dummy load to attenuator mod #dummyload


KEN G4APB
 

Hi all,
I have come up with a simple addition to the QRPLabs dummy load that turns it into a 26dB attenuator. It only requires the addition of a 56ohm resistor and a bnc connector.
This can provide a very useful protection between the QCX-mini and a signal generator when testing. I have managed several times to accidentally get it transmitting a message at full 5 watts into my sig gen while actually attempting to change the receiver frequency.
I have used 18x1k resistors instead of 20 to maintain the 50 ohm match at both ends. this gives a resistive source and load of 55.55ohms. Two of the 1k resistors are paralleled to give 500 ohms series R. The Pi network created gives 26dG attenuation.

Careful use of unused pads has been used to create a neat package. See my photos.

73 Ken G4APB


KEN G4APB
 

sorry forgot the schematic..


KEN G4APB
 

and another side pic (could not load all at the same time...
R1 and R16 are NOT connected to the TOP pcb, but are joined mid-air and linked back to an unused PWR pad. The 56 ohm resistor used a ground and spare pad too.
73 Ken g4apb


wb4hio@...
 

Very nice, Ken.
Thanks for the info.
Reversely and for several years now, I've been using Bird model 10A-MFB-10 ( also -20 and -30 dB ) attenuators as combination dummy loads / attenuators.
72 / 73,
Bill, N4QA


KEN G4APB
 

For those of you that do not want to tie up a DVM with the dummy load to read the voltage when doing RF power measurements, I have used a QRPLabs Clock unit and the temperature probe inputs simply with potentiometers on the inputs to set a suitably scaled reading on the display.

See my attached photo showing bottom RH corner a reading of 24.6 volts corresponding to my QCX-mini output power of 5.6 Watts as measured on my ATU-100. The scaling I chose (0-50) will handle up to 20 watts corresponding to 50v input for 5 volts to the input to the clock temp probe input.

73 Ken G4APB


KEN G4APB
 

Note to Hans and potential builders;
3.4 Fit jumper W2-W3 on the top PCB
Fit a jumper wire at W2-W3 on the TOP PCB only.

But,  the picture shown is the bottom board with the bnc connector fitted!
Confused me for a while!!!!
73 Ken g4apb 


wa8yan.radio
 


Although Hans has a clear, written in red, statement about this. Capable, intelligent people can and do still get it backwards.  I know because I'm one of them.  A simple ohm meter check at the conclusion of the build and certainly before connecting to any transmitting device, would be to check for 50 ohms across the BNC output.

Perhaps Hans can add this to the instructions.... in spite of it's obvious nature.

Once I got it right, and after an embarrassing re-read of the red letter warning, I now have a FB 20W dummy load.... I can even use on my antique HW-8.  

Just sayin'...........

Phil WA8YAN


Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: "KEN G4APB via groups.io" <lfoofui.nbz42@...>
Date: 6/25/21 4:14 PM (GMT-05:00)
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] dummy load to attenuator mod #dummyload

Note to Hans and potential builders;
3.4 Fit jumper W2-W3 on the top PCB
Fit a jumper wire at W2-W3 on the TOP PCB only.

But,  the picture shown is the bottom board with the bnc connector fitted!
Confused me for a while!!!!
73 Ken g4apb 


wa8yan.radio
 

Perhaps it would also be better to say "do not install on the board the BNC connector is on" rather than top board, bottom board since top and bottom are relative to how you are holding it.  (I'm saying that was my error..... even though I'm sure it wasn't) HI HI.
73 Phil WA8YAN



Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: "KEN G4APB via groups.io" <lfoofui.nbz42@...>
Date: 6/25/21 4:14 PM (GMT-05:00)
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] dummy load to attenuator mod #dummyload

Note to Hans and potential builders;
3.4 Fit jumper W2-W3 on the top PCB
Fit a jumper wire at W2-W3 on the TOP PCB only.

