Peter wrote:
>
>Rich said;
>
>>2. add a coaxial RF choke [4 to 5-metres of coax wound single-layer on
>>3" to 4" ABS plastic sewer pipe] to the dipole's feedline to keep RF from
>>returning to the radio-room (and the mains) on the outside of the shield.
>>The best place for the choke is at the dipole's center feedpoint
>
>The dipole is fed with open wire line, so that it can be used on other
>bands. RF ammeters in the remote automatic antenna tuner suggest the
>currents in the two feed wires are substantially equal. One leg of the
>dipole runs over the house, and my suspicion is that the field produced by
>it induces currents in the house wiring. probably ferrite chokes on the
>feed in and out of the RCD are the best answer, although the form of the
>switchbox and its location make that a little difficult physically.
>
There's also something strange happening... You'd imagine that the RCD
should be a simple passive device, immune to RF, because it's basically
a mains transformer. The primary is bifilar, and normally carries equal
and opposite line and neutral currents so there is no magnetization. The
secondary is a solenoid that triggers the spring-loaded trip switch only
if a fault condition causes any *difference* between those two currents.
So what's to react to RF in such a device? It's also hard to imagine
substantially different RF currents being induced in the line and
neutral conductors. But maybe the fault signal is electronically
amplified - in which case the RCD becomes vulnerable to RF. A word with
the manufacturer's technical department might be in order.
A clip-on RF current meter can be very useful to show which parts of the
mains wiring are involved, and to what extent. I've just gone through
something rather similar here, after extending the inverted-L for Top
Band, which brought the hot end too close to the house. My problem was
RF getting into the mains and causing TVI. The RF current meter was an
absolute godsend, because it shows which cables are carrying stray
currents, and whether the attempts to stop them were actually working.
Things that helped were a large ferrite choke with all three mains
conductors wound through it, and a three-wire mains filter for the shack
supply. I realise that you can't realistically pass the whole house
mains supply through a filter, but a choke is 'non-invasive'.
>>3. replace the RCD with a conventional breaker and inform house
>>residents that it is no longer safe to take a shower or bath with a hair
>dryer.
>
The other residents of Peter's house are an engineer and two cats, none
of whom would take kindly to that proposal.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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