The forum is read-only currently.

Adding Kiwi to my website

2»

Comments

  • Yes - it works. I just connected to it and had a look around.

    You might want to do some antenna experiments. You seem to have some noise there and the vertical is pretty deaf on LF and MF where I have tried it.

    I got some real improvements on my antenna by laying out a loop on the ground which was easy and effective. I made a simple isolation balun with a ferrite ring and 2 turns on the primary winding at the RX end and six turns on the secondary at the loop end. This antenna killed a lot of noise that I had before and has been FAR more sensitive than I ever thought it could be. The wire is just varnished copper, magnet wire and cost about a fiver.

    I first saw this antenna idea on a page run by G8JNJ. His is amplfied. Mine is not. I thought, 'That can never work,' after about forty years of trying to put antennas as high as I could to make them work. Was I wrong!

    I have about 40 meters of 28 swg wire in a rectangle with one side of it running along a hedge about a meter off the ground and the other three sides either lying on top of the gravel or slightly covered by gravel. I've been really pleased by how well it works. When I first got mykiwi I had it on a long wire about 18 feet off the ground and although I had bigger signals, the snr was FAR worse than what I get now. On 5649 khs, I can hear the planes transmitting back to Shanwick from 30 west which is mid Atlantic. You can get great performance out of a square of wire fifteen feet by fifteen feet, as long as you make a simple transformer to match the impedance of the loop to the 50ohm or so that the rx expects to see.

    Try tuning 5505khz usb for Shannon Volmet. It broadcasts continually and should be a big signal during morning and early afternoon. It fades heavily as darkness comes in. I use that one and 198KHZ AM to evaluate my different antenna experiments.

    Experimenting with antennas using the dbmw signal gauge on the KIWI to evaluate performance is a great way to test how the antennas are working.

    Take a spin here on my loop on the ground with no pre-amp. I still get a pile of noise around 18-25 mhz druing the day from a my neighbours plasma tv, but the LF end of things and 40 meters are clean enough.

    http://ne499lr.proxy.kiwisdr.com:8073/

    There is often only one radio slot available because I am doing wspr decoding on the kiwi as well. If it doesn't connect, just look in later.

    Good luck in your experiments.

    Tony
    KA7U
  • Hi All,

    Details of my 'Loop on the ground' (or technically just above it) can be found on this webpage.

    https://www.g8jnj.net/loop-on-the-ground

    Treat the page as a preview as it's more of a working notebook and not really fit for publication yet.

    It may also contain some errors and content that will eventually be removed if I decide it's not really worthy of inclusion.

    I hope it may encourage other KiWi owners to experiment, as I've found it to be about 10dB more sensitive than typical 1m diameter loops. Although it's still about 5dB below the sensitivity required to hear galactic noise throughout the 20-30MHz frequency range.

    The S/N stats on http://rx.linkfanel.net/ (although not very accurate) currently show my KiWi and LOG to have a value of just under 32dB, which is probably amongst the best of all KiWi's worldwide.

    For comparison purposes most Kiwi's using 1m loops shown on the site typically manage around 20dB and most E-Probes achieve about 15dB.

    You can take a listen to my KiWi using a 10ft per side loop and pre-amplifier on this url http://southwest.ddns.net:8073

    Regards,

    Martin - G8JNJ
    cathalferrisKA7U
  • edited February 2020
    Martin @G8JNJ ,
    Outstanding results on your KiwiSDR with this antenna and nice write up. I'm curious why you chose the RPA-1 preamp instead of the LZ1AQ for this antenna?
    Ron
    KA7U
  • edited February 2020
    >
    >I'm curious why you chose the RPA-1 preamp instead of the LZ1AQ for this antenna?
    >

    Hi Ron,

    The RPA-1 has a 50 Ohm input impedance, so it was easier to match to 450 Ohms, plus the IMD performance is better.

    Unlike small diameter loops, the LOG has a fairly flat (approx 400 Ohm) feedpoint impedance across the desired frequency range, so the mismatch losses are relatively small.

    If you look at the graphs on the webpage, you can see the S/N variation with different values of termination impedance.

    There probably are better antennas, but if you have the space, the 30ft per side version is a pretty good broadband performer, has a reasonable degree of noise rejection, is omni-directional, relatively low profile and doesn't need constant repairing when it's been windy.

    Regards,

    Martin - G8JNJ
    KA7U
  • edited February 2020
    Martin's kiwi and amplified loop are extremely good performers, best I've seen so far, but even a wire loop on the ground without amplification is surprisingly good, especially if some of it can be trailed along a fence or hedge between two and three feet above the ground. I have actually been lightly covering the on the ground parts of mine (three quarters of it in fact) with about half an inch of gravel, so the dog and I don't tangle ourselves in it while walking about, and it still works just the same.

    It sounds mad, but it works FAR better than a long wire at 18 feet because it loses large amounts of noise pick up so although the signals are lower, you ought to get a much better SNR.

    There is more on this loop on the ground idea here and this is where my matching transformer design came from. I wound mine on a small ferrite ring that I had in the scrap box:

    http://www.kk5jy.net/LoG/
Sign In or Register to comment.