HRWB049-Understanding RF Receiver Specifications

Eric Swartz WA6HHQ, co-founder of Elecraft, joins us to guide our understanding of RF receiver performance specifications.  Eric introduces us to common receiver specs such as Sensitivity, Noise Floor, Dynamic Range, Intermod Dynamic Range, Phase Noise, and RMDR.  He tells us what they mean in real-world receiver performance terms, how they are tested, and whether it’s better to have a higher or lower number in each one.  It’s also the final episode before the 2018 Hamvention and George and Jeremy share our plans for our Booth, special offers, and exclusives for show listeners who stop by booth 3104 in Xenia.

Show Topic Begins at 1:09:36

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Sam Zeloff - Garage Chip Fab

https://hackaday.com/2017/02/25/the-fab-lab-next-door-diy-semiconductors/

https://hackaday.com/2018/04/24/first-lithographically-produced-home-made-ic-announced/

https://hackaday.com/2018/05/03/more-details-on-that-first-home-made-lithographically-produced-ic/

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RF Receiver Specifications Guide from Eric Swartz WA6HHQ

Elecraft Mailing List - http://www.elecraft.com/elist.html

Sensitivity - How well can the receiver hear weak signals?

• Minimum Discernible Signals - noise is generated inside the radio from the amplifier stages and how much amplification is available in the receive chain to bring a signal above the radio’s internal noise floor
• As sensitivity increases, you can degrade dynamic range
• To measure, start by injecting weak signals until you observe the signal level out of the speaker roughly double in amplitude (3dB)
• Lower values are better (bigger negative number), allowing you to detect weaker signals
• Most HF radios are between -125 to -130 with -135 to -138 being on the higher side of performance

Noise Floor

• The internal noise figure generated by the radio with the antenna removed

Dynamic Range

• Strong Signal Handling - how does the radio perform when there are strong signals adjacent to where you are tuned?
• IMDR3 - Intermodulation Dynamic Range
• When multiple strong received signals overload the first receiving amplifier in your radio, the signals get clipped
• When the radio has a broad banded receiver, this clipping begins to act as a mixer and creates intermodulation showing up at different frequencies
• Additional unwanted signals are created in the receiver when multiple strong signals are present
• To measure, begin with two signals apart - the difference between the MDS/sensitivity and the level required to set the signal generator to to cover up the weak signal
• Higher values are better - 90dB range above noise floor is average, mid 90’s to 100 dB is on the higher side of performance

Blocking Dynamic Range

• A strong signal overloading your receiver thereby reducing the gain of the receiver.
• Receivers can have challenges when a strong signal is physically near the radio
• To measure, inject a signal until it causes receiver overall gain to drop one DB
• Higher values are better - typical better than 130dB of BDR, mid 130s to 140s is on the higher side of performance

Phase Noise

• An indication of the quality and “cleanliness” of local oscilator (VFO, or Crystal Master Oscillator)
• Denotes whether they introduce jitter or noise to the received signal
• Lower is better

Reciprocal Mixing Dynamic Range (RMDR)

• RMDR is tied to phase noise
• Impacted by how clean your oscillator is
• To measure, listen in 500hz bandwidth and measure how strong an injected signal has to be to raise the noise floor on the freq you are tuned to (1-3dB noise floor increase)
• This ratio is the RMDR
• Higher values are better - 110-115 dB
• As multiple signals get closer, the RMDR drops

Sherwood Engineering Receiver Comparison List - http://www.sherweng.com/table.html