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pa0nhc fixed 73dB 50 Ohm attenuator 20180829.

Copyright. The use, copy and modification of all info on this site is only permitted for non-commercial purposes, and
thereby explicitly stating my radio amateur call sign "PA0NHC" as the original writer / designer / photographer / publisher.

Preliminary development data.

In- and output impedances : 50 +/- 0.2 Ohm.
Attenuation : 73 +/- 0.2 dB.
Max input : 0.25W..

        Intended use :
Calibrating receiver S-meters to S9, by using a 0dBm signal generator as signal source.
With an extra step attenuator the full range of the S-meter can be calibrated.


0dBm generator + fixed 73dB attenuator. Output S9 +- 0.2dB.


Total attenuator dimensions : abt. 2.5 x 3.5 x 9 cm3.

IARU "S"

SW
dBm

VHF
dBm

Japanese "S"

9

-73

-93

9

8

-79

-99

7

7

-85

-105

5

6

-91

-111

3

5

-97

-117

1

4

-103

-123

(0)

3

-109

 

(0)

2

-115

 

(0)

1

-121

 

(0)

        According to IARU :
Short Wave : S9 = 50 uV (-73dBm), 1 s-point = 6 dB (2x received voltage difference).

VHF : S9 = 5uV (-93dBm).

         Japanese equipment :
often have S-meters which are indicating differently :
1 s-point = 3dB (2x transmitted power difference).

The total package consists of seven little double sided PCBs.
The main PCB contains the attenuator circuit. 
The other six PCBs are for the construction of a cheap, but neat enclosure. Already painted.

The attenuator circuit consist or 5 stages.  All stages are of the "PI" type, and are connected in series. Fairly accurate results are achieved, by using standard value resistors, connected in parallel. Easy soldering is ensured by using axial wired, 2.5x6.5mm 0.25W metal film resistors, and RM8.6 / 1mm PCB holes.

A full PCB "ground" plane ensures a low inductance ground path, and small parasitic capacitances between each resistor and "ground". This compensates a little for the self inductance of the used resistors, with the goal to achieve a wider frequency range.

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