Topics

PTT pop hack

 

Folks,

After much poking and probing with instruments I found the reason for the power pop when you press the PTT.

When PTT is pressed the TX voltage floods the mic preamp. Capacitor C122 charges up and the charging current flows into t4 and then
D15 - thereby for a fraction of a second the carrier leaks through and if you are listing with another RX you will hear a "tong" kind of sound.

Solution is to stop this flow through the diode then R106 - R220 to ground.

In my analog VFO version I desoldered the R106's center pin and put in a 0.1 capacitor in series. This stops the capacitor charge current from routing though the mixer diode.

For better measure add a 1K resistor across C107. I found a constant 30mV there which was unbalancing my diodes and the carrier balance pot R106 was more to clockwise than needed!

For the digital VFO board or boards without R106 trimmer, cut the track between D20 and R38 and solder a smd 0.1 cap there.

Result is a significantly reduced pop which is not bothersome anymore.

Farhan please incorporate this hack.

Cheers for a pop free Sunday!

--
Raj, vu2zap
Bengaluru, South India.

MVS Sarma
 

Nice Raj
Thanks for the efforts in arriving at the solution.
sarma
 vu3zmv

On Sun, Mar 5, 2017 at 12:03 PM, Raj vu2zap <vu2zap@...> wrote:
Folks,

After much poking and probing with instruments I found the reason for the power pop when you press the PTT.

When PTT is pressed the TX voltage floods the mic preamp. Capacitor C122 charges up and the charging current flows into t4 and then
D15 - thereby for a fraction of a second the carrier leaks through and if you are listing with another RX you will hear a "tong" kind of sound.

Solution is to stop this flow through the diode then R106 - R220 to ground.

In my analog VFO version I desoldered the R106's center pin and put in a 0.1 capacitor in series. This stops the capacitor charge current from routing though the mixer diode.

For better measure add a 1K resistor across C107. I found a constant 30mV there which was unbalancing my diodes and the carrier balance pot R106 was more to clockwise than needed!

For the digital VFO board or boards without R106 trimmer, cut the track between D20 and R38 and solder a smd 0.1 cap there.

Result is a significantly reduced pop which is not bothersome anymore.

Farhan please incorporate this hack.

Cheers for a pop free Sunday!

--
Raj, vu2zap
Bengaluru, South India.








--
Regards
Sarma
 

Stephan Lauffer
 

Thanks, Rai!

What is about adding this note to the wiki? There are some very helpfully posts on this list. It would be nice if we would find the tips and tricks on the wiki, too.

(https://groups.io/g/BITX20/wiki)

Am 05.03.2017 um 07:33 schrieb Raj vu2zap:

Folks,

After much poking and probing with instruments I found the reason for the power pop when you press the PTT.

When PTT is pressed the TX voltage floods the mic preamp. Capacitor C122 charges up and the charging current flows into t4 and then
D15 - thereby for a fraction of a second the carrier leaks through and if you are listing with another RX you will hear a "tong" kind of sound.

Solution is to stop this flow through the diode then R106 - R220 to ground.

In my analog VFO version I desoldered the R106's center pin and put in a 0.1 capacitor in series. This stops the capacitor charge current from routing though the mixer diode.

For better measure add a 1K resistor across C107. I found a constant 30mV there which was unbalancing my diodes and the carrier balance pot R106 was more to clockwise than needed!

For the digital VFO board or boards without R106 trimmer, cut the track between D20 and R38 and solder a smd 0.1 cap there.

Result is a significantly reduced pop which is not bothersome anymore.

Farhan please incorporate this hack.

Cheers for a pop free Sunday!
--
Stephan, dc8lz

 

I will leave it up to you guys!

I am happier with a soldering iron than a pen !!

Cheers
Raj

At 06-03-2017, you wrote:
Thanks, Rai!

What is about adding this note to the wiki? There are some very helpfully posts on this list. It would be nice if we would find the tips and tricks on the wiki, too.

(https://groups.io/g/BITX20/wiki)

Kelly Jack
 

Hi,

Tried this and it didn't work for me. I cut the trace between R106 centre pin and R38. Scope indicated that the carrier burst was still there also.

I am wondering why a new cap in the path to ground would stop the current when C122 wouldn't stop this current itself. Scope indicated that the carrier burst was still there also.


Regards


Simon

VK3ELH




alf
 

see message #21536

Kelly Jack wrote:


Hi,

Tried this and it didn't work for me. I cut the trace between R106 centre pin and R38. Scope indicated that the carrier burst was still there also.

I am wondering why a new cap in the path to ground would stop the current when C122 wouldn't stop this current itself. Scope indicated that the carrier burst was still there also.


Regards


Simon

VK3ELH




 

Hi! Simon,

I suggested a cap that is in series and not to ground. The cap c122 charging when the TX voltage came on was the issue.
It helps if there is a 1K resistor parallel to C107 to reference/path to ground for decreasing the carrier burst.
Check if the cut track is really cut or a bit of copper left is causing the issue.
I desoldered the center pin of the preset, lifted the preset's desoldered pin and added a leaded cap in series.

