Dual Gate MOSFETs:
Chapter 6 includes considerable information
on IF and RF amplifiers for receiver applications. Some
of the circuits use dual gate MOSFETs, a component that
was popular about 20 years ago, but not in common use
these days. The dual gate FETs are still available
and are highly recommended for AGC amplifiers, or
for low noise applications. I got a very interesting
note recently from Mark, WU0L. Mark had purchased
some BF998 surface mounted
dual gate MOSFETs from Bob, KE6F, Via EBay. I also
got some of these parts from Bob. Mark beat me to the
punch and has built the AGC IF amplifier that was used in the Progressive
Communications Receiver. This circuit, from QST, November,
1981, is included on the EMRFD CD. Mark reports
"good gain and no stability problems" with his version of the
circuit. He did his own circuit board. Many thanks
for the info Mark, and many thanks to Bob for supplying the parts.
A data sheet for
the BF998 is available from the Philips web site at: http://www.semiconductors.philips.com/
CD Problem: On Jan 25,
2004 we discovered a problem with compact discs distributed
with the 2nd printing of the book. It appears that text is missing
from all of the QST/QEX/HR/Microwave-Update articles in the collection,
only to be replaced by a page from another article. The CDs with the first printing
are generally OK. The ARRL folks have fixed this problem and the books being
shipped are good. This problem was only present
with the 2nd printing of the book. The CD with the
2nd printing has a silver cover.
The replacement CDs will be blue. If
you have a defective CD, you should contact ARRL and ask
for a replacement. The files with the 3rd
printing are fine. (17Apr09)