Topband: Toroidal common mode choke

[donovanf at starpower.net]

In the real world, receiving (or transmitting) problems are often caused by faults rather than by inadequate design. The most common problems are connectors and deteriorated coaxial cable caused by poor installation practices and moisture entry.

Faults are best found through regular inspections, rather than (as many of us do) waiting for the fault to become so severe that its obvious.  A DX resistance measurement of your transmission line performed inside your shack takes only a few seconds and will reveal many of the most common faults.  A VSWR sweep with an MFJ-259 or your favorite instrument is also very useful.  VNA and TDR measurements are also very helpful if you have that capability (you should!).

Keep records of your measurements so that changes will be apparent.  Any change is cause for an investigation.

73
Frank
W3LPL


---- Original message ----
>Date: Tue, 20 Nov 2012 08:42:26 -0500
>From: "Tom W8JI" <w8ji at w8ji.com>  
>Subject: Re: Topband: Toroidal common mode choke  
>To: <topband at contesting.com>
>
>> On paper I agree but what about real world? Topbanders seemed to do quite 
>> well with the old 43 mix and the resultant lower impedance.
>>
>> How much is good enough?
>
>That's a good point.
>
>It seems we tend to go to extremes of black and white and abandon common 
>sense or reasoning in everything we do these days. That pattern has crept 
>into some very simple things, perhaps so one answer fits all and no one ever 
>says "it depends".
>
>> I havent changed any of the 43 material in the house since they removed 
>> the noise from each consumer device; some have been in place for over 30 
>> years going back to the prior QTH. As new stuff is added I use 31 mix, 
>> seems to work the same.
>
>I've never been a big proponent of peppering a system with beads, because 
>often a common-mode series impedance by itself is the least efficient way to 
>do mitigation. It takes a terrible CM signal levels to cause problems, if 
>connectors are good and the antenna is a reasonable distance away. If the 
>antenna isn't a reasonable distance away, then correcting the source is 
>often better.
>
>It's really a big soup of things, and I think some of this has gone beyond 
>sensible solutions. I lived years without problems without any ferrite 
>cores, BUT I grounded feeders sensibly and looked at the system. It all 
>about ratios and changes in CM impedances.
>
>Once something fixes something, it all seems the same. After all, fixed is 
>fixed.
>
>Correct me if I am wrong, but it seems we think noise all comes from common 
>mode and if we add increased suppression things get better and better with 
>nearly no limits. We become almost anorexic with suppression. What really 
>happens is once antenna noise dominates, which can even happen without any 
>suppression at all in many systems, all the rest is a wasted effort. In 
>other systems once the feedline has reasonable suppression, direct radiation 
>takes over. We can add a billion beads to the feeder and nothing changes.
>
>There should be more focus on telling people how to find problems, and less 
>on treating every system the same.
>
>I was visiting a friend and he told me stories about building massive bead 
>strings a few feet long on Yagi antennas!! Someone should stop the bead 
>madness enveloping us, and get us back to rational thought.
>
>73 Tom 
>
>_______________________________________________
>Topband reflector - topband at contesting.com