CONAR RECEIVER MODIFICATIONS !!!
"....a face only a mother could love."
This mod replaces the speaker
This is not a modification per "se" or maybe it is... you be the judge.
Here is the problem. The CONAR has a built in speaker. Fine and good. But when the enclosure is bolted on, it acts like a small drum and physically magnifies the background noise.
There is another problem as well. The speaker has a small permanent magnet in back that sticks out so far, it touches the T4 IF transformer can. That's the IF transformer right before the diode detector D2!
What happens is that sounds are transmitted through the speaker frame into the T4 IF can. The whole chassis seems to vibrate, and to top it all off, the tight "drum" enclosure makes everything worse.
First thing to do is find a modern speaker that matches the 4 hole pattern. Radio Shack has some I am sure. But I was lucky and found several the fit the hole pattern in my junk box. The new modern speakers have a stronger magnet but they also have a lower profile. The rear end of the magnet is now about an inch away from the IF can when everything is assembled.
The next thing I did was take several strips of thick duct tape and used it to hold the fabric of the speaker grill in place. Then I used 4 small black plastic grommets and place them between the duct tape and the speaker frame, through the four metal screws so that the speaker is now physically isolated from the metal cabinet.
The last thing I did was placed some "peel and stick" rubber feet on the bottom of the metal cabinet of the receiver. This keeps the sound from traveling through the metal cabinet into the desk.
Everything sounds much better now!
I would be willing to bet no one at CONAR or NRI did an acoustics check to see what the effect would be of having the speaker mounted inside the cabinet.
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Conar Transmitter Manual - and - Conar Receiver Manual