TenTec Pegasus - RF in mic audio

Discussion in 'Microphones, Speakers & Audio Processing' started by VE3TMT, Aug 7, 2018.

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  1. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    Not sure if this is the correct forum (admin, please feel free to move if not)

    Radio is the TenTec Pegasus, headset is a Koss SB40. I've used this headset with numerous radios over the years and never had a problem with RF in my TX audio. The Pegasus is another story.

    I run the mic gain at 5/10, speech processor is not used.

    Only sporadically I hear RF in my monitored TX signal (using the Pegasus TX monitor)

    When I listen to my signal on my RSP1A, I don't hear it, but other ops have mentioned a slight hint of it during QSOs. I bought some Fair Rite mix 31 snap on cores and put three of them on the mic lead that runs from the inside of the mic jack to the PCB. I have one on the outside cord as well. I also soldered .01uf caps from the mic audio lead to ground and the speaker audio lead to ground.

    Not sure what else to try. I've heard if the power supply is too close to the radio this may cause it?? Power supply is an Astron VS-35M and the Pegasus sits on top of it. I had it about three feet away at one point with no change.

    The Pegasus is also grounded to my cold water pipe, it's the only ground I have access to. With or without this connection, the RF is still there.


  2. KW6LA

    KW6LA Ham Member QRZ Page

    Max What antenna, how close to the radio? The feed line / Power too?
  3. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    Antenna is either A3S or DX-B sloper. Antennas at at other end of house on top of tower, so not proximity effect. RFI is there when running 50 or 500W.

  4. KW6LA

    KW6LA Ham Member QRZ Page

    Placing a LINE ISOLATOR at the output of the transceiver or linear amplifier, prevents RF from traveling along the outer surface of the coax's shield. Any RF current flowing on the coax braid that can be radiated or coupled to other equipment is forced to ground by the very high impedance of the LINE ISOLATOR. RF current always takes the path of least resistance.
    It can work if this is the problem (CM ). Radio Works sells them. Bypass cap in the mic .01uf has helped in some cases. Good luck!
    K7TRF likes this.
  5. KM3F

    KM3F Ham Member QRZ Page

    What level of SWR do you normally see?
    The antenna being at the other end of the house and on the tower is no guarantee there won't be any RFI to the equipment.
    Your still in the RF fields.
    Take it one step at a time.
    The headphones can pick up separately.
    The Mike cable can be another source.
    Sometimes if your in the RF field, the only course is to do something with antenna location.
    Make sure all the cables are shielded and al connectors are tight.
  6. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    SWR on 40 is below 1.3 across the band, ditto on the beam on 20, 15 and 10.

    The headset is a KOSS SB40, it's primarily a computer headset, but I've used it on many radios with no RF issues at all.

    Yesterday, I sunk a 6' ground rod about 5 1/2' in, and ran SEPARATE ground wires from the back of the Pegasus, the computer, the tuner and the amp through the shack wall out to the ground. I also moved the Pegasus away from the power supply. I'm still getting RF on the mic audio and my in shack monitor for the outside camera still cuts out when I transmit on 40m. 40m always seemed to be the worst band. I've got mix31 cores on the coax from the radio, on the wires inside the Pegasus from the back side of the mic jack to the PCB, and on the headset wires where it plugs into the front of the Pegasus.

    I'm at a loss. I really can't think of anything else to try.

  7. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    Installed the MFJ-915 at the output of the Pegasus and it appears to have solved the RFI problem.

    Thanks for all the tips.
  8. AA7QQ

    AA7QQ Ham Member QRZ Page

    It almost sounds like an issue with the computer hash getting into the Pegasus. I had that issue for a while & finally swapped out a quality, ferrited USB cable. All fixed. My Pegasus, 100A homebrew switcher supply & MA1000B are right alongside of eachother.

    One thing that the Pegasus is sensitive to is input voltage. It can sound like RF on the mic.

  9. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    Hi Ed, well I've noticed even with the isolator in line the RFI is still there.

    By USB cable are you referring to the comm cable between the Pegasus and the computer?

    The power supply is an Astron VS35M. The Pegasus sits right on top of it. I may try moving things around a bit.

    Another observation, I only hear the RFI in the headset, not in the shack speakers.

  10. AA7QQ

    AA7QQ Ham Member QRZ Page

    You might try a ferrite on the headset wires. Getting it all correct can be a pain with cheaper cables. I actually use a good quality USB3.0 ti serial adapter. For a headset, I use a Plantronix DSP headset.
    When first installing, I had all sorts of issues. Just that USB cable solved it. Of course, I left all of the ferrites in place.
    Now, if you are using a serial to USB adapter piece, throw it away, Get the whole adapter cable & spend some money on ot.
    Also, I "Think" the Pegasus has only mono output. Be sure to use a mono to stereo adapter.
    Last thing, be sure that you are NOT plugged into the "Speaker" jack.
    Another thing to watch for, is to NEVER connect the audio output shield to ground, as it can blow the audio amp.


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