[hpsdr] Mercury Level Cal

[W4sc]

All,

In level calibration of Mercury RX, be aware of the following that may
leave you with a less than optimal calibration. A good, consistant
calibration could not be obtained while attempting on 14.2MHz at -70dbm.

If you use a signal generator connected via a cable, make sure the
inter-connecting cable is of good quality and condition and no longer than
required.  In the specific case, it was determined that the interconnect
cable (RG-58)  had a bad connector, and the shielding effectiveness was not
good enough. Leakage into the setup from external sources (ie computer
clocks, and general
electrical noise, external radio signals ect, ect.) should be eliminated.
Level calibration was being attempted on 14.2 MHz, and in this particular
case the 20M band seems rife with computer and other external noise.
Possibly due to the 14.314MHz crystal osillator within the host itself.

Level calibration was eventually performed at 15MHz, first at -70dbm, then
at -90dbm.

The following is suggested to mitigate this leakage problem:

1) Use a good quality inter connect cable, such as a double shielded RG-142
This can give about 20db better isolation over RG-58 type cable.
2) Use the Elecraft signal generator (XG1 or XG2) connected directly to
Mercury.. This will eliminate the interconnect. Be sure of the SGx output
level.  This setup may also benefit from having a shield around the
generator.
3) Find and use a "quiet" frequency.


de Ben W4SC