[Elecraft] KBPF3A switching frequencies and performance

[Brian Hunt]

This thread also got my curiosity up.  Several years ago I upgraded my 
K3 #41xx with the KBPF3 including the 'A' mod of the capacitor on the RF 
board.  I never really checked it out except for the 630 meter coverage 
and transmit capability - both were as advertised.

Using a wideband noise generator (QRP Guys K7QO Noise Bridge) I tuned 
from about 500 kHz up to 30 Mhz and was able to identify the filter 
switch-over points (most of them anyway).  I measured the received noise 
level using the P3 dBm scale.  At none of the switch points was the 
noise level more than about 5 dB different from one side to the other.  
By continuously tuning and watching the display, it was apparent that 
the differences were mainly due to roll off of one filter segment or the 
other.  The gain was uniformly consistent across each of the ham bands 
but sometimes rolled off at the KBPF3 switch points.  The area between 
7.41 MHz and 8.4 MHz is kind of no-man's land due to the first IF being 
there.  At the IF frequency the gain was down >50 dB.

73,
Brian, K0DTJ

On 4/20/2021 08:57, w4sc wrote:
> A little back ground,,
>
> The effort started as a result of my using WWV at 15.000000 MHz for calibrating the reference oscillator.  Tuning from 14.999999 to 15.000000 MHz I noticed a 9 to 12 Db drop in signal strength of WWV.
>
> .......