[Elecraft] KBPF3 upgrade kit and instructions now available

[Wayne Burdick]

Hi all,

The long-promised KBPF3 modification kit is now available. It applies to the KBPF3, K3 RF board, and optionally to the KRX3 sub receiver. It allows the K3 or K3S to receive signals in the 100-500 kHz range with good sensitivity. This is an interesting part of the spectrum, with 

For full details on the mod kit, see:

   http://www.elecraft.com/order_form_parts.htm#K3%20Parts

Also see below for an excerpt from my original posting about signals in the 100-500 kHz range.

73,
Wayne
N6KR


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In honor of the FCC's proposed "2200 meter" allocation (137 kHz), we decided to see if we could improve the K3's receive sensitivity in the 100-500 kHz range. This extended coverage is made possible by the new synth (KSYN3A). 

After a lot of digging, we discovered the cause of the wide-band low-frequency noise. We also found a way to shift the passband of the KBPF3 lower. 

With a couple of simple modifications, the MDS (minimum discernible signal) can be improved by about 25 dB at the low end (100 kHz). Here are some test results (preamp off, 400-Hz bandwidth): 

137 kHz -114 dBm FCC's proposed 2200 meter band
160 kHz -117 dBm low end of the "Low-Fer" band
250 kHz -126 dBm test frequency in the long-wave beacon band
472 kHz -133 dBm 630 meter experimental band

This represents an improvement throughout the range, but especially at the low end. I believe -114 dBm MDS should suffice at 137 kHz, given the high band noise in this range. 

Another indication of how well the mods work: With no antenna connoted, the K3's S-meter now just barely flickers (S1) at 100 kHz. Without the mods, the no-antenna S-meter reading could be as high as S7 due to the noise source we've now identified (a voltage regulator). (By the way, this regulator noise had no impact on frequencies about about 500 kHz.)

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