[amsat-bb] Re: full duplex w/ 2 HT's
ko6th.greg at gmail.com
Sun Jun 3 19:45:36 PDT 2012
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.
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 -
> 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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