Hardware to convert from 144 MHz to 70 MHz
The local oscillatorThe local oscillator uses quartz crystals to provide very low noise sidebands. Click here for details of the local oscillator
The mixerThe A balanced mixer with J310 junction-FET transistors running as switches is used. To get the dynamic range required to fit the 70 MHz input of the 70 to 10.7 MHz converter it is necessary to use several transistors in parallel both in the mixer and in the IF output amplifier.
The RF amplifier and filterTwo RF stages with very low gain are used. These amplifiers use parallel J310 transistors, a way to avoid RF power transistors containing beryllium oxide.
Click here for details of the 144 MHz amplifier and filter
The complete 144 to 70 MHz converterThe schematic diagrams contained in the links above as well as the DC supply schematics are laid on a double sided PCB. The unit has two channels so there are two RF amplifier/filter units and two mixer/IF units.
All the layout files for the EDWIN CAD system as well as all PCB production files can be down loaded here CAD files for 144 MHz unit There is also a photo of the assembled unit.
The 144MHz to 70 MHz converter described here is a free design. All the information on this page is free and may be used by anyone for any purpose
Testing and tuningThe RX144, the 144 to 70 MHz converter can be tested and tuned by means of simple standard instruments if the unit is connected to a RX70 unit, in turn connected to a RX10700, a RX2500 a computer with a Delta44 board installed running Linrad. Look here for details: Testing and tuning the RX144
Sensitivity and noise figureThe NF (noise figure) of the RX144 itself is 7 dB, but when the unit is used together with a RX70, a RX10700, a RX2500 and a modified Delta44, the system noise figure is 12 dB at the 144 MHz inputs when the Delta44 is run at minimum gain.
Intercept pointFor the RX144 unit, the 1dB compression point is at +13dBm. The third order intercept point, IP3 is at +27dBm. The unit is limited by the J310 mixer.