Brian,
Laptops "get away with it" because they use their internal battery
like a capacitor. And, they're not really too susceptible to noise in
general. Nature of the beast...
Regards,
kurtt
Kurt Pawlikowski, AKA WB9FMC
The Pinrod Corporation
ku...@pinrod.com
(773) 284-9500
http://pinrod.com
On 5/10/2011 15:32, Brian Alsop wrote:
> Roger,
>
> You should see the crummy "DC" waveforms put out by typical laptop
> switching supplies. I bought a bunch at a recent hamfest. Put each one
> on a 'scope to observe the output. One had a 0.5 volt sawtooth
> superimposed over the DC value. Another have ringing with introducing a
> swing of over a volt in magnitude around the DC value. I tested at zero
> and full load. None of these problems went away. The rest were far
> from clean. Some were IBM branded.
>
> No way would I put my rig on one of these beasties.
>
> I don't know how laptops manage to tolerate them.
>
> The only other thing is yes were hamfest items and could have all been
> rejects or something.
>
> For what it is worth, I did find one good supply but it was for a Kodak
> printer. However, it put out 25 volts. The output was very clean at
> all levels of load.
>
> 73 de Brian/K3KO
>
> On 5/10/2011 19:35, Ross Primrose N4RP wrote:
>> On 5/10/2011 3:13 PM, Jim Brown wrote:
>>> If it were my radio, I would add one or two silicon diodes in series
>>> with the positive lead to reduce the voltage to about 14 volts. For a
>>> 10W K3, I'd guess that 5A diodes would be just fine.
>> I'd thought about that as a possibility. Heat could be an issue,
>> especially if I want it to be easily portable, at 5A, that's about
>> 3.5W/diode assuming a 0.7V drop.
>>
>>> If it's a laptop supply, I would also be concerned about RF noise that
>>> it might produce.
>> I'm concerned about it too, but the laptop supply is already in hand,
>> and without a laptop, so it's worth a try. I know the old desktop PC
>> supply I'm using now has broadband noise at 7.070-7.080, so maybe this
>> one will be better (and definitely a lot smaller!).
>>
>> 73, Ross N4RP
>>
>
>
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