[Hackrf-dev] TX Trouble

[w***@nehp.net]

Hi Gang,

I'm trying to TX, specifically I'm trying to implement the Hack RF
tutorial video about writing a waveform (like a car door opener) to file,
and then transmitting it later from file.

Here's a screen shot of my flowgraph and the error I'm getting.

I've seen a forum page on it somewhere saying to check the HackRF serial
number. That's not the problem. The help page also said something about
a USB port and power sharing, that I didn't really understand. It said to
look for a certain file: /tlp or /tpl. Anyway, I didn't have that file
on my computer.

Any advice?

Thanks,

Brian

[Andrew Rich]

Try a simple fm Tx

Sent from my iPhone

Post by w***@nehp.net
Hi Gang,
I'm trying to TX, specifically I'm trying to implement the Hack RF
tutorial video about writing a waveform (like a car door opener) to file,
and then transmitting it later from file.
Here's a screen shot of my flowgraph and the error I'm getting.
I've seen a forum page on it somewhere saying to check the HackRF serial
number. That's not the problem. The help page also said something about
a USB port and power sharing, that I didn't really understand. It said to
look for a certain file: /tlp or /tpl. Anyway, I didn't have that file
on my computer.
Any advice?
Thanks,
Brian
<Screenshot from 2017-10-13 20-51-16.png>
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[Simon Kennedy]

Hi Brian

As you can see from the error message the flow graph is unable to establish
the connection to the HackRF. Obviously this could be as simple as not
having the device plugged in to the computer. I'm going to discount this
:-) but just double check by running dmesg immediately after plugging it in
and you should see reference to the HackRF connecting.

More likely is that the device string is wrong. If you have the latest
firmware loaded (run hackrf_info to check) dated 2017 then reference the
HackRF like 'hackrf=<serial number>'

If not, and I am casting my memory back here, I seen to remember a problem
using hackrf=0 but just try 'hackrf' on its own or 'hackrf=1'

HTH
Simon.

Post by Andrew Rich
Try a simple fm Tx
Sent from my iPhone

Post by w***@nehp.net
Hi Gang,
I'm trying to TX, specifically I'm trying to implement the Hack RF
tutorial video about writing a waveform (like a car door opener) to file,
and then transmitting it later from file.
Here's a screen shot of my flowgraph and the error I'm getting.
I've seen a forum page on it somewhere saying to check the HackRF serial
number. That's not the problem. The help page also said something about
a USB port and power sharing, that I didn't really understand. It said

to

Post by w***@nehp.net
look for a certain file: /tlp or /tpl. Anyway, I didn't have that file
on my computer.
Any advice?
Thanks,
Brian
<Screenshot from 2017-10-13 20-51-16.png>
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https://pairlist9.pair.net/mailman/listinfo/hackrf-dev

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[w***@nehp.net]

Hello All,

I'm still having trouble transmitting from file, a car door clicker
waveform that I saved, similar to one of the tutorial videos.

For one thing, the TX light comes on when I start the flowgraph, but when
I close it, the light stays on. Is that normal?

And, generally speaking, what are things to look for when debugging TX
problems? I can think of two problems: I'm not transmitting with enough
power, or I messed up the waveform somehow when I recorded it.

Regarding the first, I've tried setting the RF gain as high as it will go,
and I've tried different antenna lengths.

Regarding the second, I'm worried that I may have saturated HackRF when I
recorded the waveform. Is there a way to tell, if I view the recorded
waveform in the QT GUI time domain plot? Anything above 1 V or below -1
V? I guess the waveform would look clipped, but it appears so quickly,
that it is hard to tell. Same question on transmit: how can I tell if I
am saturating?

I'm also aware of the trick in the video about multiplying by a constant
to increase SNR. Any other ideas?

Thanks,

Brian

[Dominic Spill]

Post by w***@nehp.net
I'm still having trouble transmitting from file, a car door clicker
waveform that I saved, similar to one of the tutorial videos.
For one thing, the TX light comes on when I start the flowgraph, but when
I close it, the light stays on. Is that normal?

It's normal, but not intentional. There's a bug somewhere in the process
of tearing down the flowgraph and stopping the HackRF. It's on my todo
list to hunt this down and fix it.

Post by w***@nehp.net
And, generally speaking, what are things to look for when debugging TX
problems? I can think of two problems: I'm not transmitting with enough
power, or I messed up the waveform somehow when I recorded it.
Regarding the first, I've tried setting the RF gain as high as it will go,
and I've tried different antenna lengths.

Those are likely to be your biggest issues, along with incorrect antenna
length for the frequency of the signal. What's the frequency of the
signal? 315 MHz? 433 MHz?

In terms of your signal, make sure that it's being transmitted on the
frequency that you think it is, and try to reduce noise if you can (i.e.
filter it in GNU Radio). If you ahve another SDR, such as a RTL-SDR
dongle, you could take a look at the transmitted signal by receiving with
that.

Post by w***@nehp.net
Regarding the second, I'm worried that I may have saturated HackRF when I
recorded the waveform. Is there a way to tell, if I view the recorded
waveform in the QT GUI time domain plot?

I like to look at it using gr-fosphor or the FFT sink.

Post by w***@nehp.net
Anything above 1 V or below -1 V? I guess the waveform would look

clipped,

Post by w***@nehp.net
but it appears so quickly, that it is hard to tell.

If you set trigger levels you can have the display hold when the part that
you want is in view. You'll want to filter to avoid noise interfering with
this.

Post by w***@nehp.net
Same question on transmit: how can I tell if I am saturating?

Again, having another SDR to view the signal is handy, but there are other
options. You could clean up the file with some filtering and view it using
gr-fosphor or inspectrum.

[Chuck McManis]

I second the suggestion that if you have a second HackRF or spectrum
analyzer you look at what is coming out of the antenna. That will tell you
if your flow graph is correct.

Also, if you're just trying to clone a car key fob (unlike say a garage
door opener) you should be aware that the key fob radio usually sends a
rolling code (it changes every time) so you cannot just record it, and then
replay it, and expect to open a car door with it.

--Chuck

Post by w***@nehp.net
Hello All,
I'm still having trouble transmitting from file, a car door clicker
waveform that I saved, similar to one of the tutorial videos.
For one thing, the TX light comes on when I start the flowgraph, but when
I close it, the light stays on. Is that normal?
And, generally speaking, what are things to look for when debugging TX
problems? I can think of two problems: I'm not transmitting with enough
power, or I messed up the waveform somehow when I recorded it.
Regarding the first, I've tried setting the RF gain as high as it will go,
and I've tried different antenna lengths.
Regarding the second, I'm worried that I may have saturated HackRF when I
recorded the waveform. Is there a way to tell, if I view the recorded
waveform in the QT GUI time domain plot? Anything above 1 V or below -1
V? I guess the waveform would look clipped, but it appears so quickly,
that it is hard to tell. Same question on transmit: how can I tell if I
am saturating?
I'm also aware of the trick in the video about multiplying by a constant
to increase SNR. Any other ideas?
Thanks,
Brian
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