Topband: Magnetic Loops

[Herb Schoenbohm]

A better and easier and lower cost solution IMHO would be a pair of  
phased K9AY by using the MFJ-1026 and adjusting them for the best null 
on the noise location.  Unfortunately this will also reduce the signal 
from the nulled direction but would allow some slicing of the noise from 
the shack without all the ambiguities of field nulling of the noise.


Herb Schoenbohm, KV4FZ




On 5/21/2013 12:29 PM, Richard (Rick) Karlquist wrote:
> On 5/21/2013 8:40 AM, Bob K6UJ wrote:
>> Sometimes my local power line noise is about S8 or so on 160.
>> I am considering the purchase of one of these magnetic loop antennas 
>> for receiving to see if it helps.
>> Anyone have one of these ?  How well does it perform ?  One better 
>> than the other ?
>>
>> Pixel Technologies RF PRO-1B
>> Wellbrooke Communications ALA 1530
>>
>> Bob
>> K6UJ
>
> It is important to understand that these loops have
> a circumference of 10 feet, which they are limited
> to because the manufacturers want to offer a bandwidth
> up to 30 MHz.  Also, they are untuned, again because
> the manufacturers want to offer a broadband solution.
> Very little signal is available from such a small untuned
> antenna, and hence these antennas require a high gain
> preamp.  Depending on your location, the amplifier
> noise may be the limiting factor on sensitivity.
> One of the commercial loops claims to have 0.5 dB noise
> figure, however I measured 3 dB on a sample of one.
> These issues are simply physics, no matter who builds
> the loop.  IMHO, a so called "Moebius" configuration
> doesn't fundamentally change anything with respect
> to these tradeoffs.  As the inventor of that design
> states, it is only an advantage for its intended purpose
> of EMP weapons testing.
>
> If you are primarily interested in 80/160 meters, then you
> might want to look at my NCJ article:
>
> http://www.n6rk.com/loopantennas/NCJ_loop_antenna_N6RK.pdf
>
> This loop is normally 20 feet in circumference and can
> be made up 40 feet in circumference to get additional
> signal.  Also, it is tuned, which produces much more signal.
> I use it with no preamplifier (besides the one built into
> the radio), although a little gain wouldn't hurt.
>
> Due to popular demand, I will be offering assembled
> versions of this loop for people who are not able to
> build the homebrew version described in NCJ.
>
> Rick N6RK
> All good topband ops know how to put up a beverage at night.
> _________________
> Topband Reflector