Hi Glen and all, Duplexers
I've had quite a "play": http://www.unixservice.com.au/hamradio/repeaters/duplexers/basics.html But to this point, in the Australian amateur repeater scene here, there's no communication on needs. there is still a Yahoo group but none it seems of the current repeater maintainers ever post or read it. Test equipment: I now have an Advantest U3641N the 75 ohm version. Alan VK2ZIW On Thu, 16 Jul 2020 11:00:58 +1000, glen english wrote > posted here for the benefit of all the non-RF people : > > Hi Alan. OK roger all that. as you know, duplexors, cavity filters, > bla bla are my home game... > > if you have interaction problems between them the cable lengths are > wrong between the filters. > > IE the coupling is wrong. > > with a single filter, with loops lined up in line, can you get good > VSWR ? > > lengths : Stay away from half waves (in coax) and super short > lengths. If it was designed for UHF, the lengths will be too short. . > > depending on how you have the loops configured, a quarter wave in > coax is a good start and what I would recommend . > > Also, are these bandpass or bandpass notch ? They will need to be > bandpass notch otherwise you will not have a hope of making > rejection / insertion loss. > > they can be made BP-N without difficulty.put T adaptors on the tops > of each filter loop connector, (IE a single loop is used), and a > high quality series cap inserted in series with the loop in the > can) to generate a zero. > > AND just use good quality RG58 for interbay.... cable leaking is a > huge load of BS, especially when there is a antenna just nearby . ha > ha I see people touting their 140dB isolation cable when the antenna > is about 20meters away... > > BTW I wrote a T800 windows programmer... > > I can come up there some time with one of my VNAs.... you are not far. > > On 16/07/2020 10:49 am, Al Beard wrote: > > Thanks Glen, > > > > This bug wasn't going to be a "show stopper" as my intended > > receiver is an SSB one with no squelch or mute. With a FM > > transceiver, muted audio maybe the only one available lest > > the radio speaker would emit annoying noise all the time. > > > > BTW: My development here atm is on the Banana Pi M2 Berry with > > a 300Gb SATA laptop hard disk, not an SSD. All in a Tait T800 > > series module box. The T800 2m system is ready. Synthesized, > > all 144.025 to 147.975 channels are in the eprom, Rx & Tx. > > 21.4 MHz IF. > > > > A cavity set is a problem, I have a set of six 6" RFS 3/4 wave > > 70cm cavities that on 1/4 wave tune to 145 - 148 MHz nicely. > > On making coupling loops and inter-cavity leads, have difficulty > > with interactions. Also need better test equipment to resolve to > > a 100db notch. Or at least 80db, ie. two cavities let alone three. > On 16/07/2020 8:31 am, glen englis > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 --------------------------------------------------- Alan VK2ZIW OpenWebMail 2.53, nothing in the cloud. _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
