1. BITX20@groups.io
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Re: si5351 crosstalk #radiuno

Miles Silk <miles.silk@...>
 


On Sep 8, 2018 1:30 PM, "Gordon Gibby" <ggibby@...> wrote:
Unfortunately in the uBitx design all three clocks are feeding impedance is a good bit lower than the maximum one suggested.  

These outputs are CMOS outputs, are they not?

So they have active device up and active  device down, and the impedance is constantly changing as one device turns on and the other turns off.  It’s a digital system made out of analog parts.

So sure, running through a 50 ohm transmission line you would get some reflections, to a higher than 50 ohm load, but the line lengths  so tiny fractions of a wavelength here that probably doesn’t make that much difference.   

I’m not familiar with ground bounce, but because of these low impedance loadings, signals are getting coupled  from one output to the other.




On Sep 8, 2018, at 12:26, Arv Evans <arvid.evans@...> wrote:

Allison

Thanks.  You may have just saved me from overloading some of a recent purchase of Si5351a devices.
I too was under the impression that 50 ohms meant 50 ohms, instead of "use a 50 ohm line and a much
higher termination".  That though does raise a question regarding 50 ohm line with significantly higher
impedance termination at the extreme upper frequency limits?  Might this cause higher reflected signal
on that 50 ohm line?  Maybe it doesn't matter?

Arv
_._


On Sat, Sep 8, 2018 at 10:03 AM RCBoatGuy via Groups.Io <ijnfan-HamRadio=yahoo.com@groups.io> wrote:

Allison,

I'm afraid if you tested the way you described in your original post on this thread, you weren't testing for crosstalk.  I believe what you measured wasn't cross-talk at all, but rather ground bounce due to current starvation of the Si5351 output buffers.

I've attached the Si5351 datasheet.  On page 5, Silicon Labs gives the following specs:

Vddox, output buffer voltage => 3 ranges, 1.8V +/- 0.9V (5%), 2.5V +/- 0.25V (10%), and 3.3V +/- 0.3V (9.09%).   The Raduino uses a 3.3V supply for Vddox.

Iddox -  output buffer supply current per output => 2.2mA typical, 5.6mA max

Zo, output impedence @ 3.3V => 50 ohms

Note this is output impedence, which is very misleading.  The spec is not saying to use an output load of 50 ohms (Rload).  It is saying we need to drive thru a 50-ohm impedence to reach the destination Rload.  So we need to calculate the mimimum output load (Rload) that the output driver can drive.

Rload = Vddox/Iddox = 3.3 / 0.0056 = 589.3 ohms.  This is the minimum load the output can drive, as it gives the maximum allowed output supply current.  Exceed this spec and you enter current starvation on the power supply to the output buffer.

You stated that you used both a 50-ohm load (not impedence) and a 25-ohm load (not impedence) for your cross-talk testing.

With a 50-ohm load, Iddox = V/R = 3.3 / 50 = 66mA, which is more than 10x the maximum allowed output buffer supply current.

With a 25-ohm load, you subjected the part to 132mA Iddox! 

In both cases, the output buffers are so power starved that the chip internally can't supply enough Vddox to control the output buffers.  The result is ground bounce on all the outputs, not cross-talk.  This is typical behavior for digital chip output drivers whose output specs are violated in such a manner.  It also explains why you didn't see as much signal on the Si5351 outputs as you expected. 


The Zo spec was meant to say that the chip was designed to drive thru a 50-ohm impedence (either a 50-ohm coax or a 50-ohm micro-strip line on a PCB) to its load (Rload), not that you could use a 50-ohm or 25-ohm termination as the Rload.  An example of this appears on page 22 of the Si5351 datasheet.  Here the datasheet describes using the part to drive 2 clock outputs with 180 degree phase difference, but the example circuit shows driving the Si5341 clock outputs thru a 50-ohm coax to a voltage divider for the receiving circuit that presents an Rload of 511 ohms + 240 ohms = 751 ohms to each  Si5351 output buffer.  This gives an Iddox = 3.3 / 751 = 4.4mA, well within the 5.6mA max Iddox spec.

I suggest you repeat your cross-talk tests using an appropriate Rload value at the end of a 50-ohm line for each clock output and see how much cross-talk you see.

73,

Carl,  K0MWC
Re: si5351 crosstalk #radiuno

Gordon Gibby <ggibby@...>
 

Unfortunately in the uBitx design all three clocks are feeding impedance is a good bit lower than the maximum one suggested.  

