08 April 2013

23cm biquad and coax

After a long a careful theoretical planning, I moved the 23cm RX-only biquad antenna in a more permanent location, not obstructing the view out of the balcony.
Since the antenna is now closer to the coax entrance into the shack, I could shorten the cable: what a better chance to take a couple of measurements?

After fixing the antenna in place I fired up SDRsharp and tuned the local 23cm beacon. Its carrier was peaking -40dB (relative). Then I cut at least 4 metres off the coax cable (unknown 75 ohm), re-soldered the TV-plug at the shack end and measured again: carrier now peaks at -35 dB (relative). That's about 5 dB S/N improvement.

Lacking proper instrumentation I cannot certify the gain is due just to the shorter coax, or to any other factor like: impedance match (remember my antenna R+jX was never measured), better coax-to-connector(s) junction, ... In any case apparently now I have 5 more dB of RX "power" for the next 23 cm event.

I am still after a simple method to remotely turn my antenna over a 90° range (max). I have few ideas but they are mechanically too complex for my time and tools.