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Overdriving risk with closely spaced antennas?

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Francesco Doenz
Francesco Doenz Member ✭✭
edited March 2020 in SmartSDR for Windows
I have four antennas very close together on my balcony, a levy type and a Mazzoni Baby loop for transmitting connected to the antenna 1 and 2 inputs on my 66000M, and a Wellbrook active loop and a vertical active  ARAV from Dxeng, connected to the receiver inputs A and B.
  
When I tune the baby loop or the Levy ( with just 10 watts power) I notice on the panadapter spectral display that the receiving antennas go wild? I was thinking that if full duplex is off, then the antennas not assigned to transmitting are switched out of the RF signal path? 
Is there any risk for the receiving antennas and radio if I transmit with power?
Many thanks for your inputs and help as usual!!

Answers

  • KD2OM
    KD2OM Member ✭
    edited February 2020
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    For one thing, the Wellbrook should be at least 10 meters away from transmit antennas if I remember correctly. There is a procedure in the Flex download section on how to determine the coupling between the antenna ports. Loop antennas have a pretty strong field near them which is why they suggest not to be too close them when transmitting. I would think a balcony would be way too close for comfort.

    73,
    Steve KD2OM
  • Ha Gei
    Ha Gei Member ✭✭✭
    edited February 2020
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    We have FO0AAA loop, about 15-20 meters from several TX antennas , connected to the RX antenna port. We run Full legal Power and had no problems yet. Nor the preamp or the input had any problems yet. I suspect you overdrive the preamps and that still brings enough power over the relays into the input to look weird. 
     
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited February 2020
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    Thanks Steve for stepping in! Yes of course I know the balcony is overcrowded by the antennas, and in fact I guess the easiest is to just keep one antenna, anyway I cannot see a clear winner of these four antennas, I would even say that the cheap home made Levy is the best...but I just read the articel of Tim about grounding systems in the ham shack...well I am in a chalet, fourth floor just under the roof and of course no ground, it might be the root of my shack going haywire when transmitting!
    Anyway, again thanks for stepping in!
  • Andy - KU7T
    Andy - KU7T Member ✭✭
    edited February 2020
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    FDX off does not protect the radio from overload. It only protects your ears. Input stages could still be damaged. Andy KU7T
  • Larry _ NY8T
    Larry _ NY8T Member ✭✭✭
    edited February 2020
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    If your Flex receiver is overloaded to the danger zone you will see a box pop up on the screen telling you so and if you keep transmitting it will continue to pop up more warning boxes. I have experienced this quite a few times when running a 6500 and 6300 at the same time, never any damage.
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited February 2020
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    Many thanks for all your inputs, does anybody have an opinion or experience with the "DX Engineering Receiver Guard Electronic RF Limiters DXE-RG5000HD"?
  • KD2OM
    KD2OM Member ✭
    edited March 2020
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    We have tested one of those protectors where I worked, it worked as specified. I use receive protectors from Cross Country Wireless for my two KiwiSDR WSPR receivers. They also work, I have not had any problems with them

    73,
    Steve KD2OM 
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited March 2020
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    Many thanks for your input, looks like Cross Country Wireless products are quality products!
    Visited your home page on QRZ.com,...well I am a greenhorn in this hobby with not technical background....but I take my pleasure with it!!
    As for now my priority is getting rid of some of these antennas on my balcony, easiest way to solve interference among them, and amazingly for now my modified Levy seems to be the best inspite of being really low cost compared to all others!!image
  • KD2OM
    KD2OM Member ✭
    edited March 2020
    Options
    What a great balcony Francesco, and view too. I am not sure what happens with a Wellbrook when no power is applied, Andy Ikin, the owner answers questions if you contact him. I have an active whip that has a PTT input which opens a relay when transmitting, you could use something like that to disconnect antennas when you key your transmitter. There are also bandpass filters that contesters use which might help. The receive protectors I use will handle up to 150 watts. I picked the. Mainly because they work better at VLF. 

    73,
    Steve KD2OM 
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited March 2020
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    Well, today after extensive listening I got rid of the vertical active antenna, it's obvious that the noise floor is much more than the Wellbrook and Baby loop as well the Levy, so the remaining shootout is between these three, and amazingly I must admit that the Levy lets me understand better than the Wellbrooks, the Levy has less noise, I do not understand why, it seems not logical, I own the Wellbrooks ( two of them as you may see on the photo) since  my years as SWListener, so I am used to them but I must admit the Levy seems to outperform them!! And the baby loop is very close to the Levy, I am waiting for experienced buddies to visit me here in the mountains, I am as you know a greenhorn in the hobby....will let you know which is the next antenna to be excluded!!
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited March 2020
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    And I forgot, but I grounded the Flex, the amplifier and the Palstar to the the radiator in my shack which is also my sleeping room, just on the balcony, and I could see on the Panadapter the noise floor diminishing...could have been thinking about it before, but it was reading Tim's article which woke me up!!
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited March 2020
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    I highly recommend that you determine if you are exceeding the RF threshold for the SCU by filling out the FLEX-6000 Full Duplex Power Calculation Worksheet
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited March 2020
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    Many thanks I will look into it and let you know!! But I am careful not to use duplex...
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited March 2020
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    Dear Tim,
     At least I did my homework and tried to fill out the work calculation sheet, as you may see I get a positif result of 45dBW for the external power watt margin, Calculated with an amp power of 500W.   Are my calculations correct? Many thanks in advance as usual for your help!
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited March 2020
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    At first glance, the calculations look correct.
  • Francesco Doenz
    Francesco Doenz Member ✭✭
    edited March 2020
    Options
    Many many thanks for having taken the time to check!!

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