I have an ICOM-725 (HF system, 100W output) connected to a MFJ tuner
and then about 120 foot feedline run to an antenna I made myself.

I can get the SWR on the MFJ tuner to read nearly 1:1, but the
transmitter display shows only about a 25% power output.

It occurs to me that the impedence that the tuner is "seeing" is so
high that the transmitter simply cannot supply the necessary current,
i.e., as with any voltage source that gets swamped.

Make sense, or am I barking up the wrong tree?

Thanks.

Thomas

"Thomas" wrote in message
m...
I have an ICOM-725 (HF system, 100W output) connected to a MFJ tuner
and then about 120 foot feedline run to an antenna I made myself.

I can get the SWR on the MFJ tuner to read nearly 1:1, but the
transmitter display shows only about a 25% power output.

It occurs to me that the impedence that the tuner is "seeing" is so
high that the transmitter simply cannot supply the necessary current,
i.e., as with any voltage source that gets swamped.

Make sense, or am I barking up the wrong tree?

Thanks.

Thomas

what does your wattmeter read when the transmitter is connected to a 50 ohm
resistive load?

Thomas wrote:
I have an ICOM-725 (HF system, 100W output) connected to a MFJ tuner
and then about 120 foot feedline run to an antenna I made myself.

I can get the SWR on the MFJ tuner to read nearly 1:1, but the
transmitter display shows only about a 25% power output.

Is the power output knob on the IC-725 fully clockwise?
What magnitude of forward power does the tuner indicate?



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Running into a 50 ohm dummy load allows full transmitter output.

Yes, the IC-725 power output know was fully clockwise.

When connected to the antenna the IC-725 indicates 25 - 50% power (not
much needle deflection difference between the two) and the tuner power
meter indicates in the 25W to 50W range.

So it works into the the dummy load, next steps?

Thanks.

Thomas

Cecil Moore wrote:
Thomas wrote:

I have an ICOM-725 (HF system, 100W output) connected to a MFJ tuner
and then about 120 foot feedline run to an antenna I made myself.

I can get the SWR on the MFJ tuner to read nearly 1:1, but the
transmitter display shows only about a 25% power output.


Is the power output knob on the IC-725 fully clockwise?
What magnitude of forward power does the tuner indicate?



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Replace your jumper with a good quality 3 ft RG-8X jumper....

"Thomas" wrote in message
m...
I have an ICOM-725 (HF system, 100W output) connected to a MFJ tuner
and then about 120 foot feedline run to an antenna I made myself.

I can get the SWR on the MFJ tuner to read nearly 1:1, but the
transmitter display shows only about a 25% power output.

It occurs to me that the impedence that the tuner is "seeing" is so
high that the transmitter simply cannot supply the necessary current,
i.e., as with any voltage source that gets swamped.

Make sense, or am I barking up the wrong tree?

Thanks.

Thomas

On Thu, 12 Aug 2004 20:29:10 -0400, Thomas wrote:

So it works into the the dummy load, next steps?

Hi Thomas,

Add a choke at the load (the antenna). Foldback of power, even in the
face of 1:1 SWR, is suggestive of poor transmission line decoupling.
One test is to vary the length of the line. If the SWR changes, this
is a certain indicator of the problem.

73's
Richard Clark, KB7QHC

Thomas wrote:
So it works into the the dummy load, next steps?

Theoretically, common-mode currents can cause
weird problems like this one. It's possible that
common-mode currents are causing an erroneous SWR meter
reading and the differential SWR is not actually 1:1.
Does the SWR meter reading change when you touch the
tuner chassis or run your hand up and down the coax?
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Richard Clark wrote:
One test is to vary the length of the line. If the SWR changes, this
is a certain indicator of the problem.

Heh, heh, that's how I tune my antenna system - vary the length
of the ladder-line until the 50 ohm SWR is close to 1:1.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

MFJ has some notes, as in my 969 manual, about avoiding certains lengths.
Get the manual from www.mfjenterprises.com and have a look.

Regards Jan

"Thomas" skrev i meddelandet
m...
I have an ICOM-725 (HF system, 100W output) connected to a MFJ tuner
and then about 120 foot feedline run to an antenna I made myself.

I can get the SWR on the MFJ tuner to read nearly 1:1, but the
transmitter display shows only about a 25% power output.

It occurs to me that the impedence that the tuner is "seeing" is so
high that the transmitter simply cannot supply the necessary current,
i.e., as with any voltage source that gets swamped.

Make sense, or am I barking up the wrong tree?

Thanks.

Thomas