G.E. SuperRadio III "DX" !!

[John Wilke K9RZZ]

So here's the motivation.

I like listening to 104.9 WTKM in Hartford, WI. It's 35 miles away and gets clobbered by the very loud Spanish station on 104.7. There a few sweet spots in the house where I can just get WTKM, but that's not acceptable. I've tried making some directional antennas, but that's just not cutting it. There must be a better way!

So I decided to modify my SuperRadio III for better selectivity.

This is not a difficult mod if you are careful and take your time.

Remove the screws from the back cover, remove the all the knobs including the power button on the top. Carefully remove the back cover.

http://members.aol.com/j999w/SR3DX1.jpg

Here's the stock ceramic filter:

http://members.aol.com/j999w/SR3DX2.jpg

The markings indicate E10.7A with the red dot on the left, this is a Murata filter. Checking the list here:

http://www.geocities.com/rbrucecarter/part_numbering_guide.txt

E10.7A center dot SFE10.7MA19 350 950 (750) (3)
E10.7A center dot SFE10.7MA20-A 330 680 (615) (4)
E10.7A left and center dot SFE10.7MA8-A 280 650 (520) 6 (4)
E10.7A left dot SFE10.7MA5-A 280 650 (520) 6 (4)
E10.7AA left dot SFE10.7MA5A10-A 280 590 (480) (2.5)
E10.7AB SFE10.7MA5B10-A 280 650 (3.0)

This filter has a bandwidth of 280khz. This is very wide ... we can do better than this! I'm going to replace it with a 110khz Murata ceramic filter.

I have had good luck recently finding new filters from these two sources:

http://www.dxfm.com/IF%20Filters/IF%20Filters.htm
http://www.stevemcvie.com/DXING.asp

(I've found the SNR filters to be just as good, or better, than the Murata.)

In order to get the circuit board loose, you have to gently pull the pully off the tuning resistor:

http://members.aol.com/j999w/SR3DX3.jpg

and unsolder the AM antenna wires:

http://members.aol.com/j999w/SR3DX4.jpg

Carefully remove some of the hot glue that restricts the movement of the speaker and power supply wires. There is a ground wire on the left side of the circuit board that must be unsoldered. Then you can gently manipulate the board to get at the bottom.

http://members.aol.com/j999w/SR3DX5.jpg

Be careful as you unsolder the old filter. Don't use a lot of heat or pull very hard on the filter (they do break rather easily :o ).

http://members.aol.com/j999w/SR3DX6.jpg

Solder in the new 110 khz Murata filter.

http://members.aol.com/j999w/SR3DX7.jpg

This is an important step! TAKE A BREAK. Get a drink of water, go get the mail, and take a breather.

Now carefully reverse your steps. Resolder any wires you had to remove earlier. Replace that dial pully, and put it all back together.

Now you have a rare G.E. SuperRadio III DX !!

http://members.aol.com/j999w/SR3DX8.jpg

Are you sure you did it right? Plug it in, turn it on, and enjoy.

Here's what WTKM sounded like before the mod. as I sat here in the basement:

http://members.aol.com/j999w/WTKM_PRE.mp3

Now it sounds like this as I tune between WTKM and the offending spanish station:

http://members.aol.com/j999w/WTKM_POST.mp3

I simply park the radio where ever I am in the house, tune in WTKM and enjoy. No more 'sweet spots' for me. :p

Total cost: 90 minutes of bench time and $1 in parts.

I know there is quite a following of the SR3. Hopefully this will help a few of you enjoy it even more!

73,

John K9RZZ

[John Wilke K9RZZ]

I'm really liking the way it's performing, however the tuning is tricky. Tuning of weak stations done with pressure on the knob rather than turning it and it appears that the radio does tend to drift a little (?). With all that in mind, it might be a little more user friendly with 150khz filter instead of 110. I really like the 110 because I need to park next to a very loud station to hear what I want, but for general DXing, the 150 would probably serve well. Certainly much improved over the 280khz stock filter! ;)

THis morning while tuning around with the stock whip, I was listening to both Chicago and Madison, WI stations (~75 miles) and heard both Green Bay and Sturgeon Bay stations (~120 miles).

I'm looking forward to having this in the garage this summer while working on projects.

73!

John K9RZZ