I am currently building a radio - sound card interface for my IC-730
so i can use PSK31. AIUI, the mic that came with the rig contains a
preamp, so presumably the radio is expecting an audio level above a
usual mic. Does this mean I can simply use the audio level from the
sound card straight into the Mic input on the radio via a 1:1
transformer for isolation, with no need for a voltage divider to bring
the level down?

Thanks.

wrote:
I am currently building a radio - sound card interface for my IC-730
so i can use PSK31. AIUI, the mic that came with the rig contains a
preamp, so presumably the radio is expecting an audio level above a
usual mic. Does this mean I can simply use the audio level from the
sound card straight into the Mic input on the radio via a 1:1
transformer for isolation, with no need for a voltage divider to bring
the level down?

Thanks.
====================================
Transformer does not need to be 1:1 exactly
Suggest you include an approx 1000 Ohms trimpot to fine adjust the mic
port input from the transformer. Assuming the radio audio input
impedance is in the order of 500 Ohms.


Frank GM0CSZ / KN6WH

Highland Ham kirjoitti:
wrote:
I am currently building a radio - sound card interface for my IC-730
so i can use PSK31. AIUI, the mic that came with the rig contains a
preamp, so presumably the radio is expecting an audio level above a
usual mic. Does this mean I can simply use the audio level from the
sound card straight into the Mic input on the radio via a 1:1
transformer for isolation, with no need for a voltage divider to bring
the level down?

Thanks.
====================================
Transformer does not need to be 1:1 exactly
Suggest you include an approx 1000 Ohms trimpot to fine adjust the mic
port input from the transformer. Assuming the radio audio input
impedance is in the order of 500 Ohms.


Frank GM0CSZ / KN6WH




Please note that a single trafo only in mic line doesn't isolate
satisfactory.
Otherwise there will still remain humming earth loops.

If your rig has a phone patch or a line input it is preferred to use
these. You need not to play with plugs .
In many rigs the VOX is not controlled via line input. In that case PTT
rules on the air.

Be ready to use a trafo also in headphone output line and a relay or an
opto isolator for PTT.

It is most simple to use COM port RTS or DTR for PTT.
KISS: Connect a high bright led and a 5V dil relay in series directly
into RTS. Led is very nice to show "On the Air".

postipoika

On 20 Jun, 04:28, Highland Ham
wrote:


====================================
Transformer does not need to be 1:1 exactly
Suggest you include an approx 1000 Ohms trimpot to fine adjust the mic
port input from the transformer. *Assuming the radio audio input
impedance is in the order of 500 Ohms.

Frank * * GM0CSZ / KN6WH

Thanks. I'll give that a try.

On 20 Jun, 13:34, Postipoika
wrote:

Please note that a single trafo only in mic line doesn't isolate
satisfactory.
Otherwise there will still remain humming earth loops.

If your rig has a phone patch or a line input it is preferred to use
these. You need not to play with plugs .
In many rigs the VOX is not controlled via line input. In that case PTT
rules on the air.

Be ready to use a trafo also in headphone output line and a relay or an
opto isolator for PTT.

It is most simple to use COM port RTS or DTR for PTT.
KISS: Connect a high bright led and a 5V dil relay in series directly
into RTS. Led is very nice to show "On the Air".

postipoika

Hi Postipoika,

Unfortunately, my rig doesn't appear to have a line input, so using
the mic connector looks like the only option.

I had already planned to use another transformer to isolate the
headphone socket on the radio from the soundcard, and an optoisolator
on on RTS for PTT, although I may get away with just using the VOX.

wrote in message
...
On 20 Jun, 13:34, Postipoika
wrote:

Please note that a single trafo only in mic line doesn't isolate
satisfactory.
Otherwise there will still remain humming earth loops.

If your rig has a phone patch or a line input it is preferred to use
these. You need not to play with plugs .
In many rigs the VOX is not controlled via line input. In that case PTT
rules on the air.

Be ready to use a trafo also in headphone output line and a relay or an
opto isolator for PTT.

It is most simple to use COM port RTS or DTR for PTT.
KISS: Connect a high bright led and a 5V dil relay in series directly
into RTS. Led is very nice to show "On the Air".

postipoika

Hi Postipoika,

Unfortunately, my rig doesn't appear to have a line input, so using
the mic connector looks like the only option.

I had already planned to use another transformer to isolate the
headphone socket on the radio from the soundcard, and an optoisolator
on on RTS for PTT, although I may get away with just using the VOX.
=========
Tom -

That is correct, the low-gain or "zero" models (last digit in model number
being zero of sold-state late 1970s /early 1980s vintage radios) from Icom
(IC-730 being one) ..... did have this problem (pre-amp was in microphone
and inside the radio on the input)
http://www.heilsound.com/amateur/tips/all_icom.htm

You are correct in that you MAY not need the voltage divider -- having an
adjustable input such as that with the Jim Mitrenga, N9ART sound card
interface "A Flexible Digital-Mode Interface". BTW, although that
RadioShack relay is no longer available -- there is an NTE equivalent that
is a "drop-in replacement".
http://www.farcircuits.net/
http://www.qsl.net/wm2u/images/interface_n9art.pdf

w9gb