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RE: dual feed problems -- REPLY --


The 100dB notch filter only has about 0.4db loss at 2401, which will add 
slightly to the noise figure.  The logic is that you would need to be using 
a reasonably large dish for the L Band uplink (eg >1m) so your rx 
performance would then be well above the "average".  So a little bit of 
loss isn't going to matter.

The filter must be located between the feed and preamp (if you use one), or 
feed and converter if you do not have a preamp.


Charlie G3WDG

At 23:32 04/01/03 -0900, you wrote:
>Good stuff!
>I will likely try the dual L/S circular patch feed of W0LMD on my 2.4m
>center-fed dish.
>I have an associated question:  I will be using a 435 MHz IF converted
>Drake 2880 for downconvertor preceded by an DEM preamp.  I wonder if the
>preamp will suffer any desense from my approx. 15w L-band uplink?  I can
>insert a notch filter ala G3WDG between the preamp and convertor without
>impacting NF, but I would guess that is not the case if the filter preceeds
>the preamp.
>But then I guess desense would be worse than higher NF on this big dish.
>Ultimately, I would like a dual-sense circular patch feed for 1269-1296 so
>that I may also operate eme with the dish...guessing that may be a second
>generation feed.  It would be nice to simply change freq between AO-40 and
>eme.   But perhaps running 125w on 1296 is a bit dangerous for the S-band
>receiving equipment.  Interesting engineering challenge in any case.
>Note: 1296-eme Tx is RHCP and Rx is LHCP (I think).  So having AO-40 Rx in
>RHCP provides another configuration problem.  Oh well, swapping feeds may
>be the only solution.
>73, Ed - AL7EB
>I will maintain my existing mode-US set up separately:
>436CP42 & 33-inch helix-fed offset dish/MKU-232/unmod Drake.
>At 06:34 PM 1/4/2003 -0500, Gunther Meisse wrote:
> >JC
> >Not a problem. Dual band S + L are common and there is even a tri-bander,
> >70cm + S + L patch which I understand does a wonderful job. I personally
> >just got an S + L dual patch from Dr. Robert Suding, and have run a dual S +
> >L Helix for over a year with not problem. De-sensing is an issue. You must
> >have down converters that have a VERY selective filter on the front end or,
> >as I do, use a digital filter on the front end of the down converter. I have
> >a 50db and a 100db filter and the 50 seems to be plenty.
> >Regarding feeds contact Dr. Robert Suding W0LMD at:
> >Dr. Robert Suding [roberts@qadas.com]
> >His web site is: www.ultimatecharger.com He has all the info you will need
> >and he sells the dual and triband Patch feeds.
> >I use the filters from a Ham named (I Think, or close) Sudling, in England.
> >I had a hard drive crash and have lost a number of my reference contacts.
> >Perhaps someone on the -bb will pipe up with his call and web site.... They
> >are great filters!!
> >Hope some of this info is of help.
> >73
> >Gunther Meisse
> >W8GSM
> >AMSAT LM: 594
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