Weather Station Hardware > Davis Instruments Weather Stations
Weatherlink console - intermittent loss of outdoor temperature / humidity
johnd:
--- Quote from: Mattk on December 27, 2024, 09:44:50 PM ---
--- Quote from: kba293 on December 27, 2024, 08:53:57 PM ---.... Does changing the station number shift the transmit and receive frequency band, or does it just encode the bits differently within the same bandwidth?
--- End quote ---
Changes the freq within the region's spread spectrum band.
--- End quote ---
A common misconception. AIUI the frequency schedule/sequence remains the same whatever the channel number, as does the encoding.
What changes is the delay from some master clock reference before each data packet is sent, which is increased by 1/16 second for each channel increment. It's not well-explained exactly how the clock timing works (except presumably in the documentation from TI, who I believe are the chip makers for the CC series of wireless chips) but it seems like all transmitters within range of one another can somehow synchronise their signal timings to each other. (hence the syncs, resyncs etc stats in the wireless diagnostics).
The effect is similar to if each transmitter were broadcasting on a different frequency, ie if 2 transmitters are attempting to use the same time slot then the signals could interfere and is a common cause of apparently poor reception, but moving to different time slots will clear the problem.
Mattk:
Obviously some don't really understand the generic functioning in regard spread spectrum.
johnd:
--- Quote from: Mattk on December 28, 2024, 06:04:20 AM ---Obviously some don't really understand the generic functioning in regard spread spectrum.
--- End quote ---
Yes, so it would seem. [tup]
@mattk: Was there something in my explanation that you don't agree with? If so what is it? Always happy to learn and be corrected. Some aspects of the VP2 stations are not well documented by Davis and the wireless protocol is one example.
Mattk:
@johnd yes the question was does the Freq change and the very simple answer is yes it does and without getting into the complexities of FHSS that is the simple answer. 900Mhz Spread Spectrum which Davis uses which includes the US 915MHz, EU 868MHz, AU 915MHz and NZ 921MHz bands uses Frequency Hopping which changes frequencies within a specific range.
Freewave systems for example make extensive use of 900MHz Spread Spectrum technology with the hopping patterns controlled by a FreqKey, hop table size and number of separate channels. One can see a very similar basic setup with Davis and the Point-to-Point and Point-to-MultiPoint repeater network design.
Just a note regard Davis US/AU 915. The US 915MHz and AU 915MHz were both once the same (similar) 902-928MHz range then AU sold half the spectrum to a Telco and the unlicensed AU component left was 915-928MHz and that created all sorts of crap.
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