Date: Thu, 4 May 1995 19:55:03 -0400 From: ao944@yfn.ysu.edu (Jack Decker) SETTING THE PROGRAM PRESETS ON THE DRAKE SA24 STEREO ADAPTER Written May 4, 1995 If you have an older-technology TVRO system, you may have a Drake SA24 Stereo Adapter. This unit is used to decode stereo programming when the satellite receiver is monaural. In order for the SA24 to operate, the TVRO receiver must have a jack labelled "subcarrier out" or "sca out" or something similar. This jack is then connected to the SUBCARRIER IN jack on the Drake. The cable used to make this connection should be rated for use through 8 MHz (audio type cable is not recommended). On the front panel of the SA24 there is a PROGRAM switch, which is a knob with positions marked 1-4 and TUNE. The TUNE position is used for manual tuning of stereo subcarriers. The 1 through 4 positions are the presets. Unfortunately, these are set by the factory to positions that are for the most part no longer useful. This is because few programmers, if any, still use matrix or MPX stereo. Virtually all stereo signals that accompany TV programming, and most stereo audio programming is now discrete stereo (or "separate" as it is referred to on the SA24). Here is how the four switch positions are preset at the factory: POSITION FILTER SUBCARRIER A SUBCARRIER B MODE 1 WIDE 5.8 MHz 5.8 MHz MAT 2 WIDE 5.8 MHz 6.8 MHz MAT 3 NAR 6.3 MHz 6.48 MHz SEP 4 WIDE 6.8 MHz 6.8 MHz SEP Of these, the first two are not useful because they are set to decode matrix signals. The third might be useful if you happen to listen to a radio signal that has subcarriers on 6.3 left and 6.48 right (e.g. WFMT-FM, WQXR-FM, CBN Radio Network, American Urban Radio Network at the time of this writing). The fourth is useful if you are watching a TV signal that has a mono subcarrier on 6.8 MHz that you want to listen to. Many users might want to retune some of these positions. In order to do this, you have to remove the cover from the unit. Then, for each switch position, there are four DIP switches and two potentiometers that may need to be set. After removing the cover, you'll see two 8-position DIP switches side by side, Each group of four switches applies to one of the PROGRAM switch positions. The key to knowing which switches are used for what purpose is as follows (please excuse the crude ASCII diagram): < POS. 1 >< POS. 2 > < POS. 3 >< POS. 4 > ON I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I N M M S N M M S N M M S N M M S OFF A A P E A A P E A A P E A A P E R T X P R T X P R T X P R T X P When you want to store a particular program setting, first tune in the program manually (with the PROGRAM switch in TUNE). When you have set it up properly, set the DIP switches as follows: 1) If you had to press the "NAR" button on the front panel, then turn on the DIP switch marked "NAR". 2) Assuming you had to press the SEP button on the front panel, turn on the DIP switch marked SEP. Make sure the two middle DIP switches are OFF. If by some odd chance you actually found a program broadcast in matrix or MPX stereo, you'd set the appropriate DIP switch on and leave the SEP switch off. Note that you should have a maximum of two out of a possible four DIP switches set when you are through, and if two are set, one of them will be the NAR position. In most cases you will also want the SEP switch set. Once this is done, tune the left and right channels using the potentiometers. There are eight of them near the front of the unit, two for each PROGRAM switch position: 0 0 0 0 0 0 0 0 1A 1B 2A 2B 3A 3B 4A 4B The "A" channel is the left channel, and "B" is the right channel. It's easiest to tune these channels if you disconnect the opposite channel's output wire (at the back panel) so that you only hear the single channel you are trying to tune. Note that separate mode subcarriers are sometimes very close together, so it may be hard to tell which is which unless you can do it while tuned to one of those "tone and bars" patterns that has an audible "LEFT - RIGHT" indication. Use a small screwdriver (such as a jeweler's screwdriver) to set the controls. If you want to have a monaural preset, simply set both the "A" and "B" pots associated with that preset to the same (mono) subcarrier. Don't try to tune any of the other controls unless you are absolutely sure of what you are doing (however, if you ARE the adventurous type and manage to discover how to make the unit tune beyond the normal limits [below 5.5 MHz, or especially above 8.0 MHz] PLEASE let me know!). And if the instructions above aren't clear to you, don't attempt any retuning. I believe the above instructions are accurate (they are condensed from the SA24 instruction manual) but cannot guarantee this, and under no circumstances will I assume any responsibility if you muck up your SA24. Follow the above instructions ONLY AT YOUR OWN RISK. Finally, here are a few specs on the SA24 that may prove helpful to someone (again, these are from the manual): IF Frequency 10.7 MHz IF Bandwidth 150 or 500 KHz, selectable Tuning range 5.5 - 8.0 MHz Input Impedance 72 ohms Sensitivity 10 mV Deemphasis 25 microseconds (75 microseconds MPX) Frequency response 15 Hz - 15 KHz Harmonic distortion <1% THD Output impedance 600 ohms unbalanced Output level 250 mV nominal Feel free to include this as part of any FAQ or repository of home satellite/ TVRO information. And remember, if you know how to tweak the SA24 in order to make it tune higher than 8.0 MHz or lower than 5.5 MHz, I would really appreciate it if you'd let me know! Jack Decker Internet address: aa931@detroit.freenet.org (preferred) Alternate internet addresses: ao944@yfn.ysu.edu or jack@grfn.org