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Band Pass Filters


Recommended AKE1 - AKE5 kits were used in the Frontend. Some differences in the measured parameters could be due to tolerance of the components (L,C). I note the considerable effect of the top and bottom BPF box covers on the measured characteristics (stopband) also. My results of BPF measurements correspond to the open box.

BPF Insertion Loss, BW

BPF Insertion Loss, IF Rejection, Image Rejection

BPF Input Impedance


N2PK VNA in double signal generator mode, together with USB Spectrum Analyzer SA44B and 2-way home made measuring kit was used for IMD measuring. Block diagram shows two amplifiers, two low pass filters, two 2dB attenuators and one hybrid combiner in the home made kit.  It was necesary to measure IMD of the set first. As will be explained in other part of this website, OIP3 at the combiner output depends on the used frequency and the signal output level. From 1.8 MHz to 28 MHz OIP3 reached from +58 dBm to +60dBm in quite narrow  range of output levels.  Such conditions were suitable for BPF IMD measurementNoise floor level of my USB spectrum analyzer limited IMD measuring possibility in 20kHz spacing. That was the reason, why I used 10 kHz spacing between two signals. Little difference in levels of IMD products and noise floor of the spectrum analyzer affecting the measurement accuracy, in every case. As a prevention against generating own IM products, I used from 30 dB to 50 dB  attenuation at the input of spectrum analyzer. Normally it is good enough to use 20 dB of attenuation (30 dB for sure) for input levels around 0 dBm, but I measured with output levels till +20 dBm, so it was necessary to increase input attenuation.

Pictures show home made  amplifier in two sections, changeable LPFs and integrated combiner for IMD measuring. Mitsubishi MOSFETS RD00HHS1, RD00HVS1 and RD06HHF1 used in every section. Maximum output level +22dBm with fine settings possibility allows easy adjustment of signal levels as needed.

My measuring results are comparable to MarteinĀ“s. I lost 1-2 dB in lower bands, but I am better in the higher bands. Except of 160m and 6m, all results are in the range of +50dBm plus/minus 1 dBm.  Measurement hardware, differences in the filter construction, scattering of component parameters, not accurate BPF impedance matching and different signal levels can cause differences in both results. Even heating of measuring kit could affect the measurements.


OIP3  dBm
(space 20kHz)
Insertion LossIIP3OIP3  dBm
 (space 10 kHz)
Insertion LossIIP3
160+46.7 -0.64+47.34+47.05-0.85+47.90
6+44.6   -3.36+47.96+45.1 -2.95+48.05
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