[R-390] Two questions

Fri, 29 Mar 2002 10:42:45 -0500

To answer the second question.  More than one capacitor is placed on
parallel in a bypass circuit to bypass different frequencies.  In the
larger capacitor, there is a lot if inductance due to the way it was
made and its physical size. This cap is effective for low frequencies
but not even seen by the higher frequencies.  The smaller cap is used to
bypass the higher frequencies.  Sometimes you might see another one or
two capacitors in parallel, again to bypass different frequencies.  

On a side note.  You will also see capacitors in parallel in an
oscillator circuit.  There are a number of reasons for this.  One to get
an oddball capacitance, 2. to reduce the RF heating in the capacitors
due to dielectric loss, and finally to compensate the oscillator for
changes in temperature. Each of the parallel capacitors may have a
different temperature coefficient.

73

Glenn 
WB4UIV

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Scott, Barry (Clyde B)
Sent: Friday, March 29, 2002 10:13 AM
To: R390 (E-mail)
Subject: [R-390] Two questions

1.  Did all 390 models include the squelch.  It was an option on the
390A.

2.  I was looking at a schematic (a keyer) a couple of days ago and
noticed there were two caps in parallel -- a 22mfd and a 4700pfd.  These
feed a solid-state VR.  Why would it be necessary to have this
arrangement?  When caps are in parallel, doesn't the circuit see this as
simply the sum of both capacitances -- in this case 22.0047mfd.  It
would seem the 4700pfd is insignificant with respect to the 22mfd cap
and I can't see the need for it.  Any thoughts as to why this was done?

3.  Hammarlund.

Thanks,

Barry(III) - N4BUQ
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