Ensemble II VHF RX

Posted on Feb 4, 2014

Replacing the front-end with a circuit that down-converts VHF signals in the 2m, 4m or 6m bands to HF signals that can be received in the RX`s `back-end` (which is essentially the Ensemble II RX). The parts provided in this kit permit the builder to select which of the major VHF bands to implement; all the parts for all the options are included in the kit.

Ensemble II VHF RX
Click here to download the full size of the above Circuit.

Band-specific parts are identified throughout the documentation; the builder makes his/her choice at build-time. The builder will find invaluable information at the website of Fred PE0FKO, especially the setup of the software and firmware, as documented in the excellent users manual from Bob G8VOI. This kit reuses a large percentage of the design of the Ensemble II RX (HF/LF) kit. Refer to that kit`s home page for a theory discussion on the radio. This kit reuses the following stages, basically untouched, from the Ensemble II RX: The main difference is in the RF and COntrol stage, which is based upon an earlier design for a VHF add-on board for the Softrock V9. 0 RX. The theory of the Software Designed Radio can be gleaned from the Ensemble II RX documentation. Here, we will concentrate on the differences (where the RF/Auto BPF functionality is replaced with the stage described in the following paragraphs. This discussion will use, as an example, a 144 MHZ signal that will be down-converted to an IF in the apporpriate HF frequency range for detection in the "standard SDR" stages. The incoming signal from the Antenna terminal (or, via a jumper wire from J1/P100 Pin 1), e. g. , 144MHz, is filtered, then pre-amplified by Q1 and fed to a double-balanced mixer, U7. U7 also receives a Local Oscillator signal via from the Si570`s (U3`s) LO Out. This local oscillator signal must be at a frequency (in our example, 115. 2 MHz)...

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