Re: Guy Atkins' E100 IF Filter Modification Article


Steve Ratzlaff <steveratz@...>
 

As the guy doing "official" filter mods on the E100, if you send your radio to me, I would like to comment on that article. If you're going to install a filter yourself, you should remember some things in addition to what the article said. Be very careful unsoldering the stock IF filter; it's easy to lift the pads on the bottom of the board if you use too much heat or leave the iron on the pads too long. I use a soldersucker and a fine tip on the iron; I haven't lifted any pads for the last 5 or more radios I've worked on. Once the solder is removed, use a fine tip small screwdriver to rock the filter leads on the bottom side where the pads are, and free them from any remaining solder. On the top side, use the same small screwdriver to pry the filter out--you can use the large electrolytic cap on one side of the filter as one lever point for the screwdriver and the small electrolytic cap on the other side of the filter as the other lever point. Do not pry on the other two sides where the FM monolithic filters are!! Usually the filter pops right out after several back and forth prying movements, if you've removed all the solder from the pads and freed the leads from the pads. Inspect the pads after the filter is removed; all 3 pads must be open, you may need to use the soldersucker to remove more solder so the pads are open, or use a toothpick to clear the holes while heating the pads.
When removing plastic from the frame for the new, larger filter, don't bother using a Dremel tool. It takes less than a minute to use diagonal pliers to snip out the plastic. Note that the picture in the article shows too much plastic removed. The lanyard post must also be removed, and of course the lanyard. (Remove the screw on the top side going into the lanyard post first.) Note too that the plastic needs to be removed more to the left than the picture in the article shows. The filter MUST NOT extend under the display board (as the article photo wrongly shows)--otherwise you are very likely to short parts on the bottom of the display board. Cut out enough plastic, with the lanyard post, so the filter sits in the frame more to the left and is clear of the display board. Once the plastic section with the lanyard post is removed, there is enough space for the filter to fit and be completely clear of the display board. Note too that the "ground" of the main board where the new filter coax cable grounds attach is not a true ground, but in fact is the positive voltage supply. But the display board shield (on the bottom of the display board) is true ground. Make sure the exposed ground of the new filter coax cable connection to the board does not touch the bottom of the display board! I use a piece of black electrical tape over the coax ground point to make sure it can't short to the bottom of the display board.
Make sure you have wrapped the whole new filter with  very thin insulating material; I use clear box tape. There is also an RF choke on the top side that can touch the left side of the filter; I carefully bend that choke out of the way so it doesn't touch the filter.
This is not an easy mod to do, by any means, especially if you are trying it for the first (and only) time, on your own E100. Use the info from the article plus my updated comments, take your time, and you hopefully will have a successful filter installation, and the radio will work when you're finished! The new filter works fantastically well compared to the stock very-wide, off-frequency filter.
Incidentally, reports of the stock radio being 1 or 2 kHz off in display are totally related to the cheap stock filter. I've swept several of those stock filters on the bench, and most have their peak several kHz away from the desired IF center at 455 kHz. The new filter is centered precisely at 455kHz and the radio will now always display the correct tuned frequency. All the new filters I've measured on the bench are 2.5 kHz bandwidth. Depending on your hearing, you may find the slight loss of treble response of the much narrower filter to be worth off-tuning up or down 1 kHz to restore some treble. My (old) ears don't notice improvement by off-tuning.
73,
Steve

----- Original Message -----
Sent: Saturday, December 06, 2008 1:44 AM
Subject: [ultralightdx] Guy Atkins' E100 IF Filter Modification Article

Hello Guys,
 
     Recently a trio of fanatical Washington state experimenters finally succeeded in creating a modified Ultralight radio with both extreme sensitivity and extreme selectivity-- the "fully modified" Eton E100.  Designed by John Bryant, Guy Atkins and myself, this little DXing dynamo uses an innovative Slider loopstick for great sensitivity, and a Murata CFJ455K5 IF filter for razor-sharp selectivity.
 
     The designer of the selectivity modification, Guy Atkins, has written a very interesting article on this great technical breakthrough, which gives the tiny E100 selectivity normally only found in expensive table receivers.  Guy's classic article has just been uploaded to the Ultralight Radio File section of DXer.Ca, the home web site of the fast growing Ultralight Radio enthusiast group.  With many photos and clear technical instructions, Guy's article can assist any technically experienced hobbyist in creating his own super-selective E100, to join in the legendary fun of chasing transoceanic DX with a modified pocket radio.  Enjoy!
 
     73,  Gary DeBock
 
      



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