[Hackrf-dev] transmitting with one HackRF and receiving with another -- advice needed

[Rachel Citchlow]

Hello all,
I am trying  a setup with two HackRFs with their antenna ports connected to
one another with an RF cable with a 30dB attenuator in between. I would
like to send something with one of them and receive with the other.

My steps were as follows:

1. started with lesson1.grc receiver with center_freq of 97M, and channel
freq of 96.3M. Added a file sink  in parallel with the osmocom source to
save the I/Q samples as received by the HackRF. I thus obtained a data
file, data.bin,  with a part of a song played on the local music channel
96.3.

2. In lesson1.grc, substituted the osmocom source by a file source pointing
to data.bin. Played lesson1.grc and was able to hear the audio the same way
as in step 1. This confirmed that data.bin contains good I/Q samples.

3. Connected the two HackRFs to each other and played a sample signal on
one and received it with the other, saw a strong narrow spike on the
receive FFT plot:
rachel at radio1:~/Documents/playback$ hackrf_transfer -c 10 -f 96300000 -s
2000000 -a 1 -x 20

4. Transmitted data.bin on one HackFR and tried to receive with lesson1.grc
on the other.
rachel at radio1:~/Documents/playback$ hackrf_transfer -t data.bin -f 97000000
-s 2000000 -a 1 -x 20
This did not work. On the receiving end, I saw the FFT plot get several
narrow spikes and generally rise up, but it did not look like the FFT plot
in step #1. A different noise pattern (different from when nothing was
transmitted) and some clicking came out of the speaker.

What am I missing? Advice appreciated.
thanks
Rachel
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