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TX near the kiwi

Hello
What is the safe distance of the kiwisdr for me to transmit with 100 watts ??
THankyou
RIck from South Am?rica

Comments

  • What antennas are you using and what are the relative orientations?

    It's not a specifically easy question to answer, as there are a few factors in play. If the RX antenna is a small loop, with the null average pointed at your dipole antenna, then the distance could be quite small. But it you've got an OCFD tx and a longwire rx in parallel then you're going to need more distance.
  • would be 2 dipole antennas: one north south, another east-west
  • Use a relay to terminate the SDR input.
    Assume the antennas are too close for safe use of a 100W transmitter at unknown frequency and act accordingly.
    The reception will be wiped out anyway so just drop it, if you want something off the shelf there are item for sale (E.G. MFJ-1708SDR)

    There other threads on here about protecting the front end, for example back to back signal diodes (most easily fitted to the green anntenna ports), smal signal lamp as fuse, that would be worth doing straight away as the impact on reception will be minimal but it could save your Kiwi.
  • I use the receiver protectors from CrossCountry Wireless on my three KiwiSDR's and routinely transmit at the 100 watt level.
  • For what it's worth, my kiwi is on a 190m beverage. I have a big 200m+ delta loop I use for transmitting ~800W. One leg of the delta is nearly parallel and about 15m away from the beverage at the kiwi end. I've installed 1N4148's diodes on the kiwi input. I also have a 9:1 voltage transformer between the kiwi and the beverage. I have no protection on the GPS input. I have not burned out anything and it's been over a year.
  • I concur with @njc. It turns out to be pretty difficult to get high coupling between two antennas. period. In the near-field not all the energy is available. In the far-field, apertures don't permit high transfer. I once tried (at low microwave) to minimize loss between two air-separated antennas. The best I could practically do was with two largish dishes spaced a couple of dish diameters. I presume were they totally coupled by circular guide or something it would have been different but as a practical matter in free space, it's tough to get better than -20 dB even when you try. With two monopoles or dipoles spaced a wavelength or less getting much more than even -40 dB isn't easy, as I remember. You can certainly model this with NEC or similar.

    40 dB below 1 kW is 100 mW and not enough power to damage protection parts, either external or even those within the Kiwi, I suspect.

    Lightning strikes may be another matter all together...
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