Problem with Kenwood TS-480 operating PSK-31

Discussion in 'General Technical Questions and Answers' started by WS2L, Mar 26, 2011.

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  1. WS2L

    WS2L Guest

    My set-up for operating is as follows:

    Kenwood TS-480SAT
    Butternut HF-6V vertical
    MFJ-989C antenna tuner
    Rigblaster Nomic
    DigiPan for PSK-31
    MMTTY for RTTY

    My problem is that whenever I transmit in PSK-31 on Upper Side Band and MMTTY on Lower Side Band. I use the internal tuner once in a while to bring SWR down flat. The problem is that when I transmit a digital signal several seconds into my transmission my SWR goes up higher and higher till it pegs the meter on the radio and also shows a high SWR on the meter in the tuner. This does NOT happen in any other mode only USB and LSB while using digital modes.

    Yesterday I tested each band into a dummy load and my SWR was perfect. Once I put the antenna in line then it starts up again. I have been running this combination for a year now with no trouble but now I can't seem to operate on SSB at all, not even voice.

    Any ideas what it might be ?

    Should I be looking to send it to kenwood for a check up and possible repair ?

    Tnx in advance for your advice.
  2. K8JD

    K8JD Ham Member QRZ Page

    I would take a close look at the antenna/feedline for problems.
    Why do you need an internal tuner, and an external tuner :confused: when you have an antenna that should have been adjusted for a very low SWR when you installed it !?!?!? ,
  3. K7MH

    K7MH Ham Member QRZ Page

    I had a problem not long ago with my 989C where the variable cap shaft for the antenna was loose. After being adjusted it would very slowly rotate around from it's own weight towards being more meshed. It took a while before I noticed why I had to keep adjusting the tuner!!
    Set the 2 caps to 3 or 4, 6 or 7, somewhere in there and watch the pointer for a while. It might even make a difference just how warm/cold they are from room temperature.
    Last edited: Mar 26, 2011
  4. WG7X

    WG7X Ham Member QRZ Page



    It sounds like spurious emissions to me. I had a similar problem once with a Kenwood TS-940.

    The reason that testing into a dummy load shows no problem is that the dummy load accepts all frequencies of RF with out feedback. Thus no SWR problem.

    Into an actual load such as those presented by a resonant antenna or a tuner, the spurs show up as reflected power because that is exactly what they are, since most of the spurs will be on a band(s) other than what the system is set for.

    What you need to see this is a spectrum analyzer, something not present in most ham shacks.

    Yeah, it's probably time for a visit to the radio doctor.

    73 Gary
  5. WG7X

    WG7X Ham Member QRZ Page

    Think man, Think!

    I can think of a couple of reasons:

    • Antenna in use is a bit narrow-banded, so operator uses internal tuner to make transmitter happy.
    • External tuner might just possibly be in "Bypass position" enabling operator to use the included SWR meter. This would enable him to check accuracy of internal tuner.

    By-the-way, not everyone worships at the altar of resonance, expecting each and every antenna in the arsenal to exhibit the "perfect" 1:1 ratio of VSWR.

    VSWR is a poor indicator of antenna performance; after all, the aforementioned dummy load shows a 1:1 ratio at almost all frequencies, but does not radiate too well...

    So, calm down a bit, OK...

    Here, I'll throw in a few exclamation points and question marks for you, just in case you ran out with that last post:


    Use them sparingly to make them last, OK?

    73 Gary
  6. KT1F

    KT1F Ham Member QRZ Page

    What happens if you transmit a steady carrier at similar power to the digital modes? I mean in tune mode or CW with the key down or AM or something. Does the same thing happen then? You need to see if it's related to the digital mode (which seems unlikely) or it happens whenever your tuner / tuner / antenna combination receives continuous power for a while.
  7. WS2L

    WS2L Guest

    The external tuner is there to make the Amp happy.

    Also may I remind everyone that this ONLY happens while operating SSB, all other modes do not produce the same results. I can get a flat SWR on all bands with the 989C and can operate CW, FM, etc with no problem, the problem is ONLY when operating SSB.
  8. KT1F

    KT1F Ham Member QRZ Page

    The fact that it does not happen on a dummy load points to either Gary's theory of spurious output on a different frequency or perhaps RF feedback getting into something. It might be useful to know if there is something about the digital audio making this happen. Does it happen on normal phone SSB? If you could find something that you know generates a clean audio sine wave and transmitted that at about the same power level then it would answer that question. If you send an audio sine wave over SSB without overdriving or other problems then it should produce essentially the same RF as CW with the key down.
  9. NI7I

    NI7I Ham Member QRZ Page

    If this is a new condition, I wouldnt think that spurs are the problem. They would have existd before. I would look at thgings that could have changed.. Feedlines/connector degradation.. Radial field / connector degradation, somthing of that nature.. Grabbing at straws .. another thought would b that, autotuners often, especially on low power, forget the matching solution and search for a new one.. sending the apparnt swr way up.. food for thought..

