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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Have Radios Gotten Better in the Last 5or even 25 Years?
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?
IMDThird Order IMD
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
IMD 20 kHz Away
12 kHz Wide
12 kHz Wide
First IF Filter at 70.455 MHz
First IF Filter at 70.455 MHzWide & Close Dynamic Range
2 kHz Spacing
20 kHz Spacing
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