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Old 15-08-2022, 08:16   #1
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SSB Transmit Causing Alarms

Hello,

I've searched through most of the SSB threads but haven't found the answer to this question.

I have an Icom M700pro on my boat with AT-130 tuner and an insulated backstay antenna.

Currently getting good send/receive via sailmail which was used during a recent solo trip to Maine.

The boat has a high bilge alarm which goes off after the upper bilge pump has been running for more than 2 minutes. Also the boat has a low oil pressure alarm.

Both of these alarms chirp and scream during the intervals when airmail is on transmit, as well as every LED light in the boat turn into strobe lights.

Is there a solution to this problem? some reddit forums speak to a grounding issue?
I'm currently using a Kiss counterpoise which works great, no issues at all with sailmail getting a connection, I'm not opposed to a copper strap to a through hull but would avoid the work if necessary.

Any insight is helpful
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Old 15-08-2022, 08:53   #2
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Re: SSB Transmit Causing Alarms

It really ins't a "grounding" issue.

The amount of power being transmitted out the antenna is very large, especially with the kind of high modulation you have when transmitting data. This doesn't usually happen as much with voice calls because the average power level is a lot lower.

Some of the power is getting picked up by wires in the boat and converted back to electricity, and making your alarms "chirp." (That's a simple answer, but it's the gist of it.) It is emphatically NOT a problem with your radio or antennae. it is the wiring in your boat.

There are some things you can do to try to minimize it, which involve shielding the wires from picking up the radiated electromagnetic waves from the antenna. Use twisted pair wires everywhere you can, or run the wires inside metal conduits. People who go through this are usually try to avoid interference the OTHER way: noisy electrical equipment interfering with radio reception.

Or you just live with it.
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Old 15-08-2022, 12:03   #3
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Re: SSB Transmit Causing Alarms

Ship station operators used to rape a neon indicator tube onto the antenna feed line a a check that the transmitter was outputing properly, you appear to have achieved the same thing without any effort in your part.

It's probably easier to revise your perception than the boat wiring.
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Old 15-08-2022, 12:35   #4
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Re: SSB Transmit Causing Alarms

One or more wire lengths in a common circuit (including a ground or neutral wire) is likely a resonant length causing parasitic pick- up of stray RF. Sometimes it can be minimized with wiring through certain ferrite cores. The only way to determine which is trial and error.
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Old 15-08-2022, 12:58   #5
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Re: SSB Transmit Causing Alarms

Along with the other answers, I submit that the cause is called Common Mode Currents. These are currents that are being returned to the radio on the feed line and therefore causing the feed line to act like an antenna. It happens all the time even to ham operators in their ham shacks.

The fix is to install a common mode choke in the transmission line at the tuner. It will be located between the tuner and the radio. But make sure it is at the coax input of the tuner, not the output of the radio. The Common Mode Choke will reduce, if not eliminate the stray RF currents on the coax.

Common Mode Chokes can be made with coax cable. They are called Ugly Baluns. Or one can purchase a Common Mode Choke. Check with Balundesigns.com for Common Mode Chokes.

All this is JMHO
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Old 15-08-2022, 15:41   #6
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Re: SSB Transmit Causing Alarms

Quote:
Originally Posted by Jeffmg View Post
Both of these alarms chirp and scream during the intervals when airmail is on transmit, as well as every LED light in the boat turn into strobe lights.

This is common.


Quote:

Is there a solution to this problem? some reddit forums speak to a grounding issue?
I'm currently using a Kiss counterpoise which works great, no issues at all with sailmail getting a connection, I'm not opposed to a copper strap to a through hull but would avoid the work if necessary.

Any insight is helpful

Kiss counterpoise probably contributes to the problem.


For your oil and bilge alarms, twist the wires. Especially twist the wires going to sensors. Also twist the wires providing power if possible. You can twist wires together with a drill, or purchase wire that is already twisted.


Applying ferrite cores will usually help, as Brian indicates. There are snap-on cores that are easier to install but they are most useful at VHF. For HF usually you have to wind the wires through the core several times to get good results. Search for "cable ferrites" at your favorite electronics supplier and limit the search to material #31 which is for HF, like this:


https://www.digikey.com/en/products/...ASwB2AcxABfSUA


Just order some that are the right size for your situation and wrap the cables through them, 3, 4, 5, 10 times, depending on how flexible the cable is and how much length you have to work with, see whether you get the results you want, and adjust. Ferrites aren't very expensive. They will work best close to the problem i.e. the LED that's flashing.
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Old 15-08-2022, 15:42   #7
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Re: SSB Transmit Causing Alarms

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The fix is to install a common mode choke in the transmission line at the tuner. It will be located between the tuner and the radio.

