[Lowfer] L.F. LOOPS

[Peter Cranwell]

I am using a balanced loop, with the balanced varactors accross the loop 
feeding a preamp.  The preamp sends the amplified signal over twisted pair 
using CAT-5 cable.  Power and varactor control goes out over the CAT-5 using 
other twisted pair.  Depending on the preamp gain, you may have problems 
using twisted pair in the vicinity of the loop due interaction with the loop 
magnetic fields.  I initially had feedback.  I settled mine down by dressing 
the return leads along the support pole (steel) and reversing the wires from 
the preamp to the loop.

It's a cheap solution as the CAT-5 is a lot less costly than coax.

Not sure you can get that full tuning range as the loop's distributed 
capacity my limit it.  If you tap the loop, you will reduce the signal 
level.  I am using MVAM109 varactors and I think 26 turns on 4 foot loop 
arms (roughly 5 foot on the side) spaced over roughly 4 inch stringers.

Pete

----- Original Message ----- 
From: "Chris Trask" <christrask at earthlink.net>
To: "Discussion of the Lowfer (US, European, &amp; UK) and MedFer bands" 
<lowfer at mailman.qth.net>
Sent: Tuesday, August 26, 2008 11:10 PM
Subject: Re: [Lowfer] L.F. LOOPS


> Rick,
>
>>
>> Hi all,
>> I was just looking for opinions on feedlines for small loop antennas.I
> built a
>> 3 ft square loop with about 24 turns .I plan to to tune it from  about
> 160 -500
>> khz. It wil be placed outdoors.I havent decided how to feed it yet.Should
> I link
>> couple or direct couple it?Should I coax feed it or use twisted pair.? I
> have
>> some nice 22 ga. shielded twisted pair.
>> I will also be remote tuning it using varicaps.
>> Any input would be greatly appreciated.I have read too many loop articles
> recently
>> only to become more confused!
>>
>
>    Funny you should bring this up as I'm going to put a paper about
> varactor tuned loops for HF on my webpage soon, maybe as early as tomorrow
> if everything goes well.  I'll post a message on this group when I do. 
> Even
> though it's oriented towards HF receiving loops, you may find information 
> in
> it that will be useful for what you're doing.
>
>    I found that coupling to the loop balanced, operating the varactors
> balanced, and keeping the impedance stepping balanced until the very last
> stage before going to coaxial cable does wonders for reducing harmonics 
> and
> intermodulation problems with AM BCB stations.  The transformer 
> construction
> is a critical item for good performance, and I used a combination of
> powdered iron toroids and ferrite balun cores to get good results and keep
> the cost down.
>
> Chris
>
>     ,----------------------.       High Performance Mixers and
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