Topics

Audio isolation w/ digital modes #ubitx

Rob French (KC4UPR)
 

I'm looking to use my uBITX on digital modes.  So, on the one hand, I should probably just plug the inputs in and go... on the other hand, I've seen plenty of discussion about isolating the audio I/O via transformers, to mitigate digital noise on the lines.  Question:  would 4:1 audio transformers be acceptable for this purpose, instead of 1:1 isolation transformers?  My rationale includes:

(1) On the output... it seems to me that the LM386 output (I have a V5 board) is way too high to be sending straight into a computer soundcard line input.  (I don't actually know this, it just seems right...)  Obviously I can turn the volume down, but what about using the 4:1 transformer, with the "4" on the LM386 side, and the "1" on the computer side?

(2) On the input... I'm thinking here that computer sound card line output would be higher than the mic input for the uBITX.  So in this case again, the "1" would go on the computer side, and the "4" on the uBITX side of the transformer.

Thoughts?  (My real rationale, of course, is that 4:1 transformers are what I actually have on hand...)

Regards,
-Rob

Gordon Gibby <ggibby@...>
 

Sure.  Take a look at public schematics and you’ll often see a bunch of resistors to cut down the levels


Especially on the input to the transmitter microphone, you are  going to want to have some way to adjust it....




On Aug 4, 2019, at 08:58, Rob French (KC4UPR) <robert@...> wrote:

I'm looking to use my uBITX on digital modes.  So, on the one hand, I should probably just plug the inputs in and go... on the other hand, I've seen plenty of discussion about isolating the audio I/O via transformers, to mitigate digital noise on the lines.  Question:  would 4:1 audio transformers be acceptable for this purpose, instead of 1:1 isolation transformers?  My rationale includes:

(1) On the output... it seems to me that the LM386 output (I have a V5 board) is way too high to be sending straight into a computer soundcard line input.  (I don't actually know this, it just seems right...)  Obviously I can turn the volume down, but what about using the 4:1 transformer, with the "4" on the LM386 side, and the "1" on the computer side?

(2) On the input... I'm thinking here that computer sound card line output would be higher than the mic input for the uBITX.  So in this case again, the "1" would go on the computer side, and the "4" on the uBITX side of the transformer.

Thoughts?  (My real rationale, of course, is that 4:1 transformers are what I actually have on hand...)

Regards,
-Rob

_Dave_ K0MBT
 

I don't think that isolation is a bad thing. The two that I set up for digital use an isolation transformer into the mic and speaker. One one used a dpdt switch and the other I didn't have a switch handy so I used a spare stock relay. I call it an A/D control.

For some reason on the mic input side of the radio I needed to adjust the power level to get more than 1 watt output.

Ashhar Farhan
 

It is best to start simply. I used the wsjtx in listening mode by keeping the laptop near the speaker.
Keep adding circuitry until it works to your satisfaction.
- f

On Sun 4 Aug, 2019, 6:57 PM _Dave_ K0MBT, <davesters@...> wrote:
I don't think that isolation is a bad thing. The two that I set up for digital use an isolation transformer into the mic and speaker. One one used a dpdt switch and the other I didn't have a switch handy so  I used a spare stock relay. I call it an A/D control.

For some reason on the mic input side of the radio I needed to adjust the power level to get more than 1 watt output.



JT Croteau
 

I will be adding this dedicated line-out circuit to my build for digital modes.


N1ESE 

On Sun, Aug 4, 2019, 09:20 Ashhar Farhan <farhanbox@...> wrote:
It is best to start simply. I used the wsjtx in listening mode by keeping the laptop near the speaker.
Keep adding circuitry until it works to your satisfaction.
- f

On Sun 4 Aug, 2019, 6:57 PM _Dave_ K0MBT, <davesters@...> wrote:
I don't think that isolation is a bad thing. The two that I set up for digital use an isolation transformer into the mic and speaker. One one used a dpdt switch and the other I didn't have a switch handy so  I used a spare stock relay. I call it an A/D control.

For some reason on the mic input side of the radio I needed to adjust the power level to get more than 1 watt output.



Edward Reynolds
 

My opinion only, others jump in, a 1 to 1 transformer should be fine, make adjustments in the computer soundcard settings (microphone in, and speaker volume out) use Receiver volume to adjust for the signal so the software can convert to text. I’ve built interfaces using 1 to 1 transformers and used it on different radios with no problems. But this is my opinion. 
Cheers 
Ed n7snt 


On Aug 4, 2019, at 5:58 AM, Rob French (KC4UPR) <robert@...> wrote:

I'm looking to use my uBITX on digital modes.  So, on the one hand, I should probably just plug the inputs in and go... on the other hand, I've seen plenty of discussion about isolating the audio I/O via transformers, to mitigate digital noise on the lines.  Question:  would 4:1 audio transformers be acceptable for this purpose, instead of 1:1 isolation transformers?  My rationale includes:

(1) On the output... it seems to me that the LM386 output (I have a V5 board) is way too high to be sending straight into a computer soundcard line input.  (I don't actually know this, it just seems right...)  Obviously I can turn the volume down, but what about using the 4:1 transformer, with the "4" on the LM386 side, and the "1" on the computer side?

(2) On the input... I'm thinking here that computer sound card line output would be higher than the mic input for the uBITX.  So in this case again, the "1" would go on the computer side, and the "4" on the uBITX side of the transformer.

Thoughts?  (My real rationale, of course, is that 4:1 transformers are what I actually have on hand...)

