Diversity Reception with Noise Floor Enhancement

Mystery Ham

Diversity
Reception with Noise Floor Enhancement

A feature suggestion to enhance the ability to discern a signal by balancing, and mitigating distracting changes in, background noise intensity.

Diversity Reception allows the listener to monitor the same signal with diverse antennas with the intent that what might occur on one receive system, that might cause a loss of intelligibility, may be mitigated by the configuration of the other antenna  on the other receive system allowing the signal to be properly copied.  Normally this would be done with stereo headphones with the master and **** receiver slices placing audio into their respective right and left channels rather than mixing them.  The brain does the rest of the work.

However, the brain tends to focus on quick changes or modulations in intensity, pitches, and frequency in an audio signal.  This is one of the reasons that modulated, or quickly fluctuating noise can contribute to listening fatigue.   AGC can also have an undesired effect where a strong signal triggers gain reduction and the noise disappears and slowly returns according the speed mode selected.  If the gain adjustment is fast, the rapid disappearance and reappearance of the noise under the signal is just as distracting to the brain as other listening annoyances.

What is Noise Floor Enhancement?

Noise Floor Enhancement is a feature suggestion for diversity receive capable systems to provide a means to balance, and optionally stabilize, the audio levels of each receive systems’ noise floors on the band on a continual basis while the feature is engaged.  This occurs regardless of being tuned to a signal, scrubbing through the band, or parking on noise watching the spectrum scope bucking like a wild horse, while listening in Diversity Receive mode.

How is it an enhancement? (Does it solve a problem?)

Noise Floor Enhancement solves several problems; primarily, however, its function is to automatically balance and stabilize the audio levels of the Calculated Noise Floor around the tuned frequency on each receiver thereby enhancing the listener’s ability to discern a signal that might otherwise be unintelligible due to rapidly fluctuating band conditions, unequal fluctuation between the two receive systems, failure to account for narrow-banded antenna characteristics while scrubbing through the band, or simply having a mis-adjusted audio setting left over from a prior listening session.

Consider the following example, albeit simplified, for automatic balance of the noise floors.

Receiver on Antenna 1 noise floor at -90dBm.  Signal peak at -87dBm

                Receiver on Antenna 2 noise floor at -130dBm. Signal peak at -121dBm

                Audio gain on both receivers equal; as was set from a prior listening session.

Because the audio gain on both receiver slices happens to be the same, the audio from antenna 1’s signal with peaks 3dB above the noise is very audible, however, not copyable.  The audio from antenna 2’s signal with peaks 9dB above the noise is much more copyable due to the better signal to noise ratio, however, due to the audio gain being equal on both receivers, the audio level from the second receiver is at or below the hearing threshold because the second receive system’s signal was 48dBm lower so the opportunity to copy the signal was missed because it was not possible to discern the audio from the receiver on the 2nd antenna. 

With Noise Floor Enhancement, the audio levels representing the Calculated Noise Floor around the tuned frequency of the receivers are balanced (equal).  As a result, the audio level from the weaker signal with a better signal to noise ratio on antenna 2 is now greater than the audio level from the stronger signal with lower signal to noise ratio on antenna 1 and the signal may now be copied.

Noise Floor Enhancement Balance, as in the example above, keeps the audio level representing the calculated noise floor equal between the right and left channel, though it may fluctuate up and down.

The option of Stabilization would add the capability to keep the audio level representing the calculated noise floor constant regardless of actual noise floor changes in the band.

With Noise Floor Enhancement with balance and stabilization, all fluctuating elements in the background noise that might prove distracting are stabilized and the brain may now focus on the actual signal rather than noise fluctuations.  Though the signal itself may fluctuate more, the brain’s focus is already where it should be, on the signal.

 

What is a Calculated Noise Floor value?

Calculated Noise Floor is a value determined by examining the spectrum above and below the tuned frequency in search of an average value amongst the lowest levels within that range. 

Where does this data come from? In a Flex Signature Series 6700 or 6700-R receiver in diversity receive mode, the band has already been sampled by both Spectral Capture Units, the data from the SCU for the Master Slice Receiver has already been analyzed for graphing and is also graphed in the spectrum scope of the panadapter display (as should be the graph from SCU for the **** Slice Receiver.) 

The ability to perform the calculation, presumably, has already been demonstrated in that the peak signal within the passbands of both the master and **** slice receivers have already been identified and displayed in their respective S-Meters.  The Calculated Noise Floor value can be determined by examining the spectrum up and down from the tuned frequency and performing an algorithmic averaging of some percentage of the lowest values found in a similar fashion.  In fact, different algorithms and what distance from the tuned frequency to search (likely a multiple of the current passband) might become selectable options.

What is a Calculated Audio Level of the Calculated Noise Floor Value?

The Calculated Audio Level of the Calculated Noise Floor value is the audio level of the noise you would hear if the signal suddenly went away and you were left with background noise.

Why go through the trouble when you can wait for a breath or a pause in the audio?  Because in the time it took to ask the question, the noise floor went through seven 10db fluctuations on the Master receiver slice with the horizontal dipole antenna and eight 15db fluctuations on the **** receiver with the vertical antenna causing me to miss fifteen syllables.  The goal is near real-time information that is relevant to each instant in the near real-time listening process.

Under what conditions might Noise Floor Enhancement fail?

Noise floor Enhancement might fail when the band is so congested the value of the noise floor cannot be accurately determined, and, when the one or both signals are exceptionally strong.  However, diversity reception isn’t needed under latter condition where the noise floors are audibly nearly imperceptible compared to the peak signals.

What might a Noise Floor Enhancement interface look like?

A NFE button located next to the DIV button in the master receiver slice, a means to add stabilization to balance, and a dropdown menu selecting range each side of the bandpass filter or receive frequency to search for minimum values for the noise floor.

Also, with NFE engaged, the audio levels would be set at 50% in the master and **** receiver slices and the controls would not reflect the automatic adjustments...  This enables the operator to adjust the level of the master and **** channels according to his or her physical hearing ability or listening environment needs.

Cheers,

Mystery Ham