Neither the instructions nor the errata speak to the regulator bypass
in the KRX3. The "instructions" do not provide information in either
bypass.
73,
... Joe, W4TV
On 2015-06-24 8:42 PM, Wayne Burdick wrote:
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
* * *
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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