40 dB attenuator built by DK5LH

40 dB attenuator built by DK5LH
Click to enlarge  

I received a very interesting email from Hartmut DK5LH, in which he informed me that he successfully built the
PA1B  40 dB attenuator.    Click for schematic. 
He is very pleased with the excellent accuracy of the attenuator, that makes this attenuator suitable for measuring purposes.

Hartmut uses the attenuator to measure the power of his transmitter (2 watts) with a power meter for -80 dBm to -10 dBm
The attenuator is used to reduce the output power of the set to a value that is less than 0.1 milliwatt. (-10 dBm)

40 dB attenuator with metal film resistors of  2 watt and 600 mW  -  DK5LH  

Resistors
Hartmut has used resistors, that he ordered at the firm Reichelt.   Resistors 2 watts.
In his email Hartmut writes:
Ich habe diese widerstände nicht ausgemessen, sondern einfach so genommen. 
Offensichtlich sind dieses sehr genau. 
which means:
I did not measure the resistors, but just used them. 
Obviously  they are very accurate.

Accuracy
The attenuator is built with good available metal film resistors from the E12-series, with an accuracy of  5%. It shows an  excellent accuracy, because in practice the resistors show a accuracy of 1.5 %, or better.
The picture below shows the excellent accuracy of each of the four attenuator sections.

Hartmut is very pleased with the excellent accuracy of his 40 dB attenuator. His attenuator shows an attenuation of 40,5 dB, with the maximum attenuation, with all sections switched to ON. He has calculated the attenuation with the method of measuring DC voltages.

Thank you, dear Hartmut for emailing the beautiful pictures and additional info.
It's my pleasure to show your beautifully built attenuator.

PA1B Attenuator

I developed attenuators that very accurate and fast to operate. In order to get the best power distribution, the attenuator section with the lowest attenuation is placed in front. I use these attenuators in very low power CW QSO's.

PA1B Fast and accurate power attenuator for CW QSO's

Line up of the sections
While testing and making measurements with 5 watts, I noticed that the attenuator section of 20 dB gets warm with in 10 or 20 seconds. So I changed the line up of the sections. By placing the attenuator section of 3 dB  in front, this sections will dissipate half of the input power. This line up and the choice of the attenuation, makes it possible to get an attenuation of 10 dB, with the sections of 3 dB and 7 dB switched ON. An extra 10 dB gives an attenuation of 20 dB.

10 dB = 3 dB + 7 dB 
20 dB = 3 dB + 7 dB + 10 dB

CQ WW DX CW 2014

I had great fun in the CQ WW DX CW contest of 2014.
I had my inverted vee repaired just in time for the contest.

But most of all, I was very curious, how fast the
PA1B Fast and Accurate 40 dB Power Attenuator
would be in a large contest with enormous activity.

I am very happy with the attenuator.
As I mentioned before, the fast attenuator can be switched instandly.
So I am immediately ready to answer a CQ.

I started on 10 m and went to a lower frequency each time a band closed.
At times when the signals were getting stronger, I tried to use a lower power in the next QSO's.
On 40 m the band was too busy to use a very low power.
When I was on 40 m, the other bands were closed, so all other operators were also on this band.
So I made most QSO's on 40 m with 3.6 W. (Category less than 5 watts)

The inverted V works fine.
Since a long time I could make a few QSO's with less than 10 mW.
I used a power of about 4 watts down to 1.6 milliwatts.
The two QSO's in the column of  2.5 mW in the table were made with 1.6 mW and 1.8 mW.
(500 mW means more than 250 mW and less than 500 mW)

The start of the CQ WW DX CW contest

23 dB   Click to enlarge

After repairing the Inverted V, I took part in several contests.
The first contest was the CQ WW DX CW contest.

I was eager to use the 

"PA1B Fast and Accurate 40 dB Power Attenuator" 

in a contest with a large activity.

In the first 5 QSO's were made with 3 watt to 400 mW.
After 5 QSO's the signals were getting stronger, so I could use the attenuator. With signals over S9, it was possible to make QSO's with a power of 72 mW and 36 dB.

The 18^th QSO, with RM5A, was the first QSO below 10 mW with 7.2 mW. So this was very promising.

YZ7Z - 1.8 mW       RM5A - 7.2 mW 

The 19^th QSO with YT7Z was made with 1.8 mW with the attenuator switched to 23 dB and the set on 360 mW.
An attenuation of 23 dB gives a power ratio of 1/200.

