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Usb sound card.

 

Does anyone know if those cheap Usb sound card adapters offer any isolation between PC and radio? I plan to try out these things with my isolated interface for digital modes. The plan is to use an Usb to serial adapter for the PTT, and one of these sound card dongles for audio, and a Usb to DIP adapter (exposed PCB) to pick up power for a 5V relay module with opto isolation. All on a 4 way Usb hub. The object is to have one connection to PC. And just hoping I can get away without the audio transformers for the lines in and out.
 

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I have worked with a lot of cheapy ones from aliexpress they wont have any isolation. I use a vox interface just for that. It does add more cables to the mess but it works.

Gl
73
David
N8DAH

 

I had one that looked similar to your Ebay post and it didn't have any isolation between the computer ground and the audio in and out ground. I did the VOX interface as well. I intend my Bitx to be mostly portable so I skipped the transformers in this one to save space and just added a resister and some caps to get some DC isolation. We will see if that was a mistake but it seems to be working fine as of now.
 

Please see the link given below





Thank you
73
Ameer Khan VU3SQM

On 12-Jun-2017 7:42 AM, "John Smith via Groups.Io" <johnlinux77=[email protected]> wrote:
Does anyone know if those cheap Usb sound card adapters offer any isolation between PC and radio? I plan to try out these things with my isolated interface for digital modes. The plan is to use an Usb to serial adapter for the PTT, and one of these sound card dongles for audio, and a Usb to DIP adapter (exposed PCB) to pick up power for a 5V relay module with opto isolation. All on a 4 way Usb hub. The object is to have one connection to PC. And just hoping I can get away without the audio transformers for the lines in and out.
 

I previously made the FLDGI CW keying circuit, and it works great. But better than that is using the rig controls for serial port PTT. Tests with the relay module and the Usb to serial adapter Indicates it's working very well. Next is the audio. I plan to use the Easy Digi schematic design for the audio connections with 600ohm audio transformers, and a 2kR across the lines and a 104C on the + line, of the radio side. The only hard part seems to be wiring all those stereo audio mini jacks. 3 on both the interface box, and the radio enclosure. Audio in, out, and PTT, and hard wire the audio adapter. Plus Allard's new wires from the Nano.

Has anyone thought about RF signal attenuation? I tried a 240ohm resistor inline with the antenna to better handle the bigger stations near by. It gave me the results I was looking for, but again it seems too easy for a proper solution. If there is nothing wrong with that, I might use a switch to bring it in and out of circuit.

I just happened to think that the attenuation would be both ways. Humm.
 

Not quite sure what you're trying to do, but here's some links on implementing an RF gain control.
? /g/BITX20/topic/4238539
???



On Sun, Jun 11, 2017 at 09:21 pm, John Smith wrote:
I previously made the FLDGI CW keying circuit, and it works great. But better than that is using the rig controls for serial port PTT. Tests with the relay module and the Usb to serial adapter Indicates it's working very well. Next is the audio. I plan to use the Easy Digi schematic design for the audio connections with 600ohm audio transformers, and a 2kR across the lines and a 104C on the + line, of the radio side. The only hard part seems to be wiring all those stereo audio mini jacks. 3 on both the interface box, and the radio enclosure. Audio in, out, and PTT, and hard wire the audio adapter. Plus Allard's new wires from the Nano.

Has anyone thought about RF signal attenuation? I tried a 240ohm resistor inline with the antenna to better handle the bigger stations near by. It gave me the results I was looking for, but again it seems too easy for a proper solution. If there is nothing wrong with that, I might use a switch to bring it in and out of circuit.

I just happened to think that the attenuation would be both ways. Humm.

?
 

Your first link was about amplified audio, and the second was more like what I am talking about with attenuation of RF. When a strong station comes on, they sound distortedly loud even when I turn the volume almost all the way down. My experiment with the resistor softened them enough to eliminate the distortion and sound like most other stations. And I like the audio gain as is from stock. I need it for QSO night.?

On that second link, do you have other ideas along these lines? Or is that my best bet?


On Sun, Jun 11, 2017 at 09:31 pm, Jerry Gaffke wrote:
Not quite sure what you're trying to do, but here's some links on implementing an RF gain control.
? /g/BITX20/topic/4238539
???

?
 

If incoming signals are too strong to go through the receiver without distortion, you need to reduce the gain. ?The bitx40 has an audio gain control already, that happens at the tail end of the radio. ?For really strong signals, we're better off with an RF gain control, RF gain happens at the front end of the receiver near the antenna. ?That way we don't overload all those parts of the receiver that happen before the audio gain control.

The first link talks about many different methods of gain control, including two methods of RF gain control. ?The one by Don Cantrell where you mess with power into the existing amplifier at Q1 is an elegant solution that probably works just fine. ?The second link is Don's blog post about it. ?The second RF gain control method is described in post 20538 and 20541 where you add a 10k pot between K2 pin 14 and K1 pin 12, that is a trace that is only used during receive and not during transmit. ?The second method is a bit harder to do well, because if you mount the 10k RF gain pot on the front panel it really should have two pieces of coax off to where you cut that trace between K1 and K2 since it is sometimes dealing directly with an extremely low level received signal from the antenna.

Adding a 240 ohm resistor at the antenna might work well enough if you have an antenna tuner between that and the rig to match the rig's 50 ohm transmitter. ?I suppose if you are talking to somebody close you want to reduce transmitted power anyway. ?But you will be wasting most of the power from the transmitter, better to reduce mike gain (or R136) if you want to cut transmitter power.
?