It decreases the burst but reduces it to an acceptable level.

The charge up current spike of the cap C122 has to route to ground but we don't want it to go through the mixer diode and
momentarily unbalance the mixer.

A pic of what you did might give us a clue! I am not in town or I would send you a pic of what I did.

Cheers
--
Raj, vu2zap

At 07/03/2017, you wrote:

Hi,

Tried this and it didn't work for me. I cut the trace between R106 centre pin and R38. Scope indicated that the carrier burst was still there also.

I am wondering why a new cap in the path to ground would stop the current when C122 wouldn't stop this current itself. Scope indicated that the carrier burst was still there also.


Regards


Simon

VK3ELH

Kelly Jack
 

Raj

I cut the track beteween the wiper of r106 and r38 and confirmed the break with my multimeter. Then put the cap across that break. 

The reference in my earlier post to "path to ground" was refering to the path through the diode and then on through r39, ie the path we are putting the cap in series with.

Regards



Simon VK3ELH

 

OK Simon,

What I had not mentioned is that the carrier balance pot needs to be re adjusted. Listen to the carrier leak in a near by Rx and adjust for a
minimum or scope the output after removing the mic connector and adjust the 106 for minimum carrier.

Make sure the series cap you put is not more than 0.1uF.

At 08/03/2017, you wrote:

Raj

I cut the track beteween the wiper of r106 and r38 and confirmed the break with my multimeter. Then put the cap across that break.

The reference in my earlier post to "path to ground" was refering to the path through the diode and then on through r39, ie the path we are putting the cap in series with.

Regards



Simon VK3ELH

Kelly Jack
 

Raj

I checked the balance using my scope. The balance didnt seem to need any adjustment and the leakage measured the same as without the cap.

The cap was 0.1uf.

While a current burst through the diode unbalancing the mixer makes sense as an explanation for this I still don't understand why a 0.1uf cap in series would block the current flow if c122 wouldn't.


I really would like to find a solution to my ptt pop as I find it to be too unpleasant for headphone use.


Regards 


Simon VK3ELH 

 

Simon,

This hack does not address the sound in the BITX40 speaker. This is entirely a different issue.

In my unit the power meter would deflect to more than 500mW when the PTT is pressed. IF I listened to my commercial RX I could hear a
"clonk/tong" sound. After the mod the meter barely moves.

What I am trying to do is not allow the C122 to charge via the diode. C122 BLOCKS the DC from getting to the diode but the cap charge current goes through to the diode when PTT is pressed. You need to put a 1K resistor parallel to C107 to route this current to ground.

If the mic amp had 2 stages and if the second stage is always powered on then there will be no problem.

AFAIK in a 4 diode mixer this wont happen as there are two diodes that will conduct and cancel any carrier leak in the trifilar transformer.

The amp pop would have not been there if it was left powered on but the audio was muted in a stage before it. Farhan has kept BITX40
as simple as possible. We can make it more elaborate in design if we wish.

If the audio pop is to be removed then keep the amp powered on and use a 2n7000 across the volume control and mute it on TX.

At 08/03/2017, you wrote:

Raj

I checked the balance using my scope. The balance didnt seem to need any adjustment and the leakage measured the same as without the cap.

The cap was 0.1uf.

While a current burst through the diode unbalancing the mixer makes sense as an explanation for this I still don't understand why a 0.1uf cap in series would block the current flow if c122 wouldn't.


I really would like to find a solution to my ptt pop as I find it to be too unpleasant for headphone use.


Regards


Simon VK3ELH

Kelly Jack
 

Raj


It appears I have misunderstood what this mod is trying to achieve from the start.

Thankyou for your explanations.


Regards 


Simon VK3ELH 

 

No problem Simon,

Now its good time at Melbourne for a beer or to try another hack on bitx40.

Try this:

1. Power the audio stages directly by connecting 12V line to the junction of R111, R113 and D18.

Now you will hear your own voice during TX and we need to mute it.

2. Take a 2N7000 or similar and connect SOURCE to ground, DRAIN to the top of the volume control (M1/M2).
feed the TX 12V through a 10K or nearby value to the gate.

This should mute the amp during TX.

If this works for you then remove the diode D18!

Caveat: I have not tried it as I am at the coffee farm this week. Itching to get back to my board but it will be Monday next!
While in TX mode some RF might get into the amp stage and be just as annoying.
Then we have to work more on that! A 0.01 across the volume control might fix this if it happens.

Cheers
Raj

At 08/03/2017, you wrote:

Raj


It appears I have misunderstood what this mod is trying to achieve from the start.

Thankyou for your explanations.


Regards


Simon VK3ELH

Baruch Atta <baruchatta@...>
 

"... Power the audio stages directly by connecting 12V line to the junction of R111, R113 and D18.
Now you will hear your own voice during TX and we need to mute it..."

Is that so bad - to hear your own voice during transmission?  Would this alone reduce or eliminate the pop on keying the transmitter?
Also, this could be a nice sidetone monitor when injecting a tone into the mic when attempting to use the BitX for CW?