These outputs are CMOS outputs, are they not?

So they have active device up and active  device down, and the impedance is constantly changing as one device turns on and the other turns off.  It’s a digital system made out of analog parts.

So sure, running through a 50 ohm transmission line you would get some reflections, to a higher than 50 ohm load, but the line lengths  so tiny fractions of a wavelength here that probably doesn’t make that much difference.   

I’m not familiar with ground bounce, but because of these low impedance loadings, signals are getting coupled  from one output to the other.

image1.png


On Sep 8, 2018, at 12:26, Arv Evans <arvid.evans@...> wrote:

Allison

Thanks.  You may have just saved me from overloading some of a recent purchase of Si5351a devices.
I too was under the impression that 50 ohms meant 50 ohms, instead of "use a 50 ohm line and a much
higher termination".  That though does raise a question regarding 50 ohm line with significantly higher
impedance termination at the extreme upper frequency limits?  Might this cause higher reflected signal
on that 50 ohm line?  Maybe it doesn't matter?

Arv
_._


On Sat, Sep 8, 2018 at 10:03 AM RCBoatGuy via Groups.Io <ijnfan-HamRadio=yahoo.com@groups.io> wrote:

Allison,

I'm afraid if you tested the way you described in your original post on this thread, you weren't testing for crosstalk.  I believe what you measured wasn't cross-talk at all, but rather ground bounce due to current starvation of the Si5351 output buffers.

I've attached the Si5351 datasheet.  On page 5, Silicon Labs gives the following specs:

Vddox, output buffer voltage => 3 ranges, 1.8V +/- 0.9V (5%), 2.5V +/- 0.25V (10%), and 3.3V +/- 0.3V (9.09%).   The Raduino uses a 3.3V supply for Vddox.

Iddox -  output buffer supply current per output => 2.2mA typical, 5.6mA max

Zo, output impedence @ 3.3V => 50 ohms

Note this is output impedence, which is very misleading.  The spec is not saying to use an output load of 50 ohms (Rload).  It is saying we need to drive thru a 50-ohm impedence to reach the destination Rload.  So we need to calculate the mimimum output load (Rload) that the output driver can drive.

Rload = Vddox/Iddox = 3.3 / 0.0056 = 589.3 ohms.  This is the minimum load the output can drive, as it gives the maximum allowed output supply current.  Exceed this spec and you enter current starvation on the power supply to the output buffer.

You stated that you used both a 50-ohm load (not impedence) and a 25-ohm load (not impedence) for your cross-talk testing.

With a 50-ohm load, Iddox = V/R = 3.3 / 50 = 66mA, which is more than 10x the maximum allowed output buffer supply current.

With a 25-ohm load, you subjected the part to 132mA Iddox! 

In both cases, the output buffers are so power starved that the chip internally can't supply enough Vddox to control the output buffers.  The result is ground bounce on all the outputs, not cross-talk.  This is typical behavior for digital chip output drivers whose output specs are violated in such a manner.  It also explains why you didn't see as much signal on the Si5351 outputs as you expected. 


The Zo spec was meant to say that the chip was designed to drive thru a 50-ohm impedence (either a 50-ohm coax or a 50-ohm micro-strip line on a PCB) to its load (Rload), not that you could use a 50-ohm or 25-ohm termination as the Rload.  An example of this appears on page 22 of the Si5351 datasheet.  Here the datasheet describes using the part to drive 2 clock outputs with 180 degree phase difference, but the example circuit shows driving the Si5341 clock outputs thru a 50-ohm coax to a voltage divider for the receiving circuit that presents an Rload of 511 ohms + 240 ohms = 751 ohms to each  Si5351 output buffer.  This gives an Iddox = 3.3 / 751 = 4.4mA, well within the 5.6mA max Iddox spec.

I suggest you repeat your cross-talk tests using an appropriate Rload value at the end of a 50-ohm line for each clock output and see how much cross-talk you see.

73,

Carl,  K0MWC
Re: Simple spur fix

Jerry Gaffke
 

Warren,

That IMD could be in the IF amps (Too much gain for 2n3904's at 45mhz?  Mixer overload?)
or in the power amp.  If IMD gets worse when RV1 is cranked up, that would suggest it's in the PA.
If it's in the 45mhz IF, the new filter will help but is too wide to clean up the immediately adjacent channels.
Seems it should be straightforward to clean up this IMD on v5, but may take lots of small hacks to 
clean up existing rigs.  Fortunately, at 5 or 10 watts out it seems to not be just too bothersome as
I don't recall any reports of trouble in the forum.  But it should be fixed on v5, and v3,v4
should not be used with an external high powered linear.

