame has weather
stripping. You need to keep some perspective.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Michel Rouzic
Guest
|
| Posted:
Thu Dec 01, 2005 5:16 pm Post subject:
Re: Building a (cheap) software radio |
|
|
Jerry Avins wrote:
| Quote: | Michel Rouzic wrote:
...
grounded? as in electrically connected to the ground? if so then no,
i'm on the first floor (or maybe in your country you would call that
the second floor). and i can't really close the window on the wire
anyways, due to the shape of the window thing.
The window frame could be connected to earth in some way. A #30 enameled
wire is less than 1/64th of an inch in diameter. Surely, you have room
for that! A bare #22 wire (a pretty standard size for radio work) is
about 1/40th of an inch, also no problem if the frame has weather
stripping. You need to keep some perspective.
|
oh, the wire i was thinking about using is very rigid and about half a
millimeter thick. where do you find those wires? |
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Michel Rouzic
Guest
|
| Posted:
Thu Dec 01, 2005 5:16 pm Post subject:
Re: Building a (cheap) software radio |
|
|
Christen Fihl wrote:
| Quote: | ... does it mean that a softrock with a lowband kit will only receive
signals between 3.75 and 10 Mhz,
Should be between 3 and 30MHz!
Yes, and not only between, but also only on fixed frequencies,
controlled by a crystal.
And what will the DDS-60 change to it?
It will make you tune anything between 0 and 60MHz, commercial, fax,
anything, not just amateurs.
The crystal is then replaced by the frequency oscillator.
|
crap, too late for ordering a softrock 5.0 :-/. know any alternative? |
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