I put the BitX away for awhile until I could find a solution to the popping!  I use earphones exclusively, no speaker, and the pop sounds like a bolt of lightning to me. 

thanks
Joe W3TTT




On Wed, Mar 8, 2017 at 3:03 AM, Raj vu2zap <vu2zap@...> wrote:
No problem Simon,

Now its good time at Melbourne for a beer or to try another hack on bitx40.

Try this:

1. Power the audio stages directly by connecting 12V line to the junction of R111, R113 and D18.

Now you will hear your own voice during TX and we need to mute it.

2. Take a 2N7000 or similar and connect SOURCE to ground, DRAIN to the top of the volume control (M1/M2).
feed the TX 12V through a 10K or nearby value to the gate.

This should mute the amp during TX.

If this works for you then remove the diode D18!

Caveat: I have not tried it as I am at the coffee farm this week. Itching to get back to my board but it will be Monday next!
While in TX mode some RF might get into the amp stage and be just as annoying.
Then we have to work more on that! A 0.01 across the volume control might fix this if it happens.

Cheers
Raj

 

Joe,

Last week I tested this suggestion and it does not help much. It reduces the pop but not much.
Next week when I am back in town I will try some other ideas and see.

Switching the 12V on/off is causing it, including the relay which cuts out the volume control M1 M2 points!

Raj, vu2zap


At 06/04/2017, you wrote:
"... Power the audio stages directly by connecting 12V line to the junction of R111, R113 and D18.
Now you will hear your own voice during TX and we need to mute it..."

Is that so bad - to hear your own voice during transmission?  Would this alone reduce or eliminate the pop on keying the transmitter?
Also, this could be a nice sidetone monitor when injecting a tone into the mic when attempting to use the BitX for CW?

I put the BitX away for awhile until I could find a solution to the popping!  I use earphones exclusively, no speaker, and the pop sounds like a bolt of lightning to me.Â

thanks
Joe W3TTT




On Wed, Mar 8, 2017 at 3:03 AM, Raj vu2zap <vu2zap@...> wrote:
No problem Simon,

Now its good time at Melbourne for a beer or to try another hack on bitx40.

Try this:

1. Power the audio stages directly by connecting 12V line to the junction of R111, R113 and D18.

Now you will hear your own voice during TX and we need to mute it.

2. Take a 2N7000 or similar and connect SOURCE to ground, DRAIN to the top of the volume control (M1/M2).
feed the TX 12V through a 10K or nearby value to the gate.

This should mute the amp during TX.

If this works for you then remove the diode D18!

Caveat: I have not tried it as I am at the coffee farm this week. Itching to get back to my board but it will be Monday next!
While in TX mode some RF might get into the amp stage and be just as annoying.
Then we have to work more on that! A 0.01 across the volume control might fix this if it happens.

Cheers
Raj

Jerry Gaffke
 

Here's a thought, those with a Nano might be able to use it to sequence the transition:  

    Mute audio with a FET at volume pot,  shut down any transmission with another FET at BPF

    Wait 10ms or so

    Swap the power rails

    Wait 10ms or so

    Unmute the above



On Thu, Apr 6, 2017 at 08:05 pm, Raj vu2zap wrote:

Last week I tested this suggestion and it does not help much. It reduces the pop but not much.
Next week when I am back in town I will try some other ideas and see.

Switching the 12V on/off is causing it, including the relay which cuts out the volume control M1 M2 points!

 

Steve Greer
 

Is there a way that we can use the mute feature of the lm386 on ptt.  The datasheet says ground I believe pin8 will mute the lm386 and this would eliminate the pop in the ear????

Engineer
 

Yes I think this may work if the mute unmute is a silent operation 


Sent from my iPhone

On 20 Apr 2017, at 12:22, Steve Greer <km4ous@...> wrote:

Is there a way that we can use the mute feature of the lm386 on ptt.  The datasheet says ground I believe pin8 will mute the lm386 and this would eliminate the pop in the ear????

Allard PE1NWL
 

Yes I tried this already, but I still got a pop each time I connected the
pin to ground...

73, Allard PE1NWL

On Thu, April 20, 2017 13:22, Steve Greer wrote:
Is there a way that we can use the mute feature of the lm386 on ptt.  The
datasheet says ground I believe pin8 will mute the lm386 and this would
eliminate the pop in the ear????

Engineer
 

Simple brute force solution use a small relay to disconnect the speaker on tx keep a 1k resistor as a load and to keep the output capacitor charged pop should go

Sent from my iPhone

On 20 Apr 2017, at 12:40, Allard PE1NWL <@pe1nwl> wrote:

Yes I tried this already, but I still got a pop each time I connected the
pin to ground...

73, Allard PE1NWL

On Thu, April 20, 2017 13:22, Steve Greer wrote:
Is there a way that we can use the mute feature of the lm386 on ptt. The
datasheet says ground I believe pin8 will mute the lm386 and this would
eliminate the pop in the ear????