[RFI] DFing progress

Hare,Ed, W1RFI w1rfi@arrl.org
Wed, 18 Dec 2002 10:36:37 -0500

What I suggest for an attenuator is a simple 10-dB design for a pi-net attenuator. The input Rs go to ground, with a resistor in between them.  For 10 dB, the input and output resistors should be 100 ohms and the series resistance should be 72 ohms.

Now, replace the 72-ohm resistor with a 500-ohm trimpot. You can now set the attenuation to range from a couple of dB to tens of dB. The pad is not a perfect match any more, but on receive, for this purpose, that is just fine. 

Ed Hare, W1RFI
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Internet: w1rfi@arrl.org
Web: http://www.arrl.org/tis

> -----Original Message-----
> From: Pete Smith [mailto:n4zr@contesting.com]
> Sent: Tuesday, December 17, 2002 7:55 PM
> To: rfi@contesting.com
> Subject: [RFI] DFing progress
> I wented to let everyone know that I've succeeded in mating the Moxon 
> rectangle antenna from the March 2001 RFI receiver project to my Icom 
> IC-Q7A handitalky.  I cobbled up the antenna out of aluminum 
> rod, mounted 
> it to a board with screw eyes, and threaded the ends of the 
> rod for nuts to 
> attach the feedline.  The resulting antenna resonated at 137 
> MHz first try, 
> and has a broad front lobe, fair attentuation off the sides, 
> and a very 
> narrow cardioid-style notch off the back, all just as advertised.
> The only small downside is that the thing is almost too 
> sensitive.  Anyone 
> got any suggestions for a simple non-calibrated attenuator 
> that I could put 
> between the antenna and the radio to make it work a bit 
> better close in to 
> the noise source?
> 73, Pete N4ZR
> Happy Holidays
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