[Lowfer] L.F. LOOPS

[Peter Cranwell]

I have some slop in the leads from my preamp to the loop.  If I clean up the 
wiring I may be able to reduce the stray capacitance and increase the tuning 
range.

Thanks

I'm still in recovery mode from as lightmning strike.  It may be a while 
yet.

Pete
----- Original Message ----- 
From: "Chris Trask" <christrask at earthlink.net>
To: "Discussion of the Lowfer (US, European, & UK) and MedFer bands" 
<lowfer at mailman.qth.net>; "Discussion of the Lowfer (US, European, & UK) and 
MedFer bands" <lowfer at mailman.qth.net>
Sent: Wednesday, August 27, 2008 9:19 AM
Subject: Re: [Lowfer] L.F. LOOPS


>     I was using single-ended varactor and then a preamp in my earlier 
> designs, but this time I tried balanced varctors and wideband transformers 
> to match the loop to the cable, sending the control voltage up the cable 
> rther than by a separate set of wires.  Turned out to be much quieter with 
> almost as much gain, so the S/N ratio is actually better this way.
>
>     I'm using MVAM109 varactors same as you, and I can get close to two 
> octaves at HF frequencies.
>
>>
>>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, & 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
>>>    /    What's all this     \    Amplifiers for RF Communications
>>>   / extinct stuff, anyhow?  /
>>>   \  _______,--------------'           Chris Trask / N7ZWY
>>>  _ |/                                  Principal Engineer
>>> oo\                                  Sonoran Radio Research
>>> (__)\       _                             P.O. Box 25240
>>>  \  \    .'  `.                     Tempe, Arizona 85285-5240
>>>   \  \  /      \
>>>    \  '"        \                 IEEE Senior Member #40274515
>>>     .       (  ) \
>>>      '-| )__| :.  \              Email: christrask at earthlink.net
>>>        | |  | | \  '.       http://www.home.earthlink.net/~christrask
>>>       c__; c__;  '-..'>.__
>>>
>>>                       Graphics by Loek Frederiks
>>>
>>> _______________________________________________
>>>>From the Lowfer mailing list
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>>
>>_______________________________________________
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>
>
> Chris
>
>     ,----------------------.       High Performance Mixers and
>    /    What's all this     \    Amplifiers for RF Communications
>   / extinct stuff, anyhow?  /
>   \  _______,--------------'           Chris Trask / N7ZWY
>  _ |/                                  Principal Engineer
> oo\                                  Sonoran Radio Research
> (__)\       _                             P.O. Box 25240
>  \  \    .'  `.                     Tempe, Arizona 85285-5240
>   \  \  /      \
>    \  '"        \                 IEEE Senior Member #40274515
>     .       (  ) \
>      '-| )__| :.  \              Email: christrask at earthlink.net
>        | |  | | \  '.       http://www.home.earthlink.net/~christrask
>       c__; c__;  '-..'>.__
>
>                       Graphics by Loek Frederiks
> _______________________________________________
>>From the Lowfer mailing list
> Send messages to: Lowfer at mailman.qth.net
> To sub/unsub visit: http://mailman.qth.net/mailman/listinfo/lowfer
>