Math:
23 dB is 10 dB + 10 dB + 3 dB
The power ratio is 10 * 10 * 2 = 200
So the power is 360 mW / 200 = 1.8 milliwatts.

With one hand on the keyer and one hand on the switches of the attenuator, I can switch the power in a "milli"second.  Now I never miss an opportunity to answer. hi.

Immediately after each QSO I note the power of the set and the position of the attenuator in dB.
Further I calculate and note the power.

PA1B Power Attenuators for QSO's

In the CQ WW DX CW contest, I used the PA1B fast and accurate 40 dB power attenuator for QSO's. During the contest I experienced that the attenuator is even faster than I expected.
I am very happy with this fast attenuator.

The attenuator has sections of 20 dB, 10 dB, 7 dB and 3 dB.
In most situations one switch is switched OFF and an other is switched ON, to increase the power with an step of 3 or 4 dB. Which makes the attenuator easy to operate, with one hand.
I experienced that with this attenuator, the power can be increased instandly.
So I am immediately ready to give my call again, with slightly more power.

PA1B Fast and accurate 40 dB power attenuator for QSO's            

Until now I used an attenuator of 10 dB or 20 dB and the adjustment of the FT-817 to set the power for QSO's with very low power. E.g. 50 mW. When I must increase the power of the FT-817, because my signal was not heard, I must push the botton of the menu to set thepower 3 times to double my power.
The time to change the power of the FT-817 is too long to be ready to answer the next CQ, when my signal is not heard.
But now I never miss an opportunity to answer.

Fast attenuators (click)

You find more, interesting  info on attenuators 
on my website: PA1B QRPp page (Click)

Fast and accurate 40dB Power Attenuators for QSO's on the PA1B QRPp page

Fast in QSO's
A simple way to reduce the power of your QRP set to milliwatt level, without modifying the set, is the use of attenuators.
The combination of 20 dB, 10 dB, 7 dB and 3 dB is fast to switch, when you want to increase your power in QSO's.
In one move, one attenuator section is switched OFF and an other is switched ON, to increase the power with a step of 3 db or 4 dB.

Last week the PA1B QRPp page was updated:

Click to read more about the interesting
PA1B Fast and accurate 40 dB Power Attenuators for QSO's.
Specially designed to use in QSO's with very low power.

Schematic and building info of the 6 watt Power Attenuator

PA1B 40 dB Power Attenuator

PA1B Fast and accurate 40 dB Power Attenuator for QSO's

This Power attenuator is  fast in CW QSO's, because
7 dB and 3 dB can be switched instandly..

The attenuator is also very accurate.

Power Attenuator

All attenuator sections are designed for an maximum input power of 6 watts. The continuous power is 1.5 watt.
The power resistors, with a lower ohmic value, dissipate most of the power and an other resistor is added in parallel, to arrive accurately on the wanted ohmic value. 

The power attenuator sections of 20 dB and 10 dB are build with 7 resistors, since they must dissipate much more power than the other sections.

The large resistors are resistors of 2 watts. The resistors with 2 stars (**) are resistor of 1/2 watt and the resistors with 1 star (*) are resistors of 1/4 watt.
I built my attenuator with metal film resistors of 2 watts, 600 mW (*) and 400 mW (*)

Asymmetrical attenuator
To reduce the number of resistors, I chose for asymmetrical sections in the attenuator. 
Input and output can not be exchanged.

Schematic

PA1B Fast and accurate 40 dB Power Attenuator for QSO's.
Power 6 watts built with resistors of 2 watts, 1/2 watt and 1/4 watt
Click to enlarge

The switches on the front.      20 - 10 - 7 - 3 dB        

Reversed order

The schematic goes from left to right.
Please notice that the layout on the switches, inside the box goes from right to left.
So you will find the the resistors of 150 ohm and 330 omh to the right.

Notice the reverse order with respect to the schematic

R2 and R5 are also placed

PA1B 20 - 10 - 7 - 3 dB power attenuator measured

We measured the new built 6 watt PA1B  Power Attenuator, in the shack of Mischa PA1OKZ.
The attenuator is built with metal film resistors of 2 watts, 600 mW and 400 mW, from the E12-series.
I was curious how well the metal film would do HF.       Click for schematic

Conclusions
* The 20 - 10 - 7 - 3 dB  sections are very accurate
* The 20 and 10 dB  sections show an accuracy of 0.1 dB to 0.2 dB at 30 MHz
* When all sections are switched OFF, the attenautor has a attenuation of
    0.13 dB at 1 MHz  to 0.61 dB at 30 MHz.
    This "extra" attenuation is frequency dependent.

