Topband: Using shielded CAT5 data cable as feedline for active antenna; benefits of multi-turn K9AY loop/SAL/etc?

Dennis egan.dennis88 at
Sat Jan 2 11:03:25 EST 2016


We installed and I used exactly such an antenna at VE3/N2WQ this past year.
The loops were easy to construct, and the project was built around 3x3" 
of wood.  The loops were located around 400ft from the shack; one thing we
did find was that, even doubling up on the power and ground wires of the 
cable, we had to feed about 18.5V into the coax at the shack end to get 
voltage at the loops to run the amps.  As we turned the voltage up past 
the 13.8V,
you could hear the output go up greatly.

The loops were erected last April; preliminary use showed there was enough
directivity that switching directions on the AM band (on the proper 
resulted in different stations being received on the radio.  I can't say 
there was
a great deal of directivity, but there was some.  I also used the loops 
in the WPX
CW contest as VA3CCO; their biggest contribution was the reduction in noise
picked up by the antenna.  There was a thunderstorm 50 miles south of us 
the contest; the 80M delta loop on Europe picked up too much noise and Qs on
80M required several repeats due to the static crashes.  Using the 
loops, the static
crashes were minimized and I was able to get the SN with only one 
I didn't make a lot of 80M Qs- it was almost summer and in WPX 80/160M
usage is pretty light- but it did help.

In my mind, the effectiveness of the loops is still an open question, 
particularly if
you weighed their performance against that of other reduced size Rx 
I would not rule them out, either.

LZ1AQ also recommended constructing both the loops and the short vertical
elements, as the short vertical elements were better for low angle 
arriving signals.
We did get the loops built, but the wx was bad and we never did get the 
elements added on.  The preamps all included the switching to go between the
two antennas at the touch of a switch.

Dennis W1UE

On 1/2/2016 10:45 AM, Pete Smith N4ZR wrote:
> I was recently reading a web page by LZ1AQ 
> <>.  It is full of fascinating data and 
> design equations for the use of small magnetic loop antennas.  There 
> were two points, in particular, that caught my layman's attention:
> 1.  He recommends using shielded CAT5 data cable with RJ-45 connectors 
> as feedline.  The obvious advantage is having three pairs left over 
> for voltage supply and control.  See 
> <> for more information.
> 2.  He cites experimental data showing that coplanar crossed loops and 
> multi-turn quad loops both offer very significant improvement in the 
> recovered signalcompared with a single loop.  See 
> <> 
> to check whether I got this right. Anyway, it occurred to me to ask if 
> anyone has ever tried multiturn K9AY, SAL or flag/pennant receiving 
> antennas, and did you see something similar?
> Any other critiques of his design would be appreciated.  The price is 
> certainly right, and the construction looks good. A couple of 1-meter 
> coplanar loops wouldn't be at all hard to construct.

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