receiver cuts back on gain

Discussion in 'General Technical Questions and Answers' started by N3QK, Oct 15, 2020.

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  1. N3QK

    N3QK Ham Member QRZ Page

    I need help or suggestions solving a receiver problem. I have tried 3 different receivers and all three experience the same problem. While listening to the received signal on two transceiver radios, and one receiver, suddenly the signal strength goes from 20 over S-9 signal to s-3 or 4. When I push the PTT key on the transceiver, the receiver comes back to life but soon afterwards fades back to reduced gain. On just the receiver, turning it off turning it back on restores that signal but soon it fades back to reduced signal. Signal loss is either due to antenna or coax but I'm not certain which. Has anyone ever experience this problem and what did you do to cured it?
     
  2. N8YX

    N8YX Ham Member QRZ Page

    Describe the cabling setup. Are you running the second receiver as a sub-receiver via the transceiver's external antenna connector or are they separate w/ separate antennas?
     
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    @K4KYV has mentioned several times a phenomenon he calls "Signal Suck Out" when having two or more receivers connected to the same antenna where one radio loses the signal, but the other still recieves it fine. He hasn't described the cause, that I recall.

    I assume the cause is some sort of resonance/regeneration effect between the radios [possibly at the IF frequency]. It could be a similar interaction between your three radios.

    Perhaps the theory of interaction could be tested by adding some sort of isolator/transformer/circulator in the feed line to prevent interaction between two or all three radios.

    Q: So, you have all three radios connected simultaneously to the same antenna?
    Q: Are we talking about 70 year old Boat Anchors or modern solid state radios?
    Q: Commercial, Amateur or Consumer grade radios?



    Experiments
    -
    Ensure that AGC on all radios is set to OFF or FAST.
    -Ensure that NB and NR/DSP is OFF on all radios
    -Ensure Auto Notch is OFF
    -Ensure FILTERS are WIDE or OPEN
    -A 1:1 Current Type UnUn might do the trick.
    -Another idea is to add/subtract feedline length to one of the radios.
    -For both devices, test in feedline to each radio.
    -Does the effect occur on All or different bands?
    -Does increasing the distance between radios cause the effect to cease?
    -Does placing a metal sheet or large metal object, e.g. file cabinet, metal box, between the radios etc change it?
    -Using clip leads or wire, bond the three radio's grounds or chassis together.
    Perhaps someone has a suggestion for the correct device.
     
    Last edited: Oct 15, 2020
  4. K1LKP

    K1LKP Platinum Subscriber Platinum Subscriber QRZ Page

  5. AJ8MH

    AJ8MH Ham Member QRZ Page

    I had a similar problem. I had a trap go bad on a TH3JR. The screw that connected the inductor to one of the driven elements would open until I hit it with a little RF. It was intermittent for months until I took the beam down to check all the connections. So, look for a poor connection including the PL259's.
     
  6. KB1CKT

    KB1CKT Ham Member QRZ Page

    How soon is soon? Seconds, minutes, hours? And what band are we talking about?

    I like AJ8MH's proposal, but, if power cycling a receiver causes it to work properly, then I am tempted to think power supply. Maybe hook up a voltmeter and watch. It'd be very odd but maybe the PS drops in voltage, but can output correct voltage when under a large load--no it doesn't make sense, but what the heck, might as well rule it out.

    lastly, is there anything "exotic" in the path? Like a remote switch which is remote controlled, and which may be cycled when you cycle power to the radio. I dunno what, just grasping at straws here.
     
  7. KP4SX

    KP4SX Premium Subscriber QRZ Page

    What model is this receiver?
     
  8. N3PM

    N3PM Ham Member QRZ Page

    Any chance of trying all three on a different antenna system? Even a piece of wire stuffed in the SO239.
    This should narrow it down to the existing antenna system or the radio/PSU side.
    Mike N3PM
     
  9. AJ4SN

    AJ4SN Ham Member QRZ Page

    It sounds like an antenna connection issue as AJ8MH describes. I have had very similar problems with T/R relays which would be ok when transmitting, but were intermittent on receive.
     
  10. WR2E

    WR2E Ham Member QRZ Page

    @N3QK "you've got mail"

    Doesn't look like anyone quoted him... this should 'ring his bell'
     

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