Re: [amsat-bb] Drake 2880

["Dave Metz" <Dave.Metz@xxxxxxxxxxxxxxxxx>]

 > From:          "Joel B. Black" <jbblack@mindspring.com>
 > To:            "AMSAT BB" <amsat-bb@AMSAT.Org>
 > Subject:       [amsat-bb] Drake 2880
 > Date:          Sun, 5 Mar 2000 16:01:28 -0600

 > After reading many different articles concerning the Drake 2880 mods, I
 > realized that the Drake originally worked with TV.  Now, isn't TV 75 ohms?
 > What happens to your Z if you feed from your 50 ohm output to the 75 ohm
 > input of the 2880?  Is there an impedence bump?  Is this really something to
 > be concerned about?
 > 
 > Tnx es 73,
 > 
 > Joel B. Black, K2SAT

Dear Joel,

Absolutly not.  The worst case SWR would be 1.5:1 with a 50 ohm to 75 ohm
mismatch.  Take a look at a Smith Chart and you will see that this is so.
No, you do not need a balun.  In fact, the balun would create a greater loss
then the mismatch would.  

Note that 75 ohm CATV coax is widely used on FM UHF repeaters in 
50 ohm systems and it works just fine.  I use it myself.

--73-- David WA0AUQ



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