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Help with Omni V

Sep 21st 2011, 20:29

KB4SRN

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
My Ten Tec Omni V develops an oscillation a few seconds after it is turned on. This completely covers the incoming signal and shows a full deflection on the s meter. If I switch between VFO's it will sometimes stop, disconnecting the antenna will stop it, as will turning the rig off and then back on. It has even occurred while I was transmitting and the receiving station said it wiped out my signal. Many times it starts again and I go through the process once more. After 5 or more minutes the rig seems to settle down and works just fine. I took the radio to Ten Tec, but they could not find a problem with it and said it did not do it while they had it. When I got it back and hooked it up the noise started as soon as I turned the radio on. I don't know if they hooked it to an antenna or just a dummy load. It only occurs when an antenna is connected and a signal is present. Ten Tec thinks it is caused by a local signal, but my Paragon, Scout, and Yaseu 450 have never picked it up. Anyone have any ideas. It's a great radio but this problem is preventing me from enjoying it. I would love to get it back into service.
Sep 21st 2011, 23:02

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

Have you tried powering it with a different power supply? There might be an interaction between the rig and PS.

Zack Lau W1VT
ARRL Senior Lab Engineer
Sep 21st 2011, 23:05

W1RFIAdmin

Joined: Jul 25th 2011, 14:25
Total Topics: 0
Total Posts: 0
A bit more information may be helpful, but let me take a start at this based on the question.

If this is occurring on both transmit and receive, that would strongly suggest that the power-supply is generating the noise and impacting the rig on both transmit and receive. There is relatively little circuitry that is common between the two functions. To test this, if you have another power supply that you can use, or a 12-volt battery, try running the rig from that supply or battery. Watch the polarity of the hookup to the supply or battery, as you don't want to blow up your rig trying to fix it!

It is also possible, btw, that the report you received about the noise impacting your transmitted signal was mistaken. If the ham on the other end heard a noise, he could have attributed that to your signal.

If the noise really does impact the receiver only, the fact that it doesn't do it when there is no antenna suggests either that the noise is external to the receiver of that whether the receiver generates the noise or not is sensitive to the impedance at the input of the recevier.

To test this, if you have a different antenna, try using it on the receiver. This will generally be a different impedance. I would not transmit into an antenna that would present a non-50-ohm load to the transmitter, btw, as I never completely trust SWR protection circuitry.

If you have a 6- or 10-dB attenuator, you can connect it to the receiver input and connect your antenna to the input of the attenuator. This will present about a 50-ohm source impedance. If the noise goes away, that may suggest the front end of radio has some instability.

What does the noise sound like? That may provide some clues to help me or others provide better answers.

73.
Ed Hare, W1RFI
ARRL Lab
Technical forums moderator
Sep 22nd 2011, 18:56

KB4SRN

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Tried the radio on a different power supply but problem is still there. I will try to take a short video of the problem if you are interested. The problem has appeared on both 80 and 40 meters with different antennas (dipoles) that are cut to frequency. As for the transmitted report, when I unkeyed the noise was present. I switched the radio off and back on at which time it was gone. The receiving station reported that my signal suddenly went to a high pitched squeal.
Sep 22nd 2011, 19:02

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
You might try listening for the oscillator signals used in the Omni V--it sounds like one of them may be unstable. You can do this with the other rigs that you own.

Zack Lau W1VT
ARRL Senior Lab Engineer

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