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

Naar Blijdorp met Eneco

Als trouwe klant van Eneco, kregen een aanbieding om met Eneco gratis naar Blijdorp (Rotterdam Zoo) te kunnen gaan.
Dus besloten we al snel om met onze kleindochters te gaan.

We hebben genoten.

Apen met roze konten leidde tot grote hilariteit.

Neushoorn, Giraffen en een opa's lieveling, de otter

  Eneco, bedankt voor het fijne bezoek.

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