TVI. FILTERS.


               diagram g4wpw

The High pass filter is for insertion into the lead from the TV antenna to the TV, The insertion loss of this filter is very low,it is of the ( braid breaker ) type for HF and VHF/UHF frequencies.
The Filter comprises of a 1 inch by 2 inch double sided copper clad printed circuit board,The Upper side of the board has a " cross " pattern cut into the copper and the underside has a single cut lengthways as seen on the diagrams. The 3 coils consist of 4 turns of 18 swg enamel wire a quarter of an inch in diameter spread to half inch length,2 soldered on the upper side of the board and the remaining coil soldered on the underside. R1 is a 1meg ohm or above 1/4 watt resistor soldered as shown this is the static discharge path.( I used a 4.7 meg ohm.) 2 short lengths of TV antenna cable ( about 6 inches each ) are connected as shown to the upper side of the board ( the braids are on the same side and the center core's are on the same side THIS IS IMPORTANT ) TV antenna coaxial male plug can be fitted on the end of one cable and a female plug to the end of the other cable this makes connection and removal easy.


Circuit Diagram of The Filter.
              diagram g4wpw

L1 and L3 are on the upper side of the board L2 on the underside C is the capacitance of the copper "plate's" between both sides of the board approx 2pf for each capacitor.
BASIC PRINCIPLE'S This combined braid-breaker and high pass filter prevents HF signal currents from flowing down the inner and outer of the TV antenna coax cable.L1,L2,L3 have a low reactance to HF and VHF signals,thereby by-passing( shorting )the interfering currents. The capacitors have high reactance to HF/VHF signals,effectively blocking these "interfering"signals from the TV receiver. At the TV receive frequencies the conditions are reversed, the capacitors presenting a low impeadance path to the TV received signals enabling them to pass,and L1,L2,L3 presents a high impeadance at this frequency thereby having no effect on the received TV signals. R1 is for static discharge of the outer screen of the TV antenna coax.



THE FINISHED FILTER.




FARADAY LOOP FILTERS.( Braid Breaker )


               Diagram g4wpw

The Faraday loop filter comprises of 2 loops of the TV antenna coax 2.5 inch 
diameter,tape'd side by side, The TV antenna feeder is cut and each loop is soldered
to its own braid as shown above.The loss on this type of filter is high and should 
only be used in a good TV signal area.



                Diagram g4wpw.

Above is the modern version of the braid breaker type of filter it comprises of a 
1 inch square of double side'd copper pcb with a saw cut down the center,the 
TV antenna feeder is connected as shown on the above diagram,the board is cut the
same on both sides,and the coax connections are the same on both sides I have found 
the insertion loss to be much lower than the Faraday loop. it is also a good idear
to fit a 1 meg ohm resistor between both braid connections of the pcb as a static 
discharge path.