the coax was 3m long, made of RG174 cable. So, may be this is the culprit. I had another 4m long hyper flex cable, but I did not tried it unfortunately. Yes, I can try to add a counterpoise, and see if this disappears. Hope it will, because QMX was again a joy to operate.
It does not seem ridiculously short to me but I would still try to play with lengths and counterpoises.
Yannig F4IUJ