Jerry


On Sat, Sep 8, 2018 at 09:30 AM, Warren Allgyer wrote:
Before the mod the radio showed terrible IMD at any input level higher that about 25 mV and, at that level, the radio produced less than 2 watts. If it turns out the filter is a 'magic bullet' and the radio can actually sustain this level of input with acceptable IMD, then the input audio stages need more gain.
Re: Simple spur fix

George
 

Sorry: +/- 7.5 kHz 3 dB
Re: Simple spur fix

George
 

Hi all, good job. 
1.The output  of 45-2pole in C22 position needs transformer 50/600 and small C <10 pF- it will have close to flat responce.
2.As I wrote befor as main filter I used SMD: DSF753SDF 4POLE marked as D45015GQ +/-7.5 dB. I put it on board on the back side and used transformers 4t/10t in small binocular 2402.
Best to all George.
Re: Right-sided relay harmonic attempted fix for v3/4 ubitx

Jerry Gaffke
 

All three relays are de-energized during received, so contacts are as shown in the uBitx schematic
with a path through the 10m filter.
At the start of transmit, the following routine gets called (file ubitx_20.ino of the stock HFSignals firmware)
Should be readable enough even if you've never seen C code before.

Jerry


#########################################
void setTXFilters(unsigned long freq){
 
  if (freq > 21000000L){  // the default filter is with 35 MHz cut-off
    digitalWrite(TX_LPF_A, 0);
    digitalWrite(TX_LPF_B, 0);
    digitalWrite(TX_LPF_C, 0);
  }
  else if (freq >= 14000000L){ //thrown the KT1 relay on, the 30 MHz LPF is bypassed and the 14-18 MHz LPF is allowd to go through
    digitalWrite(TX_LPF_A, 1);
    digitalWrite(TX_LPF_B, 0);
    digitalWrite(TX_LPF_C, 0);
  }
  else if (freq > 7000000L){
    digitalWrite(TX_LPF_A, 1);
    digitalWrite(TX_LPF_B, 1);
    digitalWrite(TX_LPF_C, 0);
  }
  else {
    digitalWrite(TX_LPF_A, 1);
    digitalWrite(TX_LPF_B, 1);
    digitalWrite(TX_LPF_C, 1);
  }
}
##################################


On Sat, Sep 8, 2018 at 09:33 AM, Brent Seres/ VE3CUS wrote:
Just a question, and I apologize if it's been covered before.
Could someone tell me the LPF relay sequencing for the existing ubitx configuration? What relays are energized for what frequency ranges? I want to figure out the logic for building an off board LPF solution using a cleaner layout and switching (ie..1 relay path only per filter...or separate relays at the input and output of each filter....basically a more symetrical, conventional layout.

Thanks for everyone's help

Brent
Re: Right-sided relay harmonic attempted fix for v3/4 ubitx

Brent Seres/ VE3CUS
 

Just a question, and I apologize if it's been covered before.
Could someone tell me the LPF relay sequencing for the existing ubitx configuration? What relays are energized for what frequency ranges? I want to figure out the logic for building an off board LPF solution using a cleaner layout and switching (ie..1 relay path only per filter...or separate relays at the input and output of each filter....basically a more symetrical, conventional layout.

Thanks for everyone's help

Brent
Re: Simple spur fix

Warren Allgyer <allgyer@...>
 

More data...... Comparison of CW power out with SSB power out using the added 45 MHz filter:



The chart was made by adjusting RV1 to maximum key down CW power, and then keying PTT with an input tone at the specified level. There are a couple of caveats here:
1) 120 mVrms is far above the audio level that caused unacceptable IMD before the filter mod. IMD must be checked and the audio levels adjusted to make it acceptable.
2) 120 mVrms is also far above the output level of most microphones, at least without shouting. If IMD is bad at this level then the audio level must be reduced. Before the mod the radio showed terrible IMD at any input level higher that about 25 mV and, at that level, the radio produced less than 2 watts. If it turns out the filter is a 'magic bullet' and the radio can actually sustain this level of input with acceptable IMD, then the input audio stages need more gain.

Kees, I have no plan to change out the original filter at this point. It is pretty moot until we know what the IMD is.

