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G8MNY > TECHNI 14.07.26 15:44l 63 Lines 2747 Bytes #10 (0) @ WW
BID : 64892_GB7CIP
Read: GUEST
Subj: Mains Plugtop Filter Adapter
Path: JH4XSY<N3HYM<IW2OHX<PI8ZTM<CX2SA<OK2PEN<GB7CIP
Sent: 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.
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ 7A L 1.2mH
ｳ() ｳ L<ﾄo-oﾄﾂﾄﾄ(((()ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ< L
ｳ ｳ ｳ � 0.3uFｳ ｳ ｳ 270k
ｳ ｳ PLUG VDR ｱ = = = X2 === ｳ ｱ VDR /ﾁ\Neon SOCKET
ｳ ﾛ ｳ 1 ｳ ｳ ｳ ｳ 2 \ﾂ/
ｳ ｳ N<ﾄﾄﾄﾄﾄﾁﾄﾄ())))ﾄﾄﾄﾂﾄﾄﾄﾁﾄﾄ(ﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄ< N
ｳ ｳ � ｳ ｳ
ｳ ﾟﾟ ﾟﾟ ｳ PINS 4n7=== ===4n7 LOAD
ｳ ｳ Y ｳ ｳ Y
ｳ ｳ E<ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ< E
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
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
L<ﾄo-oﾄﾂﾄﾄ(((()ﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ< L
ｳ � 0.3uFｳ ｳ ｳ 270k
PLUG VDR ｱ = = = X2 === ｳ ｱ VDR /ﾁ\Neon SOCKET
1 ｳ ｳ ｳ ｳ 2 \ﾂ/
N<ﾄﾄﾄﾄﾄﾁﾄﾄ())))ﾄﾄﾂﾄﾄﾄﾁﾄﾄ(ﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄ< N
� ｳ ｳ
PINS 4n7=== ===4n7 LOAD
Y ｳ ｳ Y added
E<ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄ(((()ﾄﾄﾄﾄ< E
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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