It is also easy to enable full output frequency range of these old obsoleted ESG generators, using simple GPIB commands:

SERV:PRODUCTION:CAL:BEGIN;
SERV:PRODUCTION:CAL 165,2,4000000000.000000;
SERV:PRODUCTION:CAL:END;
SERV:PRODUCTION:CAL:STORE 165;
SERV:PRODUCTION:CAL:PUP;

After instrument is rebooted I can output higher frequency out of the RF port, with drawback of the reduced output power stability.