K9YC:
> So Carlos is using two 5 KOhm chokes with the DXE circuit (that is,
two ground rods).
No, N4IS is not using the DXE style but one similar to yours
with multiple turns of coax through a toroid (although he uses mix 77
instead of 31).
There are at least 3 different styles of RX chokes:
1. W2DU which uses 50-100 small ferrite beads on the outside of the
coax. The coax does not pass but once through any bead. No ground
is necessary.
2. Toroid chokes (W1HIS, K9YC, N4IS, etc). This is multiple turns
of coax through a large toroid (mix 31, 43 or 77 depending on desired
frequency characteristics). This style is electrically similar to
the W2DU style but uses multiple loops of coax through a large toroid
to achieve similar impedance. No ground is necessary.
3. I *believe* the DXE style physically breaks the flow of common
mode current through the shield by using isolated transformer
windings through a 1:1 binocular core transformer. These look
similar to the Beverage transformer shown near the bottom of the page
below, but are a 1:1 transformer with 2-3 windings per side. (I'm
guessing about all this since I've never actually examined one).
http://w8ji.com/core_selection.htm (see photo near bottom of page)
DXE recommends connecting the longest length of coax to the grounded
connector. If you look carefully at the top photo below, you'll see
the left connector has an insulating spacer beneath it. You connect
the shortest run of coax to the ungrounded (left) connector and the
longest run to the grounded (right) connector.
http://www.dxengineering.com/pdf/RFCC-1-Rev2.pdf
"The DX Engineering RFCC-1 receive feedline common-mode choke is the
most effective solution
to common-mode noise or unwanted signal ingress available to date.
The DX Engineering RFCC-1
provides thousands of ohms isolation between the input and output
coaxial shield connections while
passing desired signals, including dc or low frequency ac control
signals. The RFCC-1 has
extremely high isolation impedance which effectively blocks
common-mode noise or unwanted
signals, even in the presence of very poor grounding."
It would be interesting if someone could define "extremely high
isolation impedance". :-)
73, Bill W4ZV
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|