In article ,
Gary Schafer wrote:

You didn't say how far away from the dynaplate the tuner was? I would
bet that you have a fairly long run with your ground lead to it as
seen in most boats where the antenna system has problems.
You need to have a very short distance between the tuner and the
ground plate, not more than a few feet. Lots of people install the
tuner close to the antenna and run a long ground lead. That is the
wrong way to go as it then allows the coax and power leads that go to
the tuner to become part of the antenna system as well as the radio
itself and its power leads, which you don't want.

Also if you operate in fresh water rather than salt water you may need
more surface area for a ground.

Sail boat or power boat?

73
Gary K4FMX

On Sat, 13 Aug 2005 22:42:52 -0400, Newbie Ham
wrote:

Hi Everybody

I hope this isn't the wrong place to ask. if it is, please let me know
where I should post.

I have a Kenwood TS50 installed on a boat with a SGC autotuner. The
tuner is grounded to a dynaplate.

I also have a 2000watt inverter/charger built into the boat for ac power
creation from 12v batteries.

Something strange is going on and I jusr don't know where to start
trouble shooting.

When I transmit on frequencies like 14300MHZ usb, no problem.

If I transmit on 7628 LSB 100watts the FET's in my inverter blow up! As
soon as I key the mike I hear a loud pop and there goes another fet.

I've changed them twice now and since the inverter is bolted into an
awkward spot and weighs 70 pounds (it's all transformer), removing the
inverter and changing them ain't fun.

Tonight I went so far as to disconnect (as in unplug) the AC supply to
the inverter and switch it completely off. As in no LEDS lit, everything
off.

Yet as soon as I keyed the mic, POOF. The fets just blew apart.

Any thoughts as to what might be happening?

FWIW, the coax from radio to tuner runs within about 2 feet of the
inverter, the radio and tuner are powered from the batteries which power
the inverter. So the inverter and radio share Pos. and Neg.

I can only think of a few ways this might be happening:

1) Radiated signal from the coax leaking into the inverter.
2) Radiated signal passing into the inverter via the shared positive or
negative feeds.
3) Some weird ground loop issue.

I have no ideas as to how to diagnose this and trouble shoot it without
having to replace fets everytime. And that's a big job.

Any thoughts would be greatly appreciated.


Sounds like you got this problem nailed Gary.... I would suspect that
the RF Ground between the tuner and the radio is somewhere close to 1/4
Wave and is the Power wires to the inverter are also near 1/4 Wave for
the 40 Meter band, or maybe 1/8 Wave. A couple of good RF Type .1 uf
Caps across Inverter Power Leads, at both ends, should tame the problem,
after the RF Ground is shortened up to make it a good Low Impedance,
Wideband RF Ground.

Bruce in alaska
the Inverter
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add a 2 before @