Topics

tx pop

Ashhar Farhan
 

i have been trying to hack out the tx pop. it is a far more intricate problem than it does seem at first. to cut a very long and painful story short, i am not yet there. but i have a partial solution.

add a 470uf (or a 220uf) capacitor in parallel to C50. The C50 is the 1uf capacitor that feeds the detector signal to the audio pre-amp. Increasing this to 470uf, prolongs the 'switch on' time of the audio preamp just enough to not hear the TX-to-RX thump.

can someone else too try this out?

i call it a partial solution because it doesn't suppress the rx-to-tx pop (which is not as bad as the tx-to-rx pop).

- f

K9WIS
 

This sounds an awful lot like the problem the NORCAL guys had when they released the 38 Special transceiver kit many years ago...They nicknamed the issue 'The Thump" .Not sure they ever came up with a solution..try to track down old issues of QRPp..there was a lot of discussion about it in there. There maybe some folks on QRP-L that were around during that era.

Brian K9WIS

Xcott Craver
 

I decided to hack around the issue with a little external phone/mic interface box, made from a "deluxe" AAA battery case:



This connects a conventional headset and mic input and provides a PTT button, which I needed anyway.  A little switch adds a potentiometer to the phone line, and it's a simple matter to flip the switch before I press PTT.  This also attenuates the keyer sidetone.

If I were clever, I'd find a way to patch in the pot and trigger PTT with the same pushbutton, but better is the enemy of done.

Thanks, Xcott K2CAJ

John Backo
 

Ash:

Have you seen the solution of Small Wonder QRP?
http://smallwonderqrp.blogspot.com/

The blog date is Novenber 3, 2017.
His is a solid state replacement for the relays, etc.
It is an interesting approach.

john
AD5YE

ohwenzelph
 

So, re the uBitx, (& not Bitx40v3)

ohwenzelph
 

What would be the smallest reasonable volt spec for the 470uf cap parallel to C50?

Ashhar Farhan
 

Any voltage would do. It has just a few 100 millivolt thump.
- f

On 9 Jan 2018 4:30 am, "ohwenzelph via Groups.Io" <Ohwenzelph=yahoo.com@groups.io> wrote:
What would be the smallest reasonable volt spec for the 470uf cap parallel to C50?

 

Farhan,

I have been thinking of diode switching in the audio stages. The TX 12v can block the RX preamp and vice-versa.

I have to get back to town to try!

Raj

At 09/01/2018, you wrote:
i have been trying to hack out the tx pop. it is a far more intricate problem than it does seem at first. to cut a very long and painful story short, i am not yet there. but i have a partial solution.

add a 470uf (or a 220uf) capacitor in parallel to C50. The C50 is the 1uf capacitor that feeds the detector signal to the audio pre-amp. Increasing this to 470uf, prolongs the 'switch on' time of the audio preamp just enough to not hear the TX-to-RX thump.

can someone else too try this out?

i call it a partial solution because it doesn't suppress the rx-to-tx pop (which is not as bad as the tx-to-rx pop).

- f

Marc Jones
 

Is this Mod for the Bitx-40 of the Micro-Bitx ?  Starting to get a bit of a muddle reading posts now on here , Not knowing what version of BITX there for ..


On Tue, 9 Jan 2018 at 4:29, Raj vu2zap
<rajendrakumargg@...> wrote:
Farhan,

I have been thinking of diode switching in the audio stages. The TX 12v can block the RX preamp and vice-versa.

I have to get back to town to try!

Raj

At 09/01/2018, you wrote:
>i have been trying to hack out the tx pop. it is a far more intricate problem than it does seem at first. to cut a very long and painful story short, i am not yet there. but i have a partial solution.
>
>add a 470uf (or a 220uf) capacitor in parallel to C50. The C50 is the 1uf capacitor that feeds the detector signal to the audio pre-amp. Increasing this to 470uf, prolongs the 'switch on' time of the audio preamp just enough to not hear the TX-to-RX thump.
>
>can someone else too try this out?
>
>i call it a partial solution because it doesn't suppress the rx-to-tx pop (which is not as bad as the tx-to-rx pop).
>
>- f




 

Mark,

This topic refers to uBitx. Both B40 and uB have similar issues as the audio preamp and mic amp are identical.

Raj


At 09/01/2018, you wrote:
Is this Mod for the Bitx-40 of the Micro-Bitx ?  Starting to get a bit of a muddle reading posts now on here , Not knowing what version of BITX there for ..


Mark  'Gw0wvl' ...

Sent from Yahoo Mail on Android

On Tue, 9 Jan 2018 at 4:29, Raj vu2zap
<rajendrakumargg@...> wrote:
Farhan,
I have been thinking of diode switching in the audio stages. The TX 12v can block the RX preamp and vice-versa.
I have to get back to town to try!
Raj
At 09/01/2018, you wrote:
>i have been trying to hack out the tx pop. it is a far more intricate problem than it does seem at first. to cut a very long and painful story short, i am not yet there. but i have a partial solution.
>
>add a 470uf (or a 220uf) capacitor in parallel to C50. The C50 is the 1uf capacitor that feeds the detector signal to the audio pre-amp. Increasing this to 470uf, prolongs the 'switch on' time of the audio preamp just enough to not hear the TX-to-RX thump.
>
>can someone else too try this out?
>
>i call it a partial solution because it doesn't suppress the rx-to-tx pop (which is not as bad as the tx-to-rx pop).
>
>- f

q q
 

I tried the 470uF on my uBitx and yes it does suppress the TX --> RX thump quite well.

73
Bob
N1ETS

KD8CGH
 

Am I correct that the suggestion is to take a leaded 470 uf electrolytic capacitor and attach it over surface mount C50 with the + side facing the trace to R50?

