"J M Noeding" wrote in message
...
On 13 Mar 2005 15:18:03 -0800, wrote:



also, when people refer to ASK and FSK, is ASK basically an audio
output that's been sent over FM? and FSK is more like CW, only to a
receiver that can monitor both mark and space (0 and 1) frequencies?

thanks again!
jason

always thought amplitude-shift-keying was mainly used for morse
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

I believe he meant AFSK (audio frequency shift keying) vs FSK (frequency
shift keying).

Dee Flint wrote:
"J M Noeding" wrote in message
...
On 13 Mar 2005 15:18:03 -0800, wrote:



also, when people refer to ASK and FSK, is ASK basically an audio
output that's been sent over FM? and FSK is more like CW, only to a
receiver that can monitor both mark and space (0 and 1)
frequencies?

thanks again!
jason

always thought amplitude-shift-keying was mainly used for morse
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

I believe he meant AFSK (audio frequency shift keying) vs FSK
(frequency
shift keying).

yes, that is what i meant. i didn't even know amplitude shift keying
existed.

am i correct about afsk being audio tones transmitted over FM, while
fsk is just alternating between two non-modulating frequencies?

jason

In article .com,
wrote:

yes, that is what i meant. i didn't even know amplitude shift keying
existed.

am i correct about afsk being audio tones transmitted over FM, while
fsk is just alternating between two non-modulating frequencies?

That's pretty close, but not exactly on target.

AFSK can be used on top of either AM or FM. In amateur systems it's
most commonly used with FM.

FSK shifts the carrier frequency... a process which counts as a
modulation. The amount of frequency shift (in Hz) and the rate at
which you shift it (also in Hz) vary a lot from one usage to another.
There are both narrow-band and wide-band FSK modulations in use.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
In article .com,
wrote:

yes, that is what i meant. i didn't even know amplitude shift keying
existed.

am i correct about afsk being audio tones transmitted over FM, while
fsk is just alternating between two non-modulating frequencies?

That's pretty close, but not exactly on target.

AFSK can be used on top of either AM or FM. In amateur systems it's
most commonly used with FM.

FSK shifts the carrier frequency... a process which counts as a
modulation. The amount of frequency shift (in Hz) and the rate at
which you shift it (also in Hz) vary a lot from one usage to another.
There are both narrow-band and wide-band FSK modulations in use.

thanks! also, i was just reading about mixers... and getting confused.
i've run some matlab programs to figure out how you can take something
at frequency x and frequency y, and end up with an output of frequency
(x-y). one transmitter's mixer i saw took a 160mhz and 14mhz input to
get a 146mhz output. adding or multiplying them together certainly does
not yeild 146mhz. so how does that work?

thanks for the help!
jason

I believe he meant AFSK (audio frequency shift keying) vs FSK
(frequency
shift keying).

yes, that is what i meant. i didn't even know amplitude shift keying
existed.

am i correct about afsk being audio tones transmitted over FM, while
fsk is just alternating between two non-modulating frequencies?

jason


You are partly correct. If audio tones are fed into the microphone input
(audio stages) of an AM or FM transmitter you are generating AFSK. If an
audio tone is fed into a SSB transmitter it will generate a single output
frequency. If the tone is switched off and on , it will be received as a CW
transmitter being keyed off and on. Some newer transceivers generate CW
this way. If the tone is shifted in frequency , the output will be a
carrier shifted the same ammount. This is received the same as a FSK
transmitter. You can get the same effect if you have a crystal controled
transmiter and switch a capacitor across the crystal to change the
frequency.
There is almost no way to tell the differance between the two. If 100% pure
tones are used and everything else it 100% correct then there is no
differance in the transmitted signals. As always nothing is 100% and you
can tell the differance with very close and strong signals. This is still
close enough it does not matter.

In article . com,
wrote:

thanks! also, i was just reading about mixers... and getting confused.
i've run some matlab programs to figure out how you can take something
at frequency x and frequency y, and end up with an output of frequency
(x-y). one transmitter's mixer i saw took a 160mhz and 14mhz input to
get a 146mhz output. adding or multiplying them together certainly does
not yeild 146mhz. so how does that work?

