KX3 broadcast-band receive measurements

[wayne burdick]

We've had quite a few questions about broadcast-band reception on the  
KX3 (0.5-1.7 MHz) and how the KXAT3 ATU helps in this range.

The KXAT3 option module includes some extra elements that reconfigure  
its ATU L-network as a preselector for the AM broadcast band. This  
helps reject receive image responses in the broadcast band. The center  
frequency of the ATU's preselector automatically tracks the VFO.

We optimized the preselector for use with typical HF antennas, which  
appear very reactive in the AM broadcast band. You could of course use  
a tuned antenna for this range as well.

We now have some preliminary performance measurements. With the ATU  
installed, a 500-kHz signal comes up about 23 dB in amplitude, and the  
third-harmonic image drops by about 40 dB. This is typical for the  
lower portion of the band. Harmonic image rejection will get even  
better as you go higher in the broadcast band, because at some point  
the 160-meter low-pass filter starts rolling off. At the high end of  
the broadcast band, the 160-meter band-pass filter is also kicked in.

Recent firmware changes allow the KX3 to receive down to 310 kHz,  
although the high-pass filter, which protects the PIN diodes in the T/
R switch, causes increasing attenuation as you tune lower.

73,
Wayne
N6KR

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[Edward R Cole]

Wayne,

This is interesting as creation of a ham band on 461-478 KHz will be
submitted to WARC 2012 (resolution 1.23).  The ARRL Experimental
Group (WD2XSH) already has been operating in the 495-510 KHz band and
has provisional permission to use 461-478 KHz while under study by WARC.

The K3 operates fine on 495-510 KHz by using the TEST mode to produce
1mw output in transmit, but will not tune below 490-KHz.  If the KX3
can operate on 461-478 that may make it the first radio available for
this "hopefully" new ham band.  I believe the ERP=5w is being
considered for this new band, so not a lot for DX.  The ARRL
Experimental Group is currently approved for ERP=20w on 495-510
KHz.  I get about 4w ERP driving with 100w into an inverted-L antenna
(43x122 foot). My signal has been heard 2893-mi using WSPR.


73, Ed - KL7UW, WD2XSH/45
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