DENON TU-1500
Description: AM/FM/FM Stereo RDS tuner Rotary tuning/preset knob 40 station random AM/FM memory Dot Matrix alpha-numeric display Radio Data System (RDS) with Radio Text function Wide/Narrow IF selectivity control Infrared remote sensor eye on front panel Manual character input; station name (8 characters) Low impedance output (100 ohms) Optional RC-824 infrared remote control RCA unbalanced outputs Rack mount kit included 2U rack spaces. $359.00
Altho no longer sold, this tuner from Denon is a favorite of FM DXers'. I have used one for many years as a general tuner. One problem I noticed was alot of co-channel slop fom many semi-local stations, blocking many frequecies from use for DX. With several 50KW, one 100 KW station nearby, I know there is not much I can do about it. However the slop form the many semi locals can be cured by usuing narrow filters in the IF stage of the tuner. (Note however that the modification needed to install the narrower filters ( for better selectivity ) on any new tuner will likely void the warranty because most tuners aren't made with the idea of replacing the filters to they're 'hard-wired' rather than having sockets.
Greg Gortman of Lexington, Kentucky offers a variety of high quality MuRata 10.7 MHz IF filters for FM receivers and tuners. MuRata filters are considered by DXers and audiophiles to be the best available. Until now these filters were very difficult to acquire in small quantities. I emailed Greg ( lcs175@yahoo.com) and received a speedy reply. Taking Greg's advice,I decided to go with the 180 khz Low Loss filters first, I may slide down to 150 but wanted to test the 180s first. He mailed out the filters the same day.
The cost per filter is $1.50 each. Shipping is fixed at $2.00 for any quantity in the U.S.A. Pay with cash, check, or money order. There is no minimum order, no small order/processing fee, and no outrageous shipping or handling fee. To order filters, e-mail to lcs175@yahoo.com Dont forget to include your shipping address. He ships most orders immediately, ahead of payment in order to speed the process. Mail your payment for the filters to Greg Gortman 3469 Keithshire Way Lexington, KY 40503
AVAILABLE FILTERS
110 kHz – For serious DX work, this extremely narrow filter is useful for reducing or eliminating adjacent channel splatter and revealing those weak stations next to strong locals. This filter is originally designed for separating stations in Europe where channel spacing is only 100 kHz, as compared with the 200 kHz standard in North America. Insertion loss is listed at 7.0 +/- 2.0 db.
150 kHz Low Loss – This very useful filter is the same value filter used in the super narrow IF setting of the Onkyo T-9090II. This filter has the advantage of a very low insertion loss. Listed insertion loss is 4.5 +/- 2.0 db. The factory super narrow filters in a T-9090II have an enormous insertion loss specification of 14db max, which is common to older filters. Updating older filters with modern low loss ones often yield an increase in signal strength and sensitivity.
180 kHz Low Loss – This filter is an all around performer because it provides maximum signal strength and excellent sound quality. With the lowest insertion loss of any filter available, listed at 3.5 +/- 1.5 db, analog tuners with old high loss filters really wake up when updated with this filter. It is also wide enough to allow RDS information to pass in most cases. Tuners with 3 or more filters are still quite selective using all 180s. This filter is an excellent choice in the wide slots of tuners with selectable IF paths.
180 kHz Flat Group Delay – Also called GDT type filters. This type of filter is designed for maximum sound quality at the expense of slightly higher insertion loss. The insertion loss specification is listed at 7.0db maximum, and I find it provides about the same signal strength as a 150 kHz low loss. It is useful for tuners you use for listening to music or news, or, if you are an audiophile DXer. You can also set up a selectable IF tuner for both high quality sound and DX at the same time by using this filter in the wide slots and 150s or 110s in the narrow. The 180 kHz value still provides very good selectivity for capturing distant stations. Many digital tuners use 180 kHz values in the narrow slots from the factory. I also find that Murata 180s provide the same selectivity as Toko 150s.
OTHER TUNERS THAT CAN BE USED FOR FM DXING
Yamaha T-80 / T-8 (you do need to do filter mods to get the best selectivity out of them)
Carver TX-11 This tuner has 180khz filters in it stock and the specs were about 30db adjacent selectivity without any mod. You can pull the 180s and replace them with 150s or 110s and get much better selectivity, but sound quality suffers.
Onkyo T9090
Onkyo T450 (will also need narrow filters)
LET'S MODIFY THE DENON
With filters now in hand let's install them. I recomend using sockets for the filters so you can change them later if needed. You can use pieces from an IC socket or a SIPP socket.. I keep 40 pin sockets handy for project like this. They run about $ 1.80 from Jameco Electronics Part number 78642
Remove the 4 side scres and 2 on the back holding the cover. There are screws holding the Antenna input and the audio output jacks. Remove those scres as well as the 2 screws holding the circuit board.
With a felt tip pen mark the "RED DOT" location on each of the 4 filters. There are 2 plug in cables that run top the display board. Carefully remove them.... They are different sizes so you can't mix them up. I left the power supply connection in tack as I was able to turn the board over without removing it.
Don't hurry...(I did) I nopticed that I had marked one of the filters incorrecly. Forunately, I had a bunch of pictures I could refer back to. If you look at the far left filter above, the red dot doesnt match up with the black dot. I found that I had marked the filter incorrectly.
Then using solder wick, remove the filters. Carefully solder in the 4 SIPP sockets. Check to make sure they are soldered well with no trace shorts, Plug in the filters matching thr red dots with the marks you made earlier. Replace all the screws in reverse order.
Re-install the tuner, and start DXing....
Prior to installing the filters, I did a complete FM Bandscan. I then did a re-scan following the installation of the new low lss filters. The reults were very encouraging. Altho I didnt get rid of the co-channel proglems from my high powered locals, I was able to open up 13 channels that can now be used for DXing. I also noticed that some of the "marginal" stations are much "cleaner"
COMING SOON: We hook up a KatRuud RDS Monitor with software
