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Author Topic: Assistance with MFJ-1026 & FT950 required  (Read 1424 times)
ZS1X
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Posts: 7




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« on: August 19, 2012, 01:01:33 PM »

Apologies, I posted this topic in the wrong forum earlier.  I am new to eHam.
Hi,

I recently purchased an MFJ-1026 Noise Cancelling Unit.  I am very happy with the results but wish to use the T/R function to switch this device into bypass mode when transmitting as this is highly recommended.  I have an FT-950 and as far as I understand I can use the TXGND and GND connection to switch the MFJ into bypass mode when transmitting.  Can anyone tell me if this is correct?  Do I have to use the Linear Din Plug connection or can I use the Tuner connection as well?  Also are these the correct connections that I mentioned?

They state in the user manual that you should not use the device with an internal tuner unless the SWR is below 2:1.  If the unit is switched into the off position, would it be ok to use the internal tuner then to tune bands that are slightly higher that 2:1 SWR?

73's
ZS1X
Dirk Lotz
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N4CR
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Posts: 1688




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« Reply #1 on: August 19, 2012, 04:01:29 PM »

They state in the user manual that you should not use the device with an internal tuner unless the SWR is below 2:1.  If the unit is switched into the off position, would it be ok to use the internal tuner then to tune bands that are slightly higher that 2:1 SWR?

No.

If you have an external tuner, you can put it before the tuner so the tuner presents a good load to both the noise reduction unit and the radio. When your antenna tuner that is internal to the radio is tuning your antenna system, it doesn't change the SWR outside the radio. it adjusts the SWR inside the radio after the tuner.

It's not so much the tuning process that is the issue, it's the voltage extremes that are present in a high SWR circuit. When tuned, the voltages outside the radio are increased since the radio isn't limiting power.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
ZS1X
Member

Posts: 7




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« Reply #2 on: August 19, 2012, 09:57:42 PM »

Thank you Phil,

That makes sense.  However if the MFJ unit is turned off can it still cause damage even in the bypass mode while using the rig?

I would just like to cover all aspects before really start utilizing this unit.  There are two bands that are basically noise free here where I live and I therefore do not need the MFJ to be switched on when using these frequencies.  I would use it mostly on 40m where most of the noise is and the SWR there is perfect. 

So, if I do use the internal tuner and keep the MFJ unit switched off (bypass mode) while using these bands, can it then still cause damage?

73's
Dirk
ZS1X
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N4CR
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Posts: 1688




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« Reply #3 on: August 20, 2012, 12:52:45 AM »

On or off, you are going through the same relay. It's electronically switched when it's powered on and Normally Open with the power off.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
ZS1X
Member

Posts: 7




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« Reply #4 on: August 20, 2012, 03:11:42 AM »

Thanks,
What bothers me is that even if you put the MFJ between the tuner and the rig you then would still stand a chance to damage the unit as the SWR will be over it's limit while performing the tuning operation whether it's a manual or auto tuner.
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N4CR
Member

Posts: 1688




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« Reply #5 on: August 20, 2012, 06:02:59 AM »

Thanks,
What bothers me is that even if you put the MFJ between the tuner and the rig you then would still stand a chance to damage the unit as the SWR will be over it's limit while performing the tuning operation whether it's a manual or auto tuner.

Tune at reduced power.

Further than that, the SWR outside the radio doesn't change at all when the tuner in the radio runs. It only changes the SWR inside the radio. What is outside the tuner doesn't get tuned and the SWR remains there regardless of what happens inside the radio.

The power levels go up and down as the tuner seeks different combinations and the radio self protects by dropping power while this happens.

Tuners don't change the SWR in the feed line.
« Last Edit: August 20, 2012, 07:01:17 AM by N4CR » Logged

73 de N4CR, Phil

Never believe an atom. They make up everything.
ZS1X
Member

Posts: 7




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« Reply #6 on: August 21, 2012, 08:52:50 AM »

Thanks for the advice Phil,
73's
ZS1X
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