I guarantee it’s the switch. There’s a report on RFI on a DLI rackmount switch
on my website. Turned out they use PWM to drive the relay coils. 7 ns risetime
on the signals! That coupled to the AC line and out it went. You need CM chokes
on ALL conductors connected to that device. I did the station engineering for
the W6TCP 4-band remote EME station and ended up using a small fortune worth of
ferries there.
Gary Johnson NA6O
> Dear friends,
>
>
>
> I have noticed something that puzzles me. When I turn ON a pair of AC fans,
> my VHF noise floor *drops.*
>
>
>
> Background: My EME station is remotely operated. Everything is mounted at
> the antenna, about 100m from my house. All the equipment is contained
> within a fiberglass enclosure that is part of the antenna base. 220VAC and
> a fiber optic control line are the only cables to/from the enclosure. You
> can see a photo and some description on my QRZ page
> https://www.qrz.com/db/W9IP .
>
> The enclosure has two 170mm 110VAC muffin fans for ventilation. I can turn
> the fans on/off remotely using a Ethernet PDU
> <https://www.apc.com/us/en/product/AP7901B/rack-pdu-switched-1u-20a-120v-852
> 0/> without switching anything else in the system. My location is rural
> and the closest neighbor is at least 200m away. I do have some strong FM
> broadcast stations a few km away but their overload effects are completely
> (?) mitigated by helical filters mounted at the antenna feed.
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