    I would look for somthing that has changd.

  10. K0RGR

    K0RGR Premium Subscriber QRZ Page

    It sounds like something is getting hot from the 100% duty cycle digital transmission, and that's causing it to change value, resulting in high SWR. But if it doesn't happen in CW mode when you put a brick on the key for a few minutes, then that does point to some kind of spurious emission from the radio. I can't imagine how RF feedback would be involved in this, but it might be possible. Once the SWR is bad, if you switch quickly over to CW and try the same thing, do you still have a high SWR? If you generate CW by injecting a tone into the radio, as you do for RTTY or PSK, what happens?
  11. WS2L

    WS2L Guest

    I do not operate a lot of Phone, mostly CW and digi modes. When I have operated SSB no one has ever made any negative comments about my audio. Guess I will have to try a few QSO's to see what I get in return.

    Lee now that you mention it I just changed the coax from the antenna to the shack but the problem began before I did this. I actually changed coax to see if that was the problem.

    It seems more and more like isolated incidences. This morning I was on 30 meters operating PSK-31 and my SWR was flat with no jumps or increases in SWR. I am going to double check that the feedline is doing it's thing properly then move on to the connection to the antenna. I am at a loss for words because this ONLY happens on SSB, it does not effect any other mode.
  12. WG7X

    WG7X Ham Member QRZ Page

    Think about this...


    When you operate CW the radio is basically in a steady state. On/off is all you get but when the key is down the RF basically remains at a constant level. When you use SSB the level of RF in the transmitter is constantly changing with the voice peaks. This is a much more unstable position and allows the transmitter to generate spurs.

    This problem on my Kenwood TS-940 was only apparent on Ten meters and only when using SSB. I only mention this because your problem sounds exactly like the problem I had. It's worth checking on.

    I'm not sure when my problem began occurring but the symptoms were the same and only on one band. I sent the radio to Cliff at AVVID in Dallas. He fixed it up and it has not had that problem since.

    73 Gary
  13. W8JI

    W8JI Ham Member QRZ Page

    Everything you said points to spurious emissions, which is commonly a low frequency parasitic in the power amp. Since radios use a low pass filter on the output and almost always have a very gradual roll-off in filtering on lower frequencies, the low frequency parasitic can blow right through the radio filters. It also mixes with the main signal to create spurs.

    Things that indicate it COULD be a parasitic are:

    1.) It is or seems clean on a dummy load.

    2.) It is or sounds like a time-heat function, and the indicated SWR problem only appears in some modes.

    I've had this problem with Kenwoods and Yaesu's. I have an FT757GX I had to retire from mobile service because it would oscillate on hi-Q antennas. This is a difficult problem to replicate because it often appears with certain load impedances OUTSIDE the normal band. Often a change in length of a cable or type of antenna will make it go away.

    My 757 for example was perfectly clean on a dummy load, or on an antenna with a long feedline. It only oscillated with a narrow band mobile antenna and only sometimes.

    By the way, my 757 oscillated on all modes, yet on carrier the strong carrier masked the problem! When it oscillated it had spurs every few hundred kilohertz no matter what mode when hot when on a high Q antenna.

    I'd look at spurs first, since it is time/mode sensitive. Like Gary says, you problem sounds like a problem I had with a TS 440S Ameritron used on the bench as a test radio and like I had with a 757GX on high Q loads. We caught the Ameritron one right away because tuned input circuits would sometimes tune, sometimes not and because we had a spectrum analyzer running and saw the spurious when the inputs would not tune right.

    73 Tom
  14. WS2L

    WS2L Guest


    Thank you so much for all of the valuable information, I am leaving tomorrow to go to Ft Lauderdale, FL until Friday so I will have limited time to play around with it today. I'm catching a 6:00am flight back to NJ on Friday when I can concentrate more on this issue. Thank you also for taking me seriously as I know after 33 years as a ham I should be able to figure this out by myself.

    I will keep everyone updated on what I did and what results that I get from each option I try.
  15. WS2L

    WS2L Guest

    Since yesterday (Sunday) everything appears to be working fine again. I can operate SSB, RTTY and PSK-31 without the SWR going whacky. Now I am really confused but as long as it keeps working I will not complain. Now all I have to do is solder the cable and connector for my Yaesu FL-2100F and my station will be completely set up.

    I have a gut feeling that this is not going to last very long but I'm going to enjoy it while I can.
  16. WS2L

    WS2L Guest

    It looks like I spoke to soon, just as fast as the problem disappeared it again reappeared this afternoon when calling CQ on 20 meters PSK-31. I'm off to Florida in the morning to see a concert at the Bank Atlantic Center in Ft Lauderdale and a Hockey game the next night. I'm returning Friday morning so I guess I will deal with it over the weekend while the wife is still in Florida.

    If anyone down in the Ft Lauderdale wants to meet for lunch email me at:


    I can check my email from my cellphone except for my address.
    Last edited by a moderator: Mar 29, 2011
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