View Full Version : Dropout with FM25B
11-15-2002, 12:59 PM
I built the FM25B this week and am testing it for use in a single large room (church) about 60X40ft. I seem to have significant dropout of the signal in many spots in the room. I am just using the included whip antenna as I assumed it would be sufficient to cover one room. Can anyone offer insights as to the cause? Subtractive reflections or not enought power?
Also, what is the correct impedance for the FM25B output? 50 or 75 ohms? I see posts where people have used both 50 and 75 ohm coax to connect to it but I assume that one is preferable.
11-18-2002, 02:08 PM
I too, am using the FM-25B in a church of similar size, and didn't experience dropouts like you describe. Our entire campus can be covered with the whip antenna, and the power set at about 1/2. Even at its lowest power setting, the signal was only occasionally fading.
We are using it currently to provide audio to our crying baby area as well as inexpensive assistive listening. I hope to expand the system with an external antenna to micro-broadcast to the neighborhood, including some shut-ins from the parish.
What type of radio are you testing with, walkman or boom-box?
If testing with a walkman, I suggest first of all testing with a digital receiver, because they're more stable. Also, your reception will vary widely with the position of the headphone cable, because walkman-type receivers use it as an antenna. I've found the most consistent results occur with digital walkmans in the $30 price range.
Try testing with a digital boom box to confirm if you are having problems. If your power is already max-ed out, then go over your work carefully, paying special attention to parts orientation in the PLL section of the circuit.
As for cable impedance, these low power kits aren't generally particular as to the impedance.
[ November 18, 2002: Message edited by: Paul Pederson ]
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