To Choke Or Not To Choke

Most Cruising boats are equipped with a High Frequency (HF) Radios onboard to extend the range of verbal and technical data communications. Participation in radio nets to obtain weather information, downloading GRIB files and email communication are just a few of the different uses for the HF radio. Some HF radios like the ICOM M802 radio are equipped with Digital Select Calling (DSC) and Emergency Broadcast functions. The DSC operates similar to that of the VHF radio, but has a much longer range. The VHF is limited to the immediate line of sight or the horizon. Dazzler is equipped with an ICOM M802 HF radio, an SCS Pactor modem, an ICOM AT140 tuner and a backstay antenna. The grounding system for the radio antenna is a large Dynaplate.

One of the issues that has plagued me for the last several years, eight to be exact, is that when I am underway utilizing the Auto Pilot, F.R.E.D. (Freakin’ Remarkable Electronic Device), and attempting to broadcast on certain frequencies of the HF radio, stray frequencies interrupt F.R.E.D. and cause him to change into standby mode thus resulting in a crazy Ivan. In other words Dazzler turns off course. Initially, it isn’t such a bad thing, but if the sails are up in a strong blow or your navigating through narrow channels the result could be a more urgent issue.

F.R.E.D. is a Simrad AC42 computer and viewed by a B & G Zeus 3 Chart plotter. Dazzler is equipped with a complete host of other Simrad electronics to assist with navigation.

While operating under F.R.E.D.’s capable steering control with my HF radio on, I could hear a consistent tone that pulsed through the radio. I first contacted ICOM USA in an attempt to discover the source of the repeating tone on the radio. I am sure you may already know the result of that conversation. Yep! It’s not our radio equipment. Okay, then I contacted Navico Tech Support in the USA regarding my Simrad electronics. I got the same answer from them; It’s not our equipment. Well it had to be coming from somewhere and the tech support arena was unhelpful.

I began trying to approach the issue from a diagnostic angle. I started removing one IMG_3997piece of Simrad and cable at a time. Additionally, I installed radio ferrite chokes to the cables in an attempt to stop any stray radio frequencies (RF) from the attached equipment. When completed, I had ferrite chokes on every cable. However, I still had the pulsing tone on the HF radio and when attempting to broadcast on certain frequencies in the, 40 meter band, with F.R.E.D. engaged a crazy Ivan would ensue.

I had given up for a year or so and decided that my ghost wasn’t going to get any better and F.R.E.D. and Ivan would continue their boat domination struggle. Recently, while in Santa Rosalia, I was reading a radio article from the Internet that spoke specifically about depth transducers and their propensity to generate stray RF along their cables. Although I had a ferrite attached to the transducer cable near the AC42 auto pilot computer, I did not have a ferrite attached to the cable next to the transducer itself. Where the transducer is located on Dazzler is less than a meter from my HF radio and less than a foot between the antenna cable, power cable and the depth/speed transducer cable. A light went off in my head. Yes, it might have been a dim light but a light nonetheless. While in Santa Rosalia, I removed the depth/speed/temp transducer to clean it. While completing the cleaning of the transducer, I decided to attach a few ferrites to the transducer cable near the transducer and near the connector approximately one meter away.img_4003.jpg

Now for the real world test! Before I closed up the floorboards, I activated the HF radio and F.R.E.D. No more pulsing tone. Now onto test Two! I conducted a series of tests on different frequencies in the 40 meter band with F.R.E.D. engaged. F.R.E.D. remained engaged without shifting to standby mode. Problem solved.

I write this article for all of those who have expressed similar HF/auto pilot issues and I offer this as a possible solution to mitigate your frustration. I chose to Choke!


Captain Dan
SV Dazzler


Author: Dan & Jilly

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