[Lowfer] New Loop NG

[Tim Brannon]

Peter,
I also read John Andrews' reply.  Two more questions...

1.  Is your pick-up loop electrically isolated from the tuned loop?;  i.e.
is there any wire connection between say, the coax shield and the main loop?
As I understand it, you want to ensure that there is only inductive coupling
to the pickup loop--the tuned loop should be "floating" electrically with no
DC connection to the pickup loop.

2.  What kind of capacitors are you using in your switching bank?  I would
suggest using silver-mica caps for the best Q.  Ceramic disk caps may limit
the Q of the tuned circuit and cause the broad tuning.  You might try
connecting an old air-dielectric variable capacitor ala the BCB variety for
comparison--if its clean and in good condition it should have excellent Q,
and might give you some insight into what's going on.

Tim Brannon
Dallas

----- Original Message -----
From: "Peter Barick" <A20PJB1@wpo.cso.niu.edu>
To: <lowfer@mailman.qth.net>
Sent: Monday, April 15, 2002 10:25 AM
Subject: [Lowfer] New Loop NG


> LowFERs,
> Re: My New Loop Ain't Working
>
> I built a new loop late last fall, even had it up on a mast at 20 feet
> but _not_ connected. Then the uninvited Minnesota winds came and
> prevented further outside work. I took it down.
>
> This weekend it was Texas-like outside and I resumed efforts testing
> the loop, which includes a tuning box with a group of switchable caps in
> series w/ the loop and a 1:1 LF balun. This was new, the series tuning,
> as other loops I tried were parallel tuned. I had everything outside
> including my receiver so I could experiment "on the spot." The loop was
> in a stand, 7 feet high at center. Oh, as a standard, a test antenna of
> 40 feet of wire thrown into a tree at one end, was used. I knew of a NDB
> in S. Wis. over 100 miles away at about 200 kHz and used it as a tuning
> target.
>
> My results were not good and very disappointing. The loop barely copied
> the NDB that was heard at abt S4 on the wire. So here's the setup. The
> loop is 5-pointed, about 6-feet dia. It's spider-wound and started w/ 27
> turns, no. 22 covered wire. I couldn't seem to find a noise peak in the
> 100-300 kHz range so I removed 4 turns, leaving 23. this seemed to
> resonate about 200 kHz using around 200 pfs for tuning. The sig was now
> equal to the wire but I found no expected sharp peak for resonance. It
> seemed the wire had won this race.  It loop did exhibit directional
> properties, however. Yea!
>
> I tried one thing different, a 1-turn pick-up loop 3 inches inside the
> mail loop. This produced a stronger signal level when fed directly into
> the coax to the rx. Then the balun didn't make a difference when
> bypassed or not, still series tuned, as before.
>
> Anyone see a problem with all of this? I'd like some tips to possibly
> try for next weekend when I'll give it a fresh go.
>
> Left out of this, for now, is a mast-located pre-amp that is to follow
> the 1:1 balun. I won't use it until I feel the loop is working
> properly.
>
> Peter
>
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