36dB Attenuator for 20 W by PH2LB

This beautiful attenuator is designed and built by Lex PH2LB.

0...36 dB attenuator built by PH2LB  -  Click to enlarge the pictures

Power
The attenuator can handle a maximum power of 20 watt.
At first I did not realized why Lex designed the attenuator for 20 W. Like many HAMs I thought, that 20 W is QRO. But please notice that 20 W is the Maximum power.  The chosen maximum power of 20 watts for the attenuator is an excellent choice. The attenuator can easily handle a power of 5 watts, without getting hot. The nominal power of the attenuator is 5 Watt.

This was an eye-opener for me. hi.

0...36 dB attenuator by PH2LB
with 2 W resistors 

Derating
A resistor that  dissipates its maximum power will get very hot.
So it is good practice to choose the maximum power 4 times higher then the continuous power.
Lex choose for  a maximum power of 20 watts, to reduce a power of 5 watts.
The resistors have a maximum power of 2 watts. With a power of 1/4 of the maximum power, the resistors will dissipate about 500 mW each and they will get warm, but they will not get hot.

The 20 dB section

Visit the article on the 36 dB attenuator on the web site of Lex PH2LB.

PA1B Power Attenuator Calculator
Lex used the PA1B Power Attenuator Calculator to design his 36 dB attenuator for 20 watts.
This unique spreadsheet in Excel calculates the number of resistors and the values of the resistors from the E12-series for an attenuator section.

In the picture below I show the input values for the section of 20 dB, for a maximum power of 20 watts, that is built with resistors of 2 watts.

PA1B Power Attenuator Calculator - Input values for the 20 dB section

Just download the PA1B Power Attenuator Calculator and play with the values. The calculator has no restriction on the power.

10 dB attenuator for 5 W built by Stefano IZ1OQU

I received a very nice and very interesting e-mail from Stefano IZ1OQU.

Dear Bert,
I'm IZ1OQU and my name is Stefano, from Italy, and I'm writing you to thank you for the attenuators that you have so simply and clearly explained on your website.
I built one, 10 dB, for my SSB DXing activity. It's really fantastic and I wonder how people can receive me with 50mW SSB!
I tryed on 20, 12, and 10 m bands with same good results, with three top-qrb of 2300 kms (Russia, Finland and Georgia).
Everything under 2000 kms it seems easy to reach. I use vertical dipoles, so not that big antennas even though they are full-sized for their bands.
I'm gonna build a 20dB attenuator to reduce more!
Thank again for your job.
All the best '73
Stefano IZ1OQU

10 dB Attenuator for 5 watts built by Stefano IZ1OQU

In a further e-mail Stefano wrote:

I designed the 10dB attenuator for 5 W of max input power. 
5 W is the output of Yaesu FT817. 
You know: it has 4 switchable fixed power outputs: 0,5 W - 1 W - 2.5 W and 5 W.
With 0,5 W and 10dB attenuation, I can have 50mw. On 5 W, it falls to 500mW which is the standard low power - usually enough for many European QSO's.
The 5 W design let me switch on all the 4 power output even though it needs more resistors to handle the power. I could use bigger resistors of 2 W, but the only shop around here is not well supplied for values over 1/2 W. 

Stefano used the Power Attenuator Calculator from the PA1B QRPp page to design his attenuator.
This Calculator is developed to design Power Attenuators for 5 watts or more, built with resistors of a modest power, such as 2 W or 1 W.
I am very pleased to answer the questions that Stefano had.
Thanks Stefano for the questons.

Power Attenuator by Mark DL6YYM

Mark DL6YYM designed a power attenuator for 5 watt, using resistors of 1/2 watt. The attenuation of the attenuators, from the left to the right, is 20 dB, 10 dB, 3 dB and 3 dB. Seen from the front. This enables Mark to lower the power from 0 dB to 36 dB, in steps of 3 dB or 4 dB.

Click to enlarge

Mark built a beautiful enclosure for the attenuators.

This picture shows the interior. Seen from the back, you can see the 20 dB section on the right, behind the coax. This section has the larger number of resistors. The 10 dB is visible to the left of the 20 dB section.
At the left you can see the two 3 dB sections, each built with a total of 7 resistors.

Click to enlarge, to see all the details.

Mark used the PA1B Power Attenuator Calculator, to design the attenuators.
You can find the Calculator on the PA1B QRPp page,  This Calculator in Excel enables you to design an attenuator for any power, using common resistors from the E12-series. E.g. 1/2 watt. Mark used Open Office. Please note, that in Excel or Open Office you must use the decimal COMMA or POINT according to your national language. These attenautors are what I had in mind, when I developed the Power Attenuator Calculator. hi

The shack of DL6YYM.

I thank Mark for sending the pictures and for the great feedback on the attenuators.

Interesting info

Click on the interesting links on the top of the Blog.
I brought same interesting info from the PA1B QRPp page to this Blog and I wrote new pages.

The pages contain info on:

* How to work with the Lowest Possibe Power in QSO's.
* 10 dB Power Attenuators for 500 mW to 5 Watts.
   Build a simple attenuator for 10 dB to use with your set.

* The Excellent Power Attenuator Calculator.
   With this speadsheet in Excel you can design your
   own Power Attenuator for
   any power you want, build with in good available 
   induction free resistors from    the E12-series.
   The higher the input power the more resistors are
    needed.

* How to use the data from the WSPR database to
   make an detailed 
   WSPR Propagation Analysis.

Power Attenuator Calculator

Yesterday I made additions and changes to the Power Attenuator Calculator.
This spreadsheet, can be used to design Power Attenuators.

With this excellent Power Attenuator Calculator you can design attenuators of 3 dB, 10 dB or 20 dB, for any Input Power you want, which are built with good available resistors of the E12-series, with a maximum power that you can chose yourself.

I use attenuators for QSO's with very low power.
A 10 dB attenuator reduces the 500 mW from my FT-817 to 50 mW.

The new Calculator will show up later on the PA1B QRPp page, but via the Public link to Dropbox Power Attenuator Calculator you can download the calculator in advance.
Take a look and get your self a shopping list for an attenuator.

Bert PA1B