Topband: Receiving loops

[Brian Miller]

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 at wmata.com
> To: topband at 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