RadioBanter - Speaker Output Conversion

RadioBanter (https://www.radiobanter.com/)

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- - Speaker Output Conversion (https://www.radiobanter.com/homebrew/21649-speaker-output-conversion.html)

G8YWL

November 16th 03 10:10 AM

Speaker Output Conversion

Frank Dinger

November 16th 03 01:47 PM

Does anyone know how I can convert the output from a speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so the
winding ratio of the transformer should be in the order of sqrt 100 is in
the order of 10 to 1. So you would have to find any (small )tansformer with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms the
transformer ratio would have to be in the order of sqrt 50000/10 = sqrt
5000 = approx 70.

If you can't find an audio transformer for this application , just try a
small power supply transformer ,since these will pass the low freq audio sig
used for SSTV.

Good luck

Frank GM0CSZ / KN6WH

Frank Dinger

November 16th 03 01:47 PM

Does anyone know how I can convert the output from a speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so the
winding ratio of the transformer should be in the order of sqrt 100 is in
the order of 10 to 1. So you would have to find any (small )tansformer with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms the
transformer ratio would have to be in the order of sqrt 50000/10 = sqrt
5000 = approx 70.

If you can't find an audio transformer for this application , just try a
small power supply transformer ,since these will pass the low freq audio sig
used for SSTV.

Good luck

Frank GM0CSZ / KN6WH

G8YWL

November 16th 03 02:50 PM

Thanks Frank and Bill - I suspected that it was an impedance matching
problem but could not be sure - now I'll find someon's olf tranny:)

Graham

"Frank Dinger" wrote in message
...
Does anyone know how I can convert the output from a speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so
the
winding ratio of the transformer should be in the order of sqrt 100 is in
the order of 10 to 1. So you would have to find any (small )tansformer
with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms
the
transformer ratio would have to be in the order of sqrt 50000/10 = sqrt
5000 = approx 70.

If you can't find an audio transformer for this application , just try a
small power supply transformer ,since these will pass the low freq audio
sig
used for SSTV.

Good luck

Frank GM0CSZ / KN6WH

G8YWL

November 16th 03 02:50 PM

Ralph Mowery

November 16th 03 03:14 PM

Does anyone know how I can convert the output from a speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so
the
winding ratio of the transformer should be in the order of sqrt 100 is in
the order of 10 to 1. So you would have to find any (small )tansformer
with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms
the
transformer ratio would have to be in the order of sqrt 50000/10 = sqrt
5000 = approx 70.

This is totally the wrong way to go. Part of the idea is fine but the main
problem is cutting down the voltage level from the laptop to a very low
level the sound card can use. By going to a stepup transformer you have
just raised the voltage by your factor of 10 or 70.

As this type of audio frequency response is not that critical , a simple
resistor network of about 100,000 ohms in series with the sound card output
and a 1000 ohm reisitor across the input of the mic socket should be in the
ball park.

For an inespensive interface, (about the cost of the cables ) do a Google
search for RASCAL. It is a Rigblaster type interface at almost no cost.

Any of the popular psk31 type audio interfaces should work as they all are
just lowering the leverl of the sound card to the mic input.

Ralph Mowery

November 16th 03 03:14 PM

Does anyone know how I can convert the output from a speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so
the
winding ratio of the transformer should be in the order of sqrt 100 is in
the order of 10 to 1. So you would have to find any (small )tansformer
with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms
the
transformer ratio would have to be in the order of sqrt 50000/10 = sqrt
5000 = approx 70.

This is totally the wrong way to go. Part of the idea is fine but the main
problem is cutting down the voltage level from the laptop to a very low
level the sound card can use. By going to a stepup transformer you have
just raised the voltage by your factor of 10 or 70.

As this type of audio frequency response is not that critical , a simple
resistor network of about 100,000 ohms in series with the sound card output
and a 1000 ohm reisitor across the input of the mic socket should be in the
ball park.

For an inespensive interface, (about the cost of the cables ) do a Google
search for RASCAL. It is a Rigblaster type interface at almost no cost.

Any of the popular psk31 type audio interfaces should work as they all are
just lowering the leverl of the sound card to the mic input.

xpyttl

November 16th 03 05:16 PM

Graham

I don't think impedance matching is as much of an issue as the level. From
what I can tell, Bill had it right. All it takes is a couple of resistors.
You got to reduce the level A BUNCH. I don't know if Bill's 100:1 is right,
I found the values for my Icom by experimentation, but it's pretty close.

Keep in mind that you want to run the computer's speaker volume pretty high
to reduce quantization error. If you adjust the resistance and mike gain so
that your power out is somewhat below max when you are generating SSTV, it
should be pretty close.

Digipan suggests a 100K in series and a 1K in parallel ... seems like I had
to get more extreme, but then I'm connecting up an Icom.

...

