Problem with Kenwood TS-480 operating PSK-31
My set-up for operating is as follows:
Butternut HF-6V vertical
MFJ-989C antenna tuner
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.
I would take a close look at the antenna/feedline for problems.
Why do you need an internal tuner, and an external tuner when you have an antenna that should have been adjusted for a very low SWR when you installed it !?!?!? ,
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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 by K7MH; 03-26-2011 at 07:29 PM.
"Oh what a tangled web we weave when first we practice to receive."
-Otto Watt Sept. 5 1925
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.
Think man, Think!
I can think of a couple of reasons:
Originally Posted by K8JD
- 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?
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.
The external tuner is there to make the Amp happy.
Originally Posted by K8JD
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.
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.
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.
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?
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