The following article I originally published to my mailing list and blog in 2008. I’ve heard several more stories of Cellular Carrier enforcement (usually very friendly but firm) against interference caused by Cellular Repeater devices on Yachts. Today I got another call from one of my customers in Miami, Florida. This time AT&T visited them – and asked them to shut off a Digital Antenna DA4KSBR (DA4000 SBR) Cellular Repeater device. It was causing interference to the cellular network/tower in the area. So in the interest of informing the public and my customers I am again publishing (re-publishing) this article here on my blog. What seems to happen is that the Cellular Repeaters inside antenna “receives” the outside antenna causing the system to go into a “Feedback” loop – which causes spurious radio frequency transmissions (“interference”) causing big problems for the same cellular carrier or different cellular carriers in the area. Here’s the article:
ASMT Bulletin: Big Trouble in “Little Amplifiers” – Cellular Amplifiers/Repeaters
11:05:40, Categories: AST Happenings, 587 words
ASMT Bulletin… I received the following information from Captain John on Trinity Motor Yacht – Serendipity II. I’ve already heard reports (AT&T Wireless Engineer here locally) that Digital Antenna amplifiers, and particularly the DA4000SBR type of “repeaters” can cause problems to cellular providers towers. I had never received an actual report from a yacht customer of having any problems (other than non-working units that get replaced) with the gear. Well now I’m a believer. Now I have a real life report of a problem happening. And it was with a DA4000SBR that had been replaced already so it’s fairly new. For those of you running Digital Antenna DA4000SBR “repeaters” you might want to consider taking it out. If you cannot, then at least check it periodically. Maybe add it to your daily checks or “watchstander list of checks” to check and see if the unit has a green light. If it (“occassionally and briefly blinks “Red”".) Unplug it right away. When you plug it back in watch it even more closely after that. If it continues to be found to occassionally and briefly blink “Red”… you’ve got a problem!!!!
We are all responsible for radio signals that we emit from our equipment. We need to be good R.F. (Radio Frequency) neighbors to others on the airwaves and especially to radio carriers such as cellular service providers. We should do whatever we can to make sure that our gear is not causing harmful interference. I am going to stop recommending Digital Antenna DA4000SBR for this purpose. If I get reports on any other Digital Antenna gear I may stop recommending their amplifiers altogether. I’ve been told that it is already a very grey area to even be authorized to run such amplifiers and that such use may go away any day now. I’ve been told that newer cellular tower systems already employ power control capabilities that monitor and adjust automatically the cellular tower power, and the power from customer cellular equipment. Amplifiers, going forward, may not even be as necessary as *some people* think they are. A good antenna and cable system may be all that’s needed to have a good Cellular Internet and Telephone System.
I wanted to touch base with you to let you know about the Digital Antenna PowerMax I “was” using with the Ericsson Cell Phone/Data Alltel Network came knocking on my hull yesterday saying an interferance was coming from our boat to their Channel 294 A-Band and blocking cell phone calls. She showed me on this really cool frequency tracking device and the spike in the frequency. As soon as I shut the power off to the PowerMax the problem disappeared. She told me these particular units made by Digital Antenna have caused problems in the past.
Before unplugging the unit we both noticed the usually green power light would occassionally and briefly blink “Red”. So the unit must have been on the blink again. Remember in November  you found the unit not working at all and I had it repair.
I am removing it from the boat for good and attaching the antenna directly to the Ericsson. So there will be no worries about this in the future. But I thought you might want to know about this product and that I am not an isolated incident.
John & Crew
M/Y SERENDIPITY II
Alan Spicer Telecom / Alan Spicer Marine Telecom
communications (at) marinetelecom.net
+1 954 683 3426