Topics

Noise Burst #bitx40

John
 

Any simple cure for the noise burst when you key the mic? There is a burst of noise from the speaker as well as a transmitted noise burst.
I see some suggest that the audio preamp  Q16 stays active after change-over to transmit due to residual charge in the supply line filter capacitor.
Maybe there needs to be some sequencing of the Tx/Rx change over relays so the audio and antenna relay switches before the Tx/Rx power supply relay.
Any suggestions?
--
John VK6JAH

Nick VK4PP
 

John
 

Thanks Nick.

I will try that fix for the audio amp noise burst by muting the LM386 via pin7.

Seems that there are two problems here.
One is the audio noise burst which your fix addresses.
The other is a burst of RF noise as charging capacitors in the microphone amp unbalance the balanced mixer at the start of a transmission.

I have looked through the Wiki and there are lots of discussions about curing the audio burst, there is not much about fixing the RF noise burst.

I have been thinking about putting a FET in the line from the mic amp to the balanced mixer to act as an isolating switch while the mic amp settles down. Use an RC time constant on the gate to delay turn on. Use some steering diodes so that the fet is on via the Rx line during receive, goes off when the Rx/Tx changeover occurs and comes on after a delay via the Tx line when in transmit.

-Cheers-
John VK6JAH

 

John et al : 

The RF burst on PTT closure, on the BITX40, has been addressed by Allard (PE1NWL) in his Raduino Code.  

https://github.com/amunters/bitx40

His approach is to shut down the CLK output on the SI5351 for 50 mS on PTT closure and wait for things to settle before re-enabling it to allow TX.  

There is also a simple hardware mod that can be used to reduce this burst from 50 mS to less than 20 mS so that the delay time can be reduced in the code.
The mod is to change C124 from 47uF to 4.7 uF. C124 is near Q12 (mic input).  See message #29101 in this group for the original discussion on this. 

Cheers

Michael VE3WMB 

 

Here is full description (from message #27395) of what is happening : 

"When the radio goes into TX, that cap has to charge up via R127 -- which takes a LONG time.  During that time, Q12 is also powering up and C122 has been sitting at zero volts, so it starts charging as well.  This is the response of the Microphone Amplifier to the rising edge of the TX signal -- and the net result is that the Balanced Mixer (T4/D15/D16) is knocked out of balance until the amplifier stabilizes.  The result of that is a spurious RF transmission that looks like the one I have attached as a file.  The RF rises almost immediately to about 5-8 watts, within 5 ms drops down to about 3 watts, builds back up to 5-8 watts in another 5 ms, then slowly decays over a period of 60 ms decays down to close to zero.  (All of this observed with the PTT line held)."

The thread starts with message #27393.

Cheers

Michael VE3WMB 

Jerry Gaffke
 

Allard's fix to the Bitx40 carrier burst using a delay in the code is described here:
    https://groups.io/g/BITX20/message/33756
    https://groups.io/g/BITX20/message/34189


There is also Raj's fix, strictly hardware, no code:
    https://groups.io/g/BITX20/message/33707
    https://groups.io/g/BITX20/message/33742

Those are all in the same thread.
The rest of the thread is worth browsing as well.

Jerry, KE7ER


On Tue, Jun 26, 2018 at 05:35 am, Michael Babineau wrote:
John et al : 

The RF burst on PTT closure, on the BITX40, has been addressed by Allard (PE1NWL) in his Raduino Code.  

https://github.com/amunters/bitx40

His approach is to shut down the CLK output on the SI5351 for 50 mS on PTT closure and wait for things to settle before re-enabling it to allow TX.  

There is also a simple hardware mod that can be used to reduce this burst from 50 mS to less than 20 mS so that the delay time can be reduced in the code.
The mod is to change C124 from 47uF to 4.7 uF. C124 is near Q12 (mic input).  See message #29101 in this group for the original discussion on this. 

Cheers

Michael VE3WMB 

Allard PE1NWL
 

Yes, raduino_v1.27.7 fixes this problem.
Download it from https://github.com/amunters/bitx40
and install the related (minimal) mods (see instructions included).

73 Allard PE1NWL

On Tue, June 26, 2018 17:32, Jerry Gaffke via Groups.Io wrote:
Allard's fix to the Bitx40 carrier burst using a delay in the code is
described here:
    https://groups.io/g/BITX20/message/33756
    https://groups.io/g/BITX20/message/34189

There is also Raj's fix, strictly hardware, no code:
    https://groups.io/g/BITX20/message/33707
    https://groups.io/g/BITX20/message/33742

Those are all in the same thread.
The rest of the thread is worth browsing as well.

Jerry, KE7ER

On Tue, Jun 26, 2018 at 05:35 am, Michael Babineau wrote:


John et al : 

The RF burst on PTT closure, on the BITX40, has been addressed by Allard
(PE1NWL) in his Raduino Code.  

https://github.com/amunters/bitx40

His approach is to shut down the CLK output on the SI5351 for 50 mS on
PTT
closure and wait for things to settle before re-enabling it to allow
TX.  


There is also a simple hardware mod that can be used to reduce this
burst
from 50 mS to less than 20 mS so that the delay time can be reduced in
the
code.
The mod is to change C124 from 47uF to 4.7 uF. C124 is near Q12 (mic
input).  See message #29101 in this group for the original discussion
on
this. 

Cheers

Michael VE3WMB


John
 

Thanks for all the replies.

I will do the raduino update as well as the mod to mute the LM386.
Should fix the problem.

Great to have all the support.
Cheers
--
John VK6JAH

John
 

Installed raduino v1.27.1 and it works fine. No RF noise burst on transmit. Great piece of software Allard. 
Now looking to do more hacks of the hardware to take full advantage of the software features.
73
--
John VK6JAH

Allard PE1NWL
 

Thanks John,
glad to hear you like the software.

73 Allard PE1NWL

On Fri, June 29, 2018 06:21, jah12@... wrote:
Installed raduino v1.27.1 and it works fine. No RF noise burst on
transmit. Great piece of software Allard. 
Now looking to do more hacks of the hardware to take full advantage of the
software features.
73
--
John VK6JAH

John
 

Hi Allard
Went to add a Tune button to my BitX40  Raduino but cannot get it to work.
As suggested, added a push button in series with a 1K resistor between pin A1 on connector P1 to ground, as well as a 4K7 resistor between the hot side of C107 at the balance mixer to pin D6 on connector P3, but no carrier output for tuning when button pressed while in transmit.
Rig works fine transmitting ssb.
Looking at my BitX40v3 board (dated 2016) I see that there are no diodes D15 and D16 in place and no balance pot R105 in place. I wonder if I have an upgraded board that has had changes made, and the Tune wire from D6 to C107 needs to attached to another point on the BitX board?
Also D6 remains Low (0v) at all times. Is there some lines in software that needs to be 'Uncommented" or altered to get D6 to toggle between Rx andTx?
Regards
--
John VK6JAH

John
 

Sorry Allard.
Figured it out now.
I did not have the BitX in CW mode via the Function push button.
All works now!
Cheers
--
John VK6JAH

Allard PE1NWL
 

If you set semiQSK to ON (in the SETTINGS menu, CW params), then the radio
will automatically switch to CW mode as soon as the CW key (or tune
button) is pressed.
To return to SSB mode, just press the PTT switch on the mic.

73 Allard PE1NWL

On Sat, June 30, 2018 09:30, jah12@... wrote:
Sorry Allard.
Figured it out now.
I did not have the BitX in CW mode via the Function push button.
All works now!
Cheers
--
John VK6JAH



John
 

Thanks Allard, I will check that out.
73
--
John VK6JAH