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Showing posts with label greece. Show all posts
Showing posts with label greece. Show all posts

Monday, October 25, 2021

Putting a Ceramic Filter in the "Mate for the Mighty Midget" Receiver


It is really simple.  I had one of the +/- 3kHz (6 kHz wide) 455HT filters on hand.  The spec sheets call for 2000 ohms at both ends, but looking at the schematic it appeared that I already had high impedance on both sides of the filter.  I put a .001 uF cap on the input side to keep the DC voltage off the filter (see above and below). This capacitor allows us to avoid the dreaded problem of electro-migration that is so nicely described by SV8YM here: 


Tasos also provides a good description of the innards of those little black boxes that contain ceramic filters. 

Once you get the filter in your receiver, you have to carefully place the BFO signal in relation to the filter passband.  I have trouble properly sweeping 455 kHz filters -- my HP8640B will not go that low.  Nor will my Antuino (I need to modify the code -- someone help me please).  I know the NanoVNA will do the job, but I just couldn't seem to get it to work.  So I went "old-school" and manually swept the filter using my FeelTech sig gen and my Rigol scope.  This gave me a rough idea of where the passband was.  I put the BFO on the low end of the filter passband, at 451 kHz.

   
With this filter the MMM RX has become a real asset.   The 6 kHz bandwidth allows for nice reception of both SSB signals and AM sigs.   I may try to use one of the +/- 2 kHz filters  (4 KHz wide), but so far I have not been able to find a source for this part. 

Monday, November 11, 2019

SV3ORA's Amazing Homebrew Web Site

Kostas Giannopoulos has  a lot of really great homebrew information on his QRP web site.  It is reminiscent of the JF1OZL site. Check it out:  http://www.qrp.gr/index.htm 

For an example that his apropos of recent ET-2 discussions, Kostas has an extensive page with  many, many versions of his hyper-minimalist rig:  


Link to this project: http://qrp.gr/allbandtrx/

Thanks to Kostas for putting together such a great site.  And I really like the name of the site: Discrete Electronics.  FB. 

Thursday, July 26, 2012

Our Electric Vocabulary


Bob, W8SX, alerted us to this really excellent video. You guys will like it. Thanks Bob!

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