开云体育

  1. BITX20
  2. Topics

DC blocking cap between souncard and ubitc mic input. #ft8 #ubitx

 

Is dc blocking capacitor necessary between sound card audio output and mic input of ubitx during digital modes?. I made a direct connection between above without DC blocking cap. Though? my ubitx received so many, very few logged my cq calls as per pskreporter. Any advices?
Gordon Gibby
 

开云体育

We made the mistake of not dc blocking mic inputs of some commercial vhf rigs —-bad distortion in input stage?


On Mar 4, 2019, at 16:41, Praba Karan <vu3dxr@...> wrote:

Is dc blocking capacitor necessary between sound card audio output and mic input of ubitx during digital modes?. I made a direct connection between above without DC blocking cap. Though? my ubitx received so many, very few logged my cq calls as per pskreporter. Any advices?

Joe Puma
 

开云体育

could something like a 600:600 transformer solve that issue too? I’ve ?been putting them between all my audio and mic I/O’s when connecting to pc/soundcard

Joe
kd2nfc



On Mar 4, 2019, at 10:24 AM, Gordon Gibby <ggibby@...> wrote:

We made the mistake of not dc blocking mic inputs of some commercial vhf rigs —-bad distortion in input stage?


On Mar 4, 2019, at 16:41, Praba Karan <vu3dxr@...> wrote:

Is dc blocking capacitor necessary between sound card audio output and mic input of ubitx during digital modes?. I made a direct connection between above without DC blocking cap. Though? my ubitx received so many, very few logged my cq calls as per pskreporter. Any advices?

Gordon Gibby
 

开云体育

Transformer Makes it worse. ?
Do not short the dc bias voltage—likely it will take input transistor or op amp to un-usable ?bias?


On Mar 4, 2019, at 17:27, Joe Puma <kd2nfc@...> wrote:

could something like a 600:600 transformer solve that issue too? I’ve ?been putting them between all my audio and mic I/O’s when connecting to pc/soundcard

Joe
kd2nfc



On Mar 4, 2019, at 10:24 AM, Gordon Gibby <ggibby@...> wrote:

We made the mistake of not dc blocking mic inputs of some commercial vhf rigs —-bad distortion in input stage?


On Mar 4, 2019, at 16:41, Praba Karan <vu3dxr@...> wrote:

Is dc blocking capacitor necessary between sound card audio output and mic input of ubitx during digital modes?. I made a direct connection between above without DC blocking cap. Though? my ubitx received so many, very few logged my cq calls as per pskreporter. Any advices?

 

There is a voltage on the MIC circuit, you NEED a 1:1 transformer and/or a blocking cap, or your laptop/tablet/soundcard will freak out at the least, or get damaged at the worst.

The MIC in on my V4 uBitx needs quite a high level, so LINE OUT on a computer (etc.) is well suited to it without the need for attenuation, but there is no way it will work correctly without something to do away with the voltage on the line, especially if the sound device is auto-sensing.
 

...more on this here: /g/BITX20/message/65994
 

Agreed that the supplied voltage on the mic capsule will give you hassels. With a 600:600 transformer things will be worse. The supplied voltage will now go through the transfomer winding to ground. Only solution is to stop this voltage completely. Via a switch. Using the mic, switch it on. Use digi, switch it off.
Joe Puma
 

开云体育

Gordon, I’ve been using the easydigi’s, is that the purpose of cap in between both mic and audio connections to radio?

Joe

On Mar 4, 2019, at 10:51 AM, Gordon Gibby <ggibby@...> wrote:

Transformer Makes it worse. ?
Do not short the dc bias voltage—likely it will take input transistor or op amp to un-usable ?bias?


On Mar 4, 2019, at 17:27, Joe Puma <kd2nfc@...> wrote:

could something like a 600:600 transformer solve that issue too? I’ve ?been putting them between all my audio and mic I/O’s when connecting to pc/soundcard

Joe
kd2nfc



On Mar 4, 2019, at 10:24 AM, Gordon Gibby <ggibby@...> wrote:

We made the mistake of not dc blocking mic inputs of some commercial vhf rigs —-bad distortion in input stage?


On Mar 4, 2019, at 16:41, Praba Karan <vu3dxr@...> wrote:

Is dc blocking capacitor necessary between sound card audio output and mic input of ubitx during digital modes?. I made a direct connection between above without DC blocking cap. Though? my ubitx received so many, very few logged my cq calls as per pskreporter. Any advices?


 

So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?
 

Discussion of the microphone input and related DC isolation has been coming up for discussion
periodically ever since the first BITX design.? Best approach is to look at the schematic and that
of your input device to insure that proper isolation and level adjustment is provided.? Just making
statements about what should and should not be used probably should be backed up with "why it
works this way" explanations.?

