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Author Topic: Directional (Loop) Antenna for Longwave?  (Read 1839 times)

Offline ChrisSmolinski

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Directional (Loop) Antenna for Longwave?
« on: September 30, 2016, 1934 UTC »
I'm looking for ideas for a directional loop antenna for longwave.  This would be an outside antenna, but something small enough that it can still be rotated. Also, it needs to be a non resonant design, or at least have a low enough Q that it covers the entire DGPS band. An amplified antenna would be fine.

I recall many years ago having an indoor loop antenna for LW, it was, as I recall, a magnetic loop with a metal shield, and it plugged into a metal box housing the amplifier. The interface was pretty clever, it was a 1/4" headphone jack, so the signals could pass, and it was able to rotate. Obviously I want something larger than this, and it needs to be outside, unlike back in the 80s, there's too much RFI inside the house today. But perhaps an amplified magnetic loop is one avenue to consider?

My end goal is something that will be automatically rotated back and forth at a very slow rate, perhaps one turn every hour or half hour, meanwhile my SDR is recording the entire DGPS band. I want to try and maximize the total number stations I pick up, and this sounds like one possible way to do it.
Chris Smolinski
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Offline jFarley

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Re: Directional (Loop) Antenna for Longwave?
« Reply #1 on: October 01, 2016, 1413 UTC »
Non-resonant, wideband, and small enough to swing on a rotor.  I can think of a couple of possibilities.

The Wellbrook ALA100 is a favorite among NDB DXers, and available off the shelf.  But then there is the cost.

http://www.wellbrook.uk.com/ALA100M-1

Some have also gotten great results from the LZ1AQ loop at LW.

http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm

Joe Farley, Near Chicago
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Offline ChrisSmolinski

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Re: Directional (Loop) Antenna for Longwave?
« Reply #2 on: October 01, 2016, 1851 UTC »
Thanks jFarley, I'm reading through the LZ1AQ page now. It looks like it has some potential. And it's great to see that the amplifier uses common 2N2222's, not some special low noise transistors that went out of production a few years ago and are nearly impossible to find  ;D
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline skeezix

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Re: Directional (Loop) Antenna for Longwave?
« Reply #3 on: October 01, 2016, 1907 UTC »
I have both an ALA1530S+ and ALA100LN.

The ALA1530S+ is back out in the shed and use it for LW-SW. It works very well on LW. Recently picked up the ALA100LN and have a ~43' wire loop connected to that. The loop is stapled to the outside of my porch and is in the N-S plane. Comparing to a small active whip I have, it cuts out a lot of noise (which is hardly surprising, but does prove its success). I frequently listen to 540 WXYG on it and its an absolutely solid signal, from a 850W station ~75 miles away.

I would highly recommend either of these. With the ALA100LN, you can customize the size of your loop.

Tuning to 317 kHz now, its a rock solid S6 with its data stream. Being ~15 miles away, it better be. I think its mostly ESE from me, so coming in on the broadside of the loop, so signal is prob not as strong as it can be. And with the antenna stapled to the porch, hard to turn it.

A friend of mine recently suggested to set up a pair of crossed deltas that are phased. The direction can be remotely steered by changing the remote termination (variable resistors) at the far end.

For remotely & automatically changing the variable resistors, perhaps controlled by a stepper motor.

Minneapolis, MN

Offline Kilokat7

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Re: Directional (Loop) Antenna for Longwave?
« Reply #4 on: October 01, 2016, 2303 UTC »

For remotely & automatically changing the variable resistors, perhaps controlled by a stepper motor.


Vactrol's also work well in this application and might be a simpler solution (no moving parts).
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Offline skeezix

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Re: Directional (Loop) Antenna for Longwave?
« Reply #5 on: October 01, 2016, 2342 UTC »
Vactrol's also work well in this application and might be a simpler solution (no moving parts).

YES! I forgot about that and my friend (and others) were talking about that too.

Minneapolis, MN

Offline Kilokat7

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Re: Directional (Loop) Antenna for Longwave?
« Reply #6 on: October 02, 2016, 1701 UTC »
For Vactrols, the VTL5C4 seems to be popular, and I just used a pair of them in a new D-KAZ loop controller that I built.  Unfortunately they are getting hard to find now.



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Location: Western Michigan
Perseus SDR / Phased BOGs or Double Kaz
1980s pirate off-air archive