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ChatGBT

 

group,

Just asked a question of chatGBT.

What is a good design for a low power low pass filter for the 20 meter ham band

and got:

A low pass filter is a circuit that allows low frequency signals to pass through while attenuating high frequency signals. For the 20 meter ham band, which spans from 14.000 MHz to 14.350 MHz, a low pass filter can be designed to attenuate frequencies above 14.350 MHz.

Here is a simple design for a low power low pass filter for the 20 meter ham band:

  1. Determine the cutoff frequency: The cutoff frequency is the frequency at which the filter starts to attenuate signals. For a low pass filter, the cutoff frequency is the highest frequency that the filter allows to pass through. In this case, the cutoff frequency should be set at 14.350 MHz.

  2. Choose the filter topology: A simple topology for a low pass filter is the RC filter, which consists of a resistor and a capacitor. The cutoff frequency of an RC filter can be calculated using the formula f_c = 1 / (2¦ÐRC), where f_c is the cutoff frequency, R is the resistance, and C is the capacitance.

  3. Choose the component values: To achieve a cutoff frequency of 14.350 MHz, we can choose a resistor value of 100 ohms and a capacitor value of 1 nF.

  4. Assemble the filter: Connect the resistor and capacitor in series, with the input signal connected to the resistor and the output signal taken across the capacitor.

This simple RC low pass filter can be easily implemented using through-hole components on a printed circuit board (PCB). The filter can be powered using a low voltage power supply, and it should provide good attenuation of signals above 14.350 MHz while allowing lower frequency signals to pass through.


Interesting.

? ---John AC9UV

 

Group,

Then I asked:

what about one using torroids?

and got:

A low pass filter using toroids can also be designed for the 20 meter ham band. Toroids are a type of magnetic core that can be used to create inductors, which are important components in many types of filters. The advantage of using toroids is that they can provide high inductance in a small package, making them ideal for compact filter designs.

Here is a design for a low pass filter using toroids:

  1. Determine the cutoff frequency: As mentioned earlier, the cutoff frequency for a low pass filter for the 20 meter ham band should be set at 14.350 MHz.

  2. Choose the filter topology: A common topology for a low pass filter using toroids is the T-filter, which consists of two inductors and a capacitor. The T-filter can provide a steep roll-off of frequencies above the cutoff frequency, resulting in better attenuation of unwanted signals.

  3. Choose the toroid cores and wire: Toroid cores come in different materials and sizes, with different permeabilities and loss characteristics. For this design, we can use T50-2 toroids, which are commonly available and suitable for use in the 20 meter ham band. We will need two toroids, each wound with a few turns of wire.

  4. Choose the component values: To achieve a cutoff frequency of 14.350 MHz, we can choose a capacitor value of 220 pF. The inductance values can be calculated using the formula L = (R^2 + X_c^2) / (2¦Ðf_c X_c), where L is the inductance, R is the resistance, X_c is the capacitive reactance, and f_c is the cutoff frequency. For this design, we can choose an inductance value of 7.5 ?H for each of the two inductors.

  5. Wind the toroids: Wind each toroid with a few turns of wire, following the recommended winding direction for the toroid material. The number of turns will depend on the wire size and the toroid size, and can be calculated using online calculators or design software.

  6. Assemble the filter: Connect one toroid to the input of the filter, and connect the other toroid and the capacitor in parallel to the output of the filter. The toroids and capacitor should be connected in a T-shape, with the capacitor connected between the two ends of the toroids.

This T-filter using toroids should provide good attenuation of signals above 14.350 MHz while allowing lower frequency signals to pass through. The filter can be enclosed in a shielded case to prevent interference from nearby signals, and can be powered using a low voltage power supply.

-------------------------

The Sea Sprite used 250 pf but that is for the CW portion of the band. Interesting result.

---John AC9UV

On 02/26/2023 3:33 PM John Putnum, AC9UV <johnfputnam@...> wrote:


group,

Just asked a question of chatGBT.

What is a good design for a low power low pass filter for the 20 meter ham band

and got:

A low pass filter is a circuit that allows low frequency signals to pass through while attenuating high frequency signals. For the 20 meter ham band, which spans from 14.000 MHz to 14.350 MHz, a low pass filter can be designed to attenuate frequencies above 14.350 MHz.

Here is a simple design for a low power low pass filter for the 20 meter ham band:

  1. Determine the cutoff frequency: The cutoff frequency is the frequency at which the filter starts to attenuate signals. For a low pass filter, the cutoff frequency is the highest frequency that the filter allows to pass through. In this case, the cutoff frequency should be set at 14.350 MHz.

  2. Choose the filter topology: A simple topology for a low pass filter is the RC filter, which consists of a resistor and a capacitor. The cutoff frequency of an RC filter can be calculated using the formula f_c = 1 / (2¦ÐRC), where f_c is the cutoff frequency, R is the resistance, and C is the capacitance.

  3. Choose the component values: To achieve a cutoff frequency of 14.350 MHz, we can choose a resistor value of 100 ohms and a capacitor value of 1 nF.

  4. Assemble the filter: Connect the resistor and capacitor in series, with the input signal connected to the resistor and the output signal taken across the capacitor.

This simple RC low pass filter can be easily implemented using through-hole components on a printed circuit board (PCB). The filter can be powered using a low voltage power supply, and it should provide good attenuation of signals above 14.350 MHz while allowing lower frequency signals to pass through.


Interesting.

? ---John AC9UV

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