You need a nonlinear function in order to get mixing behavior, and
create the sum and difference frequencies.

If you just add (e.g.) sin 160x and sin 14x, you end up with a simple
sum of sins, and no other frequencies show up - ordinary superposition.

Run the resulting sum through a nonlinear function (e.g. square it, or
take the square root, or clip it whenever its absolute value exceeds
1.0, or something like that), and take a look at the frequency content
of what you get as a result.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Sun, 13 Mar 2005 19:32:17 -0500, "Dee Flint"
wrote:


also, when people refer to ASK and FSK, is ASK basically an audio
output that's been sent over FM? and FSK is more like CW, only to a
receiver that can monitor both mark and space (0 and 1) frequencies?

always thought amplitude-shift-keying was mainly used for morse

I believe he meant AFSK (audio frequency shift keying) vs FSK (frequency
shift keying).

The ITU emission designators for some digital modes and some typical
usage:

* A1A On/Off keying for manual reception (Morse)

* A1D ASK, Amplitude shift keying. The only recent use I have seen
is in some 433 MHz SRD (Short Range Devices)

* F1D Pure FSK (RTTY is classified as F1B)

* F2D Audio subcarrier modulated by amplitude or frequency (e.g.
1200 bit/s AX.25 packet) modulating an FM transmitter

* A2A Audio subcarrier on/off modulated by Morse code modulating
an AM transmitter (e.g. aeronautical beacons in the LF band)

* A2D Audio subcarrier modulated by amplitude or frequency
modulating an AM transmitter

* J2A Audio subcarrier on/off modulated by Morse code modulating
an SSB transmitter (many amateur multimode rigs)

* J2D Audio subcarrier modulated by amplitude or frequency (e.g.
300 bit/s AX.25 packet) modulating an SSB transmitter

On the air A1A and J2A are equivalent.

On the air F1D and J2A are equivalent and can be generated and
detected in both ways.

I hope this clarifies some of the issues.

Paul OH3LWR

"Dave Platt" wrote in message
...
In article .com,
wrote:

yes, that is what i meant. i didn't even know amplitude shift keying
existed.

am i correct about afsk being audio tones transmitted over FM, while
fsk is just alternating between two non-modulating frequencies?

That's pretty close, but not exactly on target.

AFSK can be used on top of either AM or FM. In amateur systems it's
most commonly used with FM.

That is not correct either. AFSK is used extensively with Amateur Radio
digital systems, such as PSK-31, RTTY, even CW can be and is generated
using AFSK. And the modulation METHOD is not important. It can be either
Amplitude or Frequency Modulation.

Dan/W4NTI


FSK shifts the carrier frequency... a process which counts as a
modulation. The amount of frequency shift (in Hz) and the rate at
which you shift it (also in Hz) vary a lot from one usage to another.
There are both narrow-band and wide-band FSK modulations in use.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

wrote:


thanks! also, i was just reading about mixers... and getting confused.
i've run some matlab programs to figure out how you can take something
at frequency x and frequency y, and end up with an output of frequency
(x-y). one transmitter's mixer i saw took a 160mhz and 14mhz input to
get a 146mhz output. adding or multiplying them together certainly does
not yeild 146mhz. so how does that work?


That is a fair question, and one which is frequently asked.

Look up the trig identity for (sin a)(sin b). Let a and b each be in
the form wt [w stands for greek lower case omega], so a = 2(pi)f1(t) and
b = 2(pi)f2(t) where f1 and f2 are your two frequencies in Hz. Do the
substitution & algebra on the identity, and then I think you'll see
where the signals at the sum and difference of frequencies f1 and f2
come from. :-)

The name "mixer" can be a little misleading.....it doesn't necessarily
just sum the two inputs in a linear fashion (by just adding them, like a
kitchen mixer combines the ingredients for a cake) but there is also an
element of non-linearity in the electrical network.

Depending on the nature of the non-linearity, mixing can also generate
other higher-order products, like signals at 2f1+f2, 2f1-f2, etc.
Whether this is good or bad depends on your particular application. For
example, do some reading on "intermod".