WA8TOD
Re: si5351 crosstalk #radiuno

Arv Evans
 

Allison

Thanks.  You may have just saved me from overloading some of a recent purchase of Si5351a devices.
I too was under the impression that 50 ohms meant 50 ohms, instead of "use a 50 ohm line and a much
higher termination".  That though does raise a question regarding 50 ohm line with significantly higher
impedance termination at the extreme upper frequency limits?  Might this cause higher reflected signal
on that 50 ohm line?  Maybe it doesn't matter?

Arv
_._


On Sat, Sep 8, 2018 at 10:03 AM RCBoatGuy via Groups.Io <ijnfan-HamRadio=yahoo.com@groups.io> wrote:

Allison,

I'm afraid if you tested the way you described in your original post on this thread, you weren't testing for crosstalk.  I believe what you measured wasn't cross-talk at all, but rather ground bounce due to current starvation of the Si5351 output buffers.

I've attached the Si5351 datasheet.  On page 5, Silicon Labs gives the following specs:

Vddox, output buffer voltage => 3 ranges, 1.8V +/- 0.9V (5%), 2.5V +/- 0.25V (10%), and 3.3V +/- 0.3V (9.09%).   The Raduino uses a 3.3V supply for Vddox.

Iddox -  output buffer supply current per output => 2.2mA typical, 5.6mA max

Zo, output impedence @ 3.3V => 50 ohms

Note this is output impedence, which is very misleading.  The spec is not saying to use an output load of 50 ohms (Rload).  It is saying we need to drive thru a 50-ohm impedence to reach the destination Rload.  So we need to calculate the mimimum output load (Rload) that the output driver can drive.

Rload = Vddox/Iddox = 3.3 / 0.0056 = 589.3 ohms.  This is the minimum load the output can drive, as it gives the maximum allowed output supply current.  Exceed this spec and you enter current starvation on the power supply to the output buffer.

You stated that you used both a 50-ohm load (not impedence) and a 25-ohm load (not impedence) for your cross-talk testing.

With a 50-ohm load, Iddox = V/R = 3.3 / 50 = 66mA, which is more than 10x the maximum allowed output buffer supply current.

With a 25-ohm load, you subjected the part to 132mA Iddox! 

In both cases, the output buffers are so power starved that the chip internally can't supply enough Vddox to control the output buffers.  The result is ground bounce on all the outputs, not cross-talk.  This is typical behavior for digital chip output drivers whose output specs are violated in such a manner.  It also explains why you didn't see as much signal on the Si5351 outputs as you expected. 


The Zo spec was meant to say that the chip was designed to drive thru a 50-ohm impedence (either a 50-ohm coax or a 50-ohm micro-strip line on a PCB) to its load (Rload), not that you could use a 50-ohm or 25-ohm termination as the Rload.  An example of this appears on page 22 of the Si5351 datasheet.  Here the datasheet describes using the part to drive 2 clock outputs with 180 degree phase difference, but the example circuit shows driving the Si5341 clock outputs thru a 50-ohm coax to a voltage divider for the receiving circuit that presents an Rload of 511 ohms + 240 ohms = 751 ohms to each  Si5351 output buffer.  This gives an Iddox = 3.3 / 751 = 4.4mA, well within the 5.6mA max Iddox spec.

I suggest you repeat your cross-talk tests using an appropriate Rload value at the end of a 50-ohm line for each clock output and see how much cross-talk you see.

73,

Carl,  K0MWC
Re: si5351 crosstalk #radiuno

jim
 

Indeed THIS ....Explains why I'm seeing 0.6 volts (p-p) at R103  on the 45 Mhz mixer thingie

Jim


On Saturday, September 8, 2018, 9:03:33 AM PDT, RCBoatGuy via Groups.Io <ijnfan-HamRadio@...> wrote:


Allison,

I'm afraid if you tested the way you described in your original post on this thread, you weren't testing for crosstalk.  I believe what you measured wasn't cross-talk at all, but rather ground bounce due to current starvation of the Si5351 output buffers.

I've attached the Si5351 datasheet.  On page 5, Silicon Labs gives the following specs:

Vddox, output buffer voltage => 3 ranges, 1.8V +/- 0.9V (5%), 2.5V +/- 0.25V (10%), and 3.3V +/- 0.3V (9.09%).   The Raduino uses a 3.3V supply for Vddox.

