Topband: Magnetic Loops

[Carl]

Actually a properly designed purpose built loop can offer a reduction in 
noise from the high Q selectivity offered.

A 2 turn balanced loop made from 1" mostly air dielectric CATV hardline has 
been in use here for over 25 years. Diameter is about 44" and mounted in the 
woods on an old TV rotator with the bottom about 6' above ground.

 That coax has the lowest C/foot available at the time resulting in the 
highest Q and is fed into a balanced amp using PP U310's and remotely tuned 
varactors.

The bandwith is extremely sharp and acts as a roofing filter on 160 
resulting in an improved SNR many times that the Beverages dont enjoy. It 
also does wonders DXing on the BCB where I use it the most. A smaller one 
covers 80M and the low SW bands.

Using regular RG/LM type coax results in a much lower Q and a wider BW and 
the selectivity benefit suffers.

Carl
KM1H




> Covered many times here over the years. Yes mag loops wil help loads with 
> local crud noise if they are in a certain direction you can null to. If 
> the noise is all surrounding as it would be in many high density 
> residential areas like condos or industrial zones prob not.
>
> At best mag loop lowers the noise in two directions drastically - along 
> with any signals in those two spots.  But in the non null areas there are 
> absolutely no characteristics of the loop which are beneficial for DX 
> other than getting whatever you may get.  Also know the loop has no 
> vertical or horizontal directivity except for the two sharp nulls off the 
> end of the loop so all atmospheric noise will be collected by th antenna 
> and your DX will compete I that noise floor for notice.  For most local 
> non DX work in very noisy spots these are great.
>
> If you want DX Id try a MFJ nuller and a k9ay or flag.
>
> 73 W2PM
>
> Sent from my iPhone
>
> On May 21, 2013, at 11:40 AM, Bob K6UJ <k6uj at pacbell.net> 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
>> All good topband ops know how to put up a beverage at night.
>> _________________
>> Topband Reflector
> All good topband ops know how to put up a beverage at night.
> _________________
> Topband Reflector
>
>
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