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Re: X-10 RF meter (was Re: XTB II Review)



On Thu, 04 Jan 2007 20:40:24 GMT, nobody@xxxxxxxxxxxx (Dave Houston) wrote
in message  <459d60f2.25084765@xxxxxxxxxxxxx>:

>"Jeff Volp" <JeffVolp@xxxxxxx> wrote:
>
>>"Marc_F_Hult" <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
>>news:ghfqp257tr59qhe472qjbdenvksr4tkouj@xxxxxxxxxx
>>
>>> So a one-off X-10 RF signal strength sniffer/meter could indeed be
>>> constructed *without* programming for ~$15 or so (depending in part on
>>>what is already in your electronic junk box).
>>
>>While I agree a DIY version without a custom PCB or case can be put
>>together cheaply, I don't know of any electronic distributers that offer
>>free shipping.  That can become a significant factor when buying from
>>multiple sources.
>>
>>I had used a receiver some time ago that included an analog RSSI output
>>(received signal strength indicator).  That was useful to determine how
>>to dynamically configure the RF network for best performance.  The RSSI
>>output could be monitored by a VOM.  However, because of the pulsed
>>nature of X10 signals, some type of filter or peak detector may still be
>>needed.
>
>Jeff,
>
>Don't get misled. I've been using these receivers for several years,
buying
>the RWS-374-2 direct from Wenshing in Taiwan until they raised their price
>beyond where it made sense. The Radiotronix receiver is made by another
>Taiwan company.
>
>     http://www.wenshing.com.tw/DATA/RF-MODULE/RWS-374-2.pdf
>
>The Wenshing datasheet has always labeled the two outputs "linear" and
>"digital". I see they have recently started silk-screening "RSSI", on the
>module itself, for the "linear" output but this is misleading as it
>requires further processing to use it as RSSI.
>
>In the absence of a signal, there's a continuous noise output on both the
>"linear" and "digital" pins so just measuring the voltage tells you
>nothing. When I tried a VOM yesterday, there was a negligible difference
>between signal and no signal which is why I then wrote that a PIC is
>needed.

Yes. The data sheet states: "Therefore, we can detect the original baseband
signal by simply low-pass filtering the emitter current.
The average emitter current is not very linear as a function of the RF
input level. It exhibits a 1/ln response because of the exponentially
rising nature of oscillator start-up. The steep slope of a logarithm near
zero results in high sensitivity to small input signals."

So it would appear that at minimum a low-pass filter would be needed. (I
have never examined the output of this module and know only what the data
sheet and Dave state.) Obviously the "linear" and "digital" outputs have
more than just "continuous noise output" or there would be no useful signal
for subsequent use. A simple measurement with a VOM (depending on frequency
response of VOM among other things) is in itself inadequate to determine if
there is "a negligible difference between signal and no signal" if the
signals were to be properly/adequately conditioned. But I have no pertinent
hands-on experience with this module and can't speculate more.

I looked at Dave's web site for the first time in what seems like years.
Looks like he has a wealth of new and old info and efforts. It is good to
see that the ZX-40 (a BX-24 offshoot by a different company) has breathed
new life into the BX24-AHT and Dave both.

Wonderful developments!

Happy New Year ... Marc
Marc_F_Hult
www.ECOntrol.org


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