[Lowfer] Re: E probes .v. loops

[Clint Turner]

My current LF RX system consists of a circa-1986 LF Engineering LF-400B 
E-field whip on my house.  I live in suburbia - and therefore am 
surrounded by a lot of noise, but yet, I'm *usually* able to get to the 
atmospheric noise floor in the LowFER bands - but not without a bit of 
serendipity.  (A 3-channel synchronous noise blanker also works well, 
too...)

The biggest factor in being able to do this is that my house has a metal 
roof.  The antenna itself is about 5 feet above the roof - and the 
shield of the feeder coax is bonded to the roof itself, albeit through a 
fairly long (15') piece of wire.

The second most important thing is the decoupling on the feeder coax 
itself.  I noticed early on that I needed to decouple the coax line 
coming into the house/computer and this was done by cramming a few dozen 
turns of the coax onto a core from a TV flyback transformer or two.   
Doing this simple thing makes a night and day difference in the 
performance of the system (especially below 100 KHz) - and there is just 
enough inductance that it's effect extends down to about 10 KHz or so 
before the decoupling seems to stop working.

One thing that *would* work well, too, would be to use a balanced feed 
to the antenna - e.g. twinax or something similar.  Feeding power via 
this scheme would be slightly tricky - but not something that a few 
pieces of ferrite from a junked PC switching supply couldn't do.  I know 
that this scheme works because, for a mountaintop repeater project, I 
built a twinax-based system (covering 100 KHz to 60 MHz) that has very 
good longitudinal balance - achieved with ferrite-loaded transformers, 
some faraday shielding, and some fine-tuning of balance adjustments 
(e.g. potentiometers, etc.)  Practically speaking, this "decoupler" 
could simply be put in one box (with both the "gozinta" and "gozouta") 
with the sole purpose of decoupling everything as much as possible, but 
with coax input and outputs.

Clint
KA7OEI

P.S.  If you don't mind spending a bit of money - or if you know where 
some are - I'd suspect that the video "hum eliminator" boxes would work 
well, too.  These are used to break up ground loops on video lines.  
They are typically RG-174 sized 75 ohm coax on a toroid with about 10-15 
millihenries of inductance.