[Premium-Rx] Powering receivers away from electricity grid

[Peter Gottlieb]

Sine wave inverters these days make the waveform digitally so not only is there 
noise from the circuitry but there is noise on the output waveform.  They 
usually put a capacitor or some other circuit for smoothing the output, a low 
pass basically.

I do NOT recommend you start making all the DC supplies in the rig and 
substituting for the built in power supply.

Different manufacturers of sine inverters will have different amounts of 
interference.  I picked up a 300 watt unit on ePay for 70 or 80 USD and it is 
clean on my RF-590A.  There could be a big variation from unit to unit for all I 
know but if you get one certified to tons of agencies for emissions it should 
either be quiet or be easily quietable by shielding and/or DC and AC filtering.

Peter


Eric Gauja wrote:
> 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!
> 
> 
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