Receiving antennas are about directivity, not sensitivity. That is the best way
to reduce "noise" although a very small antenna can change the signal to noise
ratio without being directional.
Sent from my iPad
On Jun 17, 2012, at 11:16, W2XJ <w2xj@nyc.rr.com> wrote:
> Sensitivity is not always important. Small loops in general receive less
> noise and the real exercise is balancing the internal noise floor
> against the actual signal received. In some cases a loss up to 20 db can
> be acceptable the numbers are easy enough to run.
>
> On 6/16/12 8:17 PM, Brian Miller wrote:
>> Hi Tim
>>
>> I also agree with the previous comments on this thread about detuning the
>> transmit antenna (or any other wires/cables that are resonant on 160M) and
>> isolating the coax feed line from the RX loop.
>>
>> It is also important to identify the direction of the main source of the
>> noise and orientate the loop accordingly so that is being properly nulled. I
>> use a small portable tuned loop to identify the direction of the noise..
>>
>> Of course, if the noise is coming from the same direction as the DX then you
>> are not going to see much (or any ) improvement in the signal-to-noise
>> ratio. Also, if the noise sources are in multiple directions then it will
>> also be difficult to null the noise properly. I have found that small tuned
>> loops (with their bidirectional nulls) are often more effective in such a
>> situation.
>>
>> One of the problems with small tuned loops made from wire is their low
>> sensitivity. Rather than using a pre-amp you can boost the output by making
>> the loop larger (e.g., a circumference of 0.1 wavelength or even larger).
>> The larger loop maintains a directional pattern similar to the smaller one
>> but also exhibits a higher radiation radiation resistance and hence lower
>> losses.
>>
>> Good luck with the experiments and let us know how you get on.
>>
>> 73, Brian VK3MI ZL1AZE
>>
>>> From: tshoppa@wmata.com
>>> To: topband@contesting.com
>>> Date: Sat, 16 Jun 2012 13:28:38 +0000
>>> Subject: Topband: Receiving loops
>>>
>>> I want to try a new receiving antenna for the summer Stew Perry. Last
>>> winter was my first foray onto 160M and I really felt like an alligator. I
>>> could work everyone I could hear, with just 100W. I think that means I
>>> need a better receive antenna. If you look at my score in the winter Stew
>>> Perry I think I did great QSO-number wise, but my average distance was
>>> very poor, I'm guessing typical alligator.
>>>
>>> I have tried pennants and K9AY's over the winter with little success.
>>> Compared to my transmitting antenna (A "T" with a poor radial system) most
>>> signals were still better, S/N wise, on my transmitting antenna. I feel
>>> like I must've been doing something wrong. Still the fact that a few
>>> signals came in on the loop with by ear much better S/N, maybe I was on
>>> the right track and just didn't try hard enough.
>>>
>>> I will be trying a small tuned magnetic loop tonight (e.g. the last one at
>>> http://www.w8ji.com/magnetic_receiving_loops.htm with the 9:1 transformer)
>>> . And maybe a terminated beverage but I'm limited to about 150'... well
>>> maybe I could run something longer down the driveway as long as I clean it
>>> up before the sun comes up and the neighbors see.
>>>
>>> I was fairly impressed with small tuned magnetic loops when I was doing
>>> some BCB DX'ing several years ago. I wasn't comparing with beverages or
>>> anything.
>>>
>>> Tim N3QE
>>> _______________________________________________
>>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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