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Re: # Downconverters and coax imp.



The 2400 MHz input to your downconverter is normally 50 ohms. If you need to
locate the preamp a few feet (and no more than a few feet) from the
downconverter, use good quality 50 ohm cable or hardline. 

The output of the downconverter at 123 or 144 MHz is nominally 75 ohms, and
losses are of little importance after the downconverter. Use the cheapest 75
ohm TV cable you can find. If you drive by an apartment complex at the end of
the month, people often throw the stuff out when they move.

Dan Schultz N8FGV

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Jeff WB3JFS asks:

Hi all!

Now that it appears that my 2.4 GHz downlink works, with much needed
additional improvements, I have a question about MMDS downconverters and coax
impedence. Most D/C would normally use 75 ohm coax as their transmission
needs. If I put a preamp at the antenna and the D/C a few feet from it, then
back to the rig, I would need to run some low loss coax like LDR400(?), etc.
and that and most of the coax in this catagory is 50 ohms.  Does it really
have much of an affect on the overall system?  From what I've been reading,
the difference between 50 and 75 ohm coax is negligiable except for over
extreme long runs, over 150 feet.



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