Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[Cinaed Simson]

On 11/09/2016 08:31 PM, David Hubbard wrote:
> On Wed, Nov 9, 2016 at 3:16 PM, Cinaed Simson  > wrote:
> 
> 
> In the NBFM receive block, try reducing Tau to 50u, and Max deviation to
> 4k.
> 
> 
> (to the hackrf-dev list this time)
>  
> Thanks, Cinaed! Playing around with max deviation in particular helps
> with reception quality, for the one good recording (see below).
> 
> I wasn't hearing anything but noise out the audio sink even eyeballing
> it on the FFT plot, the signal is 20dB over the noise floor. So I added
> a file sink, saved a few seconds of the 2.4Msps complex data output of
> the DC blocker (so almost directly out of the osmocom source). I then
> used a file source instead of the osmocom source -> DC blocker, and the
> result is loud and clear audio.
> 
> Even more puzzling is it only did it once. I collected several more
> recordings at 2.4Msps but they do not play back audio. Only the first
> recording produces audio. They all show a strong 20dB signal in the FFT
> plot and waterfall.

Try changing the audio sampling rate from 24kHz to 48kHz and increasing
the RF sampling rate to 5 MHz (if you can do it without dropping data) -
and change the resampler(s) accordingly.

Also, loose the waterfall on the source signal and add a FFT after the
low pass filter - so there's one on the carrier at the source and
there's one after the carrier has been multiplied by the 900k cosine and
filtered.

Does the spectrum after the low pass filter make sense? Can you see the
DC offset shift when you compare the 2 FFTs?

Can you see any frequencies shift?

You're sampling at 2.4 MHz - what is the Nyquist frequency?

How does that compare to 0.9 MHz?

Do you really need to shift signals by 0.9 MHz in order to avoid the DC
offset for a NBFM signal?

> 
> My grc file is attached. Possibly a lack of precision on frequency? I
> tried setting the tune_offset to values from 598e3 to 654e3, which has
> the normal effect on the first recording, but only static on the
> subsequent recordings.
> 
> I would like to add a "sync block," (is that the right term?) so that
> the graph only plays back at real time, to make it easier to change
> tuning parameters while playing back a recording. Any tips on how to do
> that? The attached grc plays back at real time but buffers a lot of
> audio at the audio sink so that changing things like tune_offset cannot
> be heard for about 2 sec.
> 
> 
> 
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Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[David Hubbard]

On Wed, Nov 9, 2016 at 3:16 PM, Cinaed Simson 
wrote:

>
> In the NBFM receive block, try reducing Tau to 50u, and Max deviation to
> 4k.
>
>
(to the hackrf-dev list this time)

Thanks, Cinaed! Playing around with max deviation in particular helps with
reception quality, for the one good recording (see below).

I wasn't hearing anything but noise out the audio sink even eyeballing it
on the FFT plot, the signal is 20dB over the noise floor. So I added a file
sink, saved a few seconds of the 2.4Msps complex data output of the DC
blocker (so almost directly out of the osmocom source). I then used a file
source instead of the osmocom source -> DC blocker, and the result is loud
and clear audio.

Even more puzzling is it only did it once. I collected several more
recordings at 2.4Msps but they do not play back audio. Only the first
recording produces audio. They all show a strong 20dB signal in the FFT
plot and waterfall.

My grc file is attached. Possibly a lack of precision on frequency? I tried
setting the tune_offset to values from 598e3 to 654e3, which has the normal
effect on the first recording, but only static on the subsequent recordings.

I would like to add a "sync block," (is that the right term?) so that the
graph only plays back at real time, to make it easier to change tuning
parameters while playing back a recording. Any tips on how to do that? The
attached grc plays back at real time but buffers a lot of audio at the
audio sink so that changing things like tune_offset cannot be heard for
about 2 sec.


filesource.grc
Description: Binary data
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Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[Cinaed Simson]

On 11/09/2016 12:06 PM, David Hubbard wrote:
> Just to follow up with a final note, this is now the waterfall plot I am
> receiving: lots of interesting digital signals, I added a DC blocker,
> and I can still "sort of" hear the ham radio transmissions.
> 
> Thanks for the help!
> 
> 
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> 

In the NBFM receive block, try reducing Tau to 50u, and Max deviation to
4k.

