[HomeBrew] about my SSB/CW tcvr project

Fri, 3 May 2002 12:17:31 +0900

Hello Henning,

What is the minority charge carrier lifetime (Tau) of the PIN diodes that
you were using? Typical PIN diodes earmarked for attenuator applications
(eg. Agilent HSMP-381x series) have Tau in the region of 1500 nS. Based on
the rule of the thumb, that PIN diodes begin to act like a pure resistor at
frequencies higher than 10 times the cutoff frequency, these diodes are
suitable for IF above 1 MHz. For those interested in going throught the
maths, the cutoff frequency is calculated from fc = 1 / ( 2 X PI X Tau).

When configured as a constant impedance PI attenuator, the attenuation (in
dB) tracks linearly with the the control voltage (in linear units) over a
relatively small range of 10 to 45 dB. Linear tracking over a larger dynamic
range may be possible using external op-amps for controlling the PIN diodes
(reference: Gary Homer, PIN-Diode driver allows Linear RF attenuation,
Microwave and RF, April 1983).

I am rooting for more future ham designs to use basic components like PIN
diodes, instead of hard-to-get ASIC like the AD603. Why? I sincerely feel
that designs that use basic components like PIN diodes are more readily
reproducible by homebrewers, especially those who reside in less developed
countries.

73,
Chin-leong, 9W2LC.

-----Original Message-----

Date: Thu, 02 May 2002 13:07:59 +0200
From: Henning Weddig <[email protected]>
Organization: DESY
To: Xu <[email protected]>
Cc: [email protected]
Subject: Re: [HomeBrew] about my SSB/CW tcvr project.

(snipped) 
I built an IF amp with "normal" silicon RF transistors and use a PIN
diode attenuator, but got into difficulties when using PIN diodes having
a not suitable minor charge lifetime Again, the gain control is not
linear.  
(snipped)