Sent: Saturday, March 08, 2014 10:25 PM
Subject: Re: LF: Microphone via WLAN (WiFi) ?
Hi Markus,
Am
08.03.2014 21:49, schrieb Markus Vester:
Hi Stefan,
that one looks like an analog video system,
2.4 GHz FM, with a dedicated receiver box. I once owned a similar set and
attempted to transfer 137 kHz directly through the video channel, without a
mixer. But with the strong in-band utility stations, the dynamic
range seemed too poor.
How many dBs?
- From memory, I'd say up some
45 dB demodulated video SNR, at least when the TX was close to the
RX. Scaled from 5 MHz to 1 Hz this sounds quite high (112 dBHz),
but in spite of some preemphasis the noise density wasn't spread evenly
across the video bandwidth. At the time I didn't measure dynamic range
properly, maybe I should take another look. Today I'd be worried of 2.4 GHz
colliding with other users, eg. my own WLAN.
On the other hand I'm not sure whether WLAN /
WiFi standard would be the best choice either when looking for low battery
drain.
What could be the alternative? It must not be a big project with special
parts, a project for experts. Ideally part 2 of the system, described in my
initial mail, should appear as a normal external USB soundcard to the
PC.
But generally you know what i mean or thinking about?
There
are cheap soundcards with 100 dB dynamic range, with some luck even 120 dB (in 1
Hz).
- 100 dBHz is not difficult. At 48 ks/s this is
just 56 dB in Nyquist bandwidth, or 9 effective ADC bits. Cheap
Bluetooth devices should be able to get that far. It should also be
achievable by a wide-FM link, audio or video.
They all run at USB, i.e. 5V, maybe even 3.3V is OK for the chip. And also
the WLAN chips, running at 5V, consuming just a few 10 mW. I also saw cheap high
gain WLAN directional antennas at amazon...
- Maybe even a few 100 mW. Switching WLAN
off in an Android device significantly increased battery life.
I'm considering to start a request to the DARC, maybe
DH5FFL, you know him? He will at least know who's the man for such a project!
Maybe DF1TY, you know, from the CQDL ;-)
73, Stefan
73,
Markus (DF6NM)
Sent: Saturday, March 08, 2014 9:11 PM
Subject: Re: LF: Microphone via WLAN (WiFi) ?
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