But,  the picture shown is the bottom board with the bnc connector fitted!
Confused me for a while!!!!
73 Ken g4apb 


Arv Evans <arvid.evans@...>
 

In a lame attempt at humor, perhaps someone should point out
that it is a "dummy" load project.  8-/

Arv
_._


On Sun, Jun 27, 2021 at 1:10 PM wa8yan.radio via groups.io <wa8yan.radio=yahoo.com@groups.io> wrote:
Perhaps it would also be better to say "do not install on the board the BNC connector is on" rather than top board, bottom board since top and bottom are relative to how you are holding it.  (I'm saying that was my error..... even though I'm sure it wasn't) HI HI.
73 Phil WA8YAN



Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: "KEN G4APB via groups.io" <lfoofui.nbz42=ntlworld.com@groups.io>
Date: 6/25/21 4:14 PM (GMT-05:00)
Subject: Re: [QRPLabs] dummy load to attenuator mod #dummyload

Note to Hans and potential builders;
3.4 Fit jumper W2-W3 on the top PCB
Fit a jumper wire at W2-W3 on the TOP PCB only.

But,  the picture shown is the bottom board with the bnc connector fitted!
Confused me for a while!!!!
73 Ken g4apb 


wa8yan.radio
 

Yup

Lead dummy
WA8YAN



Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: Arv Evans <arvid.evans@...>
Date: 6/27/21 4:48 PM (GMT-05:00)
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] dummy load to attenuator mod #dummyload

In a lame attempt at humor, perhaps someone should point out
that it is a "dummy" load project.  8-/

Arv
_._


On Sun, Jun 27, 2021 at 1:10 PM wa8yan.radio via groups.io <wa8yan.radio=yahoo.com@groups.io> wrote:
Perhaps it would also be better to say "do not install on the board the BNC connector is on" rather than top board, bottom board since top and bottom are relative to how you are holding it.  (I'm saying that was my error..... even though I'm sure it wasn't) HI HI.
73 Phil WA8YAN



Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: "KEN G4APB via groups.io" <lfoofui.nbz42=ntlworld.com@groups.io>
Date: 6/25/21 4:14 PM (GMT-05:00)
Subject: Re: [QRPLabs] dummy load to attenuator mod #dummyload

Note to Hans and potential builders;
3.4 Fit jumper W2-W3 on the top PCB
Fit a jumper wire at W2-W3 on the TOP PCB only.

But,  the picture shown is the bottom board with the bnc connector fitted!
Confused me for a while!!!!
73 Ken g4apb 


 

Good suggestions WA8YAN. I got it right but had to keep double checking. That'd be an easy way to not get mixed up. However, I did once put a large component like a BNC or whatever, on the wrong side ox a board only to laugh at my mistake when I realized lol. So one might then also have the wrong "up and down" :) but yes, it is a dummy load project hehe

On 27 Jun 2021, at 21:32, wa8yan.radio via groups.io <wa8yan.radio@...> wrote:

Yup

Lead dummy
WA8YAN



Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: Arv Evans <arvid.evans@...> 
Date: 6/27/21 4:48 PM (GMT-05:00) 
Subject: Re: [QRPLabs] dummy load to attenuator mod #dummyload 

In a lame attempt at humor, perhaps someone should point out 
that it is a "dummy" load project.  8-/

Arv
_._


On Sun, Jun 27, 2021 at 1:10 PM wa8yan.radio via groups.io <wa8yan.radio=yahoo.com@groups.io> wrote:
Perhaps it would also be better to say "do not install on the board the BNC connector is on" rather than top board, bottom board since top and bottom are relative to how you are holding it.  (I'm saying that was my error..... even though I'm sure it wasn't) HI HI.
73 Phil WA8YAN



Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: "KEN G4APB via groups.io" <lfoofui.nbz42=ntlworld.com@groups.io> 
Date: 6/25/21 4:14 PM (GMT-05:00) 
Subject: Re: [QRPLabs] dummy load to attenuator mod #dummyload 

Note to Hans and potential builders;
3.4 Fit jumper W2-W3 on the top PCB
Fit a jumper wire at W2-W3 on the TOP PCB only.

But,  the picture shown is the bottom board with the bnc connector fitted!
Confused me for a while!!!!
73 Ken g4apb 




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