To: rsgb_lf_group@blacksheep.org
References: <1435044716.20151018182802@chriswilson.tv>
 <AE906394-1308-4ACB-86A0-7FC6F8557C01@gmail.com>
 <174420693.20151020102516@chriswilson.tv>
From: =?UTF-8?Q?Wolfgang_B=c3=bcscher?= <dl4yhf@freenet.de>
Message-ID: <56261270.7080400@freenet.de>
Date: Tue, 20 Oct 2015 12:07:44 +0200
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Subject: Re: LF: Where to measure antenna current?
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Hello Chris,

About RCDs tripped by RF : That's an interesting subject, even though I 
never experienced such a problem myself (no surprise since I mostly run 
QRP on any band).

After discovering that the name RCD is also officially used here in DL 
(we formerly just called them Fehlerstrom-Schutzschalter, but that's 
another story), I read a bit on the subject and learned that there are 
indeed types designed to trip on 'higher frequency' components, and on 
very short pulses ! These types of RCDs shall react on frequency 
components up to 1 kHz. With typical tripping currents of 50 mA (or even 
less), they may even get 'critical' at a few hundred kHz (with an 'error 
current' of a few Amperes). The german Wikipedia article contains a bit 
more info about those 'Type A' and 'Type B' RCDs than the english 
article, so I quote ...

>From 
https://de.wikipedia.org/wiki/Fehlerstrom-Schutzschalter#Typen_nach_Art_des_Fehlerstroms 
:


 >>
Die zusätzliche Empfindlichkeit wird durch spezielle Magnetwerkstoffe 
für die eingesetzten Ringbandkerne und Resonanzschaltungen zur 
Beeinflussung des Frequenzgangs erreicht.
<<

Shortened, in english:
The additional sensitivity is achieved by special magnetic materials for 
the toroid core, and resonant circuits (!!) to trim the frequency response.

Maybe you are already "close to resonance" of the frequency-trimming 
circuit, or even though the RF flows as a common-mode signal through the 
core, it causes strange (non-linear) effects in the RCD's current 
transformer.

If you have a couple of 'monster' clamp-on ferrites (such as used for 
thick coaxial cables), you can attach them close to the RCD to reduce 
the problem, and (even more important) improve the counterpoise (RF 
ground) near the antenna to prevent those RF currents entering the house 
(or at least stay away from the RCD).


All the best,
    Wolf  DL4YHF .


Am 20.10.2015 um 11:25 schrieb Chris Wilson:
> Hello John,
>
> Monday, October 19, 2015
>
>
> Thanks  John,  yes it does help, much appreciated, but what I am still
> unsure  of  is  if  my  Scopematch,  that  shows  voltage  and current
> waveforms,  is  also,  on  the  current  waveform,  displaying antenna
> current? Does it not "do the same job" as a current meter?
>
> With apologies to Kev, who has never heard of anyone with so many LF
> issues ;) I have had to run half power recently, as full power is
> tripping the house RCD after a minute or so of transmitting. I am
> ordering some FT-240-77 material toroids, and building an isolation
> matching transformer, instead of the auto transforming coil, in the
> hope it cures this domestically disharmonious issue! I also have a two
> piece E core to try. The fact it also triggers the workshop alrm is
> not so big a deal as I can at least turn it off when transmitting. Has
> anyone else had issues with RCD's and LF?
>
> Thanks again.
>
>> Chris,
>> The arrangement I have here comprises a 5A FSD RF ammeter between
>> the transmitter and the antenna isolating transformer, and another
>> such ammeter (switchable between 5A and 500mA FSD) between the
>> isolating transformer and the earthy end of the antenna matching
>> network.. The intended impedance at this point is 50 ohms.
>> Hope this helps, John
>
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