"G8YWL" wrote in message
...
Thanks Frank and Bill - I suspected that it was an impedance matching
problem but could not be sure - now I'll find someon's olf tranny:)

Graham

"Frank Dinger" wrote in message
...
Does anyone know how I can convert the output from a
speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S?
It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can
check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so
the
winding ratio of the transformer should be in the order of sqrt 100 is
in
the order of 10 to 1. So you would have to find any (small )tansformer
with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms
the
transformer ratio would have to be in the order of sqrt 50000/10 =
sqrt
5000 = approx 70.

If you can't find an audio transformer for this application , just try
a
small power supply transformer ,since these will pass the low freq audio
sig
used for SSTV.

Good luck

Frank GM0CSZ / KN6WH

xpyttl

November 16th 03 05:16 PM

Frank Dinger

November 17th 03 12:23 PM

I don't think impedance matching is as much of an issue as the level.
From
what I can tell, Bill had it right. All it takes is a couple of
resistors.
You got to reduce the level A BUNCH. I don't know if Bill's 100:1 is
right,
I found the values for my Icom by experimentation, but it's pretty close.

Keep in mind that you want to run the computer's speaker volume pretty
high
to reduce quantization error. If you adjust the resistance and mike gain
so
that your power out is somewhat below max when you are generating SSTV, it
should be pretty close.

Digipan suggests a 100K in series and a 1K in parallel ... seems like I
had
to get more extreme, but then I'm connecting up an Icom.
========================
Apart from (roughly ) matching impedances ,a transformer ensures galvanic
separation between PC (laptop) and transceiver , hence avoiding any hassle
due to earth loops .
If the voltage level at the transceiver's microphone input poses a problem ,
a resistive voltage divider can always be added.

Frank GM0CSZ / KN6WH

Frank Dinger

November 17th 03 12:23 PM

Ashhar Farhan

November 18th 03 12:41 AM

"G8YWL" wrote in message ...
Does anyone know how I can convert the output from a speaker/headphones jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm asking
the wrong question.

have u actually tried connecting the output of your speaker directly
into the mic input? i bet you a 2n3904 that it would work. you can cut
down the audio output using the volume control applet.

even if you do horribly overdrive the transceiver, you dont have to
sweat because the SSB filter will clean out any out-of-passband
distortion. and sstv does not use any amplitude variations (i am not
aware of the newer SSTV modes) so clipped audio will not be very
different to the remote receiver.

as usual, i guess, you should simply plug in the sound card output
into your mic input to see what happens.

i have used my homebrew on PSK31 without any attenuation. it works
pretty well. infact, i got into PSK31 by hanging my PC's mic over the
speaker box and tuning the sigs using WinPSK. On a dare, I left my
transceiver mic on top of the PC's cambridge work speakers and started
working PSK31 dx right off. the next night i searched around for a
pair of cables and connected the rig and the PC together without any
other components.

i have used RTTY, SSTV as well as PSK31 without any electronics in
addition to ordinary cables.

- farhan

Ashhar Farhan

November 18th 03 12:41 AM

Dave Platt

November 18th 03 02:15 AM

Does anyone know how I can convert the output from a speaker/headphones jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm asking
the wrong question.

have u actually tried connecting the output of your speaker directly
into the mic input? i bet you a 2n3904 that it would work. you can cut
down the audio output using the volume control applet.

Getting proper, fine control of the volume level might be very
difficult with this approach.

even if you do horribly overdrive the transceiver, you dont have to
sweat because the SSB filter will clean out any out-of-passband
distortion. and sstv does not use any amplitude variations (i am not
aware of the newer SSTV modes) so clipped audio will not be very
different to the remote receiver.

Hmmm. How about intermodulation issues? That might cause a fair big
of gunk even within the audio passband.

as usual, i guess, you should simply plug in the sound card output
into your mic input to see what happens.

i have used my homebrew on PSK31 without any attenuation. it works
pretty well.

How the the signal actually look (and measure) on the far end? How
were the IMD levels, and how far did the PSK31 signal's sidebands
extend?

Even if it "works pretty well", I'd be concerned about shoving audio
distortion products out well away from the signal. This might not be
too much of an issue for SSTV, which is using voice-grade bandwidth,
but I _really_ wouldn't want to do it when working PSK31. One of
PSK31's benefits is its extremely narrow spectrum width, when tuned
properly.

I've seen some really beautiful (narrow and clean) PSK31 signals on
the band. I've also seen 'em with sidebands blasting out in both
directions, across the full width of the spectrum/waterfall display,
as a result of people overdriving their audio inputs or forgetting to
turn off their compressor/processor or driving their RF finals up to
get the last little bit of power out of their TX. When this happens,
the narrow-bandwidth spectum-sharing benefit of PSK31 go right out the
window, and the signal can become harder to copy reliably.

