Blast it! Just lost my whole reply again! I type slowly and it's aggravating when I have just typed out a whole reply just to have it dumped by some strange keystroke (I have no idea what it was)....arrrgggh!
So I will have to restart.
I currently have no access to the proper test equipment to test this exactly although I do have the knowledge and experience to do so. Based on my user experience with a KG-UV2D, essentially the same RF design as the UV3D, I can confirm two things about the "narrow" mode operation of the radio's receiver (the transmitter is well documented by many to alter its deviation effectively as per FCC regulations for Part 90 operation):
1) As many have already confirmed, it does NOT switch in a separate IF filter for the narrow mode so it simply uses the same single IF filter for both modes. Therefore, you will not get a tighter receive IF response when switching to "narrow" mode.
2) It DOES alter the receive audio level response when switched in to "narrow" mode either through alteration of the discriminator operation or otherwise. Therefore, you will perceive a loudness change when switching between "narrow" and standard FM modes. I must add that I can confirm this definitely only on my unit - others have said that they perceive no change on theirs so that it may be possible some units are designed slightly differently (an undocumented design change).
This is a similar approach to that used by the Uniden BCT15 scanner that I have - switching to NFM causes a shift in audio loudness response but there is no change to IF filter response. However, whereas the filter on the Uniden scanner is nearly useless on adjacent 7.5KHz separated channels even at moderate or low signal strength levels the Wouxun's receiver seems perceptibly better - much so, in my opinion. I suspect that this is due to the Wouxun's design using a better quality IF filter with tighter skirts than that used on the Undien scanner.
Of course, it would be better if two selectable filters were available, one optimized for +/-5KHz FM deviation and one optimized for the new narrower "narrowband" FM deviation of +/-2.5KHz but, as a compromise, the one used by the Wouxun is a better choice than the one used by the Uniden scanner. It isn't perfect, of course, but I would say that under low to moderate adjacent channel signal levels you're probably ok but I wouldn't expect it to handle strong adjacent channel levels especially at the US civilian VHF-High band 7.5KHz spacing. In the federal portions of the VHF-High band and all of the UHF band with the spacing of 12.5KHz you should be fine except for very high level adjacent channel levels. 6.25KHz channel spacing, of course, will present problems. Normal ham usage should be fine - in my experience, based on usage of my unit, the Wouxun seems much tighter, IF-wise, than other ham units I have used and most scanners.
Also, be aware that, as many have pointed out, the current Wouxun UV2/3D will not do the 7.5KHz channel steps for the US VHF-High band civilian portion (unless there has been a recent firmware change - I've seen some rumors of this but cannot confirm it). Supposedly, the new UV6D model will do the 7.5KHz steps but, again, I cannot confirm this.
That's my 2 cents, anyway.
-Mike
