Thanks, this probably explains it.
And it's the information I was looking for. Couldn't find it in the instructions ... My apologies if I overlooked it.
Allegedly the HackRF puts out 5dbm to 15dbm in the range 0-10MHz, increasing with the frequency.
That should work in the higher ranges.
But I will have to investigate my transmission line as well ...
Karsten Benz - ZL1KPB