WANTED: Voice Keyer & info

s.nace1 at genie.geis.com s.nace1 at genie.geis.com
Mon Dec 5 02:59:00 EST 1994

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 at ix.netcom.com (Garry Shapiro)  Mon Dec  5 08:16:04 1994
From: ni6t at ix.netcom.com (Garry Shapiro) (Garry Shapiro)
Date: Mon, 5 Dec 1994 00:16:04 -0800
Subject: Terminating Beverages In Shack
Message-ID: <199412050816.AAA01243 at ix2.ix.netcom.com>

You wrote: 

>Hi All,
>We recently put up two sets of two-wire switchable beverages at the 
>station.  We brought two runs of coax back to the shack for each set.  
>"feedpoint" has the impedance-matching and buck transformers and two 
>My question:
>Does the unused positions/directions have to be terminated into 50 ohms 
>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
>Any help would be appreciated.
>Chad  WE9V
>Loud is Cool....yeah, heh, heh, heh, LOUD is COOL!!!
>kurszewski_chad at 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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