Relative attenuation
The purpose of an attenuator is to attenuate the signal with the value 
of the sections, that are switched "ON".
In this table the attenuation with all section switched OFF is 0 dB.
The table shows the "extra" attenuation of this section, when a section is switched "ON ".

Relative attenuation of the PA1B  20 - 10 - 7 - 3 dB power attenuator    

At 10 MHz all sections are very accurate.
The 10 dB and 20 dB sections are more frequency dependent.
The section of 3 dB is the most accurate section. The section of 7 dB has an accuracy of 0.1 dB.
The section of 10 dB and 20 dB show an accuracy of 0.15 dB at 30 MHz.

I am very content with these values, considered that the resistors are resistors of 5% from
the E12-series. The measured values of all resistors in this attenuator, show that the accuracy of the resistors is about 2 %.

Absolute attenuation
This "extra" attenuation is caused by the fact, that the circuit formed by switches is not 50 ohm.
The value of 0.13 to 0.61 dB is typical for the switches that are used and the distance between the switches.
We measured about the same values in another attenuator with two section of 20 dB and one of 10 dB, that is built in the same way.

Absolute attenuation of the PA1B  20 - 10 - 7 - 3 dB power attenuator     

Inside of the box of the attenuator with simplified schematic

Building a 6 watt power attenuator

I am building an attenuator with metal film resistor of 2 watts, 600 mW and 400 mW.

Sorting out the resistors
Click to enlarge

The store had no resistors of 1 watt, so I bought the power resistors
of 2 W and made a redesign of the attenuator.
All the resistors are metal film resistors.

The attenuator is designed to for a maximum power of  6 watts.

To the right you see the blue  box with the resistors that are needed.
The 3 dB and 7 dB sections both consist of 6 resistors each.
The 10 dB and 20 dB sections dissipate more power.
They consist of 7 resistors each.

     Outside of the box with the 20 dB section to the left.                         Inside of the box. 20 dB section to the right.                     Switches set to 17 dB                                                                             Switched mounted               

Next step soldering the resistors. 

Accurate and fast 5 watt attenuator for QSO's

Please visit the PA1B QRPp page for more info on Power Attenuators.

Fast in QSO's
A simple way to reduce the power of your QRP set to milliwatt level, without modifying the set, is the use of attenuators. The combination of 20 dB, 10 dB, 7 dB and 3 dB is fast to switch, when you want to increase your power in QSO's. In one move, one attenuator section is switched OFF and an other is switched ON, to increase the power with a step of 3 db or 4 dB.

PA1B Fast and Accuarate 40 dB Power Attenuator for QSO's

PA1B Fast and accurate 40 dB Power Attenuator for QSO's

Asymmetrical attenuator
I choose to design this attenuator asymmetrically, to reduce the number of resistors.
Please notice that the resistor on the input of each attenuator section, R1, R4 and R7, consist of 5, 4,and 3 resistors.

Power
All attenuator sections are designed for an maximum input power of 5 watts.
This is a continuous power of 1.25 watt.
The attenuator sections consist each of 3 compound resistors, which each are formed by a number of resistors in parallel. These resistors are a power resistor of 1 watts and a some resistor of a modest power (1/4 watt). The resistors with a star * can be 1/4 watt.
Or you can chose  1 watt resistors for all resistors.
The power resistors, with a lower ohmic value, dissipate most of the power and an other resistor is added in parallel, to arrive accurately on the wanted ohmic value. The power attenuator sections of 20 dB and 10 dB are build with 9 resistors, since they must dissipate much more power than the other sections.

Accuracy
With two or more resistors from the E12-series in parallel,
you can accurately make any value you want.
The resistor value of the combination is most of the time within 1% of the theoretical value.
This is why an accurate attenuator section, always consists of 6 resistors or more.

Simple layout
The choice of placing resistors in parallel, leads to a very simple layout of the attenuator sections.
There's NO need for a PCB. hi.

Table for the PA1B Fast and accurate  40 dB  Power Attenuator

Click here for

PA1B Fast and accurate 40 dB Power Attenuators for QSO's

for a symmetrical attenuator built with resistors of 2 watts.