-> It looks then as if the longer the cable the easier it is to acomplish due to
-> averaging, but at less than 5" wavelength any cable inefficiency
will quickly
-> defeat the advantage gained. The tolerances must be so much more forgiving in
-> the VLF range.

 Actualy that is why at those Frequnecies the Transmitter is near or
part of the antenna. the Cable Losses Kill you. Here are some casble
loss figures.
****************
Cable Losses. 
It is recommended to use RG-6U coax cable, which has been sweep tested
to the maximum frequency in use. RG-59U coax cable should not be used
for the. down lead cable due to higher cable loss. With longer cable
runs it is recommended that RG- 11 U coax cable be used for minimum
cable loss and less voltage drop. Please refer to the typical cable loss
for RG-59U, RG-6U and RG-11U. 
CABLE TYPE 
Loss in dB per 100 teet Length 
         500MHZ  900MHZ  1450MHZ 1750MHz 2050MHz 
RG59     6.5dB   9.0 dB  11.9 dB 13.6dB  15.3dB 
RG6U     5.0 dB  6.9 dB  9.1 dB  10.4dB  11.7dB 
RG11U    3.7dB   5.2 dB  6.9 dB  7.9dB   8.9 dB 

While these happen to be 75 Ohm cables, Because that was the most handy
Chart I could find , There are the 50 Ohm Equilivents.
 First Incidently the Losses for RG 58 are about TWICE of that of RG59. 

The 50 Ohm equilivent of RG59 is RG-213 or RG-214
for RG-6 it is Times Microwave LMR 240
and for the RG-11 it is Belden 9913

There are even better Coax for that and Higher Frequency ranges but as
for Cost "IF you have to Ask you cannot afford it".
Althouhg LMR 400 or LMR 600(6.8 Db abd 4.4 Db per 100 Ft losses at 2400
GHz) are not all that bad the big Cost comes with LDF or Heliax Coax. 
As an example the 1 5/8"(Outer Diameter) Heliax only has a loss of 1.4
dB at 2400 GHz





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