So, after this testing is completed, will production KBPF3s be shipped
with the modifications?
73, Ross N4RP
On 4/29/2015 9:23 PM, Wayne Burdick wrote:
Hi all,
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.)
Here's a summary of the changes required:
RF board: Add one leaded capacitor
KRX3 (if applicable): Add one leaded capacitor
KBPF3: Remove two inductors; parallel three new capacitors
If you're interested in this low frequency range, and you'd like to try the
mods, please email me directly.
Note: To tune this range with the K3, you'll need the new synth (KSYN3A), a
KBPF3 module (on the main and/or sub receiver), and a KXV3 module. A KXV3 is
required because the antenna for the 100-500 kHz range should be connected to
RX ANT IN or XVTR IN. The ANT1/ANT2 path goes through the T/R switch, which has
a high-pass filter to protect the K3's fast PIN-diode T/R circuitry.
73,
Wayne
N6KR
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