ANOTHER HAM RADIO FAILURE 

Caution - this update contains lots of technical HAM and radio gobbledygook

Mirador is anchored in Bahia La Ramada, about 30 miles NW of Loreto, Baja California Sur on the east coast of the Baja California peninsula.  I have spent the last week trying to bring the transmitter in my ICOM 710-RT Marine HAM radio back to life.  An RF power meter attached to the transmitter antenna output indicates that the ICOM is only putting out about 2 to 3 watts of power which means boats or other HAMs more than 10 miles from me can not copy my transmissions.   All the HAMs that do hear me mention how clean, i.e. easy to read with no distortion, my radio signal is and also how weak it is.

The ICOM radio has been failing intermittently since mid-April.  You can read about all the previous radio problems and repairs in the log entries beginning with the April 11, 2003 update.  The radio was repaired in Mazatlan and worked fine for several weeks but then the transmitter began to intermittently fail in late June when I arrived in Baja. 

Bill from SV True Love, a beautiful and immaculate Waterline 53 sloop, is an electrical engineer and computer hardware designer.  He carries a Tektronix digital oscilloscope, a 50 ohm dummy antenna load, and a RF/SWR meter (measures Radio Frequency energy, and Standing Wave Ratio which is the antenna efficiency for a given frequency) on True Love.  Tackless II, a CSY 44 owned by Don & Gwen, lent me a complete ICOM 710 repair manual, including schematics, circuit layouts, and all test points. 

Bill and I spent most of one day testing and trying to repair the transmitter.  All we managed to do was let the smoke out of a coil and resistor on the power amplifier board of the ICOM.  For those of you not familiar with repairing electronics I'll explain about "letting the smoke out." 

 While testing voltages and other electrical measures on a printed circuit board it sometimes happens, mainly thru clumsiness or carelessness, that your sensing probe touches not only the contact or small wire that you desire to touch but an adjacent electrical conductor which may complete an unintended circuit, often to ground.  When you ground a device such as the coil in question it allows an abnormally large electrical current to flow which overheats one or more of the electrical components in the circuit.  When they overheat they most often emit a small to medium puff of acrid black smoke that usually forms a cute little mushroom cloud.  The smoke, as are most mushroom clouds, is not a good thing and indicates that the component is destroyed and you are in deep doodoo if you were counting on using the device being measured.

Thus the term "letting the smoke out" indicates you screwed up and further damaged whatever it was you were trying to test and repair.  Our problem was that the components in the ICOM radio are small and tightly packed.  In order to even find, let alone test, many of them I had to wear a jewelers loupe (magnifying glass) to be able to read the identifiers.  The probes from my Fluke digital volt meter that we were using were designed for use with standard 12 or 120 volt systems and were a little too large and clumsy for what we wanted to do.

Before we damaged any components we determined that the final pair of power transistors that should boost the RF signal to 150 watts were emitting a lovely, well modulated RF signal with a power of less than 1 watt.   Bill's Tektronix digital 'scope is really cool and made it very easy to see the RF signal as it traveled thru the ICOM circuits.   We also determined that the 1st stage amplifier, (a single transistor), and 2nd stage amp, (a pair of transistors), had the appropriate voltages on all three legs but there was no gain (amplification) for the RF signal from stage to stage.  We also determined that the signal being applied to the antenna was exactly the same frequency and power as being output by the final pair of power transistors. 

We had hoped to find a bad connection or loose component somewhere on the power amplifier board because of my "tapping" experience the prior couple of days.  I had set up the Airmail program running on the computer and the Pactor modem to cause the radio to emit a steady series of tones at a specific frequency while I monitored the radio's output power using the radio's built in power meter.  The radio would transmit with full power for many seconds and would then suddenly indicate no power output.  At that point I would tap the 2nd stage amplifiers coil with the handle of a medium sized screwdriver.  That would cause the radio to again transmit with full power for several more seconds.  That sequence repeated itself until I got tired of tapping.

My conclusion was that the tapping of the coil, which supplies regulated power to the 2nd stage power transistors, reestablished a contact that was broken, OR, caused some corrosion that was shorting across two contacts to come free.  We expected to find the intermittent contact or short by testing each component in turn.  But, all we did was let the smoke out. 

The next day a fellow cruiser, Rich from SV Aires, lent me his spare ICOM 706 HAM radio.  The 706 is a great radio and is probably the 2nd most commonly found radio on boats down here, after the ICOM 710.  I wired the 706 to Mirador's power supply, antenna tuner, and antenna.  I was able to receive all the normal frequencies but could not talk to anyone more than a few miles away. 

Bill and I hooked the 706 up to the dummy antenna load, (a large black box that absorbs the RF energy emitted by the radio's antenna connection via a coax cable from the antenna connection to the dummy load), and found that the 706 was putting out it's full rated power.   We then inserted the RF/SWR meter between Mirador's real antenna and the 706 and found that the SWR was greater than  5 when I tried to transmit. 

SWR is the ratio of the power being emitted by the antenna  and the power being reflected by the antenna back to the transmitter.  In my case almost all the RF energy was being reflected from the antenna back down the antenna lead to the 706 radio.  That meant that the transmitted signal had very little "oomph" behind it and could not reach very far. 

