Denon UDM31 tuner module

Source: http://sci.techarchive.net/Archive/sci.electronics.repair/200608/msg01881.html
From: Thomas Tornblom <thomas@xxxxxx> Date: Fri, 25 Aug 2006 21:21:16 GMT
My kids have a Denon UDM30 and UDM31 micro receiver/cdplayer combo, which works great, except for one thing, the tuners are too wide band. We have a local FM station on 106.5 MHz, transmitting with 4 kW, and we're trying to tune into a station transmitting with 1 kW at 106.3 MHz in Stockholm, which is about 80 km from here. I have stacked two giant FM antennas with a proper stacking filter, directed at the Stockholm transmitter, and I have great reception on weak stations way farther away. We also have great reception of a 1 kW transmitter at 104.7, transmitting from the same location as the one we're interested in. Using an old antenna instrument I can see that I have more than a 30 dB difference in signal strength between the 106.3 and 106.5 signals. I have three receivers which receives 106.3 with fair to good quality, a Denon AVR3805, an old digitally tuned Kenwood receiver, and an old analog tuner. I have also tried an old digitally tuned Pioneer car stereo, which had absolutely no problems receiving 106.3 from the antenna wiring in my house. The small Denons have big problems though, and I believe the problem is that the IF bandwidth of the filters in the tuners are too wide and they can't detect the weak 106.3 from the strong 106.5. I have seen a few sites on the net recommending changing the ceramic filters to something narrower, and that seems like a reasonable and fairly simple change. Is there anyone who have experience and/or schematics for these tuners? I looked into one of them, and the tuner appears to be a separate small module, which I didn't open as it seemed like a bit more work than I was prepared to set aside today. What bandwidth and how many are the stock filters? I assume something on the order of 280 kHz, and I'm contemplating replacing some of them with 180 kHz filters. Denon UDM31 tuner module 1
Denon UDM31 tuner module Oh, and they both have RDS, which I believe may need slightly more bw to work reliably.