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Author Topic: Tuner on 6 meters  (Read 1011 times)
WJ3O
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Posts: 5




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« on: June 10, 2017, 06:03:45 PM »

I have a MFJ 989c tuner in line which tunes to 30 MHz.  My question is can I run 6 meters direct thur the tuner on coax direct not tuning without problems to the tuner.
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WB6BYU
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Posts: 17192




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« Reply #1 on: June 12, 2017, 12:16:27 PM »

You probably won't cause any problems to the tuner.  In fact, you can try running through the tuner
on 6m and it likely won't make any difference to the tuner.

The problem with running straight through on 6m would be the resulting SWR:  the wires from the
sockets to the switch and back are not consistently 50 ohms, and mine have some bends and
kinks in them that will add extra inductance.  I'd guess that you might still see a 2 : 1 SWR with
a perfect dummy load:  that would be an interesting experiment, however, to measure it with
an analyzer and see how bad it actually is.

The meter accuracy is likely to be less accurate than normal on 6m, but perhaps still usable.

The internal dummy load increases SWR with frequency:  I don't know how much of that is due
to the resistor itself, and how much is due to the wiring inside the unit.
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AF5CC
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Posts: 225




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« Reply #2 on: June 13, 2017, 01:52:19 PM »

I used to have a MFJ 949D tuner, and when I ran my 6 meter yagi through it, the tuner was fine, but raised the SWR on the yagi when in bypass mode, to where I had to use the tuner to get a 1:1 SWR on 6m.  Turns out the crossneedle meter circuit was causing the problem.  I switched to a MFJ 941D which doesn't have a crossneedle meter, and the 6m antenna works fine with it.
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KM3F
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Posts: 794




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« Reply #3 on: June 13, 2017, 10:58:13 PM »

HF tuners are built with too much lead lengths internally for 6m past through match.
Depending on what tuner, it may be possible to rewire the pass through circuit with Coax cable to get the 50 ohm upset to a min value.
What you would need to do is test on a 50 ohm flat load for what it now presents for upset matching.
Then re-wire with Coax to get some control of the match on 6m.
As it is now if you take a look at what you have you will see just straight uninsulated wire running here to there.
On HF the mismatch is a very small percentage of the highest frequency 10m wavelength so does not upset the match all that much in the pass through setting.
Matter of fact the Coax could even be tuned each end to cancel out any reactance on 6m without affecting the HF bands.
This project would be best carried out using a 50 ohm load and an antenna analyzer.
Its no different than adjusting an antenna system.
Good luck.
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KB1GMX
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Posts: 1505




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« Reply #4 on: June 14, 2017, 10:18:11 AM »

My feeling and experience is on 6 a resonant antenna is easy and a tuner has enough loss that it is not
helpful and can be a hindrance even in bypass mode as most are not well suited for 6M.

A dipole for 6 is 115inches (give or take an inch).  Feed that with coax and skip the tuner.


Allison
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