QRM from Charging Laptop

I'm using an old IBM Thinkpad in conjunction with a receiver to monitor 136kHz overnights. Using WSPR and Opera32 simultaneously, reports are posted on two websites and my results have been better than average.

The laptop is very quiet on the LF band, even when charging, until it reaches what it thinks is 100% and then generates severe QRM on 137kHz in the middle of the WSPR/Opera allocation. The charger is a linear 16V power unit as there are some little noise bands from the usual 16V switch-mode supplies available.

I put the charger on a timer to allow 2½ hours on battery and 30mins charging for the duration but this is not foolproof, sometimes the battery thinks it's had enough and the laptop is off in the morning.

Ideally I could leave the charger on continuously as long as it stops well before the battery reaches 100%, say at 80%. This is something many technical users would like in order to conserve battery life but there's no easy solution.

(The Thinkpads are the only laptops I've trodden on or sat on with no damage and I bought a brand new one for the equivalent of about $18, ten years old mind you, so I now have several of these and a selection of cannibalised ones).

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Originally Posted by HUGH

I'm using an old IBM Thinkpad in conjunction with a receiver to monitor 136kHz overnights. Using WSPR and Opera32 simultaneously, reports are posted on two websites and my results have been better than average.

The laptop is very quiet on the LF band, even when charging, until it reaches what it thinks is 100% and then generates severe QRM on 137kHz in the middle of the WSPR/Opera allocation. The charger is a linear 16V power unit as there are some little noise bands from the usual 16V switch-mode supplies available.

I put the charger on a timer to allow 2½ hours on battery and 30mins charging for the duration but this is not foolproof, sometimes the battery thinks it's had enough and the laptop is off in the morning.

Ideally I could leave the charger on continuously as long as it stops well before the battery reaches 100%, say at 80%. This is something many technical users would like in order to conserve battery life but there's no easy solution.

(The Thinkpads are the only laptops I've trodden on or sat on with no damage and I bought a brand new one for the equivalent of about $18, ten years old mind you, so I now have several of these and a selection of cannibalised ones).

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Is this a new occurrence of a problem or something that you've been living with for a while? Has anything changed? Probably some signal from the Thinkpad telling the charging circuit to stop charging the internal battery.

-OT- How long and, what are you using for an antenna at that frequency and wave-length?

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Now the weather is cooler I can see the interference is temperature dependent and disappears off the band which is why I didn't spot it before. Certainly the Thinkpad doesn't allow overcharging, the actual batteries are quite sophisticated.

Normally the antenna is a horizontal loop at an average height of 40 feet but this is no good for LF so it becomes a base-loaded inverted L using the open feeder strapped as a vertical, the important bit for LF tx, and the entire top is capacitative loading. As it comes right into the shack it is not good as far as local noise is concerned. The loading coil is inside an old beer keg, placed outside on a corrugated iron roof, the entire being grounded. This is quite good and there is no more than 400V (peak) of RF in the shack compared to many setups, some of which have been reported as catching fire.