[R-390] computer swtiched source

[Larry H]

Hi Jose,  Unfortunately, some laptop power supplies generate very bad emi.
And, it's not  just laptop supplies, it's a lot of 'wall warts' that are
major offenders.  And the bad thing is that with most 390s and other rx's
with good power line filters built in, the emi from the wall warts enters
the rx through the antenna, and not the power line.  You can test this
fairly easily by tuning in the emi and then disconnecting your antenna.
When you do this, make sure you have tube shields on for the sensitive
tubes,  all covers on the 390, and it is correctly grounded.

So, the answer to your question is: no, an additional emi filter in the
power line of a 390 will not help.

If you are not using coax or twisted pair to feed the 390, then that makes
it much easier for noise to get into the rx.

Regards, Larry

PS: Please delete any unnecessary verbiage at the end of your post
before you send it to the server.  Thanks.

On Sun, Jan 30, 2022 at 11:59 AM jm <josemic at gmail.com> wrote:

> Hi guys,
>
> I've realised that the noise level increases when the power source of the
> laptop is on. In that case, the noise  makes extremely difficult to hear
> weak signals.
>
> Found on ebay some kind of device called "EMI individual phase noise
> filter" to be placed between the line and the radio. It's very cheap but I
> don't know whether or not would be useful.
>
> Does somebody have any experience with such type of device?
>
> Thanks, and regards
>
> Jose
> EA8DCP
>
>
>