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YAESU FT-840

Feb 24th 2013, 21:18

NOVICE1970

Joined: Feb 17th 2013, 15:17
Total Topics: 0
Total Posts: 0
I AM USING A COBRA 300 OHM FED ANTENNA FED TO AN EXTERNAL ANTENNA TUNER. WHEN I RAISE THE POWER TO 100 WATTS THE RADIO GOES BACK TO RECEIVE MODE WHEN KEYED. MY METER IS SHOWING NO REFLECTED POWER BACK TO THE RADIO, THE SWR IS GOOD.
THE RADIO AND TURNER ARE GROUNDED TO A COLD WATER PIPE

THANKS,N2OLR
Feb 25th 2013, 15:45

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

If possible, running the radio into a dummy load is a good test.

It will show that the rig/power supply can deliver 100 watts. Sometimes, a 20 amp supply will work--but you may need a 25 amp supply to get enough current on some bands. If that is the case, you may need to get a bigger power supply. Or, you may find that 50 or 80 watts is all you need, in which case you may not need a new power supply.

You could have an RF feedback issue from the antenna being too close to the radio, along with cables connecting the rig acting as an antenna to pick up RF.

Zack Lau W1VT
ARRL Senior Lab Engineer
Feb 25th 2013, 15:56

WB1GCM

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I would try improving the ground system. You may be experiencing RF feedback (hot chassis), which is a sign of a poor ground system. I would imagine you're having this trouble on 10 meters?

A cold water pipe can be used as a ground but it would not to be good engineering practice. I have also talked with many who have used a cold water pipe, but were not certain the entire path the cold water traveled was metallic.

I recommend reading W8JI's web page on station grounding.

http://www.w8ji.com/station_ground.htm

Bob Allison
WB1GCM
ARRL Test Engineer


Mar 2nd 2013, 12:26

NOVICE1970

Joined: Feb 17th 2013, 15:17
Total Topics: 0
Total Posts: 0
Thanks guys ,been off the air a long time. You gave me a good starting point.

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