Don Liu <@RUTGERS.EDU,@orstcs:liud@guille.ECE.ORST.EDU> (02/21/90)
Recently I fixed several minor problems of my new Sangean receiver. I am posting the followings in hope that some of you may use it as reference. The problems are: 1) Inacuracy in the synthesized frequency 2) Audible "hiss" 3) Crossmodulation (that is, strong local stations interference when using a good antena) My fixes are: 1) open the back cover and remove the top PC board. Set the bandwidth switch to "narrow" and tune to a weak yet clear signal. Adjust the tunable capacitor to center the frequency (very easily done). 2) Since the volume of this radio is ample, I reduced the audio gain by 50%. This cures the hiss, makes the volume control smoother and results in a better audio quality. The max volume is still enoughly big. To do this, reduce increase the two feed-back divider resistor from 100 ohm to 200 ohm. They are in board labeled B, and are connected to the audio amp pins 3 and 12 thru two 100uf caps. (symetric since there are left and right channels) 3) You may have crossmodulation if you find that a good antena would make reception worse. reduce the RF gain will help reduce the cross modulation, but the redustion is often not enough. There is a 68 ohm resistor connecting the RF gain potentiometer to ground. Shorting this resistor will increase the gain control range greatly thus fixing this problem. Another surgury I have done to my radio is to install 4 lead-acid batteries into the battery compartment and connect the "+" to power jack input. This way, a 24-hour charging will give me 3 month of play. The battery I used are 2.5 amp-hour type and is of same dimension as the D cells. I got them from a local e-junk store. Happy SWLing!
Dave Bakken <bakken@ARIZONA.EDU> (02/23/90)
In article <16096@orstcs.CS.ORST.EDU> liud@guille.ECE.ORST.EDU.ECE.ORST.EDU (Don Liu) writes: >Recently I fixed several minor problems of my new Sangean receiver. >I am posting the followings in hope that some of you may use it as >reference. > >The problems are: >3) Crossmodulation (that is, strong local stations interference > when using a good antena) [ the fix] >3) You may have crossmodulation if you find that a good antena would >make reception worse. reduce the RF gain will help reduce the cross >modulation, but the redustion is often not enough. There is a 68 ohm >resistor connecting the RF gain potentiometer to ground. Shorting >this resistor will increase the gain control range greatly thus >fixing this problem. Thanks for the info - this sounds really helpful. Just to make sure you are as precise as you sound: does mod #3 increase the gain control or just shift it down? Having less gain would be really nice for some instances, but, of course, sometimes you need high gain for strong signals. Also, are there any possible negative side-effects or loss of other performance by the mods you recommend? Thanks. Dave -- Dave Bakken Internet: bakken@cs.arizona.edu 721 Gould-Simpson Bldg UUCP: uunet!arizona!bakken Dept of Computer Science; U of Arizona Phone: +1 602 621 8372 (w) Tucson, AZ 85721 USA FAX: +1 602 621 4246
"Stephen M. Linscott" <LINSCOT@RICEVM1.RICE.EDU> (02/23/90)
I meant to send this to the list. Loose nut on the keyboard!! :-) ----------------------------Original message---------------------------- On Wed, 21 Feb 90 05:07:35 GMT Don Liu said: >Recently I fixed several minor problems of my new Sangean receiver. >I am posting the followings in hope that some of you may use it as >reference. > >The problems are: >1) Inacuracy in the synthesized frequency >2) Audible "hiss" >3) Crossmodulation (that is, strong local stations interference > when using a good antena) > >My fixes are: (stuff deleted) >3) You may have crossmodulation if you find that a good antena would >make reception worse. reduce the RF gain will help reduce the cross >modulation, but the redustion is often not enough. There is a 68 ohm >resistor connecting the RF gain potentiometer to ground. Shorting >this resistor will increase the gain control range greatly thus >fixing this problem. (more stuff deleted) >Happy SWLing! The DX-440 already has the RF gain mod. The print shows the 68 ohm resistor as "not present", and my meter confirms that the bottom of the pot is grounded. BTW, the board layout picture has the gain and BFO pots labeled backwards! 73 - Steve -