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

[Rudy Bakalov]

Dennis, Pete, et al.,

It may be useful to break the system into individual parts and then analyze/discuss its performance. Specifically:
1) The CP loops have been around for a while and have been studied by extensively. They work and work better than a single loop. Furthermore, the concept of cross anything has many other applications, including in the CAT5 cable itself. There is a high confidence that CP loops offer better SNR than a single vertical or a single loop.
2) The LZ1AQ amplifier design is fully documented and can be reviewed by anyone who wants to take the time to study it. There is high confidence that the amp works and for all practical purposes is similar in performance to other wideband amps.
3) The third aspect of the system, as Dennis described it, is the variable delay phasing unit. This comes into consideration ONLY if we are discussing a 3 element system and where directivity, rather than just SNR, matters. Dennis and I did not have enough time to fully tweak the 3 element array and I don't think we can draw a conclusion either way.
4) Finally, the CAT5 cable is simply a 100 Ohm feedline. As long as the rest of the system is designed for a 100 Ohm line we should not expect any issues. The twisted pairs deliver high noise immunity over a wide frequency range over long distances. Sounds like the ideal feedline, doesn't it!
So, going back to Pete's original question, I'd say there is fairly high confidence that a single CP RX antenna using LZ1AQ's amplifier and CAT5 cable is a fairly high performing system. Taking the next step, i.e. turning it into a 3 el array, requires further effort and may or may not work well based on the effectiveness of the variable delay unit and its setting/tuning.
 
Rudy N2WQ
      From: Dennis <egan.dennis88 at gmail.com>
 To: topband at contesting.com 
 Sent: Saturday, January 2, 2016 11:03 AM
 Subject: Re: Topband: Using shielded CAT5 data cable as feedline for active antenna; benefits of multi-turn K9AY loop/SAL/etc?
   
Pete

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" 
pieces
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 
Cat5
cable, we had to feed about 18.5V into the coax at the shack end to get 
enough
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 
frequency)
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 
during
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 
transmission.
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 
antennas.
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 
vertical
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 
> <http://www.lz1aq.signacor.com/>.  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 
> <http://active-antenna.eu/amplifier-kit/> 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 
> <http://www.lz1aq.signacor.com/docs/experimental-comparison-v10.pdf> 
> 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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