Listening in another receiver

Discussion in 'Tips and Tricks' started by N3PM, Nov 16, 2021.

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  1. N3PM

    N3PM Ham Member QRZ Page

    Testing a KX2 on SSB and listened in another receiver. Found that having the DNR on gave an inaccurate picture of the audio. Before you go chasing a transmitter problem, see if you have the monitor's noise reduction turned on.
    Mike N3PM
     
    Last edited: Nov 16, 2021
    N0TZU, K7TRF and N3RYB like this.
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Good tip.

    It's usually a good idea to make sure you have attenuators switched in on the monitor receiver as well if the rigs are located near one another.
     
    NL7W, AB2YC and PU2OZT like this.
  3. PU2OZT

    PU2OZT Ham Member QRZ Page

    Switched in? only high end receivers might feature such attenuators, or like in a by-pass, permanent installation to Rx coax line?
    40dB attenuator, various different ones?

    Wondering % radio-amateurs willing to monitor their Tx in such a way.
    But, I'd be glad to add the Station Monitor to my hybrid Kenwood, if not overpaying for one.

    Oliver
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    To "monitor in another receiver" (I do this a lot), I just use a receiver with no antenna connected at all. And use headphones!:p
     
    WA8FOZ, N7EKU, WB5YUZ and 2 others like this.
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Either way can work but I do find that kicking in some attenuation can help prevent overload when using a second receiver in the same shack to monitor a 100 watt or great transmission. But as Steve said completely removing the antenna can be enough in a lot of situations. Still if I think I'm hearing any kind of distortion when monitoring locally I'll try kicking in an attenuator before assuming transmit distortion especially for rigs that do have internal attenuators.
     
    WB5YUZ and PU2OZT like this.
  6. WA9FZB

    WA9FZB XML Subscriber QRZ Page

    If that second receiver is close enough, you might actually be able to short out the antenna terminal to ground ans still hear your signal on it.

    Now, back in the 1960's, I actually used my station receiver to monitor my CW sending/signal. I had a Drake 2B, and nothing I could transmit (up to DX-100) was able to overload that thing.

    Today's receivers. . . might let out that magic smoke if you tried using it for a station monitor. Then you'd have to replace that micro-sized surface mount fuse.
     
  7. N9DG

    N9DG Ham Member QRZ Page

    I do a similar approach, running the monitor RX with no antenna connected. The isolation without an antenna connected is more than good enough to not overload the RX.

    But instead of listening to the RX audio, I am actually watching the TX signal on the panadapter / waterfall of the SDR RX. After seeing and hearing enough poor signals on the bands vs. good ones over the years while using a GOOD spectrum display SDR, you can easily tell just by looks alone on the display if your signal is good, or not as good as it should be when you are monitoring yourself. This applies to all modes that you may use.

    I run on the air with an SDRPlay RSP1 running and watching my TX pretty much all of the time on the frequency and mode that I'm operating. Including VHF and UHF.

    It is also great for setting the deviation on FM TX as well, it is supper easy to see if the FM deviation is off. So you don't need any fancy equipment to make sure that your VHF or UHF FM rig is modulating optimally. It can be easily done with a ~$120 SDR and a modest computer. And I think it is far better approach to monitoring your own TX signal than the legacy brand and model specific "station monitor" scopes from 20 - 60 years ago.
     
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  8. AE0GL

    AE0GL XML Subscriber QRZ Page

    Indeed! I was reminded yesterday (once again) that listening to a rig under test on another nearby radio can go horribly wrong and lead you on a wild goose chase.

    The problem is that a nearby receiver may or may not be picking up the signal as intended from the output point of the transmitter. The only reliable way to make this happen is with a dummy load and a proper sampling attenuator connecting the transmitter source to the local receiver.

    In my most recent fiasco, I was testing a battery operated 40 meter low power exciter design connected to a dummy load and oscilloscope.

    No matter what I did, I was hearing (and seeing) the faint signal (as it should have been) with strong 60hz amplitude and sidebands on the CW carrier when I listened on my Icom 7300 connected to my 40 meter dipole. Changing to a short "probe" of partially stripped coax inside the shack made the situation WORSE.

    It turned out that the weak rf field bleeding into the shack was NOT coming as assumed directly from the exciter output, but was a combination of weak stray leakage from the floating shield on the dummy load back through the oscilloscope's power supply and line filter to ground! This kind of setup put 60hz AC in series with the signal and any non-linearities in the path combined the two signals. I've noticed this kind of thing in other test setups before but I was just too lazy to take the measurement properly.

    Connecting the 7300 to the properly attenuated sampling point that the other test equipment was using resulted in hearing a, pure, clean CW signal, but I didn't try this until I'd wasted hours trying to find the source of the 60hz in my device's signal chain!

    This is a VERY common measurement problem and one I've been bitten by dozens of times. I was avoiding the direct connection for fear I'd accidentally key up the transceiver and damage it or the test equipment, but that just is not a reliable way to take measurements.

    hope this helps someone puzzled by similar effects...

    Mario (AE0GL)
     
  9. NL7W

    NL7W Ham Member QRZ Page

    Properly terminate the monitor receiver with a 50-ohm dummy load. A cheap two-position antenna switch can place a low-wattage dummy on position 2. I made my own with 2 each, 100-ohm, 1/4-watt carbon resistors inside an easily solderable silver PL-259 connector.

    Engage internal attenuation to bring the signal down to something realistic.
     
    Last edited: Dec 22, 2021
  10. AA4PB

    AA4PB Ham Member QRZ Page

    A good way to check the purity of your FT8 signal. Hook a separate receiver (with no antenna) to a laptop and run WSJT-x and see if your signal looks clean on the waterfall.
     

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