Howdy Folks: I am looking for a voice keyer. I believe the DVK was a
pretty good one. If you have one, or know of one that wants to be sold,
PLEASE let me know. If you think DVK is crap and have something else
better, PLEASE let me know. Any data shall and will be greatly appreciated.
73 de Steve KN5H
>From ni6t@ix.netcom.com (Garry Shapiro) Mon Dec 5 08:16:04 1994
From: ni6t@ix.netcom.com (Garry Shapiro) (Garry Shapiro)
Subject: Terminating Beverages In Shack
Message-ID: <199412050816.AAA01243@ix2.ix.netcom.com>
You wrote:
>
>Hi All,
>
>We recently put up two sets of two-wire switchable beverages at the
KS9K
>station. We brought two runs of coax back to the shack for each set.
The
>"feedpoint" has the impedance-matching and buck transformers and two
outputs.
>
>My question:
>
>Does the unused positions/directions have to be terminated into 50 ohms
to
>work best??
>
>I am concerned that if using the NE beverage, and having the SW coax
>open-circuited (not properly terminated into its characteristic
>impedance), that it will affect the impedance in the "feedpoint"
>matching box and cause harm to the pattern/operation of the desired
>beverage.
>
>Any help would be appreciated.
>
>Chad WE9V
>Loud is Cool....yeah, heh, heh, heh, LOUD is COOL!!!
>kurszewski_chad@macmaiL1.csg.mot.com
>
>A short thought exercise will yield the answer to your question.
Consider a signal incoming from the "far" end: the one without the
transformers.It induces a common-mode signal in both wires. Since the
voltages across the "balanced" secondary are equal, current flows out
the center tap to the unbalanced secondary. There is no net flux in the
balanced transformer so there is no signal out that port, but current
does flow inthe unbalanced secondary and the signal does excit its port.
Conversely, an incoming wave from the other direction induces common
mode voltages in the wires. At the far end, the phase reverses in the
grounded wire but not in the ungrounded wire (boundary conditions: the
grounded wire has zero voltage at the reflection, the other has zero
current.) The resultant differential reflected voltage appears across
teh differential secondary and the signal appears at that port.
So? If the exit port is not properly terminated, the signal reflects
back down the two wires, does the common mode/differential mode
inversion at the far end and winds up going out the OTHER part.
Thus, misternmination or no termination effectively degrades both input
impedance and front-to-back ratio by putting energy from the "wrong"
direction into the "right" port. The F/B ratio degradation means more
noise and--for guys in the midwest--more QRM.
Terminate the unselected port.
Garry, NI6T
with two of those beasts threaded through a redwood canyon.
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