4S-Low Pass Filter
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4S-Low Pass Filter
Designed by David Cripe, NMØS
Kitted and Offered For Sale By The Four State QRP Group
Featuring the famous NMØS Spiral coils, it is a None Simpler design, as seen in the NS-40 transmitter. This innovative and highly effective Low Pass Filter (LPF) is a must have for experimeters and those wishing to make sure their rig is legal. It's available in either only in an 80M version, the 40M version is sold out. The kit includes all the components to finish the build, including a beautiful jet black pcb enclosure - another NM0S hallmark. At 3"x 2"x 3" it will fit easily in your portable operating bag, and on your desk or workbench. It is a quick build, and has been chosen as the build session kit at OzarkCon 2015.
The kit also features the Pittsburg style pc board, which also is a feature of the Ozark Patrol regenerative receiver kit. See that board here.
Simple homebrew transmitters such as the Michigan Mighty Mite and similar absolutely require an LPF between it and the antenna. So if you enjoy building and experimenting with transmitters, or want to ensure that your rigs are legal, then this is the perfect filter for you.
The FCC requires all spurious emissions below 30Mc to be attenuated by 43 dB or more, and this nifty little filter will enable your transmitter project to easily meet that spec.
NOTE: this isn't a QRP only design. It has been designed to accomodate higher power, and can be confidently installed behind a 100W rig. Also note that the kit doesn't include a balun for balanced line antennas. They are very easy to construct however, and your favorite search engine will find many examples.
Specifications and Design Features
Beautiful jet black silk screened and easy building PCB enclosure.
2nd and 3rd Harmonic Attenuation: Greater than 50 dBc with transmitter set at the middle of the band.
Maximum Power Throughput: Designed to withstand 100W.
Impedance: 50 ohms in, 50 ohms out
Extremely low insertion loss: Nearly Zero.
Enclosure Size: 3"x2"x3".
NO TOROIDS to wind. Spiral coil inductors are etched on pcb's.
High quality Silver Mica capacitors used throughout.
Assembly Manual In Spanish Translation by Jon Iza EA2SN, thank you Jon.
KØAWB's OzarkCon 2015 Build Session Assembly instructions.
Elecraft's Excellent Capacitor Identification Page Posted with permission.
Electronics 2000's Excellent Resistor Code Graphic Calculator Posted with permission.
The cost of this kit is $20, and the shipping cost is additional. The Paypal buttons below include
the shipping costs.
NOTE: The 40M version is sold out, but the 80M versioln is still in stock.
If paying by check or money order (US dollars only) please make it out to "Four State QRP Group" and send to:
Pay With PAYPAL
Four State QRP Group
Tom Brown WØMFQ
PO Box 627
St. Charles, MO 63302
The 4S-LPF was carefully kitted by the Dave Cripe family, and is shipped by Jerry Gorrell, WØCLR.
Please direct shipment related questions to Jerry
All proceeds are applied toward funding OzarkCon.   Thank you for supporting The Four State QRP Group.