Each radio frequency transmitted  requires a specific length antenna, e.g. 14 MHz needs about a 32 foot antenna, but a sailboat usually has only one fixed length antenna which in Miradors case is 32 feet long.  When the antenna length is not appropriate for the transmitted frequency the antenna "impedance mismatch" causes some or all of the energy transmitted by the radio to reflect off the antenna and travel back down to the transmitter.  Eventually it forms a standing wave (the SW in SWR) that prevents effective transmission.

Mirador, as do most sailboats, has an ICOM AT-130 automatic antenna tuner that, through the use of internal electronics, causes the antenna to appear to be exactly the right length for any frequency the ICOM radio is capable of transmitting.  Just prior to Mirador's ICOM 710 failing I repeatedly measured the SWR as less than 1.15  which is about as good as it gets on a sailboat.  So, why wasn't the antenna tuner working properly when connected to the ICOM 706?  After all they are from the same manufacturer and both are designed for mobile use powered by 12 volt batteries.

After some reading and measuring I discovered the AT-130 tunes it's internal circuits when a control signal sent by the ICOM 710 radio drops from 7.5 volts to 0 volts for more than 50 milliseconds.  The ICOM 706 radio uses the same logic to control it's tuner but provides only a 4.8 volt steady signal that it drops to 0 volts for tuning.  Thus, the 706 could not cause Mirador's AT-130 to tune the antenna and thus the SWR was way to high for the 706 to reach out and contact the world. Any SWR over 3 is not good and over 5 or so causes the radio to start decreasing it's output power to prevent damage to the radio transmitter.

Well, that was easy to fix - just allow the 710 to signal the AT-130 and then use the 706 to put the high power signal on the antenna. That should work fine as long as both radios are tuned to the same frequency.  All I had to do was connect the antenna lead to the 710, send the tune signal, and then connect the antenna lead to the 706.  Cumbersome but workable.  NOPE!  It didn't work because the AT-130 requires a minimum of 8 watts of RF energy from the transmitter to drive the tuning circuits and my 710 is only putting out 2 to 3 watts at most.

The bottom line as of today, Saturday July 19, is that I can receive HAM and SSB traffic very clearly but I can only talk to boats within 10 miles or so.  Although, yesterday a HAM in Scottsdale Arizona, which is over 500 miles north of here, said they could hear me fairly well.  But, I can not connect reliably to any radio e-mail stations.  Nor could I reach out for assistance if that were necessary.

The ICOM 710 needs to be examined and repaired by a skilled and experienced technician who has access to ICOM parts and technical support. The ICOM North American repair facility is in Bellevue, Washington about 35 miles from Tacoma where I can visit with Arlene while the radio is being repaired.

So the question is how to most cheaply get to Seattle-Tacoma?

I am planning to take Mirador to Loreto on Monday and anchor off the village breakwater.  I'll go into town and use the internet to post this WEB update and more importantly to check for airfares to Seattle from San Diego and Phoenix.   There is scheduled air service from Loreto to San Diego and Phoenix where I hope I can get a cheap fare to Seattle.  If I find a cheap fare from San Diego then I can fly from Loreto to San Diego, if that fare is also cheap.   I can do the same thing for Loreto to Phoenix and on to Seattle. 

If the airfare from Loreto is too much I can take a 30 hour bus ride to San Diego for about $90 one way. The bus goes from Loreto to Tijuana in 26 hours.  At TJ I have to get another bus to downtown San Diego where I would then have to take a taxi to the airport. 

My big concern is what to do with Mirador now that the peak Sea of Cortez hurricane season is rapidly approaching.  About 1/3, (12 during the 40 years from '52 to '92), of the hurricanes hit in either late July or August .   But only about 1/2 the hurricanes get as far north as Puerto Escondido and only 7 hit the Puerto Escondido area in that 40 year period, most of them in September and October when I hope to have Mirador 250 miles north of here.  However, Juliet did rake this area with 50 knot winds for three days in late October 2000.

I can leave Mirador in Puerto Escondido (Hidden Port) which is the best hurricane hole in the Sea of Cortez.   The entrance to the outer part of Escondido, The Waiting Room, looks SSW towards the Sierra Gigante Mountains and has only about a 5 mile fetch in which the seas can build.  The Waiting Room is encircled by hills and mountains except for the 50 yard wide entrance channel.  To get into the inner harbor from the Waiting Room a boat must traverse a 100 yard long 50 foot wide channel with a right angle exit into the inner harbor.   The inner harbor is 3/4 mile long and about 1/2  mile wide and is completely landlocked.  There are 4000 foot mountains just a few miles away in the quadrant from SW to NW.  There are 1000 foot hills in the hemisphere from S to NNE and 50 to 100' hills from NE to NW.    The bottom offers very good holding but is quite deep, 30 to 60 feet in most places.

Many cruisers leave their boats for the entire summer in Puerto Escondido and there are several Mexicans who provide boat sitting services.  I'll put down the 66 pound Spade and FX55 anchor, each with 150' of chain and 150' of rode and then plan on no storms hitting while I am in the States. 

If things work as planned I should be back in Tacoma by July 25 or 26 and then back on Mirador, with a fully functioning HAM radio, by the fourth week in August.