Topband: Magnetic Loops

[Ashton Lee]

I have the Wellbrook at 2 QTHs and it works way better than using a transmit antenna on receive. It also works very well early in the evening when signals are still iffy and coming in at all angles. My 300 foot beverage on ground starts to be quieter and therefore more effective later in the evening. The Wellbrook outperforms the K9AY I tried for sure. I don't have much local noise so I can't comment on that other than to say that the demos I've listened to on the net make the loops seem quite effective at nulling noise. Their directionality is much stronger on local signals than on DX.

If you already have extensive receive antennas these may not add much, but if you lack the space for other receive antennas these work great.

KQ0C
Ash


On May 21, 2013, at 10:29 AM, "Richard (Rick) Karlquist" <richard at karlquist.com> 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
>