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How to Read Sherwood-Style Receiver Numbers Like an Engineer

Receiver test tables are some of the most useful tools in amateur radio...and also one of the easiest ways to misuse. Rob Sherwood’s presentation “Performance Numbers...What do they mean? Interpreting the Sherwood Table” is valuable because it doesn’t just throw numbers at you. It teaches you how to think about them, and (more importantly) when they matter and when they don’t.

This article is meant to sit next to the PDF. Read them together: the PDF provides the definitions and measurement context; this write-up helps map that context to real operating goals.

The most important nuance: the table is not an overall ranking

One of the sharpest points is also the simplest: the Sherwood table is sorted by one metric (2 kHz close-in DR3). Everything else is “the numbers for that same radio,” and must be compared manually.

That’s why a radio can rank higher on close-in dynamic range and still be a different choice if your priority is weak-signal work, phase noise behavior near strong carriers (RMDR), ergonomics, filtering options, or how the gain structure behaves with your receive antennas.

What the numbers actually are (and why measurement context matters)

A lot of stretched claims come from forgetting measurement conditions. Sensitivity, noise floor, DR3, blocking, and RMDR are meaningful...but only inside the test definition and the “receive chain” assumptions behind them.

• Noise floor / sensitivity can be quoted in specific bandwidths and reference conditions (CW vs SSB definitions).
• 2 kHz DR3 exists because wide spacing-only tests often fail to reveal the close-in overload reality seen in CW/DX contest conditions.
• Preamp / attenuation states matter. The “best” setting at 10m mid-day can be exactly wrong at 160m at night.

“Better sensitivity” is not always better...especially on 160/80/40

Here’s the nuance that saves a lot of frustration: on the low bands (especially at night), many stations are already dominated by external noise and strong-signal conditions. In that situation, extra sensitivity doesn’t improve copy. It can:

• make the band sound louder (fatiguing)
• reduce headroom and increase the chance of overload/intermod
• push AGC into less comfortable behavior

The “grown-up” version of the sensitivity argument is: sensitivity matters only when your receive system isn’t already noise-dominated, and only when you can keep enough headroom to avoid overload.

Your antenna is part of the “numbers,” whether you admit it or not

Chasing weak signals on 160m using an active array is not the same as using a negative-gain Beverage. Both are “receive antennas,” but they create very different demands on the receiver.

Case A: Active receive arrays on 160m

Active arrays often include gain (at elements and/or combining stages). That can deliver higher signal levels into the receiver and enable excellent pattern control...but it can also increase overload risk when there are strong nearby stations or strong out-of-band energy.

• Priority: headroom management (attenuation range, strong front-end linearity, usable gain controls)
• Also matters: front-end selectivity and practical filtering strategy

Case B: Passive Beverage (low output, low pickup of local noise)

A Beverage typically produces a low receive voltage but with useful directivity and often a “calmer” noise presentation. In a genuinely quiet environment, receiver noise can become a meaningful part of the system noise...so sensitivity/noise performance may matter more than it does with an amplified receive system.

• Priority: clean gain only when it’s actually needed (and when it doesn’t cost you headroom)
• Reality check: if external noise dominates anyway, “more gain” won’t magically improve SNR

The AGC-threshold point is gold...because it’s about comfort and performance

One of the most operator-useful ideas is gain-structure discipline: set things so the AGC threshold sits slightly above band noise (often just a few dB). The result is a more controlled, less tiring receive experience...and often better usability in search & pounce.

Front-end selectivity: magical QRM reduction isn’t real...filtering is

A receiver can be “perfect” on-paper and still suffer in the real world if strong signals outside your ham band are hammering the front end. That’s why front-end filtering strategy matters: preselectors, bandpass filters, and (in multi-transmitter environments) additional external filtering can be the difference between clean RX and “why is my receiver acting weird?”

• Broadcast and commercial signals can dominate overload risk even when your ham-band signals aren’t extreme.
• Field Day / multi-station setups often demand more filtering margin than casual single-station operating.

Dynamic range today: often excellent...but the “exceptional cases” still exist

Many modern radios are strong performers most of the time. That doesn’t make dynamic range irrelevant. It means the pain shows up in the exceptional cases: line-of-sight S9+ neighbors, multi-station contesting, multiple transmitters on one site, or harsh RF environments where the receiver has to stay linear while still being usable.

That’s also where architecture details (roofing filters, front-end design, ADC headroom management, preselection strategy) can create a real operational advantage.

Limited attenuation can be a real disadvantage with active RX systems...and it’s fixable

If a rig offers only limited built-in attenuation and you connect it to an active receive system (active arrays, amplified antennas, etc.), you can get forced into an ugly trade:

• too much gain...and you risk overload, intermod, and fatigue
• too much “software gain reduction”...which is not always the same as real RF attenuation ahead of sensitive stages

The correct engineering response is simple: treat the station like a chain: antenna → filtering → preamp/attenuator → receiver → DSP. If one stage lacks range, add range externally. (A receive switch with a 0–30 dB step attenuator is a very practical way to do this.)

A quick “what to look for” guide (based on operating goals)

1) Low-band DX (160/80/40) with active receive antennas / arrays

• Prioritize: attenuation range, close-in DR3 behavior, practical filtering strategy, overload resilience
• Operate: don’t default to preamps at night; start by reclaiming headroom and calming band noise

2) Low-band DX with passive, low-output antennas (Beverage, small loops)

• Prioritize: sensitivity/noise only when your site is quiet enough for it to matter
• Operate: add gain only until the receiver stops being the limiting noise source

3) Contesting / Field Day / multi-station chaos

• Prioritize: close-in dynamic range, overload behavior, real filtering options
• Operate: attenuation use is normal...it’s part of running a clean, comfortable receive chain

4) Portable / SOTA / POTA / minimal antennas

• Prioritize: practical sensitivity, ergonomics, speed-of-use, and power efficiency
• Reality: “lab best” matters less than “easy to deploy and easy to listen to”

The bottom line: the “best” number is the one that matches the mission

The Sherwood-style approach is great because it pushes you away from single-number shopping and toward better station engineering: your antenna system changes the receiver’s needs; your noise environment changes the value of sensitivity; your nearby-signal environment changes the value of dynamic range...and your operating style changes what matters day-to-day.

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