Elad FDM-DUO Accessories and Information
External keypad for direct frequency entry .
FDM-DUO_at_VHF.pdf When the DUO is used above 54MHz, external filtering and amplification is needed.
This describes the requirements and gives some practical designs.
144MHz Transverter Driver To make the FDM-Duo 'look like' an FT817 used
for driving microwave transverters.
Audio Drive level The DUO has an internal soundcard for external audio in /out.
This paper describes some tests made to determine the optimum level.
The I/Q mode of operation is also described in detail
EladQuickset.pdf When using the transceiver on the different bands, its internal filters and Tx port need to be selected. Doing this via the menu is a bit tedious, so a utility was written to do the selection via CAT commands. Windows. .EXE and an example .INI file are included in
EladSet.zip
Using the External SPI Interface for frequency / band switching The D connector on the rear carries signals that, with an additional 74HCT595 latch/shift register chip, allows up to eight interface lines to be controlled as a function of the frequency setting. The frequency limits for each line can be set up individually using CAT commands.
This modern direct sampling 5 Watt HF transceiver can also be used extensively at LF and VHF using its low power output port for Tx.
Additional hardware makes life easier:
Makes life simpler when making wide frequency changes than repeatedly changing the tuning step function.
The Rx low pass filter is automatically selected in or out depending on the entered frequency.
Full archive with PIC code and PCB layouts here EladKeypad.zip
Elad-VHF-PCB 1:1 Mirrored PCB Layout for VHF Module, suitable for home built PCBs
Similar to the VHF module, but with reduced Rx gain, 500mW output and DC Volts on the transverter port for PTT control
PCB Layout 1:1 mirrored for home construction (top copper only). Board size 100 x 53mm
If the DUO is to be used for coherent communications,such as with EbNaut on LF, care needs to be taken with choice of frequency to avoid NCO
and DDS rounding errors.
This note describes how to choose frequencies or mitigate the errors that can arise
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