[1000mp] Significant audio difference between LSB/USB RCVR Aonly

[Kok Chen]

On Jan 26, 2011, at 1:15 PM, Bruno Tréguier wrote:

> Stu Ritter wrote :
>> I do hear a difference between upper and lower,
>> at least to my aged ears.
> 
> Same thing here: the sound in USB has a slightly higher pitch than in 
> LSB on my FT-100MP Mark V Field.

Bear in mind that crystal filters' skirts are not perfectly symmetrical.  You can see typical filter shapes here:

http://www.ac0c.com/main/page_ft2k_roofing_filters_why_the_inrad_filter_fails.html

In the case of USB, the suppressed carrier will be below the lower frequency skirt.  The higher frequency skirt will then determine the high frequency audio "character" of what you hear.

LSB is the mirror image of USB.  The suppressed carrier in this case is above the higher frequency skirt, so the lower frequency skirt of the filter now determines the "character" of the high frequency audio that you hear.

Where precisely you place the suppressed carrier with respect to the skirts will also determine what you hear.

You can see by looking at the audio noise passband of the receiver (tuned to band noise) as you switch between LSB and USB on a sound card based spectrum analyzer.  

73
Chen, W7AY