[Lowfer] Re: [Lowfe Worthwhile going to Shielded loop?r]

[Ed Phillips]

paulc wrote:
> 
> John,
> 
> Thanks for lending your experience to the query.
> >From your email
> 
>  My only experience with shielded receiving loops has been with small,
> > multi-turn versions. There were no significant reductions in noise, and
> the
> > extra capacitance did narrow the tuning range.
> 
> Why do  you suppose that there a common notion that says the shielded loop
> is quieter?
>  Is your loop located far enough from the house that maybe manmade noise is
> not a problem?
> Perhaps if your only alternative to listen to LF was from an inside the
> house location, the shielded antenna have its desired effect?
> Seems to me Palomar made a shielded loop for table top use.
> 
> To some extent it would seem that size doesn't matter....  for loop antennas
> anyway.  Until the antenna "gain" and system noise figure become greater
> than the noise floor, seems like the smaller antenna doesn't hurt you.
> 
> I have a nearly 3 foot long loopstick I could try in the woods sometime.
> Maybe I will do that.  It is tuned for about 160 to 190 Khz
> 
> PauLC

	Many years ago I built a tuned loop for VLF reception.  It's about 3'
in diameter and shielded with 5/8" aluminum tubing.  The loop winding is
about 6 turns of teflon hookup wire (I had a piece of cable and just
pulled it through and connected the ends appropriately) and transformer
coupled to a preamp using a dual-gate RCA mosfet.  (40673??)  The tuning
range is about 140 kHz to over 300.  When I hauled it around in my car
and used it with a modified BC-453 it appeared to work fine and was a
lot more convenient than a whip; I had no problem copying the local VLF
beacons (about 6 in 1980) as well as Mike Mideke's Z2 beacon.  However,
here at home it's a lot more noisy than my 50 foot vertical.  The
impression I have is that there's a lot of magnetic coupling from the
power lines at the front and back of our yard and that the loop is
picking that up along with the signals.  

	In summary, around the house the loop is essentially useless due to
pickup of man-made garbage but well away from power lines and
civilization it works well.  Lots more signal than a vertical, sharp
tuning, but more noise!

Ed