nescaf

Description: The NEScaf filter is designed to offer greater flexibility than previous filters for QRP (low-power) radio rigs. It features two panel-mounted controls: a single center-detent potentiometer that adjusts the center frequency of the filter's bandpass (settable between approximately 415 Hz and 1 kHz), and a dual-ganged potentiometer that allows for a continuously variable bandwidth control ranging from about 60 Hz to 1500 Hz. This smooth bandwidth variation is particularly beneficial. The NEScaf is intended to be driven by a phone or speaker-level signal, eliminating the need for modifications to the radio; it connects directly to the headphone or speaker output, making it compatible with various radios. The compact board measures around 2 inches square, allowing for installation inside many radios if desired. The kit is designed for all skill levels, utilizing through-hole components, making construction and adjustment straightforward. It is affordably priced and serves as a valuable tool for QRP enthusiasts. At the core of the NEScaf is an integrated circuit consisting of two CMOS active filters, which are highly configurable (including low pass, band pass, and notch configurations). Both filters are set up as Butterworth band pass filters and are cascaded. Butterworth filters maintain constant amplitude in the bandpass region, although the cutoff knee is not as sharp as that of Chebyshev filters. This design choice was made to ensure constant volume output, regardless of the bandwidth or center frequency settings. Two onboard trimmer potentiometers enable calibration of the center frequency and adjustment of the audio level into the filter's output amplifier. One trimmer calibrates the center frequency pot, allowing adjustment to align with a transmit offset and sidetone frequency, while the other sets the overall gain of the filter, enabling unity gain if desired. The NEScaf does not include a panel-mounted volume control; instead, it utilizes the volume or RF gain control of the connected rig. It is important to note that a case and audio/power connectors are not provided, as builders may have personal preferences. The kit includes all board-mounted components, the two panel-mounted potentiometers, a power/bypass switch, and a power-indicator LED. Builders can supply their own case and connectors for audio input/output and power, or they may order a connector kit separately. The NEScaf was initially paired with the MF10, later replaced by the LMF100, which is a drop-in replacement for the MF10, and subsequently succeeded by the LTC1060 in the spring of 2010.

The NEScaf filter is an advanced solution for enhancing audio processing in QRP radio applications. Its design accommodates a wide range of operational frequencies and bandwidths, making it suitable for various communication scenarios. The choice of Butterworth filter configuration ensures that users experience a smooth frequency response without significant amplitude variations, which is critical for maintaining audio clarity during transmissions. The dual-ganged potentiometer allows users to fine-tune the bandwidth, which can be particularly useful in crowded frequency bands where selective filtering is necessary to isolate desired signals from background noise.

The integration of trimmer potentiometers for calibration and gain adjustment provides users with the ability to tailor the filter's performance to their specific rig and operating conditions. This feature is especially advantageous when working with radios that have unique transmit offsets, allowing for seamless integration without sacrificing audio quality. The absence of a dedicated volume control on the NEScaf is a deliberate design choice, encouraging users to utilize their existing radio controls for a more streamlined operation.

The compact size of the NEScaf board facilitates easy installation within various radio enclosures, promoting versatility in its application. Builders are encouraged to customize their setups by selecting their preferred cases and connectors, enabling a personalized approach to their QRP rig enhancements. The kit's straightforward assembly process, combined with its affordability, makes it an attractive option for both novice and experienced builders looking to expand their toolkit for low-power radio operations. Overall, the NEScaf filter represents a valuable addition to any QRP enthusiast's equipment, providing enhanced audio filtering capabilities that can significantly improve communication quality.It is more flexible than previous filters for QRP rigs. It has two panel-mounted controls ” a single center-detent potentiometer that sets the center frequency of the filter`s bandpass (default value settable between ~415Hz and ~1kHz), and a dual-ganged potentiometer that provides a continuously variable bandwidth control (from ~60Hz to ~1500Hz). This ability to smoothly vary the bandwidth is very useful. The NEScaf is designed to be driven with a phones or speaker level signal. No hacking into your rig ” just connect it to the headphone or speaker output of the radio. This makes it usable with several radios. The board is small enough, at about 2 inches square, to build inside many radios however, if you so choose. This kit is suitable for all experience levels. It uses all thru-hole components, and the construction and adjustment is very straight-forward. It is reasonably priced and will be a nice addition to the QRPer`s arsenal of tools. The integrated circuit at the heart of the NESCaf is made up of two CMOS active filters. These filters are extremely configurable (low pass, band pass, notch etc). We have chosen to set up both filters as Butterworth band pass filters and to cascade the filters. Butterworth filters have the characteristic of constant amplitude in the band pass region, while the cutoff knee is not be as sharp as if the filter were configured as a Chebychev.

We considered this an acceptable tradeoff, wanting constant volume out regardless of the bandwidth or center frequency setting of the filter. There are two on-board trimmer pots. One is used to "calibrate" the center frequency pot. This allows you to adjust the frequency at which the center detent occurs. If you are using a rig with a transmit offset and sidetone of say, 700 Hz, you can use this trimmer to make that the center-detent frequency.

The other on-board trimmer adjusts the audio level into the filters output amp. Using this pot, you can set the overall gain of the filter. This can be used to set the filter for unity gain, if desired. This way, the filter could be switched in and out, and still maintain a comparable volume level in the headphones. The NEScaf has no panel mounted volume control of its own. It is designed so that you use the volume or RF gain control (if present) on the rig it is being used with.

Please Note: A case and audio/power connectors are NOT supplied. Since each builder will have his or her own personal favorite styles for these, we are not including these parts. All board-mounted parts, plus the two panel-mounted potentiometers, a power/bypass switch, and a power-indicator LED are included in the kit.

You supply your own case. You can supply your own connectors for audio in and out and power, or you can order a connector kit from us with your NEScaf filter. The NEScaf was originally kitted with the MF10. That was replaced by the LMF100, a drop-in replacement for the MF10. These were superseded by the LTC1060 in spring 2010.