[R-390] R-390A help needed

[Karsten Simon]

Jim, the antenna relay is ok. The impedance transformation 50 Ohms unsymmetric to 120 Ohms symmetric (= Twinax antenna jack) is performed by a simple isolating home brew ferrite core transformer. Its attenuation is very small, in the order of .5 dB within the frquency range .5 to 30 MHz. The -3 dB splitter exhibits equal attenuation on both outputs, probably in the order of 3.5 dB. Thus the 51S-1 sees 3,5 dB antenna signal attenuation whereas the R-390A sees 4 dB. This small difference (.5 dB) should be hardly noticeable. The R-390A's coaxial antenna input (C-Type coax) is high impedance which requires an impedance transformer (.5 dB attenuation estimated) to match the 50 Ohms splitter signal. So this connection variant will also exhibit approx. .5 dB difference in antenna signal attenuation. In my opinion the advantage of using the Twinax antenna input is that the 50/120 impedance transformer permits galvanic isolation which I expect will contribute to less antenna noise. - Currently I cannot experiment with different antenna connections as all crystals have been removed from the R-390A and are being tested for accuracy and functionality. I expect them to be back within a few days though. 
Zweibrücken: Influence from nearby France -> French cuisine, savoir vivre. Certainly one of the better places to live at inspite of nasty winter months. -- Karsten