[NLRS] Subject: DEM 222-28 Interfacing ?

[W0ZQ at aol.com]

In a message dated 7/30/2007 9:07:54 P.M.  Central Daylight Time, 
Melvynkc0p at aol.com writes:
I now have a DEM 222-28  transverter that only requires 1mW of
drive. The  Icom 706 shows 4 W out  key down on a Bird Wattmeter
at the lowest RF drive  setting. How do we  make up for the
difference ? That sounds like more than 30  dB of  attenuation
required and then relays around the pad on receive.

What  have others done ?

Mel KC0P 


One suggestion.    Terminate the 4 watt output with 50 ohm non-inductive 
resistors like the old  style carbon comp resistors ..... I think metal film may 
work depending on the  type.   Two two-watt 100 ohms in parallel would work, or 
any  combination that is close to 50 ohms and that can handle 4 watts, like 
four 220  ohm in parallel, etc, etc.   The purpose is to provide a termination  
load and the exact value is not critical as long as the Icom 706 is happy  
sending RF into it.

>From the top of this termination tap off some 28 MHz  RF with a small value 
cap like a 1 or 2.2 pf cap.   At 28 MHz, that  would be equivalent to about 3 
to 5 K ohms.   Feed that RF from the  cap into a 100 to 500 ohm pot here the 
pot wiper goes to the input of the  transverter, one end of the pot is tied to 
ground and the other end to the 1 or  2.2 pf cap.   

The small value cap and pot act as a power  (voltage) divider.

Start with the pot adjusted so that its all the way to  the ground end and 
weakly whistle into the mic while watching the 222 output for  any response.  
Slowly turn up the pot with the 28 MHz RF applied (light  whistle) while 
watching the 222 output level for a response.   If you  don't get enough drive (pot 
is turned up to max), up the capacitor value to 10  pf and try again.

73, Jon
W0ZQ  




************************************** Get a sneak peek of the all-new AOL at 
http://discover.aol.com/memed/aolcom30tour