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Author Topic: Bad PSK-31 Signal  (Read 3135 times)
KE4WLL
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Posts: 2




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« on: November 18, 2012, 07:24:45 PM »

I am new to the digital world and trying my hand at it. I have an FT-450at and a rigblaster nomic and using HRD DM-780. When I Transmitt my signal comes out like a pulsing and very distorted, I am wondering if I have a bad interface or if something else is going on. if anyone has an idea of what is going on please let me know.

Trevor
KE4WLL
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VA7CPC
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Posts: 2377




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« Reply #1 on: November 18, 2012, 11:58:08 PM »

First, a question:

. . . Who is monitoring your signal?

. . . Are you getting a report "over the air", or are you using your own loudspeaker and monitor circuit in the rig?

Second, a suggestion:

. . . While you transmit, adjust the audio _output_ in DM780 (there will be a slider control somewhere!) so that the
. . . ALC meter on the rig is _just barely_ above 0.

. . . Then, reduce the audio output just a little bit, so the ALC meter on the rig is showing "0".

Any audio output setting less than that should _not_ give a distorted signal from the rig.

.              Charles
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STAYVERTICAL
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Posts: 859




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« Reply #2 on: November 19, 2012, 02:37:35 AM »

Charles has given you some good advice and follow it first.

If you still have problems, it seems you can monitor the audio output from the Nomic with an earphone.
If that's true ( I don't have one myself - just looked on the net), then it will tell you if it is distorted.

In my experience with both homebrew and even the USB-Signalink, I have found R.F. feedback a problem.
With my homebrew versions of digimode interfaces, I was getting similar problems as yourself.
The problem was intermittent and varied by band and power.
A lot of R.F. choking with ferrite snap on suppressors fixed that in the end.

With the USB-Signalink, the audio did not distort, probably because the unit was taken offline first.
The problem in this case was RF overload in the USB cable to the Signalink.
Again a snap on ferrite solved the problem.

My problems are simply because my antennas are too close to the shack (about 25 feet).
They are also types which radiate a lot of low angle radiation, and are low on the ground as well.
I am not sure of your situation, but if Charles's good suggestions don't work out - consider some bypassing.
For a test, first run low power (have the audio control wound way back).
If you have R.F. in the lines problems, it should not be present on very low power ( a few watts).
It will also give any local monitor receivers a better chance of giving a true indication, without extreme overload.

Don't worry, we have all trodden this road too - the track is well and truly worn deep.

Good luck,

73 - Rob

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KE4WLL
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« Reply #3 on: November 19, 2012, 05:55:30 PM »

I now think i know what the Problem might be. I am using a HY-Gain vertical about 3 ft from the shack it was put as a temporary antenna. So I believe that it to much RF feedback I am getting. However it going to be a little bit before I can move the antenna to test this theory.

Trevor
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VA7CPC
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Posts: 2377




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« Reply #4 on: November 20, 2012, 05:35:45 PM »

Three feet Huh??

My antenna is in the attic, about 12' from the rig (above my head).

I have a ferrite split-bead on _every wire_ into and out of the rig and computer!  Without those beads, RFI completely destroys my signal (and sometimes makes it difficult to stop transmitting!).

There's an easy test:



. . . Reduce the rig's output power to as low as possible with its "RF Power" knob, or menu setting.

If the problem disappears, and you can transmit normally, you've found the trouble -- it's RFI.

.        Charles

PS -- as StayVertical says, this is a well-worn, deep track!
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