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Receiver third-order dynamic range measurements



 2 kHz  spacing
         
20 kHz  spacing
Receiver  
DR3 IP3
DR3 IP3
K5AM 88
 -9
91
 -5
FT-1000MP, 250 Hz     
75
 -26
95
 +4
FT-1000MP, 500 Hz 74
 -27
92
 +1
Collins 75A-4 65
 -43
72
 -33


DR3 is in dB, IP3 is in dBm.

Tests on the K5AM homebrew transceiver were
made at 14 MHz. The table shows dynamic range,
DR3, at two-tone spacings of both 2 kHz and
20 kHz. The third-order intercept point, IP3, is also
shown for both spacings.

To put the results in perspective, two other radios
were also tested. Tests were conducted for the
homebrew radio at a bandwidth of 200 Hz. Tests for
the Yaesu FT-1000MP were conducted at a
bandwidth of 500 Hz using the stock filter in the
second IF amplifier and an INRAD filter in the third
IF amplifier; tests were also run at a bandwidth of
250 Hz. Tests for the Collins 75A-4 were conducted
with the 800-Hz filter.

The measurement for the Yaesu at a bandwidth of
500 Hz and a two-tone spacing of 20 kHz is close to
that reported in the ARRL product review. For a two-
tone spacing of 2 kHz, the measurement
corresponds closely to that shown by the graph in
the ARRL lab expanded report, provided the graph is
adjusted so that its level at wide two-tone spacing
conforms to the direct measurement. The tests show
that the dynamic range of the Yaesu drops
considerably when the two-tone spacing is reduced
from 20 kHz to 2 kHz. This is because the roofing
filter rejects interfering signals only at the wider
spacing.

The homebrew radio uses no roofing filter; the dynamic
range does not degrade drastically when the possibility
of nearby signals is considered. During crowded band
conditions, significantly better third-order IMD
performance is obtained with the K5AM radio.

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