Hello Paul,

There is no need to mount a mini-whip very high.
5 meter is about optimum. Higher will give stronger signals and noise, so 
nothing is gained. 

Don't worry about the screening effect of trees on receive.
What happens is that there will be some attenuation, but the band noise is 
attenuated by the 
same amount as the signal, so signal to noise ratio is not impaired. These 
antennas provide 
ample signal levels and at LF there is a lot of leeway.

My mini-whip is mounted in a hawthorn tree and there are a couple of large 
chestnut trees 
nearby. At 400 kHz, the difference between dry and wet foliage is only 2 dB, 
which is no 
problem. 

There is no need to use an actual whip. Stefan suggest a whip of 0.3 meter. I 
have tested this 
and found that a PCB-antenna of 30 x 40 mm produces the same signal level. 
Besides a smaller 
size, which is not important of course, it will be less susceptible to 
lightning damage.

The same applies for a K9AY. There is no need to scale it for 137 kHz. The 
directive 
properties are not effected by size, only the output will suffer. You might 
mount it on your 9 
meter LNV and see how it works.

73,
Roelof, pa0rdt