Antenna comparisons

1m diameter active loop on top, EFHW underneath.  
I’m being particularly unfair to the loop as it’s less than 2m from the 2 floor house and metal fence+shed, a foot off the ground and wedged in a bush… It still performs reasonably well, and definitely shows directivity.

Loop is connected to the Softrock RXTX6.3 and the EFHW is on the Softrock 40. Should be similar in terms of performance, but the former may have an advantage.

We’ll see how this performs overnight.

UPDATE 1:

Well this was not an advertisement for running CWSkimmer under wine. Crashed after 1 hour initially, I then restarted it at 1610z (I’m an insomniac, so are some other VK operators it seems) and it collected data for another 30 minutes from the EFHW. Summary is that the loop was at most only a few dB down on the EFHW even in the direction of of the null (VK6/ZL) for those stations recognized by both stations. It also picked up plenty of Asian stations which were not captured on the EFHW. The clearest path for the loop is to the north and west.

Put in the clear, I think this antenna could really work well for at least 10mhz and below, especially if it can be rotated. Worthy of further experimentation.

What’s also interesting is watching QSB in real time on two different antennas demonstrating the benefits of antenna diversity.

UPDATE 2:

The antenna in question, not in operating position but not far off šŸ™‚

   
 

3 thoughts on “Antenna comparisons

  1. Andrew,

    What loop amp are you using? Looks like the loop is picking up a bit more signal than the EFHW? I’m thinking about receive loops and diversity reception to try and improve my extremely poor receive situation.

    73
    David
    VK3IL

    • Hi David

      I’m using the amp here:
      http://www.qsl.net/m0ayf/active-loop-receiving-antenna.html

      I’ve got my eyes on the design by Chris Trask which uses a few tricks to drop the input impedance of the amp which apparently is the most critical parameter. I need a few parts however, and it involves the most complicated transformer I’ve seen.

      See above for an update shortly. Summary, it works well as is on 40. It was a S point or two down on Mitch and Compton in VK7 this morning, but Tasmania was on the other side of the house, whereas the efhw is probably close to optimal in position.

  2. Andrew,

    Very interesting. I hadn’t seen either of those amplifiers previously. I had been looking at the following amp, which is a little pricey, but looks to have similar specs to the Chris Trask design: http://active-antenna.eu/

    May be worth doing a PCB for the Chris Trask design as a lower cost alternative? Agree the transformers look complicated, but they are probably not too hard to construct.

    It’s not high on my project list at present as I don’t have a receiver capable of diversity reception at present, but the web site above has a solution to build a multi-antenna phased array using a few amps and delay lines. That could give similar performance to diversity reception if you put perhaps 4 antennas into a steerable array. Not sure that would be so useful for a skimmer though, but may help with pulling activators out of the urban noise.

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