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.

Have you tried putting some substantial ferrite chokes on the leads in
and out of the inverter? From your description, it sure sounds like RF
is getting into the device. Some sort of destructive resonance.



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.

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.

Bob is probably about right. Things to try:
1. Get a long piece of coax and wind a choke. Use a coffee can sized
object to wind 6-8 turns of coax. Hold it together with twist ties.
2, Make sure the pl259 connectors are connected properly. If you really
are new at this, get someone who isn't to take a look.
3. run the coax away from the inverter.
4. check the ground of the radio
5. increase/decrease the length of the electrical wiring. As stated, use
lots of #43 ferrite material. Use big ferrites, and give the wiring many
turns through the donuts.
6. Do you have an amp meter to measure how much drain the radio is
taking? Maybe something strange is going on at 40 meters that would
overload the inverter.
7. Did you try keying the radio at 5 watts to see if it blows anything?
30 watts?

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?


You probably has a resonance in the DC-cable.

Try to install ferrite rings in the cables going in and out of the
inverter,( in both ends ) plus on the coax from the rig - in both ends.
Put one more than one on the DC-cables to be on the safe side.

Good luck

Rag LA5HE