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Hi Stefan was there any problem with AGC on the MIC
socket of the PC?? I doesnt seem to bea problem but I wondered if it explains
your "strange effect".
Thanks for sharing that was a very interesting
evaluation.
Alan G3NYK
----- Original Message -----
Sent: Tuesday, March 18, 2014 9:47
PM
Subject: Re: LF: Bluetooth instead?
Hi all,
I'm continuing with my report about experiments
with a wireless AF bluetooth bridge that will (hopefully) allow to transfer a
VLF or LF/MF spectrum between antenna and receiver.
Meanwhile i bought
2 RTX1 units (http://www.amazon.de/B-Speech-Stereo-Bluetooth-Receiver-Transmitter/dp/B00CB3KGYE/ref=sr_1_1?ie=UTF8&qid=1394458092&sr=8-1&keywords=B-Speech+RTX1+Stereo+Bluetooth+Receiver+und+Transmitter)
One
is used as the TX and the other one for the RX. It is a stand alone system,
actually the PC does not notice anything from the bluetooth stuff. That means,
no software or driver or firmware and all that stuff is needed, just these 2
small devices.
Now, measurements:
The measurements were done with
SpecLab and the RX connected to the MIC input of the PC where SpecLab is
running.
Noisefloor: -100 dBHz, sometimes popping up to -90
dBHz.
Dynamic range (tested with a single sine tone at 1500 Hz,
between Intermod and "O-copy"): 66 dB
Dynamic range (tested with a
single sine tone at 10000 Hz, between Intermod and "O-copy"): 45 dB
(distortion acceptable)
High cutoff frequency: ~ 20 kHz
Low
cutoff frequency: ~ 20 Hz
Power consumption of the transmitter
at 5 V DC (mini-USB) (including the red LEDs indicating a connection to
the receiver): 59 mA (~0.3 W)
Spectrum distortion / frequency
response: I've replayed a VLF recording for that test, including sferics,
MSK stations, the Alphas... Left is original, right is passed though the 2x
RTX1 system
https://dl.dropboxusercontent.com/u/19882028/VLF/L%3Doriginal_R%3DpassedthroughRTX1.png
White
noise frequency response:
https://dl.dropboxusercontent.com/u/19882028/VLF/white%20noise%20test%20RTX1%20left%20in%20right%20out.png
Strange
effects: When suddenly removing the noise input, the output just slowly
return to the background noise of the system. This can't be good for
QRN!!
https://dl.dropboxusercontent.com/u/19882028/VLF/Rauschsprung.png
There
can more QRM traces when the USB power supply is used on the RX. A traditional
transformer power supply or a battery improves the situation. However this is
not critical above 3 kHz.
Conclusion:
NOT suitable for our
purposes! :-( I'll send them back...
...and i'll spend more time to
learn what i have to choose and how to configure, maybe even homemade SMD ICs
allowing to transfer much more bandwith without A2DC codecs and such a
stuff.
73, Stefan/DK7FC
Am 10.03.2014 14:48, schrieb Stefan
Schäfer:
Hi
all,
I want to share my recent results of experiments trying to
arrange a wireless AF connection, which can be used for a VLF antenna or any
other RF spectrum such as 630m and 2200m bands. The goal is always to
decouple local QRM sources from a RX antenna installed in a quiet(er)
location, to improve the RX capability of the amateur radio station in noisy
environments.
It looks like there are some cheap and useful devices
on the market, using bluetooth technique. Last night i did some first tests!
First i simply wanted to transfer music from my smartphone to my
netbook, using the bluetooth function (never used that before). This worked
very well in the first attempt! There was no audible sound quality loss. The
sound was played on the speaker of the netbook. But, more precise, it is not
the speaker but the standard audio device! :-) That means, you can define
virtual audio cable 1 as the standard output device! And here we are, we can
feed the audio signal to SpecLab, without additional software except VAC
which runs on many LF/MF/VLF PCs anyway. This allowed me to watch the
spectrum and see if the signal is distorted or drifting or anything else.
Again there was no audible and visible indication of a significant quality
loss.
Next i wanted to get an impression about the possible dynamic
range of this wireless bridge. I uploaded a VLF recording (the original one
from 4X1RF, including my 8970 Hz signal :-) ) as a wav file to the
smartphone and played it via the bluetooth link. The signal level in this
recording is quite low and depends on the volume setting of the smartphone.
Here i saw that the background noise of the system, i.e. the dynamic range,
is 120 dB, with some noise lines/peaks peaking to -100 dB. This looked very
fine! Also the full 0...24 kHz spectrum was transferred via the bluetooth
link and it was possible to lock SpecLab to DHO38 which was included in the
recording! Next, this allowed me to watch the frequency drift of the system.
Looks quite normal for a crystal, i.e. useful for our purposes.
Now
i want to try bluetooth for VLF and LF reception and i want to do some
distance tests. 2 km distance, using a directional antenna, this would be
very fine.
At amazon, there are relatively cheap bluetooth
transmitters with an external antenna, e.g. http://www.amazon.de/B-Speech-Stereo-Bluetooth-Receiver-Transmitter/dp/B00CB3KGYE/ref=sr_1_1?ie=UTF8&qid=1394458092&sr=8-1&keywords=B-Speech+RTX1+Stereo+Bluetooth+Receiver+und+Transmitter
These do even have an external antenna and will allow to use a high
gain antenna for higher distances and help to avoid collisions with other
signal sources. Since my netbook has an internal bluetooth adapter and since
i now know that the received signal can be fed to SpecLab, it is worth to
buy the transmitter and to do further tests. This one seems to be one of the
stronger versions with 100 mW RF power. Hopefully the power consumption is
acceptable...
I will report about the progress...
73,
Stefan/DK7FC
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