Regards,
-Rob

Arvo W0VRA
 

I was able to connect the PC audio in and out directly to the µBITX audio in and out, with a little fiddling of the volume knob and PC output.  With KD8CEC's firmware, WSJT-X can see the rig as a Yaesu Ft-815, so the software can control the rig directly.  No special interface needed.

Jeff Karpinski (N0KAI)
 

I use a SignaLink which has all the isolation built in so I just brought PTT, and MIC audio to an RJ45 jack on the back. For the audio out, I tapped off the volume jack input and passed it through my own LM386 amp so bring the audio up to proper line level. The USB link to the Raduino was a source of noise when WSJT-X was communicating so I had to loop the cord through a choke a couple times.

Dennis Beverage
 

Hey Gordon, thanks for the link to your interface design.  I’ll be building one of these in the not too distant future, whenever I finally get the time to finish my V4.  This kit is a great contribution to us all, and is very much appreciated.

Sodypop🤠
KJ6VGB

Dennis Beverage
 

Excuse me Gordon, I shouldn’t have said kit where I meant the design and instruction manual.  Hope you don’t get guys trying to send you kit orders.
--
Sodypop🤠
KJ6VGB

Gordon Gibby <ggibby@...>
 

At one point I did offer it as a kit, however at that point I didn’t know how to have boards made so cheaply in China.  Trying to sell kits is a thankless effort.

The Gerber files for that little circuit are available on git hub, and people can take them and send them to China and get boards made extremely cheaply as a kit project for a club




On Aug 4, 2019, at 14:23, Dennis Beverage <Sodypop@...> wrote:

Excuse me Gordon, I shouldn’t have said kit where I meant the design and instruction manual.  Hope you don’t get guys trying to send you kit orders.
--
Sodypop🤠
KJ6VGB

Tom, wb6b
 

On Sun, Aug 4, 2019 at 05:58 AM, Rob French (KC4UPR) wrote:
just plug the inputs in and go... on the other hand
HI, I've run WSPR and FT8 with no problem hooking the output of a USB audio dongle directly to the microphone input of my uBITX and the high side of the uBITX audio pot directly to the input of the USB audio dongle. May add a fixed resistive divider for the receive audio because the receive audio is near the max for the dongle input. But haven't done so yet.

It is possible that different USB audio dongles may work better or worse in a direct hookup, but mine did OK in this regard.

The interesting thing I've noticed about sending WSPR beacon messages with the uBITX is:

I power the uBITX from a car battery jump box, with a built in charger and 12v Gel Cell. If I run the charger in the Jump Box while I'm running the uBITX, I've noticed an addition WSPR signal being transmitted, at a much lower power level, 120 Hz away. So likely ripple in the 12V caused by charging (60Hz line frequency here, with a old fashioned transformer power supply for supplying the charger) is causing the small but spurious output from the transmitter. Don't know if isolation would make a difference, as it seems to be the ripple on the power supply voltage not a ground loop. Adding a big capacitor across the 12v from the Jump Box might fix the issue. In my case I just don't charge while operating.

A previous post on the subject:
https://groups.io/g/BITX20/message/52490

Tom, wb6b

kg9hfrank@gmail.com
 

FT-815?
Cannot find that radio.
de Frank KG9H


From: "Arvo W0VRA via Groups.Io" <arvopl@...>
Date: August 4, 2019 at 12:08:07 PM CDT
To: BITX20@groups.io
Subject: Re: [BITX20] Audio isolation w/ digital modes #ubitx
Reply-To: BITX20@groups.io

I was able to connect the PC audio in and out directly to the µBITX audio in and out, with a little fiddling of the volume knob and PC output.  With KD8CEC's firmware, WSJT-X can see the rig as a Yaesu Ft-815, so the software can control the rig directly.  No special interface needed.


From: "Arvo W0VRA via Groups.Io" <arvopl@...>
Date: August 4, 2019 at 12:08:07 PM CDT
To: BITX20@groups.io
Subject: Re: [BITX20] Audio isolation w/ digital modes #ubitx
Reply-To: BITX20@groups.io

I was able to connect the PC audio in and out directly to the µBITX audio in and out, with a little fiddling of the volume knob and PC output.  With KD8CEC's firmware, WSJT-X can see the rig as a Yaesu Ft-815, so the software can control the rig directly.  No special interface needed.

David Nelson
 

I am sure he means ft-817  Dave  kc2ipx


On Mon, Aug 5, 2019 at 1:17 PM kg9hfrank@... <kg9hfrank@...> wrote:
FT-815?
Cannot find that radio.
de Frank KG9H


From: "Arvo W0VRA via Groups.Io" <arvopl@...>
Date: August 4, 2019 at 12:08:07 PM CDT
To: BITX20@groups.io
Subject: Re: [BITX20] Audio isolation w/ digital modes #ubitx
Reply-To: BITX20@groups.io

I was able to connect the PC audio in and out directly to the µBITX audio in and out, with a little fiddling of the volume knob and PC output.  With KD8CEC's firmware, WSJT-X can see the rig as a Yaesu Ft-815, so the software can control the rig directly.  No special interface needed.


From: "Arvo W0VRA via Groups.Io" <arvopl@...>
Date: August 4, 2019 at 12:08:07 PM CDT
To: BITX20@groups.io
Subject: Re: [BITX20] Audio isolation w/ digital modes #ubitx
Reply-To: BITX20@groups.io

I was able to connect the PC audio in and out directly to the µBITX audio in and out, with a little fiddling of the volume knob and PC output.  With KD8CEC's firmware, WSJT-X can see the rig as a Yaesu Ft-815, so the software can control the rig directly.  No special interface needed.