As to the original poster's question: there are a number of commercial
products designed for PC/rig interfacing, and numerous homebrew
circuits as well. The simplest designs simply include a resistive
attenuator (a fixed resistor pair, or an audio-taper potentiometer) to
drop the speaker output level down to mic levels. More complex
designs often include transformer isolation in both the TX and RX
audio paths, to break ground loops and keep RF out of the audio path.

Any interface designed for PSK31 would probably work very well for
SSTV as well. See http://www.qsl.net/wm2u/psk31.html for schematics
of both resistive and transformer-isolated versions.

On the commercial side, the best-known are probably the RigBlaster
(http://www.westmountainradio.com/) and the Rascal / GLX
(http://www.buxcomm.com).

I've used a Rascal (pre-GLX version) quite successfully, to operate
both PSK31 and VHF packet from my Dell laptop.

--
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

November 18th 03 02:15 AM

Does anyone know how I can convert the output from a speaker/headphones jack
from a Laptop into a suitable input to the Mic socket of a TS430S? It's for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm asking
the wrong question.

have u actually tried connecting the output of your speaker directly
into the mic input? i bet you a 2n3904 that it would work. you can cut
down the audio output using the volume control applet.

Getting proper, fine control of the volume level might be very
difficult with this approach.

even if you do horribly overdrive the transceiver, you dont have to
sweat because the SSB filter will clean out any out-of-passband
distortion. and sstv does not use any amplitude variations (i am not
aware of the newer SSTV modes) so clipped audio will not be very
different to the remote receiver.

Hmmm. How about intermodulation issues? That might cause a fair big
of gunk even within the audio passband.

as usual, i guess, you should simply plug in the sound card output
into your mic input to see what happens.

i have used my homebrew on PSK31 without any attenuation. it works
pretty well.

How the the signal actually look (and measure) on the far end? How
were the IMD levels, and how far did the PSK31 signal's sidebands
extend?

Even if it "works pretty well", I'd be concerned about shoving audio
distortion products out well away from the signal. This might not be
too much of an issue for SSTV, which is using voice-grade bandwidth,
but I _really_ wouldn't want to do it when working PSK31. One of
PSK31's benefits is its extremely narrow spectrum width, when tuned
properly.

I've seen some really beautiful (narrow and clean) PSK31 signals on
the band. I've also seen 'em with sidebands blasting out in both
directions, across the full width of the spectrum/waterfall display,
as a result of people overdriving their audio inputs or forgetting to
turn off their compressor/processor or driving their RF finals up to
get the last little bit of power out of their TX. When this happens,
the narrow-bandwidth spectum-sharing benefit of PSK31 go right out the
window, and the signal can become harder to copy reliably.

As to the original poster's question: there are a number of commercial
products designed for PC/rig interfacing, and numerous homebrew
circuits as well. The simplest designs simply include a resistive
attenuator (a fixed resistor pair, or an audio-taper potentiometer) to
drop the speaker output level down to mic levels. More complex
designs often include transformer isolation in both the TX and RX
audio paths, to break ground loops and keep RF out of the audio path.

Any interface designed for PSK31 would probably work very well for
SSTV as well. See http://www.qsl.net/wm2u/psk31.html for schematics
of both resistive and transformer-isolated versions.

On the commercial side, the best-known are probably the RigBlaster
(http://www.westmountainradio.com/) and the Rascal / GLX
(http://www.buxcomm.com).

I've used a Rascal (pre-GLX version) quite successfully, to operate
both PSK31 and VHF packet from my Dell laptop.

--
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!

Ashhar Farhan

November 19th 03 04:38 AM

(Dave Platt) wrote in message ...

Getting proper, fine control of the volume level might be very
difficult with this approach.

Even if it "works pretty well", I'd be concerned about shoving audio
distortion products out well away from the signal. This might not be
too much of an issue for SSTV, which is using voice-grade bandwidth,
but I _really_ wouldn't want to do it when working PSK31. One of
PSK31's benefits is its extremely narrow spectrum width, when tuned
properly.

you are quite right. about the intermod levels. i just ran a check on
my PC sound card and this is what i have to report:

1) audio output from the PC sound card is 1V v p-p. The mic input
required is 10mV (unless there is a built-in preamp in the mic, this
is common to some japanese rigs). Thus, u need a 1:100 attentuator. A
10K and a 100 ohms resistor in series would do the trick. I suggest
100 ohms so that the impedance into the mic remains low and noise
free. further, i would also suggest that u place a 1000pf across the
mic input close to the mic jack.

2) audio input required into the PC sound card is 10mV. This is as per
the PC sound specs in the web. If we assume about 50mW audio from the
transceiver across an 8 ohms load, we are looking at V = sqrt(0.050 *
8 * 2) ~ 500mV. I think that a similar attenuator will suffice at this
end too.

- farhan

Ashhar Farhan

November 19th 03 04:38 AM

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