Front end damage in multi-op stations

[gt5830b at prism.gatech.edu]

Hi Everyone,

W0CP writes,
>
> Before last weekend i would have advised you to turn on ur attenuator
> whenever possible to protect the frontend.  however, we managed to
> blow out the 10 and 20 db attenuators in one of the m/s rigs in cqwwcw.
> 73 w0cp
> 
We have experienced this problem (many times) at Georgia Tech with our
two TS940's.  We finally just went in there and took out the 1/8 watt
(or whatever) puny resistors and put in 1 watt and 1/2 watt (man-ly) 
resistors.  You have to do this before the resistors burn up the
circuit board traces or there will be a bigger problem - rewiring
the board - as we had to do with our IC735 which wasn't so lucky.
Anyway, the problem hasn't surfaced again in 2 years of m/s operation.

73 de Dave, K0DI 
gt5830b at prism.gatech.edu


>From zs6nw at leclub.co.za (Jan Zs6Nw)  Thu Dec  1 22:01:00 1994
From: zs6nw at leclub.co.za (Jan Zs6Nw) (Jan Zs6Nw)
Date: Thu,  1 Dec 94 22:01:00 +0000
Subject: RYRYRYRYRYRYRYRYRYRYRY
Message-ID: <12f.8871.400.0CAF26DD at leclub.co.za>


Remember the CQWW RTTY contest ?
Today is the last day for postmarking log entries.

         ZS6NW CQWW RTTY 1994 Score
  Single op single band unassisted high power

 Band   Zones  Countries  QTHs  QSOs  QSO points
  15m    22       67       35   418     1247

           124 x 1247  =  154,628

73
Jan Zs6nw
---
 * KMail 3.00t ®® LeClub Bulletin Board ¯¯

>From John W. Brosnahan" <broz at csn.org  Thu Dec  1 16:10:34 1994
From: John W. Brosnahan" <broz at csn.org (John W. Brosnahan)
Date: Thu, 1 Dec 1994 09:10:34 -0700
Subject: No subject
Message-ID: <199412011610.AA02233 at teal.csn.org>

The following paragraph is typical of a number of questions that I have
received about the Autek bridge and whether it can measure R + j.  Because
of the interest I felt that a general response might be in order.
 
>Can you determine R+j with the Autek RF-1 and some arithmetic???
>Since it gives composite impedance, how do I calculate the resitive 
>and reactive components. SWR is only good to one decimal place.
>I want to plug the R+j values into my L-net/T-net/Pi-net programs.
 
 
Well, yes, sorta!    The unit does not give R + j per se.  But if you measure
Z at resonance (ie where j = 0) you have R.  And if you move off frequency
a little bit the R changes very slowly compared to j so the new Z is
mostly due to j.  So by squaring and subtracting the resonant R (j = 0)  
from the square  of the off-resonance Z (which differs mostly by the 
reactance) and taking the square root of the difference you (sorta) get the j 
component and by knowing which way you moved and knowing which way the sign 
should go for what you are measuring you can determine the sign. All pretty 
messy and not accurate enough for anything except a first cut on component 
values for L (etc) networks.
 
And not very useful at all if what you are trying to measure is far from 
resonance and highly reactive, unless you know, a priori, that the Z is  
mostly reactive such as in the case of a SHORT (much less that a 1/4 wave)
vertical. In this case the Z is almost all capacitive reactance and the
Autek's Z measurement is virtually all due to -j and the Autek has the 
capability of switching to the L scale and giving the value of inductance 
required to resonate the vertical.
 
But nothing beats a good old GR-1606 (or the older 916) bridge (or a GR-1602 
swinging arm bridge for VHF/UHF).  I once bought a cherry 1602 in the wooden 
case for $5 at a flea market, so they are out there.
 
BOTTOM LINE:  The Autek is a slick little tool that can do many interesting
things and is well worth the price, but isn't a generic R + j sorta beast.   
 
73  John  W0UN  broz at csn.org