This is not to deprecate any of the statements already made, just to suggest that what works for
XYZ rigs may not be the perfect solution for a particular version of BITX.? The BITX microphone
input circuit has changed slightly over the years.?

Arv? K7HKL
_._


On Mon, Mar 4, 2019 at 10:05 AM Playthatbeat Mrdj <playthatbeat303@...> wrote:
So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?

Joe Puma
 

开云体育

The easydigi does have this blocking cap. .1uf

Joe
KD2NFC?


On Mar 4, 2019, at 12:05 PM, Playthatbeat Mrdj <playthatbeat303@...> wrote:

So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?

Gordon Gibby
 

开云体育

Joe Puma, yes that is most likely the purpose. ?Been there, done that, learned a thing.?


On Mar 4, 2019, at 18:36, Joe Puma <kd2nfc@...> wrote:

Gordon, I’ve been using the easydigi’s, is that the purpose of cap in between both mic and audio connections to radio?

Joe

On Mar 4, 2019, at 10:51 AM, Gordon Gibby <ggibby@...> wrote:

Transformer Makes it worse. ?
Do not short the dc bias voltage—likely it will take input transistor or op amp to un-usable ?bias?


On Mar 4, 2019, at 17:27, Joe Puma <kd2nfc@...> wrote:

could something like a 600:600 transformer solve that issue too? I’ve ?been putting them between all my audio and mic I/O’s when connecting to pc/soundcard

Joe
kd2nfc



On Mar 4, 2019, at 10:24 AM, Gordon Gibby <ggibby@...> wrote:

We made the mistake of not dc blocking mic inputs of some commercial vhf rigs —-bad distortion in input stage?


On Mar 4, 2019, at 16:41, Praba Karan <vu3dxr@...> wrote:

Is dc blocking capacitor necessary between sound card audio output and mic input of ubitx during digital modes?. I made a direct connection between above without DC blocking cap. Though? my ubitx received so many, very few logged my cq calls as per pskreporter. Any advices?


Joe Puma
 

开云体育

Awesome, it didn’t hit me at first. I just grabbed two off eBay for $11 for both. I have parts I was going to use on interfaces, transformers, optocouplers, the easydigi has all you need. I’ve known about easydigi for a while but now that I’m digging deeper in EE I understand what all the parts do in the circuit. Even on antenna lines. The DC cap is very necessary when doing bias t on receive antennas. You guys taught me so much lol ;)

Joe
KD2NFC?


On Mar 4, 2019, at 3:20 PM, Gordon Gibby <ggibby@...> wrote:

Joe Puma, yes that is most likely the purpose. ?Been there, done that, learned a thing.?


On Mar 4, 2019, at 18:36, Joe Puma <kd2nfc@...> wrote:

Gordon, I’ve been using the easydigi’s, is that the purpose of cap in between both mic and audio connections to radio?

Joe

On Mar 4, 2019, at 10:51 AM, Gordon Gibby <ggibby@...> wrote:

Transformer Makes it worse. ?
Do not short the dc bias voltage—likely it will take input transistor or op amp to un-usable ?bias?


On Mar 4, 2019, at 17:27, Joe Puma <kd2nfc@...> wrote:

could something like a 600:600 transformer solve that issue too? I’ve ?been putting them between all my audio and mic I/O’s when connecting to pc/soundcard

Joe
kd2nfc



On Mar 4, 2019, at 10:24 AM, Gordon Gibby <ggibby@...> wrote:

We made the mistake of not dc blocking mic inputs of some commercial vhf rigs —-bad distortion in input stage?


On Mar 4, 2019, at 16:41, Praba Karan <vu3dxr@...> wrote:

Is dc blocking capacitor necessary between sound card audio output and mic input of ubitx during digital modes?. I made a direct connection between above without DC blocking cap. Though? my ubitx received so many, very few logged my cq calls as per pskreporter. Any advices?


 

0.1uF at 300hz has a reactance around 5000ohm, at 3Khz 500ohm, so it acts as a sort of audio high pass filter. If the cap has a higher capacitance the audio response is flatter.


Il 04/mar/2019 19:15, "Joe Puma" <kd2nfc@...> ha scritto:
The easydigi does have this blocking cap. .1uf

Joe
KD2NFC?


On Mar 4, 2019, at 12:05 PM, Playthatbeat Mrdj <playthatbeat303@...> wrote:

So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?

Joe Puma
 

开云体育

So it’s not dc blocking but a audio filter??

Joe
Kd2nfc?



On Mar 4, 2019, at 4:52 PM, iz oos <and2oosiz2@...> wrote:

0.1uF at 300hz has a reactance around 5000ohm, at 3Khz 500ohm, so it acts as a sort of audio high pass filter. If the cap has a higher capacitance the audio response is flatter.


Il 04/mar/2019 19:15, "Joe Puma" <kd2nfc@...> ha scritto:
The easydigi does have this blocking cap. .1uf

Joe
KD2NFC?


