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Guy Atkins' E100 IF Filter Modification Article
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Gil Stacy
Steve,
Thanks for the tips. It would be great if you could move this post to the files section of the group. Tnx. 73 Gil |
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Steve Ratzlaff <steveratz@...>
Hi Guy,
You marked the filter common/ground pin properly. This
"ground" is a matter of convenience for the circuit designer. It's an AC and RF
ground not "ground" as referred to the common of the rest of the board or to the
negative terminal of the battery or external power supply. As long as the filter
sees an RF ground then it's happy; it doesn't matter if there's actual voltage
on it (which there is in this case). And the stock filter is a plastic case so
never would see any possible shorting to the "real ground" that the bottom
shield on the display board presents.
Steve
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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
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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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