[Elecraft] Use of MFJ ATU on the KX3

[Don Wilhelm]

John,

Yes, I would trust the KX3 more.  The KXAT3 can match an SWR up to 10:1 
- it is truly a wide range tuner.

Use a balun instead of the MFJ-971 to transition from coax to your twin 
feeder doublet.  A balun like the Elecraft BL2 provides a choice of 1:1 
or 4:1 ratio.

Do not be mislead by those who believe you need to match the 
characteristic impedance of the feedline - that is just misleading. 
Instead, you need to match the impedance presented by the twin feeder at 
the shack location, and that can vary from very low to very high 
depending on the radiator length, the feedline length and the frequency 
of operation.

If you have trouble matching on some bands, try adding or subtracting a 
1/8 wavelength of feedline for the lowest band you have trouble with.

The use of 2 tuners in-line will cause additional loss.  Any antenna 
matching device has some loss - using 2 in-line will double that loss.

73,
Don W3FPR


On 4/28/2018 6:04 AM, John Daws wrote:
> Just a query about the use of the MFJ 971 portable tuner with my KX3 (fitted
> with automatic ATU)

> The twin feeder from the doublet goes into the back of the MFJ which is then
> attached via coax patch lead to the KX3
> 
> I can bypass the Auto ATU fitted on the  KX3 menu and manually tune the MFJ
> or
> 
> Simply auto tune for each band on the KX3 ignoring the scary looking needle
> readings on the MFJ!
> 
> I trust the KX3 more