Usually the diplexer as a filter is only needed to keep the 2m tx from overloading a 70cm preamp. For a two radio setup with no preamp, it usually isn't needed at all.
73, Drew KO4MA Sent from my iPhone On Jun 3, 2012, at 10:45 PM, Greg D <ko6th.g...@gmail.com> wrote: > So, all the on-line information seems to point to this solution - putting a > diplexer (filter) on the 70cm side to tap off and absorb the incoming 2m > signal. Isn't there also a design where one puts a filter on the 2m side, to > tap off and absorb the 70 cm (3rd harmonic of 2m) signal? > > I would think that any (reasonable) 70cm receiver would have enough rejection > for a signal so far out of band, but the in-band 3rd harmonic can only be > taken care of at its source. At least, I think that's the logic. > > Is there anything worthy about the other design, or is the most common > problem that our HTs can't possibly deal with a strong 2m signal on the 70cm > side because of their "DC to Daylight" receivers? > > I've been on the mode-J birds without much of a problem with this sort of > desense, though I did have a lot of trouble on AO-40 with reflected RF when > aiming through a big oak tree behind the house. The 70cm uplink was > interfering with the 13cm downlink, and I was pretty sure at the time that it > was a 3rd harmonic sort of problem. > > Just curious, > > Greg KO6TH > > > Ronald Nutter wrote: >> Robert: >> >> I have used a duplexer on the UHF side of my satellite ops for several >> years. I find that some radios have more of a desense problem than others. >> Here is a link to my website where I briefly talk about what I do on >> portable ops and using what is referred to as a Mode J filter - >> http://www.ka4kyi.com/satellite_gear/misc_equipment/ >> >> Ron Nutter >> KA4KYI >> AMSAT Area Coordinator for Missouri >> >> On 6/2/12 11:33 AM, Robert Coppock wrote: >>> >>> >>> >>> hola, i am trying to determine the best way to work full duplex on the >>> birds with 2 HT's or radios. i cannot find any info so far on the web. my >>> concern is to keep the transmit power out of the receive radio, i guess >>> basically the difference between a diplexer and duplexer. since i am >>> efficient (lazy) i thought i would just look for suggestions here while i >>> am checking google also. what do i need, di/du/ plexer, and what is the >>> correct wiring scheme ? i will be using the arrow antenna without the built >>> in duplexer, from the 2 feeds (vhf/uhf) and 2 HT's for now. my picture of >>> it so far, is to wire the vhf radio direct to the vhf feed port on the >>> arrow, and have the uhf port on the arrow come into a duplexer, with the >>> duplexer uhf port going to the uhf radio, and the duplexer vhf port >>> terminated into a 50 ohm dummy load. also, any suggestions of specific >>> duplexers would be appreciated. i think i started on this project a few >>> years ago, but never got around to get! >> ti! >>> ng it all together. grazie mille, Robert k f 0 g cn81 in the woodwork, >>> literally, shasta/klamath national forests. >>> _______________________________________________ >>> Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. >>> Not an AMSAT-NA member? Join now to support the amateur satellite program! >>> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb >>> . >>> >> >> >> _______________________________________________ >> Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. >> Not an AMSAT-NA member? Join now to support the amateur satellite program! >> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb > _______________________________________________ > Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