Iddox -  output buffer supply current per output => 2.2mA typical, 5.6mA max

Zo, output impedence @ 3.3V => 50 ohms

Note this is output impedence, which is very misleading.  The spec is not saying to use an output load of 50 ohms (Rload).  It is saying we need to drive thru a 50-ohm impedence to reach the destination Rload.  So we need to calculate the mimimum output load (Rload) that the output driver can drive.

Rload = Vddox/Iddox = 3.3 / 0.0056 = 589.3 ohms.  This is the minimum load the output can drive, as it gives the maximum allowed output supply current.  Exceed this spec and you enter current starvation on the power supply to the output buffer.

You stated that you used both a 50-ohm load (not impedence) and a 25-ohm load (not impedence) for your cross-talk testing.

With a 50-ohm load, Iddox = V/R = 3.3 / 50 = 66mA, which is more than 10x the maximum allowed output buffer supply current.

With a 25-ohm load, you subjected the part to 132mA Iddox! 

In both cases, the output buffers are so power starved that the chip internally can't supply enough Vddox to control the output buffers.  The result is ground bounce on all the outputs, not cross-talk.  This is typical behavior for digital chip output drivers whose output specs are violated in such a manner.  It also explains why you didn't see as much signal on the Si5351 outputs as you expected. 


The Zo spec was meant to say that the chip was designed to drive thru a 50-ohm impedence (either a 50-ohm coax or a 50-ohm micro-strip line on a PCB) to its load (Rload), not that you could use a 50-ohm or 25-ohm termination as the Rload.  An example of this appears on page 22 of the Si5351 datasheet.  Here the datasheet describes using the part to drive 2 clock outputs with 180 degree phase difference, but the example circuit shows driving the Si5341 clock outputs thru a 50-ohm coax to a voltage divider for the receiving circuit that presents an Rload of 511 ohms + 240 ohms = 751 ohms to each  Si5351 output buffer.  This gives an Iddox = 3.3 / 751 = 4.4mA, well within the 5.6mA max Iddox spec.

I suggest you repeat your cross-talk tests using an appropriate Rload value at the end of a 50-ohm line for each clock output and see how much cross-talk you see.

73,

Carl,  K0MWC
Re: si5351 crosstalk #radiuno

RCBoatGuy
 

Allison,

I'm afraid if you tested the way you described in your original post on this thread, you weren't testing for crosstalk.  I believe what you measured wasn't cross-talk at all, but rather ground bounce due to current starvation of the Si5351 output buffers.

I've attached the Si5351 datasheet.  On page 5, Silicon Labs gives the following specs:

Vddox, output buffer voltage => 3 ranges, 1.8V +/- 0.9V (5%), 2.5V +/- 0.25V (10%), and 3.3V +/- 0.3V (9.09%).   The Raduino uses a 3.3V supply for Vddox.

Iddox -  output buffer supply current per output => 2.2mA typical, 5.6mA max

Zo, output impedence @ 3.3V => 50 ohms

Note this is output impedence, which is very misleading.  The spec is not saying to use an output load of 50 ohms (Rload).  It is saying we need to drive thru a 50-ohm impedence to reach the destination Rload.  So we need to calculate the mimimum output load (Rload) that the output driver can drive.

Rload = Vddox/Iddox = 3.3 / 0.0056 = 589.3 ohms.  This is the minimum load the output can drive, as it gives the maximum allowed output supply current.  Exceed this spec and you enter current starvation on the power supply to the output buffer.

You stated that you used both a 50-ohm load (not impedence) and a 25-ohm load (not impedence) for your cross-talk testing.

With a 50-ohm load, Iddox = V/R = 3.3 / 50 = 66mA, which is more than 10x the maximum allowed output buffer supply current.

With a 25-ohm load, you subjected the part to 132mA Iddox! 

In both cases, the output buffers are so power starved that the chip internally can't supply enough Vddox to control the output buffers.  The result is ground bounce on all the outputs, not cross-talk.  This is typical behavior for digital chip output drivers whose output specs are violated in such a manner.  It also explains why you didn't see as much signal on the Si5351 outputs as you expected. 


The Zo spec was meant to say that the chip was designed to drive thru a 50-ohm impedence (either a 50-ohm coax or a 50-ohm micro-strip line on a PCB) to its load (Rload), not that you could use a 50-ohm or 25-ohm termination as the Rload.  An example of this appears on page 22 of the Si5351 datasheet.  Here the datasheet describes using the part to drive 2 clock outputs with 180 degree phase difference, but the example circuit shows driving the Si5341 clock outputs thru a 50-ohm coax to a voltage divider for the receiving circuit that presents an Rload of 511 ohms + 240 ohms = 751 ohms to each  Si5351 output buffer.  This gives an Iddox = 3.3 / 751 = 4.4mA, well within the 5.6mA max Iddox spec.

