Dan, This is very interesting. It occurred to me that we can now take the CB "roger beep" and put it to good use <grin>
Tom W0IVJ Tayloe Dan-P26412 wrote: >Diversity reception reduces resistance to fades. For this, we try to >space our cell site antenna 10 wavelengths apart in order to minimize >the correlation of the fades between the two antennas. However, >diversity is also deployed on a lot of cell phone handsets today and the >antenna spacing they use is much closer than this. 7" of separation at >800 MHz is only about half a wavelength. Never-the-less we see large >improvements in the throughput capabilities even with this close >spacing. > >I guess all I am saying here is that when using diversity, it is best to >spread the antenna apart quite a ways, but that even a half wavelength >spacing provides benefits. > >I should note that the new generation of cell phone equipment is not >only making use of receiver diversity (that is kind of old hat), but >that it is now making use of transmit diversity also. Unfortunately, >that does not work with CW or SSB since sending the same signal out both >antennas causes beam forming. It only works with data modes that modify >the data from the one antenna so that it is different from the same data >from the second antenna (complex conjugate?) and requires the receiver >on the other end to understand what is going on so that it can put the >two back together. > >I think SDR is an exciting concept. One of things that we are doing for >the next generation of cell phone equipment is to do beam forming using >feedback from the other receiving end. We call this "precoding". It >seems feasible that a high tech SSB or cw QSO between a pair of >diversity transmit equipped transceivers could run a separate, slow >speed, intermittent data stream that could feedback to each other >precoding data that would allow phased transmit antennas on both sides >to automatically track and align the beam steered transmit signal to >each other in an optimized fashion. It could take the form of a small >blip of precoding data on the receive to transmit changeover. > >- Dan, N7VE > >-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Jim, W4ATK >Sent: Thursday, October 11, 2007 6:41 AM >To: Lee Mushel; [EMAIL PROTECTED]; FireBrick; FlexRadio List; Jim Lux >Subject: Re: [Flexradio] 2nd receiver option questions > >AS I remember there is more to diversity reception than just two >receivers. >Back in the war (Korea) we used three "rosettes" of rhombics fairly >widely seperated with our RCA Diversity receivers (Huge seven foot >racks). Later in my career we used diversity across Lake Ponchatrain on >6GHz, the dishes were spaced several wavelengths apart vertically on the >tower. I doubt that many hams would have the space or antenna farm to >support such activity, but then again I may be wrong. After seeing the >full sized 80M 5 element Yagi the gentleman is Japan had constructed, I >guess all it takes is $$$$$$. > >Jim, W4ATK > >-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] Behalf Of Lee Mushel >Sent: Thursday, October 11, 2007 8:34 AM >To: [EMAIL PROTECTED]; FireBrick; FlexRadio List; Jim Lux >Subject: Re: [Flexradio] 2nd receiver option questions > > >OK, Gerald, step up and explain to these kids what dual diversity is all >about! > >Lee K9WRU >----- Original Message ----- >From: "Jim Lux" <[EMAIL PROTECTED]> >To: <[EMAIL PROTECTED]>; "FireBrick" <[EMAIL PROTECTED]>; "FlexRadio >List" ><[email protected]> >Sent: Thursday, October 11, 2007 8:11 AM >Subject: Re: [Flexradio] 2nd receiver option questions > > > > >>At 05:37 AM 10/11/2007, [EMAIL PROTECTED] wrote: >> >> >>>I understood (Hope ??) that the receiver on the FLEX5k is independent >>> >>> > > > >>>of the transmitter. If so then splitband should be possible already, >>>and is the software the bottleneck. >>>Or I am to optimistic and is the hardware not able to cater for that. >>> >>>Other question >>>Can the 2nd receiver be used on the sane frequency as the main >>>receiver, BUT WITH EXACTLY THE SAME FREQUENCY AND PHASE? >>>Then you can do nice experiments with 2 small loop arials, 90 degrees >>> >>> >crossed. > > >>I believe that this came up in early discussions of the F5K design on >>the list. Here's my recollection. >>Yes, the LO to the two receivers is driven from the same reference >>oscillator, so setting to exactly the same frequency is trivial. The >>"latch" signal to the two DDSes can theoretically be asserted >>simultaneously, so the phase should be the same (but this detail is >>buried in the firmware of the F5K, perhaps a Flex rep can confirm), >>with perhaps a slight offset due to propagation delay in the wires >>which will inevitably be of different lengths, etc. >> >>So the real question is whether the audio interface brings the data >>across time aligned from all receivers. There's no reason why it >>wouldn't be so, assuming all the A/Ds are clocked at the same rate. >>Again, I suspect that this is under the control of the firmware inside >> >> > > > >>the F5K, so Flex would need to confirm. >> >>SO all you're left with is the inevitable offsets because of the >>differences in electronics among the channels (the filters on the >>output of the DDS, the RF components ahead of the QSD, etc.). >> >>As always with these sorts of things... absolute phase to 10 degrees >>is easy. to 0.1 degrees is hard. >> >>Jim, W6RMK >> >> >> >>_______________________________________________ >>FlexRadio mailing list >>[email protected] >>http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >>Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >>FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio >>Homepage: http://www.flex-radio.com/ >> >> >> >> > > > >_______________________________________________ >FlexRadio mailing list >[email protected] >http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: >http://www.flex-radio.com/ > > >_______________________________________________ >FlexRadio mailing list >[email protected] >http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: >http://www.flex-radio.com/ > > >_______________________________________________ >FlexRadio mailing list >[email protected] >http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >FlexRadio Knowledge Base: http://kb.flex-radio.com/ >FlexRadio Homepage: http://www.flex-radio.com/ > > > > > > _______________________________________________ FlexRadio mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
