Ed, see notes.
Gerald Youngblood, K5SDR President and CEO FlexRadio Systems(TM) Email: [email protected] Web: www.flexradio.com <http://www.flex-radio.com/> Tune In Excitement (TM) PowerSDR(TM) is a trademark of FlexRadio Systems On Tue, May 22, 2012 at 2:38 PM, Edward H Russell <[email protected]> wrote: > Thanks for the clarification. I assume this implies that if you are not > switching SCUs, in QSK CW there is only the diode switch, and no relay? > A reed relay is used in the SCU antenna path. In half-duplex it will open and close in <1ms. > **** > > ** ** > > Also, it is clear that the RX SCU would need to be blocked during TX. Is > this also accomplished in the software, without needing a relay activation? > **** > > ** ** > > Or to put the question very simply:**** > > ** ** > > 1 In normal QSK CW operation, between dits, is a relay closure required? > In half duplex, the reed relay will switch between dits (<1ms). > **** > > ** ** > > 2 In full duplex QSK CW operation, between dits, is a relay closure > required? > In full duplex, no. > **** > > ** ** > > Thanks,**** > > Ed W2RF**** > > ** ** > > *From:* [email protected] [mailto:[email protected]] *On Behalf > Of *Gerald Youngblood > *Sent:* Tuesday, May 22, 2012 3:16 PM > *To:* Edward H Russell > *Cc:* Ray, K9DUR; Tim Ellison; [email protected] > *Subject:* Re: [FlexEdge] 6000 series T/R switching**** > > ** ** > > Hi Ed,**** > > ** ** > > There is more to this story. The FLEX-6000 series radios have two modes > of TR switching: QSK and non-QSK. For QSK, we use reed relays for > switching the RX paths to each SCU and a PIN diode to switch the TX path. > This eliminates distortion on the RX path and improves isolation. In > non-QSK modes such as SSB and AM, we use traditional relay switching on the > TX path. This eliminates any IMD that would be caused by a PIN diode in > the TX path on the linear modes where it counts. On CW, you don't really > care about IMD since it is a single tone.**** > > ** ** > > The SCUs are capable of duplex operation so you can receive while > transmitting it you provide appropriate antenna isolation. > > Gerald > > Gerald Youngblood, K5SDR > President and CEO > FlexRadio Systems(TM)**** > > Email: [email protected]**** > > Web: www.flexradio.com <http://www.flex-radio.com/>**** > > ** ** > > Tune In Excitement (TM) > PowerSDR(TM) is a trademark of FlexRadio Systems**** > > ** ** > > ** ** > > > > **** > > On Mon, May 21, 2012 at 10:35 AM, Edward H Russell <[email protected]> wrote:*** > * > > Hi Ray, > > Thanks for the information, which is of course very general. I'm meaning > specifically what sort of practical impact does the use of PIN diode > switching have on receive and/or transmit performance, especially when the > rig is used for CW or FSK operation. > > Besides possible (theoretical?) introduction of IMD and noise as a > downside, > there are practical considerations that come into play for QSK switching, > especially at medium to high speeds. Two of these are switching time and > noise (relay chatter). > > I'm not sure the IMD or noise generated by the diodes would be significant, > or even measurable, in an operational context. But if they were, that small > effect would have to be balanced against the improved and quieter operation > of diode switching. > > Also, there is another approach that might achieve the same result. If the > radio operation is full duplex on separate antennas, it might not be > necessary to actuate the relay in order to switch to transmit. Possibly T/R > switching in full duplex could be a software operation. In that case, the > PIN diode T/R switching could be done externally, as it is now in my power > amplifier. > > Thanks & 73,**** > > Ed W2RF > > -----Original Message----- > From: Ray, K9DUR [mailto:[email protected]]**** > > Sent: Monday, May 21, 2012 11:18 AM > To: 'Edward H Russell'; 'Tim Ellison' > Cc: [email protected] > Subject: RE: [FlexEdge] 6000 series T/R switching > > Ed, > > You wrote, "Where can I get more information about what sort of IMD is > caused by PIN diodes?" > > Any diode is an inherently non-linear device. By definition, non-linear > devices generate distortion. > > Even when biased into the "linear" region of the conducting state, they are > still not perfectly linear. The farther the deviation of the current from > the bias point, the more distortion is introduced. > > A typical voltage vs current curve for a given device should be available > from the device manufacturer. > > I heard it said that another reason that relays were chosen over > solid-state > switching was to avoid the noise introduced by solid-state devices. > > 73, Ray, K9DUR > http://k9dur.info > > > > _______________________________________________ > 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.**** > > ** ** > _______________________________________________ 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.
