On Sun, Feb 20, 2011 at 2:17 PM, jim <[email protected]> wrote: > I have noticed since I got the f5k (a year+ ago) that when I am tuning a > difficult antenna thru any of my tuners, there seems to be an indication > that is obviously strange - the SWR is indicated as negative. > > > > The "pointer" motion is what the analog world would see when one went from > + > to - via infinity rather than zero. > > > > How do we have a negative SWR ??!! >
The calculation for SWR is taken from the ratio of forward to reflected power. As the tuner is tuning, both forward and reflected power are changing. If your SWR meter measures both forward and reflected power at the same instant there is no problem but the Flex radio uses an A:D converter to read them sequentially. It is possible that, the change in time and tuning causes the reflected power to be read as greater than the forward power, resulting in a negative VSWR. The only way you can get an accurate measurement of SWR in the Flex radios is when nothing is changing. Both forward and reflected power have to be constant. That doesn't happen while transmitting a modulated signal or when the tuner is tuning. Yeah, I agree, they cut a corner there. I wish it were different and they put into the hardware the means to sample both forward and reflected power at the same instant. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 [email protected] +1.767.617.1365 (Dominica) +1.931.492.6776 (USA) (+1.931.4.WB6RQN) _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software.
