On Fri, 23 Jan 2004 08:05:10 -0600, "Keith"
wrote:

OK, more details on the system. Icom 802 going to the AT-140 automatic
antenna tuner. Yes, the tuner is working, you can hear the relays clicking
when you press the "tune" button or transmit. The antenna (made by the
Digital company... I should have specified!) is on the flying bridge, as is
the tuner. The tuner is about 3' from the antenna. The antenna is right
behind and above the pilothouse. The base is maybe 10' from the wheel and
electronics, etc.

I have an M802 on Lionheart with the AT-140 tuner. Its major problem
is the tiny interconnection plugs that connect the tuner control
circuit to the main chassis of the radio. It's a dumb, STUPID
design.... I've had lots of trouble keeping the connection where it
plugs into the radio. The pins in these tiny connectors was designed
to connect a circuit board plug with a tiny cable going between
circuit boards INSIDE radios.....NOT BIG CABLES OUTSIDE RADIOS.
Idiots.

I assume your LCD display on the 802 is reading TUNE at the top so the
control cable must be making connections. The cable MUST BE SHIELDED,
FOIL SHIELDED. This keeps the RF from screwing up the tuner's data
interconnect.

At the tuner end, have your technician eliminate half your tiny plug
problems by opening the AT-140's top sealed cover (yeah, all those
screws). Unsolder the pigtail wire going from the main circuit board
inside the tuner, out through the watertight fitting to the stupid
little unwatertight plug. Throw the pigtail overboard to keep it from
contaminating anyone else's boat. Now, pull your control cable
through the watertight fitting and dress the wires so you can solder
them to the little solder rings on the main board of the AT-140.
Tighten down the watertight fitting to seal the cable to the box. I
used a dot of RTV on the inside around the cable to make sure.
Re-close the AT-140 cover paying attention that the rubber ring seal
is in place, properly. Easy on the screw torques so you don't crack
the cheap plastic. Half your control cable problems are over. I may
change out the other half on the radio to a proper connector after the
warranty runs out.


2" copper foil runs from the radio to the antenna tuner, and splits off
about midway and goes to the bilge, where it's connected to a dynaplate. I
plan to add some more foil and connect the fuel tanks and run some radials
down there as well. Lets see: the run from the radio to the antenna tuner is
about 25', and the run from that one to the dynaplate is about 10'.

You already have lots more grounds than I do on Lionheart. Looks nice
to me. Any metal screen you can add to the inside of the hull really
makes a great coupling to the seawater through the hull. (It's a nice
capacitor).


No, we didn't check the SWR. I wanted to add more foil and some ferrite
cores to see how this helps out. I wanted to do the things I can do rather
than pay the tech all those $$$ for basically grunt work. I can call him
back out whenever.

You don't need to worry about this SWR nonsense. The Icom M802 will
not transmit until it is satisfied the overall SWR of the system is
acceptable, near perfect. That's what the tuner is for. With your
short antenna, however, you may find it won't tune some of the lower
frequencies below 4 Mhz. The short whip IS part of your interference
problems. All the radiation of 150 watts of RF power is happening on
the length of this short whip.....WAY TOO CLOSE TO THE SENSITIVE,
UNSHIELDED OR POORLY SHIELDED ELECTRONICS it is tearing up.

There is also a lot of radiation coming from the strap to the
dynaplate. It's the other half of a dipole antenna and the tuner is
actually in the middle of it. There is no ground at any tuner unless
the tuner is using a steel deck for ground right under it. This is
just normal. There's nothing you can do to change it. If it didn't
radiate, noone would hear you!...(c;

No, my hand doesn't burn when transmitting! ;-)

Naw. It's only 150 watts. Too much cellular phone propaganda trying
to convince the public RF is dangerous so they can turn the phone
power down without the unsuspecting public, whos phone range just went
way down at 200 mw, raising hell with the FCC. 150 watts isn't high
power and, unless you make direct contact with the upper end of the
whip, won't burn you. 650 watts from my ham radio mobile antenna with
the high voltage corona spraying off the top and ends of the big
capacitor hat, WILL burn you...(c;

Yes, I believe the VHF cable needs replacing. It's old and probably cracked
somewhere along the line. The Link 20 DOES have the sheilded cabling as
Larry described, but the ground foil runs right alongside in the same chase.
I don't think I connected the sheild to ground though... I'll fix that.

The shield only should be connected to the LINK's SYSTEM GROUND, NOT
THE FOIL. Hooking it to the tuner's foil WILL induce a lot of current
into the cable. Only hook it on the end where the Link display is and
ONLY to the Link, itself. Tape off the foil shield on the sensor end
so it can't make contact with anything. That's a Faraday Shield.
It's not part of the signal ground for the Link.

I don't like running ANY data cabling anywhere near, to say nothing of
in the same trunk, as the RF grounding system. That whole RF
grounding system is radiating like hell! Running it beside the link
cabling, which is NEVER 100% shielded, is going to cause trouble.
Take the Link cable out of this wireway, along with everything else
with data or hooked to a transistor......or reroute the RF grounding
system to someplace by itself. Don't even run it alongside DC wiring
because the DC wiring in the boat will all become very RF "hot"
creating its own problems....especially with these damned fancy
battery chargers.
--


Keith
__
Money can't buy happiness, but it sure makes misery easier to live
with.

Money can buy a lot of happiness. Take me to a strip joint and let's
test this theory in action!...(c;


Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!