Multicoupler creating birdie?

[N9JIG]

Background:

I have a couple dozen assorted scanners, with 4 separate Stridsberg multicouplers (2 8-port and 2 4-port, all active). Each is connected to an A/S ST-2 in my attic.

A couple weeks ago I noticed a weird data signal coming in on 160.455 and then noticed it wandering up and down a few KHz. now and then.

I only heard this on the scanners connected to this multicoupler, one of my 8-port units.

I cannot find this elsewhere in the house using a handheld scanner with the squelch wide open. I thought maybe it was a sensor on one of my wireless weather monitors, but nothing was found by any of those. I also do not hear it in the neighborhood or anywhere else around the area.

Is it possible that the amplifier in the multicoupler is running away and creating this noise? Here is a sample of it:

https://dl.dropboxusercontent.com/u/18949030/160.455_data.MOV

 

[RFI-EMI-GUY]

Background:

I have a couple dozen assorted scanners, with 4 separate Stridsberg multicouplers (2 8-port and 2 4-port, all active). Each is connected to an A/S ST-2 in my attic.

A couple weeks ago I noticed a weird data signal coming in on 160.455 and then noticed it wandering up and down a few KHz. now and then.

I only heard this on the scanners connected to this multicoupler, one of my 8-port units.

I cannot find this elsewhere in the house using a handheld scanner with the squelch wide open. I thought maybe it was a sensor on one of my wireless weather monitors, but nothing was found by any of those. I also do not hear it in the neighborhood or anywhere else around the area.

Is it possible that the amplifier in the multicoupler is running away and creating this noise? Here is a sample of it:

https://dl.dropboxusercontent.com/u/18949030/160.455_data.MOV

How are those multicouplers hooked up? Are they cascaded? What is the gain from the input to output? Are the branches of the system symmetrical ?

If the gain is excessive

1) The antenna might be picking up radiation from the cables or connectors downstream and the system is oscillating. Try removing the antenna and terminating the input to the amp with a 50 ohm load. Did the oscillation stop? Make sure input and output wires are not bundled together and the cable terminations are tight. You did use double shielded cables?

2) The amplifiers downstream could be overloaded, even causing over heating.

If you have a spectrum analyzer you can look for a strong signal or signals which may be causing overload. You might need a bandpass or band reject filter ahead of the preamps.

Generally you should run the distribution system at unity gain or just slightly positive gain. This means you should remove the excess gain from the first stage with an attenuator before presenting the signals to the next stage. In some cases an attenuator between the final stage and the receiver may be helpful in improving IMD of the system. Notice the word "system".

When I was working on antenna sites I would introduce a test signal ahead of the preamp system, usually at the tower mounted preamp and I measure SINAD at the receivers. Then I would attenuate the excess System gain until the SINAD started to degrade and then I would put about 2 or 3 dB excess gain back. Sometimes the system had variable attenuators, sometimes I had to use a step attenuator to make the measurement and then install fixed pads.

 

[N9JIG]

The multicouplers are each attached to its own antenna, they are not cascaded. (BTW, I did try that once just to see what would happen, it seemed to work well...)

I don't have a spectrum analyzer, so that is a no-go for me.

The systems are fairly simple: ST-2 in the attic, RG58 coax of about 25 feet to the multicoupler, RG58 jumpers to each of the scanners.

I have 4 of these systems in place, 2 with the 8-port multicouplers and 2 with the 4-port. The coaxes all go thru the same hole in the wall and the antennas are all next to each other in the attic. Only radios connected to one of the 8-ports are hearing this noise.

Later this week I will try and swap out the multicouplers and see if it follows the device or antenna.

 

[buddrousa]

Rich have you tired swapping the two 8 ports see if the problem follows the known unit. If it does not follow the know unit swap the power supplies. See what that does for starters.

 

[N9JIG]

Mystery Solved!

Mystery Solved!

I decided it wasn't the multicoupler after all. I disconnected the antenna from the multicoupler and the noise went away. I connected a different antenna and it was there but much weaker. The two antennas are 40 feet away from each other, on opposite sides of the attic. I then connected the antenna that had the noise strongest to it to a handheld PRO106 and the noise was right there.

I took the handheld scanner with a telescoping whip antenna around the house to track it. I had done the same before but never went into the kitchen since there are few electronic devices there and none that (are supposed to) transmit.

After checking the entire house, keying in on things like the alarm system, TV's, wireless transmitters for the weather sensors etc. I looked at my antenna list and found that the antenna receiving most of this noise was directly above the kitchen. I took the scanner there and it got real strong, especially in one corner. I started unplugging things and found out the offending device was my drink cooler!

This is a small refrigerator we keep our water bottle, beer, wine etc. in. It has a door alarm on it as well as an electronic temperature controller. A second after I unplugged it the noise went away and it returned when I plugged it back in. The antenna is about 20 feet directly above. On other radios connected to different antennas in that part of the attic the signal remains but below the squelch except when the door is open, then it gets stronger.

I will decommission the use of this antenna for now and use a different one on the multicoupler. I will see if I can abate the noise from the drink cooler, if not then it goes to the next community garage sale.

 

[RFI-EMI-GUY]

Mystery Solved!

I decided it wasn't the multicoupler after all. I disconnected the antenna from the multicoupler and the noise went away. I connected a different antenna and it was there but much weaker. The two antennas are 40 feet away from each other, on opposite sides of the attic. I then connected the antenna that had the noise strongest to it to a handheld PRO106 and the noise was right there.

I took the handheld scanner with a telescoping whip antenna around the house to track it. I had done the same before but never went into the kitchen since there are few electronic devices there and none that (are supposed to) transmit.

After checking the entire house, keying in on things like the alarm system, TV's, wireless transmitters for the weather sensors etc. I looked at my antenna list and found that the antenna receiving most of this noise was directly above the kitchen. I took the scanner there and it got real strong, especially in one corner. I started unplugging things and found out the offending device was my drink cooler!

This is a small refrigerator we keep our water bottle, beer, wine etc. in. It has a door alarm on it as well as an electronic temperature controller. A second after I unplugged it the noise went away and it returned when I plugged it back in. The antenna is about 20 feet directly above. On other radios connected to different antennas in that part of the attic the signal remains but below the squelch except when the door is open, then it gets stronger.

I will decommission the use of this antenna for now and use a different one on the multicoupler. I will see if I can abate the noise from the drink cooler, if not then it goes to the next community garage sale.

Is that one of those Emerson Peltier wine refrigerators? A lot of complaints of them failing, sounds like the fans and filters go bad.

 

[N9JIG]

It is a Midea Equator CH 169-138. It has a hi-temp and door open alarm, I suspect these are the culprits.