6400M Internal Tuner

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Thinking of purchasing the 6400M with the internal tuner. Is the tuner wide range 10:1 or is it 3:1? Will be using the radio with a multiband vertical antenna. I am new to this group and my first post.

John W9QP
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Posted 2 years ago

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Photo of KB4OIF


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John.  It's 3 to 1.  Tuner works well if your antenna is close to 3 to 1.  I believe it does a little better than 3 to 1.  If it's a trap vertical, it should work.  Others may not work with it.   My 6400M has the tuner but I rarely use it now as I have a amp in line.  I use a KPA 500 and the KAT 500 combo.  
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The tuner in Flex radios are not designed for wide range. Although they do not mention an actual VSWR that is the limit, I recall 3:1 being mentioned, definitely not 10:1.

From the hardware manual for the 6400/6600:

"VSWR Range: 8.3 - 300 Ohms (80m – 10m)
6.7 - 150 Ohms (160m and 6m)

It is not recommended to attempt repeated tuning of antennas with the ATU connected to antenna systems that exceed the maximum VSWR on a frequency of interest. Some antenna systems, such as physically short multiband antennas may exhibit a very narrow range of resonance (a high Q antenna) in addition to being very reactive. The FLEX-6400/FLEX-6600 ATU is not designed to tune these types of antenna systems. An external antenna tuner that is designed to handle a wider VSWR range is recommended for these types of antennas."
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John - K3MA

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You can figure out the SWR range.  300/50 = 6:1 50/8.3 = 6:1
So it is 6:1 range on 80m - 10m

I will leave you to calculate it on 160m and 6m
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Thank you all for the information concerning the internal tuner. I will order the 6400M with internal tuner, if that doesn’t work on some bands will use my MFJ tuner. Hope to order the radio in a few weeks.