Constructing TVi notch filters

20 Meter Fourth Harmonic Filter

Constructing TVi notch filter

This was my first attempt at making a TVi Notch filter. It is designed to pass all HF frequencies, but insert a deep notch at 56.8Mhz which is the forth harmonic of 20 meters, thought to be responsible for my TVi problems.

The coils can be seen soldered to home made capacitors, made out of double sided PCB material. The holes are drilled to trim the final capacitance, about 2pf each with a 4mm drill. Dielectric used was a polythene freezer bag. A single nylon nut and bolt clamps both together.

20 Meter Fourth Harmonic Filter

The theme of the filter construction was to produce precise components, as per circuit specification, and to keep lead lengths short. Test showed that a few inches of thick connecting wire has appreciable inductance. Coils were positioned for least interaction and overall constructed for high currents and voltage working.

20 Meters Fouth Harmonic Filter

Time was spent on making tight tolerance components, and joining them close together, as possible. The result you can see, is just a circuit board. It works well in a test environment, but was ineffective when currents start to circulate. No doubt the specification held good, but provided no input to output port isolation. In its open format, virtually useless.

Second attempt at a Notch filter

This is my second attempt, using a better circuit configuration and materials. With screened and isolated input and output ports. The aluminium has a kind of brushed polished surface, so all connection points and joints were buffed up to ensure good grounding. During testing it was noticed that without ensuring good bonding unpredictable and intermittent attenuation resulted (or the lack of it) It can also be noted that it is essential when making measurements with multiple connectors, that new and fresh leads are made up. Old and tarnished connectors plagued me for many hours. Trying to measure deep notch filter response is an exacting science.

20 Meter Fourth Harmonic Filter	Constructing TVi notch filter This was my first attempt at making a TVi Notch filter. It is designed to pass all HF frequencies, but insert a deep notch at 56.8Mhz which is the forth harmonic of 20 meters, thought to be responsible for my TVi problems. The coils can be seen soldered to home made capacitors, made out of double sided PCB material. The holes are drilled to trim the final capacitance, about 2pf each with a 4mm drill. Dielectric used was a polythene freezer bag. A single nylon nut and bolt clamps both together.
20 Meter Fourth Harmonic Filter	The theme of the filter construction was to produce precise components, as per circuit specification, and to keep lead lengths short. Test showed that a few inches of thick connecting wire has appreciable inductance. Coils were positioned for least interaction and overall constructed for high currents and voltage working.
20 Meters Fouth Harmonic Filter	Time was spent on making tight tolerance components, and joining them close together, as possible. The result you can see, is just a circuit board. It works well in a test environment, but was ineffective when currents start to circulate. No doubt the specification held good, but provided no input to output port isolation. In its open format, virtually useless.
Second attempt at a Notch filter	This is my second attempt, using a better circuit configuration and materials. With screened and isolated input and output ports. The aluminium has a kind of brushed polished surface, so all connection points and joints were buffed up to ensure good grounding. During testing it was noticed that without ensuring good bonding unpredictable and intermittent attenuation resulted (or the lack of it) It can also be noted that it is essential when making measurements with multiple connectors, that new and fresh leads are made up. Old and tarnished connectors plagued me for many hours. Trying to measure deep notch filter response is an exacting science.