On Mar 4, 2019, at 12:05 PM, Playthatbeat Mrdj <playthatbeat303@...> wrote:

So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?

 

Primarily it does block DC, however it attenuates somewhat more the lower frequencies (as 300hz) than the higher (3khz).


Il 04/mar/2019 22:56, "Joe Puma" <kd2nfc@...> ha scritto:
So it’s not dc blocking but a audio filter??

Joe
Kd2nfc?



On Mar 4, 2019, at 4:52 PM, iz oos <and2oosiz2@...> wrote:

0.1uF at 300hz has a reactance around 5000ohm, at 3Khz 500ohm, so it acts as a sort of audio high pass filter. If the cap has a higher capacitance the audio response is flatter.


Il 04/mar/2019 19:15, "Joe Puma" <kd2nfc@...> ha scritto:
The easydigi does have this blocking cap. .1uf

Joe
KD2NFC?


On Mar 4, 2019, at 12:05 PM, Playthatbeat Mrdj <playthatbeat303@...> wrote:

So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?

Joe Puma
 

开云体育

okay got it, so it removes some of the lower boomieness of the audio spectrum since it wouldn’t be heard much anyway and allow more of the mid and highs to get through. my first impression was a audio filter as I am familiar with it use in that application but its good to know its blocking DC as well. I spent a few minutes reading this very basic understanding.?


Joe



On Mar 4, 2019, at 5:11 PM, iz oos <and2oosiz2@...> wrote:

Primarily it does block DC, however it attenuates somewhat more the lower frequencies (as 300hz) than the higher (3khz).


Il 04/mar/2019 22:56, "Joe Puma" <kd2nfc@...> ha scritto:
So it’s not dc blocking but a audio filter??

Joe
Kd2nfc?



On Mar 4, 2019, at 4:52 PM, iz oos <and2oosiz2@...> wrote:

0.1uF at 300hz has a reactance around 5000ohm, at 3Khz 500ohm, so it acts as a sort of audio high pass filter. If the cap has a higher capacitance the audio response is flatter.


Il 04/mar/2019 19:15, "Joe Puma" <kd2nfc@...> ha scritto:
The easydigi does have this blocking cap. .1uf

Joe
KD2NFC?


On Mar 4, 2019, at 12:05 PM, Playthatbeat Mrdj <playthatbeat303@...> wrote:

So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?





Gordon Gibby
 

开云体育

Folks, this depends on what impedance it is feeding into. ?If it’s feeding into a very high impedance say 100,000 ohms, then it ?will be relatively flat
?
Likely the input impedance is a little lower than that so I preferred to use a one microfarad electrolytic, with the plus side towards the DC bias voltage of the rig.

The transformer output is a dead short at DC, so that side is 0 V. ?

Gordon


On Mar 5, 2019, at 00:22, Joe Puma <kd2nfc@...> wrote:

okay got it, so it removes some of the lower boomieness of the audio spectrum since it wouldn’t be heard much anyway and allow more of the mid and highs to get through. my first impression was a audio filter as I am familiar with it use in that application but its good to know its blocking DC as well. I spent a few minutes reading this very basic understanding.?


Joe



On Mar 4, 2019, at 5:11 PM, iz oos <and2oosiz2@...> wrote:

Primarily it does block DC, however it attenuates somewhat more the lower frequencies (as 300hz) than the higher (3khz).


Il 04/mar/2019 22:56, "Joe Puma" <kd2nfc@...> ha scritto:
So it’s not dc blocking but a audio filter??

Joe
Kd2nfc?



On Mar 4, 2019, at 4:52 PM, iz oos <and2oosiz2@...> wrote:

0.1uF at 300hz has a reactance around 5000ohm, at 3Khz 500ohm, so it acts as a sort of audio high pass filter. If the cap has a higher capacitance the audio response is flatter.


Il 04/mar/2019 19:15, "Joe Puma" <kd2nfc@...> ha scritto:
The easydigi does have this blocking cap. .1uf

Joe
KD2NFC?


On Mar 4, 2019, at 12:05 PM, Playthatbeat Mrdj <playthatbeat303@...> wrote:

So things are actually worse when using a transformer to isolate the mic line? So things like the easy-digi etc. make things worse? this was not my experience at all. before using a transformer, i could not sustain the audio connection between my (horrible) single audio jack on my handheld PC, but after i could without issue.

So, it's possible that using easy-digi or a transformer is shunting the voltage on the mic line to ground, which could cause all manner of strange problems with the uBitx? Is this correct?





 

There is some discussion about a transformer at the mic input affecting the output. It works on two of my v3 rigs. There is a blocking cap c60, a 1uF on the input of the q6 the mic preamp. I would imagine that r60 could be disconnected without issue but I have not done this.
73
Dave
k0mbt

1 - 19 of 19