At 08:06 AM 2/21/2008, Bill Tippett wrote:
>W9OY: > > >Very true BDR is important, but all you need is enough. > > >I have 3 verticals 100ft apart one each on 160, 80, and 40. I can run my >SDR-1k on 80M running 1500W calling S-1 DX while running the F5K on 40 or 160 >calling just above the noise DX at 1500W and I don't hear the transmitter of >one radio in the receiver of the other on any band. > > Lee this is essentially SO2R where you have bandpass >filters on both the transmitter and receivers on different >bands. The SDR-1000/5000 both have RX bandpass filters which >will help reduce cross-band interference. This does not help >situations with transmitters on the same band, such as we >have in Field Day, multi-multis, or if you have a close >neighbor on a band like 160 which has a very strong >ground wave. If you've ever operated within a few >miles of someone on 160 running full power to a full >size vertical, you'll understand what I mean (I once >lived 2 miles from W0YK and 4 miles from K0RF while >in Colorado and could see their towers from mine!) This is the same >issue W8JI discovered while trying >to use an SDR-1000 on 160 in a multiop for finding >new stations or mults to work. > > Most of the serious multi-multi stations have >two RX/TX setups per band. BDR (for the RX) and phase >noise (both RX and TX) are both important issues in >situations like these. RX performance is not only >about close-in IMD but all of the above. I think >anyone attempting to use Skimmer with a QSD on the >*same* band as their TX will run into these issues. >Other solutions such as Inrad's front-end filters for >limited areas of the same band may help somewhat. or, an adaptive analog canceller at the front end. You put a small antenna or a coupled port off the Tx line and run it through a variable gain/phase so that your receive antenna has a very sharp, very deep null just for the Tx signal. While there are digital approaches to this, the analog approach is still used in some cases, because it's cheaper/easier to do the analog circuit, and knock down the "self-jammer" before the first mixer and/or you don't need as high performance a digitizer. System trades galore There's a lot of very nice RF parts from Maxim, among others, that would work real well for this kind of thing (broadband vector mods). The canceller circuit doesn't need to handle huge powers (just enough to cancel whatever shows up at the receiver input from antenna/antennna coupling). A slick thing would be to have the software in the radio generate the adjustment signals for the analog canceller. Since the relative coupling doesn't change all that fast, the adjustment signals could be sent over "flexwire" or similar. Jim, W6RMK _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
