woensdag 30 juli 2014

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. 

zondag 13 juli 2014

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.

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.

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

donderdag 10 juli 2014

First place in the YO DX HF contest 2013 for CS8/PA1B

Today I received a beautiful Award of the YO DX HF contest.
Last year I partcipated while on holiday on the beautiful island of Saõ Miguel on the Azores.

During the contest I used an end fed wire on the roof of the hotel.
In the contest I used my FT-817 with 2.5 watts or less and a homemade light weight keyer.

The envelop from Romenia arrived in the rain.
When my wife entered the room with the wet envelop, she said:
"I hope all is OK".
I immediately recognized the envelop of the YO DX contest.
Despite the rain the Award is in good condition, because it is plasticized.

My thank goes to Ovidiu YO2DFA, the contest manager of the
YO DX HF contest.
CS8/PA1B   First place in YO DX HF - Azores - Single OP - 14 MHz - Mix