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G8MNY > TECH 01.03.24 09:40l 64 Lines 2746 Bytes #999 (0) @ WW
BID : 2427_GB7CIP
Read: GUEST
Subj: Mains Plugtop Filter Adapter
Path: ON0AR<OZ5BBS<CX2SA<N3HYM<GB7YEW<LU9DCE<LU1DBQ<VK6ZRT<GB7CIP
Sent: 240301/0820Z @:GB7CIP.#32.GBR.EURO #:2427 [Caterham Surrey GBR] $:2427_GB
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.
旼컴컴컴컴컴컴� 7A L 1.2mH
�() � L<훟-o컫컴(((()컴컴컴컫컴쩡컫컴컴컴컫컴컴< L
� � � � 0.3uF� � � 270k
� � PLUG VDR � = = = X2 === � � VDR /�\Neon SOCKET
� � � 1 � � � � 2 \�/
� � N<컴컴컨컴())))컴컫컴컨컴(컴좔컴컴컴좔컴�< N
� � � � �
� 賽 賽 � PINS 4n7=== ===4n7 LOAD
� � Y � � Y
� � E<컴컴컴컴컴컴컴컴좔컴컴컨컴컴컴컴컴컴컴�< E
읕컴컴컴컴컴컴�
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<훟-o컫컴(((()컴컴컴쩡컫컴쩡컴컴컴쩡컴�< L
� � 0.3uF� � � 270k
PLUG VDR � = = = X2 === � � VDR /�\Neon SOCKET
1 � � � � 2 \�/
N<컴컴컨컴())))컴쩡컴좔�(컴좔컴컴컴좔컴�< N
� � �
PINS 4n7=== ===4n7 LOAD
Y � � Y added
E<컴컴컴컴컴컴컴컨컴컴컴좔컴컴�(((()컴컴< 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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