Τρίτη, 28 Φεβρουαρίου 2012

Power Attenuators for 5 watts

Με τον π/δ , Yaesu FT450 δεν μπορώ να δουλέψω κάτω από 5 watts. Πρακτικά δεν μπορώ
να δουλέψω qrpp, με την παρότρυνση του Τάκη sv3auw, έψαξα στο ίντερνετ για σχέδια
Power Attenuators.
 Γρήγορα κατέληξα στην ιστοσελίδα του PA1B, που ασχολείται σε βάθος με το qrp.
Η συνέχεια είναι ένα απόσπασμα από την ιστοσελίδα του . Στην συνέχεια είναι μια
αναφορά του PA3GNZ πάνω στην εργασία του PA1B.

The shown Pi-type 50 ohm attenuators are designed for an input power of 5 watts. 
They are built with carbon resistors from the E12-series.
The attenuators are placed in cascade. The attenuators can be switched on or off.
With the switch in the lower position the signal will go through the attenuator.

Attenuator of 2 x 3 dB, 10 dB and 20 dB with 5 watts Input
Attenuators for a continuous input power of 5 watts.

With these attenuators the power can be reduced in steps of 3 and 4 dB from 5 watts to 1.25 milliwatt. (0 to 36 dB)
All four attenuators should be able to dissipate 5 watts, because they can be switched independently.
For simplicity, I have chosen for 1 watt resistors in this diagram.
If you build these attenuators with resistors of ½ watt instead of 1 watt, then the maximum continuous input power is 2.5 watt.
And 5 watts with CW, because in CW the power is about half of the continuous power.

Asymmetric attenuatorsAsymmetrical attenuators.
For simplicity, the attenuators for 20 dB and 10 dB, are asymmetrical, so less resistors are needed.
The resistors R1 and R4 at the input of the attunuator have to dissipate much more power than the resistor R3 and R6 at the output.
Therefor R1 and R4 are built with more resistors than R3 and R6.
Input and output may not be exchanged.
The attenuator will be damaged if the set is connected to the output instead of the input.
Because the 3 dB attenuators dissipate far less power and therefor require less resistors than the other attenuators, they are built symmetrical.

Don't be alarmed, when the power attenuator gets warm.
You should be alarmed, when the attenuator doesn't get warm, with an input power of 5 watts.

Tjeerd "Gose" PA3GNZ was inspired by this page about attenuators and some additional info about power attenuators that I sent him.
So he designed a 10 dB attenuator for an input power of 5 watts, using 1 watt resistors.
Tjeerd uses the attenuator, to reduce the 5 watts that is coming from the set to WSPR with 500 mW.
He noticed that during the 2 minute transmission period the attenuator gets warm.
You can find the drawing of this symmetrical 10 dB attenuator, for an input power of 5 watts, on the weblog of Tjeerd
 



WSPR with 500mW

A good friend of my builded a 10dB attenuator. This means that the 5 watts signal from my
Yaesu FT950 decrease to approximately 500mW. Today I started on 20M and a few stations
 heard my qrpp signal.
Drawing made by PA1B


The ideas for creating an attenuator did I found on the webpage of Bert, PA1B.

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