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Author Topic: mfj-16010 question  (Read 1381 times)
KG6BRG
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Posts: 119




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« on: March 25, 2012, 07:21:19 AM »

Any user opinions and any thoughts on using this tuner with a random wire without a counterpoise.  The manual sort of implies this.  I've been using single wires for years and always have a counterpoise attached to the tuner ground.  This is an L-network tuner.  Some reviews say works without any RF ground.  Any comments?  Thanks.
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WB6BYU
Member

Posts: 13339




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« Reply #1 on: March 25, 2012, 08:23:54 AM »

If you don't provide an intentional counterpoise, the coax, rig, and anything else
attached to it will perform that function instead.  Sometimes the operator doesn't
notice any problems.  Sometimes they do.

Counterpoises / radials serve two primary functions:  to reduce ground losses and
to provide a place for the return currents to flow.  For a current to flow into the
antenna wire, a similar current MUST flow into the ground side of the system.
Without a counterpose / ground / radial system of some sort, that current flows
back along the outside of the coax, and the feedline and rig become part of the
antenna system.

The ground losses will depend a lot on the wire length (in wavelengths.)  Wires
shorter than about 3/8 wavelength depend on the counterpoise / radial system
for efficiency.  Longer wires aren't as critical in that respect.

I've used a lot of end-fed long wires over the years, and currently have one running
from the barn to a tree that I use with an L network tuner.  The most common
problem due to "RF in the shack" is that my keyer sticks on.  The old Argonaut was
prone to some oscillations that caused the dial lamps to flash on and off.  Whether
or not these happen depends on which band I'm using, the length of the coax between
the tuner and the rig, the number and length of radial wires connected to the tuner, etc.
If I only tried the cases that worked well, I'd say that, yes, it doesn't need radials.
Sometimes you can get by and not notice any problems (especially at low power levels.)

But other times it can be a real mess - touching the rig or plugging in headphones can
change the SWR, you get RF in the mic that distorts your signal, or the metal case of
your D-104 mic tickles your lips with RF when you talk close to it.


This isn't at all a characteristic of the MFJ-16010 tuner, but rather of end-fed wires
in general regardless of how they are matched.
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KG6BRG
Member

Posts: 119




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« Reply #2 on: March 25, 2012, 08:49:39 AM »

Thanks for the response.  I do intend on adding a counterpoise, but am just soliciting opinions, especially from users of this tuner.  It's going to be used qrp with a MFJ-9440.  At 5 watts I don't expect too much RF issues but still think a counterpoise is in order.  Cheers. 
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WA3SKN
Member

Posts: 5496




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« Reply #3 on: March 26, 2012, 05:06:30 AM »

The counterpoise is the coaxial shield connection back to the radio, and this may or may not be OK depending on the line length, among other factors. Adding a simple 1/4 wavelength wire to the tuner will keep you from having any high RF potential at the radio.  Add one for each band you plan to use.
73s.

-Mike.
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KB2CPW
Member

Posts: 304




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« Reply #4 on: March 28, 2012, 10:24:13 AM »

Although you can use it for low power without a counterpoise, you will see a vast improvement. In your contacts and rx using one.
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