K3 & Common mode

[Jeff F6AOJ]

Hi,

i am a recent K3 owner and i live at 15 km from a 300 kW AM station on 864 kHz,
on 80m dipole S-meter rise up to S9+55 with 10 dB attenuator ON.
On dummy load i can read S1 in AM or SSB, without BPF option.
With jumper between pins 1 and 3 P44E RF board, no change.

80 WAS poor and 160 unusable until i put a common mode choc in DC cable.
i got my best result with 8 turns on 4x FT-240-43 stacked.

Is anyone with experience in chocs on DC line ?

73  Jeff  F6AOJ

http://f6aoj.ao-journal.com/
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[Dave, G4AON]

8 turns on the stacked cores appear to give higher impedance on the low
bands compared to typical chokes fitted to other transceiver power
leads. Here in Europe the Kenwood TS-480SAT includes a TDK ZCAT3035-1330
choke which with 2 turns of the K3 lead (maximum that will fit) would
only give around 90 Ohms impedance compared to 820 Ohms for the
FT-240-43 with 8 turns, at 1.9 MHz.

An on-line calculator for various chokes is at: http://toroids.info/
(the TDK choke info is at: www.tdk.co.jp/tefe02/e9a15_zcat.pdf)

73 Dave, G4AON
K3/100 #80 with thankfully no broadcast breakthrough here
======================
80 WAS poor and 160 unusable until i put a common mode choc in DC cable.
i got my best result with 8 turns on 4x FT-240-43 stacked.

Is anyone with experience in chocs on DC line ?

73 Jeff F6AOJ
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[Jim Brown-10]

On Sat, 01 Aug 2009 12:32:47 +0100, Dave G4AON wrote:

>8 turns on the stacked cores appear to give higher impedance on the low
>bands compared to typical chokes fitted to other transceiver power
>leads.

Who cares -- their impedance is far too low to make a dent in HF noise. The
multiturn choke on the 2.4-inch toroids is FAR more effective. See measured data
for typical chokes in my tutorial.

> Here in Europe the Kenwood TS-480SAT includes a TDK ZCAT3035-1330
>choke which with 2 turns of the K3 lead (maximum that will fit) would
>only give around 90 Ohms impedance compared to 820 Ohms for the
>FT-240-43 with 8 turns, at 1.9 MHz.

Those chokes do nothing more than get them past EMC testing, which essentially
looks only above 30 MHz.

>An on-line calculator for various chokes is at: http://toroids.info/

This calculator ignores the capacitance in the equivalent circuit of a ferrite
choke -- that is, it treats the choke as a pure inductance, assuming an
additional capacitance will be supplied to resonate with it. It is essentially
useless for our purposes.

>(the TDK choke info is at: www.tdk.co.jp/tefe02/e9a15_zcat.pdf)

The TDK parts listed here are designed for suppression at VHF and UHF, and have
little value at HF. They appear to be a cross between Fair-Rite #43 and #61.

>80 WAS poor and 160 unusable until i put a common mode choc in DC cable.
>i got my best result with 8 turns on 4x FT-240-43 stacked.

>Is anyone with experience in chocs on DC line ?

I've done it a bit here. If your noise is coupled that way, it can help. For
this application, you don't need four cores if you can wind more turns. See the
measured data in my tutorial for 1-14 turns on single #43 and #31 toroids. For
80 and 160, #31 is far superior to #43. Above 5 MHz the two materials are quite
similar, with #43 being slightly better.

It is also possible to put a choke on only one of the conductors -- that is, as
a differential filter. A small core will saturate, but a large one will saturate
only on transmit. There's no destructive problem with saturation -- the choke
simply doesn't choke anything -- so as long as the choke doesn't saturate on
receive (lower DC current) it can be effective.

The tutorial is at http://audiosystemsgroup.com/RFI-Ham.pdf 

73,

Jim Brown K9YC


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