Suggestions for protection from nearby transmitting antenna?

Eventually I would like to leave the Kiwi up and running on the web.  The receive antenna is a center fed 80M dipole fed with a balanced feeder.  About 20' from the center of the dipole is a Hustler 6BTV vertical used on the rig, running 400W max on HF.

1)
I would be interested in suggestions for automatic protection when transmitting, not requiring me to remember to throw any switches.  I am sure I can use a signal out of the Elecraft K3 so that when transmit is enabled a control line can switch a protection circuit inline, but if RF detection circuits are safe and reliable that would be of more interest.  I have seen some circuits using gas discharge tubes as part of the protection network, but would like the safest method.  The "automatic" aspect is very important, I know I would eventually mess up and forget to take a manual action before using the rig.

2)
Is there any concern about also protecting the GPS input?  That would seem to be more difficult.

3)
What is the maximum RF input that is safely tolerated by the Kiwi input?

Any hams with specific suggestions can find my email address on QRZ.

Thanks.


Comments

  • jksjks
    Accepted Answer
    Here is some advice from Gunnar, SM3SGP, who manages the Kiwi beta test unit at the SK3W contest station in Sweden.

    "I have made the circuit described by N8VB on the QS1R Wiki pages. It consists of a small light bulb, and two diodes. I think I have changed that light bulb once, in many years of operation. We are running Multi TX Kilowatt output, but I have never had any failure of the QS1R. http://www.srl-llc.com/qs1r_latest/Documents/Schematics/qs1r_rxprot.pdf
    I also have one of those DX Engineering RX Protection units, but now connected right now."

    The Kiwi itself uses TVS diodes across the RF/HF inputs. The GPS does not due to possible capacitive loading issues. We have not done any limit testing of the inputs.
  • Great, many thanks to Gunnar and JKS.

  • jksjks
    Accepted Answer
    Note that the TVSs we use (schematic here: http://www.kiwisdr.com/docs/KiwiSDR/kiwi.schematic.pdf) are roughly equivalent to the IN4148s shown in that QS1R protector. And the Kiwi is also capacitively coupled. So just adding the lightbulb in series is probably fine. Maybe put a gas-discharge tube or neon bulb to ground after the series bulb to handle more charge impulse than the TVSs are capable of.

  • Followup question:  I finally put my input protector together and the Kiwi recovers quickly from the overload when I test with 400W CW on the nearby antenna.  So this should protect me from any accidents of forgetting to disconnect the Kiwi.  

    But of course the A/D is blasted into overload as expected and I just want to double check that there should be no need at all for me to disconnect the antenna and power down the Kiwi when operating times.  

    I plan to register my Kiwi on the web site even though my antenna is poor, and I would like to leave it running 24/7 even though it would not be very useful to anyone when I am in QSO.  Most days I only have my daily sked for an hour, so 95% of the time it should be available.

    Any concerns at all about the long periods of  A/D overload from high speed CW?  
  • So far we've had no reports of any front-ends being blown out. And a number of Kiwis are co-located at remote contest stations where high power is used.

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