This is a continuation of a previous post which I made:
Here's the update, not fully baked but hopefully useful.
This is a continuation of a previous post which I made:
Here's the update, not fully baked but hopefully useful.
I have constructed two 1/4 wave ground plane antennae, one for transmit and one for receive for use with the Linx Technologies HP series of 900 MHz transmitters and receivers. (My wife commented about the plastic box on the kitchen counter with the antenna....got to love her! She knew what a ground plane antenna looks like.)
For this test, I placed a battery operated transmitter on my mailbox and a computer powered receiver in my basement below ground (obvious) and checked the signal using a National Instruments PCI-1200 card and software with appropriate filtering and processing software (my VI is available for anyone who is interested....just let me know).
At at distance of 100 feet with an underground receiving antenna I judged the received signal to be full quieting. The NI software indicated that the received signal is 20 dB below background noise with no modulation. Following the mantra of responsible researchers I must declare that further research is needed and send money to......oops...forget that!
Anyway, so far this Linx equipment has performed to the point where I will state that it is a viable means of short range linking to part 15 AM transmitters.
I plan to perform some long range test shortly but my encouragement by the initial success has promped this report.
Neil
Neil, I know you probably know this, but here it goes for those who don't.
By modifying a part 15 Tx in any way from it's certified configuration will void certification. that means modifying a certified tx to have a ground plane antenna like neil did would void the certification on the unit.
Thank You,
Rev. Robert P. Chrysafis
Universal Life Ministries
http://www.ulc.org
Moderator Hunterdonfree
http://groups.yahoo.com/group/hunterdonfree
Rev. Robert,
You raise an interesting and good point. The devices I described are not FCC certified. They are supplied as modular components intended to be used in equipment which, if marketed, would need to be certified as a complete unit.
As supplied, these units will not function without the addition of components (power supply, antenna, frequency selector switch, power supply filtering components, audio conditioning, and mechanical support and enclosure for examples) thus they could be considered as components rather than functioning transmitter and receiver. They are also not intended to be kits since none of these outboard components is supplied.
The argument could go either way, but it appears that my assemblies are home designed and built as is permitted by the FCC part 15 rules. If one feels that this is in a gray area and is not comfortable with this interpretation then it would be best not to use the units.
Neil