Random wire questions

Useful information regarding antennas for SDR products.
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Re: Random wire questions

Postby DanubeBCL » Sun May 28, 2017 9:24 am

As a LOG is easy to build I made some experiments the last days.
The image shows a 4 x 5 m LOG and a 14 m wideband magnetic loop side by side on my Anan Angelia (portion of the 49 m band). Without a preamp the LOG is almost unusable. I added an old preamp with a PGA 103+ (which I had in my tinkerbox). This preamp is not very good for frequencies below 3 MHz and it's amplification (25 dB) is too high. But I did not want to build a new one. For frequencies above 3 MHz it works good (except for some IMD in the evenings). I applied an attenuator to make both images match.
The LOG with preamp is en par with the magnetic loop, sometimes it has a bit more SNR (the magnetic loop is directive and attenuates some signals from the side). Considering that the LOG really lays directly on the ground (sunken in high grass) the results are amazing. The magnetic loop is vertically polarised and its lower end appr. 2.5 metres above ground. It has a preamp similar to the LZ1AQ design.
The LOG unfortunately picks up a bit more noise from my neighbours than the other antennas (25 m wire, magnetic loops, active whip). I believed that when the antenna is directly on the ground the noise fields from my neighbours would not reach the LOG so much. But unfortunately this is not true. I have no explanation why the picked up noise is higher than in the other antennas. I have applied all sort of grounding and common mode chokes tricks, but no avail.
If someone has no options to bring up antennas into the air a LOG is really an considerable alternative. But as always: You need a quiet environment for this antenna, too.

73, Heinrich
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