Jerry



On Sun, Jun 11, 2017 at 10:13 pm, John Smith wrote:
Your first link was about amplified audio, and the second was more like what I am talking about with attenuation of RF. When a strong station comes on, they sound distortedly loud even when I turn the volume almost all the way down. My experiment with the resistor softened them enough to eliminate the distortion and sound like most other stations. And I like the audio gain as is from stock. I need it for QSO night.?

On that second link, do you have other ideas along these lines? Or is that my best bet?

?
 

it might be a good idea to just remive the rf amps before the mixer. there is too mucb gain for a 7 mhz radio.

- f

On 12 Jun 2017 11:37 a.m., "Jerry Gaffke via Groups.Io" <jgaffke=[email protected]> wrote:
If incoming signals are too strong to go through the receiver without distortion, you need to reduce the gain.? The bitx40 has an audio gain control already, that happens at the tail end of the radio.? For really strong signals, we're better off with an RF gain control, RF gain happens at the front end of the receiver near the antenna.? That way we don't overload all those parts of the receiver that happen before the audio gain control.

The first link talks about many different methods of gain control, including two methods of RF gain control.? The one by Don Cantrell where you mess with power into the existing amplifier at Q1 is an elegant solution that probably works just fine.? The second link is Don's blog post about it.? The second RF gain control method is described in post 20538 and 20541 where you add a 10k pot between K2 pin 14 and K1 pin 12, that is a trace that is only used during receive and not during transmit.? The second method is a bit harder to do well, because if you mount the 10k RF gain pot on the front panel it really should have two pieces of coax off to where you cut that trace between K1 and K2 since it is sometimes dealing directly with an extremely low level received signal from the antenna.

Adding a 240 ohm resistor at the antenna might work well enough if you have an antenna tuner between that and the rig to match the rig's 50 ohm transmitter.? I suppose if you are talking to somebody close you want to reduce transmitted power anyway.? But you will be wasting most of the power from the transmitter, better to reduce mike gain (or R136) if you want to cut transmitter power.
?

Jerry



On Sun, Jun 11, 2017 at 10:13 pm, John Smith wrote:
Your first link was about amplified audio, and the second was more like what I am talking about with attenuation of RF. When a strong station comes on, they sound distortedly loud even when I turn the volume almost all the way down. My experiment with the resistor softened them enough to eliminate the distortion and sound like most other stations. And I like the audio gain as is from stock. I need it for QSO night.?

On that second link, do you have other ideas along these lines? Or is that my best bet?

?
Trent Trent
 

Have you got the diagram for the interface by any chance and has anyobe heard about the release date for the uBitx yet


On 12 Jun. 2017 4:11 pm, "Ashhar Farhan" <farhanbox@...> wrote:
it might be a good idea to just remive the rf amps before the mixer. there is too mucb gain for a 7 mhz radio.

- f

On 12 Jun 2017 11:37 a.m., "Jerry Gaffke via Groups.Io" <jgaffke=[email protected]> wrote:
If incoming signals are too strong to go through the receiver without distortion, you need to reduce the gain.? The bitx40 has an audio gain control already, that happens at the tail end of the radio.? For really strong signals, we're better off with an RF gain control, RF gain happens at the front end of the receiver near the antenna.? That way we don't overload all those parts of the receiver that happen before the audio gain control.

The first link talks about many different methods of gain control, including two methods of RF gain control.? The one by Don Cantrell where you mess with power into the existing amplifier at Q1 is an elegant solution that probably works just fine.? The second link is Don's blog post about it.? The second RF gain control method is described in post 20538 and 20541 where you add a 10k pot between K2 pin 14 and K1 pin 12, that is a trace that is only used during receive and not during transmit.? The second method is a bit harder to do well, because if you mount the 10k RF gain pot on the front panel it really should have two pieces of coax off to where you cut that trace between K1 and K2 since it is sometimes dealing directly with an extremely low level received signal from the antenna.

Adding a 240 ohm resistor at the antenna might work well enough if you have an antenna tuner between that and the rig to match the rig's 50 ohm transmitter.? I suppose if you are talking to somebody close you want to reduce transmitted power anyway.? But you will be wasting most of the power from the transmitter, better to reduce mike gain (or R136) if you want to cut transmitter power.
?

Jerry



On Sun, Jun 11, 2017 at 10:13 pm, John Smith wrote:
Your first link was about amplified audio, and the second was more like what I am talking about with attenuation of RF. When a strong station comes on, they sound distortedly loud even when I turn the volume almost all the way down. My experiment with the resistor softened them enough to eliminate the distortion and sound like most other stations. And I like the audio gain as is from stock. I need it for QSO night.?

On that second link, do you have other ideas along these lines? Or is that my best bet?

?
 

Don Cantrell's tombstone cap trick at Q1 effectively removes all rx gain before the mixer.
? ?????
Some may require the additional gain of Q1 when working with a less than optimal antenna.


On Sun, Jun 11, 2017 at 11:10 pm, Ashhar Farhan wrote:
it might be a good idea to just remive the rf amps before the mixer. there is too mucb gain for a 7 mhz radio.
?

?
 

If you're using FLDIGI take a look at??

The PTT tone on the right channel eliminates the need for a USB serial adapter and relay circuit; you only need the mic and speaker wires between the sound card and BITX40. In my setup there is no difference in performance with or without the transformers but they're only $1 on Amazon so why not.
 

That's another option. I already have right channel PTT circuit in the form of the Fldigi CW keying circuit. I was wondering if I will incorporate it. The final design is still floating around in my head. When this and Allard's added functionalities are done, this will be like a all mode 40 meter radio.?

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