[HomeBrew] about my SSB/CW tcvr project.

[Henning Weddig]

Xu,

I have a lot of experience in designing IF amps... 
MOSFET�s are not the right choice at low IF�s (even 9 MHz or so). They
are low in NF but have high i/f noise wihich can reach some MHz corner
frequency. Therefore their noise figure at low frequencies are not good.
Dual gate MOSFETS can be easily gain controlled via Gate 2, but if the
gain is reduced their ability to linear amplify high level input
signals. THe gain control curve is not linear.
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.  

Momentarily I am going to built an IF amp with true dB linear AGC
characteristic using AD603�s from Analog Devices. togehter with an
associated AGC module and SSB/CW AM demodulator on different boards they
will be described in ghe German magazine "UKW-Berichte", an english
version is "VHF Communications". I am still in the process of building
and testing the units together with writing the articles.

If You are interested I can send You the prelimenarily schematics and
boardlayouts as pdf files... if I can convert them from my CAD system.

Regards

Henning Weddig
DK5LV

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