Balanced lines are critically important to keep out unwanted signals i.e. 
"10-4 Good Buddy" stuff. I have worked in one megawatt transmitting 
facilities and all critical signal lines are balanced lines.

Here in a nut shell is a wikipedia outline of how they work: 
http://en.wikipedia.org/wiki/Balanced_line

What is done in many applications where you have to transition from 
unbalanced to balanced circuits is to have an opamp circuit or transformer 
do the transition. The main problem for seismic issues is the very low 
frequencies. This is a consideration you have to plug in to your system 
design.

There are two basic ways of doing the balanced line concept. You can use 
"Twinax" coaxial cable and connections 
(http://www.altex.com/Belden-Plenum-TwinAx-Electronic-Instrumentation-Cable-100-Ohm-89207-BEL-P144273.aspx.) 
This is very expensive - I truly mean EXPENSIVE! The other way is with 
Belden Belfoil wire. This a twisted pair wire in a foil covering with a 
drain wire for the ground. For most audio work this performs nicely. Another 
way to do this is to get high quality studio microphone cable. Use only good 
cable no matter which way you go. You can buy the Belden cable as surplus to 
save money. None of this is direct burial. If you want burial you will need 
to get out your check book. PVC conduit is very cheap and you can pull a 
number of wires in the same run.

If you follow the balanced line concept with good station engineering with 
solid grounding and RFI isolation a lot of problems will disappear.

Power line issues: Having worked in electronic security power line issues 
are a big thing. Here are some ebay items similar to what I have:
http://cgi.ebay.com/PULIZZI-PC2773-22-PLUG-POWER-DISTRIBUTION-UNIT-/160487265348?pt=LH_DefaultDomain_0&hash=item255dc95444

http://cgi.ebay.com/Pulizzi-Z-Line-T982A2-Power-Distribution-Unit-New-/350401176294?pt=LH_DefaultDomain_0&hash=item519589a2e6

If you are building your own distribution system I might suggest: 
http://cgi.ebay.com/CORCOM-20VR6-POWER-LINE-RFI-FILTER-20A-120-250VAC-NEW-/370316412063?pt=LH_DefaultDomain_0&hash=item563894049f 
or 
http://www.alliedelec.com/search/searchresults.aspx?N=0&Ntk=Primary&Ntt=feed+through+capacitors

For incoming signal lines I suggest 
http://cgi.ebay.com/100PF-500V-FEED-THROUGH-CAPACITOR-blb151-/180250623900?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item29f7c63f9c. 
These are feed through capacitors. I have used these in military 
applications many times. They work and keep the junk off the signal line. 
They are also used on balanced lines in some applications.

Right now I am restoring older transmitters and repairing test equipment. So 
it is essential I keep everything "electrically quiet".

Jim











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