Scott, I use a similar filter here on VE3WFM repeater. It is a coil from an old Telco VF card that is about 1 Hy, as I recall and I put about 1.2 Mfd in series with it. This is the old seies resonant circuit that we all leaned about years ago. The whole thing is wired across the 600 ohm audio path to the transmitter and it attenuates the 131.8 HZ tone about 15 db which is enough to kill it for my application here. The bandwidth of the notch, as I recall is about +-10 Hz wide. I tuned it with an HP audio osc. and an HP vtvm and watched for the dip.
John VE3AMZ Waterloo Ont. ----- Original Message ----- From: "Scott Zimmerman" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, November 21, 2003 3:19 PM Subject: Re: [Repeater-Builder] PL/CTCSS Filter > The mitrek uses a type of passive filter. It's more of a shunt to ground > type of filter rather than a series element. If you look at the PL board > schematic closely, you will see where it connects through pin 7 to the > radio. The schematic notes (all of the theory of operation we have in this > case) says that it is a gyrator, a simulated inductance, that resonates with > a .1uF cap to produce a notch at 180Hz. I never found them to work the best, > but there is a kind of filter there. If anyone can tell us a more advanced > theory behind how this type of circuit works, I think we (or at least *I*) > might learn something. > > In order to use a thru type filter, you will need to break the audio path > somewhere. Be sure you feed your filter with a good low-impedance source, > and feed a high impedance load with it. > > Scott > > M. Scott Zimmerman > Zimmerman Electronics > Amateur Radio Call N3XCC > 612 Barnett Road > Boswell, PA 15531 > > > ----- Original Message ----- > From: "Adi Linden" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Friday, November 21, 2003 2:11 PM > Subject: Re: [Repeater-Builder] PL/CTCSS Filter > > > > > From my recollection, the filter is used in the base station > > > package - why wouldn't it be? Yes, to use the filter, JU201 needs > > > to be removed or is that a problem for you? > > > > I am using a Mitrek not a Micor. The Mitrek doesn't have a filter on the > > PL board. > > > > Adi > > -- > > Adi Linden | va3adi | [EMAIL PROTECTED] | http://adis.ca > > +-----------------------------------------------------------------+ > > IRLP Node 2590 in Sioux Lookout, Ontario > > > > > > > > > > > > > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ > > > > > > > > > > > > > > > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