I suggest you repeat your cross-talk tests using an appropriate Rload value at the end of a 50-ohm line for each clock output and see how much cross-talk you see.

73,

Carl,  K0MWC


PDF
Si5351_B.pdf

Re: Baofeng microphone mod for BITX

nemfield <nemfield@...>
 

Hi;
The paragraph description on modifying the Beofeng mic connections to the uBITX is vague. Can a schematic please posted a schematic diagram as to how the mods actually are done. 'Thank you '73 
Re: Simple spur fix

Kees T
 

Great data Warren. Are you also going to replace the other 45MHz filter with the matching one you received ? Sure shows what all working together can accomplish........ Good Soup for everyone. 

73 Kees K5BCQ
Re: Simple spur fix

Kees T
 

Raj,

Doesn't leaving R27 in place give you better impedance matching ? Did you try cutting the trace in between and just putting the filter between C22 and R27 ?

73 Kees K5BCQ 
Re: Have to adjust master calibration on power up - does not save

robert_kross@...
 

Sorry Bill.  I didn't mention that I do set it with the PTT switch, then exit the setup mode.  This set has exhibited this symptom since day 1.  I thought changing out the Arduino would have helped.  Before that I was adding caps to the reset.  Thanks anyway.

Bob
Re: Have to adjust master calibration on power up - does not save

Bill Cromwell
 

Hi Bob,

I do not see the part where you save the setting after you have set it. Press the push to talk button to save it while you are still in the calibration mode. Otherwise it does exactly as you describe and will be back to the original next time you turn it on.

Before you leave the calibration and after you have it where you want it, press push to talk. Not your CW key. Not later after you have left the calibration mode. Before you leave calibration.

73,

Bill KU8H

On 09/08/2018 09:15 AM, robert_kross via Groups.Io wrote:
When the set is first powered on, there is a tinny, high frequency
audio. When you enter the setup mode and enter calibration, pressing
the menu button, the audio is normal tone. Then I adjust the calibration
level and set it, then exit, all is well. Until I turn it off. I have
tried other software with no luck. So I re-loaded the original factory
software. I thought with all the issues you have seen with the various
ubitx versions that you people may have come across it. Thanks anyway.

Bob
--
bark less - wag more
Re: Have to adjust master calibration on power up - does not save

robert_kross@...
 

When the set is first powered on, there is a tinny, high frequency audio.  When you enter the setup mode and enter calibration, pressing the menu button, the audio is normal tone. Then I adjust the calibration level and set it, then exit, all is well.  Until I turn it off. I have tried other software with no luck. So I re-loaded the original factory software. I thought with all the issues you have seen with the various ubitx versions that you people may have come across it. Thanks anyway.

Bob
Re: Simple spur fix

Gordon Gibby <ggibby@...>
 

Wow!  Very nice work, Warren!!!!  Extremely helpful for many, many people!!

Cheers!
Gordon



On Sep 8, 2018, at 07:13, Warren Allgyer <allgyer@...> wrote:

And finally, finally (for real this time) a pic of the filter in place. The center ground lead of the filter is not visible but it bend under the case and picks up the R13 ground.

<Screen Shot 2018_09_08 at 7.10.48 AM.png>

Re: Simple spur fix

Raj vu2zap
 

Warren,

Try with both matched filters.. that should get further reduction.
I don't have a pair right now..

Raj


At 08-09-18, you wrote:
And finally, finally (for real this time) a pic of the filter in place. The center ground lead of the filter is not visible but it bend under the case and picks up the R13 ground.

[]   Content-Id: <attach_0_155268610C2228C5_22741@groups.io>
X-Attachment-Id: attach_0_155268610C2228C5_22741@groups.io
Content-Type: image/png; name="Screen Shot 2018_09_08 at 7.10.48 AM.png"
Content-Disposition: inline; filename="Screen Shot 2018_09_08 at 7.10.48 AM.png"
Re: New Website ubitx.com

freefuel@...
 

Hi Sunil,

Transformer isolation is VERY useful for eliminating ground loops and Galvanic isolation for the audio circuits. should you design a revised digital interface board provisions for installing audio isolation transformers would be much appreciated.  

-Justin N2TOH 
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