My field rig is an FT-817, with MFJ-971 tuner. Antenna is a 40M
extended double zepp Slinky with 30 ft of 300 ohm twinlead.

On 60M, I easily tune SWR down to 1.0. Power shows a full 5 watts on
FM when I test.

Am I radiating almost everything the radio is putting out? Or could I
still be having big losses in the tuner? How can I test it?

Ken KC2JDY


Ken
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Unfortunately, there's no easy way to determine what fraction of your
radio's power is getting radiated. Just about the only practical way
short of modeling or an antenna test range is to compare your antenna to
another antenna with known gain and efficiency, and even this can be
difficult to do with any accuracy. "Slinky" antennas are pretty
inefficient, so even if your tuner isn't losing much power, the antenna
itself is probably turning a good portion of it into heat.

The good news is that the antenna isn't likely to be less efficient on
60 meters than on 40. So if you're making QSOs on 40, you should be able
to do the same on 60. Just keep that twinlead dry if you want most of
your power to get to the antenna.

Roy Lewallen, W7EL

Ken wrote:
My field rig is an FT-817, with MFJ-971 tuner. Antenna is a 40M
extended double zepp Slinky with 30 ft of 300 ohm twinlead.

On 60M, I easily tune SWR down to 1.0. Power shows a full 5 watts on
FM when I test.

Am I radiating almost everything the radio is putting out? Or could I
still be having big losses in the tuner? How can I test it?

Ken KC2JDY


Ken
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remove "zz" from address)

Ken wrote:
Am I radiating almost everything the radio is putting out? Or could I
still be having big losses in the tuner? How can I test it?

Put the forward/reflected power meter on the output of the tuner. Then
calculate the losses in the feedline.
--
73, Cecil http://www.qsl.net/w5dxp



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On Sun, 20 Jul 2003 14:43:16 -0500, W5DXP
wrote:
Put the forward/reflected power meter on the output of the tuner. Then
calculate the losses in the feedline.

I am not sure how to do this test.

The tuner has a 4:1 balun built in. Losses could certainly be in the
balun.

The coax terminators on the tuner do not use the balun. A separate
SWR meter will have coax terminators, requiring the use of a
standalone 4:1 balun after the meter, into the twinlead.

This will test tuner losses, but not losses in the balun.

I guess my follow-up question is, How do I test for forward/reflected
power in a twinlead feedline?

I have an RF probe; can that be used somehow?

Ken KC2JDY

Ken
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