Saturday, May 1, 2010

30m - 10m Diplexer for QRSS use

Just an idea....

Diplexers are very popular for running VHF and UHF transceivers into the same (simple) antenna. This works since 435 is three times 145. A 1/4-wave radiator for the 2m-band is a 3/4-wave radiator for the 70cm-band.

Could this trick work on shortwave too? The 10m band is about a third of the 30m band ... well... sort of. I figure, I suitable diplexer would separate frequencies below and above about 20MHz, maybe 19MHz for good measures.
The hope is that a vertical of about 7m length would form a 1/4-wave radiator for the 30m-band and a 3/4-wave radiator for the 10m-band.
The numbers tell the following story:

wavelength for 30m: 300/10.14=29.6
wavelength for 10m: 300/28.32=10.6

30m radiator length (assuming a velocity factor of 0.95): 29.6*0.95/4=7.03
10m radiator length (assuming a velocity factor of 0.90): 10.6*0.90*0.75=7.15

A compromise could therefore be a radiator length of 7.1m to suit the 30m grabber and the 10m MEPT at the same time.

Next step, think of a 19MHz diplexer design.