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.
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