Ashhar Farhan
 

yes the +ve goes towards the audio preamp side.
- f

On 10 Jan 2018 6:14 am, "KD8CGH" <rkayakr@...> wrote:
Am I correct that the suggestion is to take a leaded 470 uf electrolytic capacitor and attach it over surface mount C50 with the + side facing the trace to R50?

Mike Woods
 

Ashhar

I completed mod today and it worked on internal speaker of uBitx going from TX to RX.  Could still hear a brief squeal on transition when I plugged into an amplified speaker.

It’s an improvement so the capacitor stays (470uF).

Thanks for the tip, and 73

Mike ZL1AXG


On Wed, 10 Jan 2018 at 2:37 PM, Ashhar Farhan <farhanbox@...> wrote:
yes the +ve goes towards the audio preamp side.
- f

On 10 Jan 2018 6:14 am, "KD8CGH" <rkayakr@...> wrote:
Am I correct that the suggestion is to take a leaded 470 uf electrolytic capacitor and attach it over surface mount C50 with the + side facing the trace to R50?

MVS Sarma
 

Try to mount the external headphones Jack, insulating its bodyfrom ground.
 Ther place a 50 ohm resistor from ground to the ccommon of the jack, instead of directly grounding, it.
This method helps reduce damage to ears. Most radios dothe same.

All the best

Regards
MVS Sarma
 

On Wed, Jan 10, 2018 at 10:37 AM, Mike Woods <mhwoods@...> wrote:
Ashhar

I completed mod today and it worked on internal speaker of uBitx going from TX to RX.  Could still hear a brief squeal on transition when I plugged into an amplified speaker.

It’s an improvement so the capacitor stays (470uF).

Thanks for the tip, and 73

Mike ZL1AXG

On Wed, 10 Jan 2018 at 2:37 PM, Ashhar Farhan <farhanbox@...> wrote:
yes the +ve goes towards the audio preamp side.
- f

On 10 Jan 2018 6:14 am, "KD8CGH" <rkayakr@...> wrote:
Am I correct that the suggestion is to take a leaded 470 uf electrolytic capacitor and attach it over surface mount C50 with the + side facing the trace to R50?


ve7hcw@...
 

the main problem of the TX pop problem is the turning on and off  the Rx and Tx preamps causing the c50 and c63 to charge and discharge resulting in a low frequency pulse along with power supply noises. By keeping the  preamps on instead of being switched will eliminate the problems and use a pair of MOSFET to switch in the Rx and Tx audio passively by  changing the resistance in the MOSFETS will not generate pulses and noise.

Ashhar Farhan
 

using the mosfets will not change the spike. the transients are generating in the modulator diodes. take them out and it goes away.

- f

On 15 Jan 2018 6:08 am, "ve7hcw via Groups.Io" <ve7hcw=yahoo.ca@groups.io> wrote:
the main problem of the TX pop problem is the turning on and off  the Rx and Tx preamps causing the c50 and c63 to charge and discharge resulting in a low frequency pulse along with power supply noises. By keeping the  preamps on instead of being switched will eliminate the problems and use a pair of MOSFET to switch in the Rx and Tx audio passively by  changing the resistance in the MOSFETS will not generate pulses and noise.


ve7hcw@...
 

It's the current charging and discharging of C50 and c63 cause the modulator diodes to conduct whereas after initial stabilization of the capacitor charges  by keeping the mic preamp and receiver preamp  powered up by connecting directly to the power supply. Then the AC audio  is switched in by the MOSFETs  which has not change in DC will not create pulse pop. Last year I had a similar problem with a commercial product I build for  PA system with mike pops on/off because of  charging and discharging capacitors. I did the same and leave the mike circuit active but use a MOSFET to isolate the AC sound when OFF and switch ON by powering the MOSFET. No DC was switched by the MOSFET  only AC result in no clicks and pops.
    The 100k resistors in the drain side of the MOSFET is to bleed the charge and stablilize the steady charge on the capacitors. The other 100k on the MOSFET source side is to make sure the gate has a charge reference to make the MOSFET work doing switching.
 W

Ryhor Harbacheuski
 

in my hands even simper elegant circuit borrowed from QCX transceiver
takes care of the pop completely, see attached.
with 300K R and 440nf C timing is just right to keep BS170 open long
enough when switched back to RX.
AF CW self control tone gets weaker with this, however in my uBITX
board 10K R253 was geniusly replaced by 1K, so this
makes CW tone loud enough with this mod.
Greg W3NW


On Mon, Jan 15, 2018 at 8:32 AM, ve7hcw via Groups.Io
<ve7hcw=yahoo.ca@groups.io> wrote:
It's the current charging and discharging of C50 and c63 cause the modulator
diodes to conduct whereas after initial stabilization of the capacitor
charges by keeping the mic preamp and receiver preamp powered up by
connecting directly to the power supply. Then the AC audio is switched in
by the MOSFETs which has not change in DC will not create pulse pop. Last
year I had a similar problem with a commercial product I build for PA
system with mike pops on/off because of charging and discharging
capacitors. I did the same and leave the mike circuit active but use a
MOSFET to isolate the AC sound when OFF and switch ON by powering the
MOSFET. No DC was switched by the MOSFET only AC result in no clicks and
pops.
The 100k resistors in the drain side of the MOSFET is to bleed the
charge and stablilize the steady charge on the capacitors. The other 100k on
the MOSFET source side is to make sure the gate has a charge reference to
make the MOSFET work doing switching.
W

Nick VK4PP
 

Hi, would you be able to provide a schematic for this Mod please?