No RF output into Quadra

SYMPTOM: I recently experienced a problem and I wonder whether somebody else came across with this anomaly. On 15 meters the 1000MP shows no power output and the Quadra shows an intermittent signal going out. The modulation is affected. If I cut the amp out everything comes back to normal on the 1000MP and the transmission is perfect. Due to high humidity on the antenna, because of heavy rains the SWR is around 1:2.the SWR on the Quadra with the tuner on shows 1:1. I have no problems on the other bands. If I reduce the power > output to about 400W the problem disappears. What could it be?  Leo CT1CSN

SOLUTION: I have had a similar problem recently when the VSWR on the antenna reached about 2.5:1. The tuner in my Quadra couldn't handle it above about 600W and dropped to zero power out. Under 600 watts it worked correctly. Once I got my antenna re-adjusted to under 2.5:1 VSWR the problem went away. This was on 40 meters.  Bill K3WA

SOLUTION: The Quadra is designed to go off-line if output VSWR > 3:1. In practice, the threshold is in the range 2,5:1 ~ 3:1. I think that there is a slight non-linearity in the VSWR calculation process, which lowers the threshold at higher power levels. I observe this behaviour in my Quadra, and it seems normal. If you keep the antenna VSWR < 2,5;1 at the amplifier output, the Quadra will stay on-line. Adam, VA7OJ/AB4OJ