G8MNY  > TECH     08.05.25 08:00z 63 Lines 2745 Bytes #56 (0) @ WW
BID : 32191_GB7CIP
Read: GUEST
Subj: Mains Plugtop Filter Adapter
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 250508/0759Z @:GB7CIP.#32.GBR.EURO #:32191 [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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