Fenu-Radio - Reuter RAP1-D WLAN-Preselektor

Reuter RAP1-D WLAN-Preselector

In the hobby scene, Software Defined Radios (SDR's) are often discussed and it is mostly about the possibilities that the software offers. Due to all the hype surrounding the software and the craving for new functions, important factors are pushed into the background. The preselection of the antenna signal is one such factor.
The radio market is flooded with cheap SDRs that promise incredible possibilities. Some of these devices do indeed receive quite well, but practically all of them lack sufficient preselection. Some SWLs or even radio amateurs do not realize how important this is. Good SDRs such as Airspy HF+ Discovery and SDRplay devices can benefit very well from a preselector. Older, analog receivers such as the Kenwood R-1000, Lowe HF-150, Alinco DX-R8, AOR AR3030 etc., which are still frequently encountered, do not have a proper preselector built in. These overload quite quickly on broadband antennas.

But what is a preselector and how does it affect reception?
A preselector is a device that is inserted between the antenna and the receiver. This preselector contains various filter combinations. These are low-pass and band-pass filters. Sometimes an amplifier is also built in to compensate for the cable and/or filter attenuation. An attenuator may also be built in. The frequencies only pass through the appropriate low-pass or band-pass filter. This filter is either switched manually by the user or automatically by any receiver control system. In this way, only a small part of the frequency spectrum is allowed through to the receiver. See block diagram below. A preselector only suppresses out-of-band interference, signals that occur outside the filter passband.
A broadband antenna, as is often used today, generally receives the entire frequency spectrum. There are countless and sometimes very strong stations in this frequency spectrum. If this broadband signal reaches the analog/digital converter (ADC) of an SDR without sufficient pre-selection, it will quickly overload. The result is then strong noise, undefinable signal mixtures and ghost stations produced by the SDR itself (or also by an analog receiver). This type of interference is also known as intermodulation or large signal interference. You can find out what such overmodulation can sound like by clicking on the following link.
>Large signal interference<
A preselector is used to ensure that such undesirable phenomena do not occur at all or are greatly attenuated. This is where the RAP1D comes into play. This was specially developed for broadband receivers (SDR), but can also be used for analog receivers. Broadband because every SDR provides a certain spectrum bandwidth. The RAP1D has three tunable bandpass filters that become broader as the frequency increases.

The RAP1D has an aluminum housing and, as you would expect from Reuter Elektronik, has a high-quality finish. The OLED display is correspondingly small, but easy to read. The inscriptions are engraved.

The actual filter circuit is located under a shielded housing and is therefore double shielded. A pleasant discovery under the hood is the high-quality optical encoder from Bourns. A guarantee for a long service life! Mechanical encoders, which are often installed in similar devices, show signs of wear after a short period of operation and no longer function properly. Due to its small size, the RAP1D is a lightweight. For this reason, an additional weight is screwed onto the underside of the circuit board. This gives the device more stability on the table.