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G8MNY > TECH 16.12.24 08:53l 65 Lines 2747 Bytes #999 (0) @ WW
BID : 21967_GB7CIP
Read: GUEST
Subj: Mains Plugtop Filter Adapter
Path: IZ3LSV<I0OJJ<LU4ECL<LU9DCE<GB7YEW<GB7CIP
Sent: 241216/0735Z @:GB7CIP.#32.GBR.EURO #:21967 [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.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ 7A L 1.2mH
³() ³ L<Äo-oÄÂÄÄ(((()ÄÄÄÄÄÄÄÂÄÄÂÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄ< L
³ ³ ³ ø 0.3uF³ ³ ³ 270k
³ ³ PLUG VDR ± = = = X2 === ³ ± VDR /Á\Neon SOCKET
³ Û ³ 1 ³ ³ ³ ³ 2 \Â/
³ ³ N<ÄÄÄÄÄÁÄÄ())))ÄÄÄÂÄÄÄÁÄÄ(ÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄ< N
³ ³ ø ³ ³
³ ßß ßß ³ PINS 4n7=== ===4n7 LOAD
³ ³ Y ³ ³ Y
³ ³ E<ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ< E
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
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 & 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<Äo-oÄÂÄÄ(((()ÄÄÄÄÄÄÂÄÄÂÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄ< L
³ ø 0.3uF³ ³ ³ 270k
PLUG VDR ± = = = X2 === ³ ± VDR /Á\Neon SOCKET
1 ³ ³ ³ ³ 2 \Â/
N<ÄÄÄÄÄÁÄÄ())))ÄÄÂÄÄÄÁÄÄ(ÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄ< N
ø ³ ³
PINS 4n7=== ===4n7 LOAD
Y ³ ³ Y added
E<ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄ(((()ÄÄÄÄ< 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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