[Premium-Rx] Powering receivers away from electricity grid

[Eric Gauja]

Dear Group Members,
                                   I would appreciate feedback on the 
subject of powering sensitive receivers away from the electricity grid, 
such as on DXpeditions. I own a WJ 8709, and have been looking at options 
for powering it away from the mains. The 8709 (normally operated on 240/110 
VAC) has internal DC supply rails of +24V, +15V, +10V , +5V 
and  -15V.  This means that it cannot be powered from a single 12V battery 
(although it could be done with a number of such batteries, but this gets 
expensive and weighs a ton!) . I have experimented with using 12/240V 
inverters - the normal grid AC supply here in Australia is 240V, but the 
situation would be similar for 12/110V inverters.  I first tried the 
cheaper"modified sine wave" inverters , but the problem of noise arose. No 
problem with the stronger signals, but the weaker signals had to compete 
with a low level background hash not present using mains operation. I then 
tried a more expensive "true sine wave " inverter, expecting much better 
results, but this was not to be. The backgound noise was a bit lower than 
when using the modified sine wave inverter, but low level signals still had 
to compete with noise from the inverter circuitry.
The inverter is in a well shielded and grounded case, and I have also 
clipped ferrite cores around the AC lead from the inverter and also on the 
DC battery leads.  I can also pick up this noise on my portable Sangean 
ATS909 receiver, powered  independently by dry cell batteries, so the noise 
appears not to come via the power leads or earth connections of the 
inverter to the WJ8709.  I have reached the conclusion (perhaps wrong) that 
even the true sine wave inverter radiates noise which because of the 
sensitivity of the WJ8709 and ATS909, is annoyingly noticeable when 
receiving low level signals.  Another possible power source that I have not 
tried is a portable petrol motor/ generator combination - the lower power 
models are not too expensive. But there seem to be some types that are 
called generator /inverters, so I suspect that the inverter portion could 
also generate significant RF noise. Has anyone had any experience with 
these and the subject of receiver DXpedition power in general?
                                                                                                                                                 Best 
Regards from Downunder!