Re: Curious about the whooshing

Posted by N5GE on Mar 10, 2009; 4:13am
URL: http://elecraft.85.s1.nabble.com/Curious-about-the-whooshing-tp2452198p2453221.html

On Mon, 9 Mar 2009 19:09:14 -0400, William Evans
<[hidden email]> wrote:

>Hello fellow Elecrafters.
>
>I have a question about which my curiosity is just getting the best of  
>me.  When I have the Sub Receiver on, linked, and all parameters the  
>same between the two receivers, and I have the Balance control set in  
>the middle, and then tune quickly across the band, sometimes it has a  
>"whooshing" sound which makes it difficult to tune and listen.  As I  
>slow down, the whoosh gets much less noticeable, but it is still there  
>as the tonal quality seems to slowly shift from bass to treble.
>
>I have 2.8kHz roofers in both receivers as well as AM filters in both.  
>All filter frequency shifts are set to 0.0, but  I'm guessing that  
>there is a slight phase difference between the two receivers  and when  
>they are tuned, the time differential in both VCOs settling down  
>varies enough to make a noticeable difference.  If I go to CONFIG:FLx  
>FRQ and change the setting from 0.00 to 0.01, I can get the same  
>effect without having to tune the two linked receivers.  Of if I  
>simply listen in either LSB or USB for a long time on one frequency, I  
>can hear the background hiss tone going from bass to treble and back  
>again at a very slow rate (This is most noticeable when no signal is  
>within the passband, but who, in their right mind would use a Ham  
>Transceiver to monitor an empty frequency!-- ooops, I guess that would  
>be me!)

:o)

I experienced the same thing and by adjusting the zero on the filters
to match in both RX's was able to remove this.  It takes some time to
get it just right, so be patient.  I know, the 8 pole filters are
supposed to be on zero, but they are not, so adjust them also.

The nice thing is that you can use the Configuration application to
set the filters, which makes it easier than doing it from the config
menu.

73,

Tom, N5GE

>
>Anyway, is my assumption about the phase difference between receivers  
>a reasonable explanation, and/or is there anything I could do to  
>eliminate the effect?  BTW, without an antenna (or the wrong antenna,  
>e.g. an 80 Mtr Dipole on 20 Mtrs), I cannot perceive it, but with a  
>resonate antenna, the phenomena appears.  I am using the same antenna  
>on both receivers.
>
>Am I far off base on my assumptions, or is there a simple explanation  
>which I have not thought of yet?
>
>Just Curious
>
>W4ISH
>Bill
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html