[amsat-bb] Re: full duplex w/ 2 HT's
glasbrenner at mindspring.com
Mon Jun 4 03:01:21 PDT 2012
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.greg at 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:
>> 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
>> 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!
>>> ng it all together. grazie mille, Robert k f 0 g cn81 in the woodwork, literally, shasta/klamath national forests.
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