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100Hz line in TX

Uli DF5SF
Uli DF5SF Member ✭✭
edited December 2021 in FLEX-6000 Signature Series
Hello,
here is a recording of my transmitted signal.
See the picture here: https://ibb.co/KxpRG4p
Where do the 100Hz lines come from? In Germany we have 50Hz AC.

In the recording only the antenna is connected directly to the TX output via a choke (W1JR). Choke has no influence.
Power supply is 35A with transformer - no switching power supply. 12V line via toroid with several turns.

Now I changed antenna with 50Ohm dummyload. See here https://ibb.co/jgqL5D7

It is a mystery to me. I have Flex-6400 with V3.2.39

Many thanks for any hints.

73 Uli, DF5SF

Comments

  • Lasse SM5GLC
    Lasse SM5GLC Member ✭✭

    Uli,

    I seem to have similar sidebands, but as they are 75-80 dB below carrier or even lower (less than yours), so it is nothing to worry about. Interesting that you seem to have non or less hum when using a d/l, this points to stray RF... try a good choke on both the DC cable and the mains. Suggest "mix -31 big clamp" from Fairrite.

    Now what could cause this? My take is that the full wave rectifier in the linear supply will create 100 Hz ripple (not 50 Hz ripple). I would make surer the diode bridge do have capacitors across the diodes to decouple the RF, i.e. 10-100 nF should do. Maybe you could try to increase the filter capacitor to see if you notice reduced sidebands?

    Just to be sure it is the PS, you could try a car battery or a switched supply to verify that the sidebands are from the DC supply.

    You may suffer from some odd-ball ground loop worsening the ripple (but this is less likely), one could try to have a good common ground for your equipment.

    /Lasse SM5GLC

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Hi Uli

    The 100hz hum (2 x 50hz) is likely coming from your power supply and it is possible not filtering as well as it should. If you have access to an Oscilloscope you should be able to see it.

    I would test with another power supply or even a 12v battery and see if it goes away.

    73

  • Ha Gei
    Ha Gei Member ✭✭

    I think, this comes , if it´s from mains at all, from the 2 extends of the sine wave. 50 cycles means 50 positive 50 negative giving 100 after full wave rectification...

    Harry, DL9NDW

    ( Grüße Ulli... )

  • Patrick
    Patrick WH6HI KauaiMember ✭✭✭

    If you think you are seeing 100 Hz from a power supply, connect a dc battery and use a battery powered laptop and run the radio. This will confirm or show if the power supply is the culprit.

    Actually what I think it is, is simply the internal and external RF leakage into the radio. That RF will beat with the actual RF. And it is dependent on where you tune and put your XMT frequency on. I see this when I use FT-8 and is dependent on where in the XMT BW I place the actual FT-8 signal. I see those signal modulate with the main signal. I have run on DC and I still see this in the monitor window. What you see on the monitor is not necessarily what goes out to the antenna. Only stuff I have seen go out is gross modulation overloads from excessive drive. But the beat products remain. Confirmed with external spectrum analyzer looking at the radiation from the antenna field.

    No radio has perfect shielding and any RF around the radio will enter in some way. This is a design and cost issue and would be extremely expensive to fix. In commercial test RF test equipment will have extreme shielding and filtering but that equipment cost 50k dollars.

    I am pretty sure the ADC’s will not convert at 100 Hz. Is another factor. On the other hand modulated 100 Hz will be seen as it is part of the RF signal frequency. This is a problem that is not an issue, just very irritating to see on the XMT signal monitor.

  • Uli DF5SF
    Uli DF5SF Member ✭✭
    Hello,
    Thank you for the tips. I will investigate it in more detail between Christmas and New Year. I will report about it.
    Another question, how can I insert links (blue) to my pictures ?

    73 Uli, DF5SF
  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    For me, I just paste pictures in. Or, you can use the Icons below to upload media.

    Do you see those or is it because of the permissions I have?

  • Uli DF5SF
    Uli DF5SF Member ✭✭
    edited December 2021
    Hello
    made some short tests I had success. With DeLock Network Isolator Nr.62619 the signal is ok.

    73 Uli, DF5SF
  • Lasse SM5GLC
    Lasse SM5GLC Member ✭✭

    Uli,

    you should zoom in... you need to have the same span as when you did the first tests to allow a good comparason.

    The close in spurs seems just as bad (or good) as when you first posted.

    /Lasse SM5GLC

  • Uli DF5SF
    Uli DF5SF Member ✭✭
    edited December 2021
    Hi Lasse,
    thank you for bringing this to my attention. It was my mistake. Now new screen shots with the same span in both axes. NO difference.
  • Uli DF5SF
    Uli DF5SF Member ✭✭
    Thank you Lasse for bringing the problem to my attention. Now I have made two new screenshots with the same resolution. NO difference

    73 Uli, DF5SF

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