Message 25862 in TECHNI.WW
From: G8MNY
Date: Tue, 14 Jul 26 06:34:00 Z
Newsgroups: TECHNI.WW
Subject: Mains Plugtop Filter Adapter
Message-ID: <64892_GB7CIP>
Path: N2MH4|DK0WUE|PI8ZTM|CX2SA|OK2PEN|GB7CIP
R:260714/0643Z 33679@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260714/0643Z 32296@DK0WUE.#BAY.DEU.EU LinBPQ6.0.25
R:260714/0642Z @:PI8ZTM.#ZH1.NLD.EURO #:56735 [Den Haag] $:64892_GB7CIP
R:260714/0641Z @:CX2SA.SAL.URY.SOAM #:1837 [Salto] FBB7.00e $:64892_GB7CIP
R:260714/0638Z 28817@OK2PEN.SP.BRA.SOAM [Sao Jose dos Campos] $:64892_GB7CIP
R:260714/0634Z @:GB7CIP.#32.GBR.EURO #:64892 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Aug 19)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
These were made for UK's BT in 3A (1A/3 KBA 85) & 7A (1A/7 KBA 85) models
before all kit came with filters. I bought a few over the years at various junk
sales. They are not just a single Voltage Dependent Resistor suppresser (VDR)
across the mains, as some "Computer spike" filters are, but have 2 VDRs either
end of a proper balanced RF power line filter.
N.B. in some versions VDR2 is L-E. This can cause problems with ELCBs & is
best removed!
The VDRs are both 275V40B, & the caps are X2 or Y type 250V AC rated. The
toroid has L & N wound on opposite sides (13 Turns each) on an unsaturated
core. It is wire up so phase currents cancel the high normal mode flux, so it
does not saturate & become "ZERO inductance" with the mains current. The
inductance L was measured for just 1 winding.
They are quite effective at reducing RFI, on noisy sources and the Shack Rx,
especially on 80/40m bands. I found much of RFI was not on the mains L & N, but
gets through the earth line. So I modified them to have a 10 turns on a 2cm dia
ferrite ring on the earth too (rated to blow a fuse). This was done on the wire
to the earth socket...
7A L 1.2mH
PINS 4n7=== ===4n7 LOAD
CONCLUSION
This is a useful addition to my kit when I put on ham demo station. I always
use an RF earth (clipped on local radiators or an outside stake) if I am using
just a random wire aerial.
See also buls on "Reducing Electronic RF QRM", "Inverter Petrol Generators" &
"Clip on QRM Probe".
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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