Sherwood Engineering. Radios Used in a Contest Environment. Rob Sherwood NC Ø B. Have Radios Gotten Better in the Last 5 or even 25 Years?. Why Did I Start Testing Radios ?. K8RRH & I purchased new Drake R-4Cs in the late 70s Used them during the ARRL 160m CW contest
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How is it Needed to Measure Dynamic Range
Sensitivity is a familiar number, normally applies to SSB.
Sensitivity = 10 dB Signal + Noise / Noise (10 dB S+N/N)
Noise Floor = 3 dB Signal + Noise / Noise (3 dB S+N/N)
Noise floor can be measured at any filter bandwidth, CW or SSB, for example
League normally only publishes noise floor for a CW bandwidth, typically 500 Hz CW filter
What is the Close-in Dynamic Range vs Wide-Spaced Dynamic Range published in QST?
(Note: recent expanded League receiver tests include close-in Dynamic Range, somewhat buried in a graph)
Why is Close-in Dynamic so important?
What if we could switch in a narrow Roofing Filter only slightly wider than the final selectivity?
This keeps the undesired strong signals from progressing downstream to the next stages
Dynamic Range Signal Level Causing IMD = Noise Floor
55 dB S9
60 dB S9 + 5 dB
65 dB S9 + 10 dB
70 dB S9 + 15 dB
75 dB S9 + 20 dB
80 dB S9 + 25 dB
85 dB S9 + 30 dB
90 dB S9 + 35 dB
95 dB S9 + 40 dB
The Orion offers the following standard roofing filters right out of the box:
The Icom IC-7800 is the other big news for the amateur community
Dynamic Range at 20 kHz: 98 dB
Dynamic Range at 5 kHz: 87 dB
Dynamic Range at 1 or 2 kHz: 78 dB