6400M Internal Tuner

john · August 2018

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. 73 John W9QP

KB4OIF · August 2018

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.
KB4OIF

Ted VE3TRQ · August 2018

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."

John - K3MA · August 2018

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

john · August 2018

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.