On Thu, 26 Mar 1998 19:17:23 -0500 CCSystems writes: >At 10:27 AM 3/26/98 -0800, "Randie Ohtsji [4555]" wrote: >ground. Depending upon the amount of metal (or lack thereof) attached >to >electrical ground, you could see quite a range of performance. Try >adding >one or more one-quarter wavelength ground-connected radials. I haven't dealt with any of these modules but all the 300 MHz garage door transmitters I've taken apart used a loop antenna. This saves space and avoids the need to have a "ground" in a hand-held plastic box. A simple loop of wire can be tuned to resonate over a large frequency band (limited somewhat by the dimensions of the loop, which should be somewhat less than a full wavelength in circumference and enclose as much area as possible) by opening it and placing an adjustable capacitor at the gap. You may be able to feed the transmitter in right across the tuning capacitor as well, but better results might be obtained by using part of the loop as a matching section: --------------- | | | |---Cm--- TX "hot" | | | | ------------Ct--------- TX "ground" In order to tune the antenna up it helps to have a better way to measure the transmitted field strength other than taking the receiver out to maximum range. One simple approach would be to remove the receiver antenna and/or place the receiver in a shielded box so it is very insensitive. Then maximum range would be very short. A field strength meter can also be constructed from an antenna feeding a rectifier diode and a sensitive analog meter. Note that working with UHF in close proximity, a lot of peaks and nulls in the field will be noted. After each adjustment, move the transmitter or receiver to a "peak" location and see if it is better (i.e. longer range) than the last one. In the initial design, make Ct and Cm both variable and adjust for best field strength. Try different positions of the coil tap to see if any improvement is noted. In a final version, the tap position and Cm could likely be fixed, but the antenna's performance will be rather sensitive to Ct, which should be adjusted on each individual unit. Don't neglect that improving the receiver's antenna would also increase range. If a strong source of interference is close to the receiver, then improving the receiver antenna won't help the signal to interference level much. The interference needs to be eliminated at its source. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]