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FT-101ZD M2 poor sensitivity

Discussion in '"Boat Anchor" & Classic Equipment' started by M0KCR, Jan 19, 2022.

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  1. M0KCR

    M0KCR Ham Member QRZ Page

    No .. but I've already injected the Marker Signal at the very end of the chain.
    That would prove that there is no issue with the cabling.
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Fair enough, but at this point things just aren't adding up. If you have an S9 + 20dB marker signal then your receiver chain is working fine and has expected sensitivity. If you disconnected the marker signal from the trimmer board and saw the marker signal go very low or to zero and then reinjected the signal at the antenna port and still got S9 +20dB then the cabling, relay, protection bulb between the front end and trimmer board are as expected. But if you still have a very deaf receiver with big sensitivity problems then something isn't adding up. So either you have a bad antenna or bad coax jumper or something like that connecting the antenna system or something is wrong with one of those tests.

    An external signal generator capable of generating signals down into the uV range would be very useful at this point to try to resolve the difference between perfectly fine marker generator results and an apparently deaf receiver.

    Without further test equipment I'm not sure what to tell you as things don't really make sense as they stand. Good luck with it, perhaps you can find a local ham with some test equipment to help out.
     
  3. M0KCR

    M0KCR Ham Member QRZ Page

    Yes, thank you .. your input is really appreciated and I agree on the signal generator at this stage ..
    I will drag the radio to a club that has the equipment.

    One question about the so called Noise Blanker, is that comparable to a Squelsh?
    Because if it is, it doesn't work ...

    If you take a look at my 2nd video (BroadCast) the reception isn't that bad .. but still no S-Meter

    73
     
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    No, a noise blanker is not like squelch, it’s for suppressing sharp impulse noise like spark plug noise in mobile installation. It will not squelch the receiver no matter how far it is turned up and does little to nothing for noise other than sharp repetitive impulse noise.
     
  5. M0KCR

    M0KCR Ham Member QRZ Page

    Ok, thank you .... that's helpful.There's really some terminology I didn't know.
    When I got the radio initially I was looking for the a Volume Knob label .. :)

    I just got AM back to work, it was a mix-up in the signal cable connectors (both are grey, but both were plugged together in the wrong way ).
    I also received an AM station with S9, so I think that's good news ...

    Would you know how the S-Meter reading is derived in circuitry?

    https://drive.google.com/file/d/144j1zjiAgEt4LCLLVOzNmrIdj9znODQB/view?usp=sharing

    73
     
    Last edited: Jan 21, 2022
  6. M0KCR

    M0KCR Ham Member QRZ Page

    Soooooo .... after going back and forth and head scratching and wondering why the Marker Signal goes through but RX is very weak I by
    coincidence found out that you have to apply the marker signal with a 50 Ohm terminator.

    If I test with a terminator the S-Meter does not move when I dial to 14.2MHz which is in line with the poor sensitivity.

    So, there you have it.
    :)
     
    Last edited: Jan 23, 2022
  7. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Hmmm, I've never once used a dummy load or 50 ohm termination with the marker signal on my FT-902DM. I'll give it a try but that's not how I've ever evaluated the marker generator signal.

    [edit]I just tested my FT-902DM marker signal on 20m with and without a 50 ohm dummy load connected to the antenna terminal. The marker signal is S9 + about 10dB in either case.

    Yup your load is changing the strength of your marker generator. So something is getting loaded down when you add the 50 ohm load. That's a good clue and should give you ideas of things to run down.
     
    M0KCR likes this.
  8. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Thinking this through it appears as though something in your RF input is driving the impedance very high such that placing a 50 ohm load across the antenna terminals forms a voltage divider and drags the subsequent signal way down.

    Looking at the trimmer board schematic you posted earlier I'd suspect either very dirty contacts in the rotary switch that selects the band trimmer, the interconnect out of the board(pin 3) or something in the L01, C07 trap or L01 that's making the input impedance of the RF preamp look very high compared to 50 ohms. I still would not suspect an active device like your input preamp as the marker generates plenty of signal when the input is not loaded down but some series interconnect in that RF input path is likely creating a lot of resistance in that path.

    [​IMG]
     
  9. M0KCR

    M0KCR Ham Member QRZ Page


    Thanks for testing ...

    That's interesting that you're getting the same signal strength with or without.
     
  10. M0KCR

    M0KCR Ham Member QRZ Page

    Thank you.

    I've cleaned all the rotary switches and traced the wires ... it all seemed well.


    .. what should the RX input impedance be?

    You've said you've got +10dB with or without dummy load.
    Shouldn't I then get at a signal with the dummy load connected?
    (It's zero on the S-Meter when I connect the 50Ohm)

    73

    I have ordered the input FET ... just to keep that possibility checked.
     
  11. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Unfortunately that isn't spec'd anywhere but shunting a 50 ohm load across the antenna terminals shouldn't kill the signal from the marker generator.

    Yes that's what I saw on my Yaesu hybrid which is configured much like your FT-101
    Yes, you should.

    If there's no connection including solder joint problems then I'd suspect either that trap circuit or the input transformer shown on the trimmer board schematic above. I highly doubt it's the input FET but I'd certainly check everything around that input preamp, especially any solder joints that may have cracked around that circuit.
     
    M0KCR likes this.
  12. G3YRO

    G3YRO Ham Member QRZ Page

    Yes, on the original FT101 series I always connected a dummy load before using the Calibrator signal to set the S Meter sensitivity . . . but it only makes a very slight difference.

    As others have said, the fact that it causes such a big drop shows that something has gone very high impedance around the front end connections.

    Roger G3YRO
     
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  13. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Did you also pull the boards, particularly the RF Unit and clean the PCB edge contacts? That's one of the first things I'd do for a problem like you're seeing. I'd also check the wiring terminal side of that RF Unit connector to make sure there's not a cracked solder joint or broken wire down there.
     
    Last edited: Feb 1, 2022
    M0KCR and KD2ACO like this.
  14. KI4ZNV

    KI4ZNV Ham Member QRZ Page

    First check DC continuity. That input goes through a coil to ground, so you should see very low resistance to ground.

    Then pin 3 of MJ1 goes through a coil to the common of the trimmer unit. So you should see very low resistance there.

    Pin 3 of MJ1 goes through a coil and a 1K resistor to pin 7 of MJ1... so you should see 1K there.

    If you aren't seeing these, start looking for where the open is.
    --scott
     
  15. M0KCR

    M0KCR Ham Member QRZ Page

    Thanks all ... much appreciated! I'll post back once I got to it ...
     

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