The CODAR pre-amplifier covers the frequency range 1.5 - 30 mc/s in three bands and has a tuned input, so that the unit has to be re-tuned with each frequency change of the main receiver. The unit contains a 6EH7 equivalent high gain pentode. The output load is an RF choke, which is tuned lower than 1.5 mc/s in frequency, so that the stage will not oscillate.
As supplied, the unit was designed to borrow power off the parent receiver. This particular unit has been modified to run off an internal power supply. The required voltages are 6.3v AC for the 6EH7 heater and between 150-200 volts of HT.
The extra tuned circuit in the unit improves image rejection of receivers and the additional gain helps with the signal to noise ratio. When tried with an EKCO Mariner the improvement in performance was very worthwhile.
© Ian O'Toole, 2009. Page created: 24/11/08 Last updated: 4/12/2009