Doesn't the AT-130 incorporate one?
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Old 15-08-2022, 19:01   #8
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Re: SSB Transmit Causing Alarms

Jammer, that is an excellent question.

I use a FT-140-43 (single core) at my antenna and it is feed of the antenna (coax fed). The tuner is a MFJ-929 and I am sure there is no choke in that one. But still, the DC side of the input and output connector are at the same ground potential. In my Common Mode Choke (which I built) the other side of the antenna (OCF Dipole) is part of the choke, and not as a separate path. Just like an Ugly Balun's shield is part of the choke and not a separate path.

But does the Icom tuners contain a Common Mode blocking hardware? Guess we'd have to ask Icom, or someone who is intimate with that tuner.

Ferrite Beads may work at the trouble equipment. I have never had success with that method, but not saying it will work for others. This is why I went with the Ferrite Core and made my own Common Mode Choke.

JMHO
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Old 16-08-2022, 04:52   #9
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Re: SSB Transmit Causing Alarms

Low pressure alarm can cause shut down of engine . You didn't face . With another alarm switch , please check the resistance in return line or in Controller.

As well , measuring current in SSB supply's each line can give some clues . Whether body ground helps to provide part of current flow or alike observations - may come out . Regards .
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Old 16-08-2022, 07:42   #10
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Re: SSB Transmit Causing Alarms

When I connect for email (I use Winlink, but used to use Sailmail), I set Icom M802 power to "mid". (Can't remember where I read recommendation to use mid power for email, but this does significantly reduce issues.)
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Old 16-08-2022, 08:22   #11
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Re: SSB Transmit Causing Alarms

Allow me for a couple more points, if I may.

First, fixing an issue does not mean you have solved the problem. In this case of alarms going off when the SSB is used. Adding ferrite beads and twisting pairs at the alarm is not solving the problem. The problem is obviously RF in the boat since the alarms activate when using the radio. So you must solve the RF issues and that should take care of other issues.

Next is the use of ALC to operate your SSB. When sending on any data service, the proper setup is to use MAXIMUM RF power, but control the amount of RF by using minimal audio gain. I too use Winlink. My power setup is maximum on the radio and then adjust the audio input (the Winlink signal) so I get 25 watts output. So even though my radio is at 100W, my actual RF power is only 25W. With that I close most all links. I say most because not always do I have a good circuit path to the other station or propagation is not in my favor.

Anyway, just wanted to chime in on this. And as always, JMHO.
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Old 16-08-2022, 21:47   #12
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Re: SSB Transmit Causing Alarms

To avoid RF interference , location of these two alarm sources have sufficient spacing . Whatever is common to all these three factors will be influencing the deciding circuits of signal conditioning or creating a false alarm signal itself .

As transmission is involved , I prefer to look into the drawing current and its path . Return terminal (-ve one ) would always be a common factor for our system . Looking on this factor may bring new observations . Regards .
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Old 17-08-2022, 10:42   #13
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Re: SSB Transmit Causing Alarms

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Originally Posted by Brian.D View Post
My power setup is maximum on the radio and then adjust the audio input (the Winlink signal) so I get 25 watts output. So even though my radio is at 100W, my actual RF power is only 25W. With that I close most all links. I say most because not always do I have a good circuit path to the other station or propagation is not in my favor.

Anyway, just wanted to chime in on this. And as always, JMHO.
Brian, it is unclear exactly what you are doing but, if you set your power output to 100W on the radio, you want to adjust the mic level, so that you hit 100W (hit, not exceed) at least on some frequencies (1 KHz sine is a good test). Otherwise, your signal-to-noise ratio is bad. You can still link but it is not optimal. Most marine radios will adjust this automatically but you are making it harder for the radio and reducing your sn ratio.
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Old 18-08-2022, 06:25   #14
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Re: SSB Transmit Causing Alarms

Pizzazz, sorry I should clarify that I am not using a marine radio. I am using an Icom IC-707 which dose not have an ALC circuit for audio/digital signals, I failed to mention that.

I am not feeding my digital signal via the mic port. It is connected to the back of the radio. The laptop audio output (or speaker output) is set to 0dBm. On VARA, the signal level is also set to 0.0dBm, but defaults to -5dBm. The SignaLink USB device is what is controlling the final audio output to the radio which in turn drives the RF to 25W. I have thought about connecting the Oscillscope to the output of the SignaLink to see what the waveform looks like, but haven't yet. Connections are solid with very little resends, except when conditions are less than ideal.
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