-- Cinaed
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Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[Simon Kennedy]

Just a thought but why don't you install gqrx? Then you can see the HackRF
in action and experiment with the settings before diving into gnuradio.

Simon.

On 9 Nov 2016 8:06 pm, "David Hubbard" 
wrote:

> Just to follow up with a final note, this is now the waterfall plot I am
> receiving: lots of interesting digital signals, I added a DC blocker, and I
> can still "sort of" hear the ham radio transmissions.
>
> Thanks for the help!
>
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>
>
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Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[David Hubbard]

On Wed, Nov 9, 2016 at 6:51 AM, Gavin Jacobs 
wrote:

> The hackrf is MUCH less sensitive than a typical handheld. If you are
> using the vertical antenna that came with the hackrf, then you will have
> trouble receiving any ham transmissions. I had the same experience as you,
> so here are some tips that got me going:
>
> - calculate the 1/4 wavelength and set the telescoping antenna to that
> length
>
> - put the antenna (and the hackrf unless you have some appropriate rf
> cable) high in the room
>
> - increase the if_gain to 40; use a QT GUI slider to decrease it once you
> acquire a signal
>
> - set the center frequency to an even multiple of MHz; then set your
> offset to hit the desired channel
>
> It takes some patience, but eventually you will get the frequency visible
> on the chart.
>
> Also, be careful not to hit PTT on your handheld, at any time, at any
> frequency, in the vicinity of the hackrf; any moderately strong rf can
> damage the front end of the hackrf. So, I suggest starting with the APRS
> frequency (in North America 144.39 MHz); you get steady traffic, you can
> hear it on your handheld, but you don't have to transmit anything.
>
>
> Unfortunately, my flowgraphs are 2000 km away right now, but we can
> probably help you get going.
>
>
Thanks, Jake! Setting the IF gain higher did the trick. I do see that my
handheld ham radio is more sensitive, but I can receive the audio signal on
the HackRF, with a signal quality that is only clear enough to know there
are voices. (I cannot hear well enough to tell what is being said.)
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Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[David Hubbard]

On Wed, Nov 9, 2016 at 9:00 AM, Silverfox  wrote:

> Some antennas do not make a solid connection with the hackrf.  Try a short
> piece of wire in the center connector.
>
> Good luck,
>
> Alan – W5ARH
>
>
>

Hi Chuck, Alan, I'm using the included vertical antenna. Thanks for the
tip, I double checked I had it attached right and that the center connector
was making good contact.

It's easy to double-check by doing FM radio reception too.

David
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Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[Chuck McManis]

Just to check off the obvious question, you are sure the antennae is the
right sex right?

On Nov 9, 2016 6:23 AM, "David Hubbard" 
wrote:

> On Wed, Nov 9, 2016 at 6:10 AM, John Ostrander  wrote:
>
>> David,
>>
>> You're likely receiving it, but 70cm is nbfm not wbfm so you're probably
>> getting loads of noise around the signal you're trying to get at. Try a
>> flowgraph like the one attached, but with the osmocom source of course.
>>
>> regards,
>>
>>
> Thanks, John! I ran your flowgraph tuned to 443.000 and looked for a
> 443.700 signal that was coming in at S9 on my handheld ham radio.
>
> I have attached the flowgraph with my modifications and the screenshot. I
> believe there's no signal. What do you think?
>
>
>
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>
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Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[Gavin Jacobs]

The hackrf is MUCH less sensitive than a typical handheld. If you are using the 
vertical antenna that came with the hackrf, then you will have trouble 
receiving any ham transmissions. I had the same experience as you, so here are 
some tips that got me going:

- calculate the 1/4 wavelength and set the telescoping antenna to that length

- put the antenna (and the hackrf unless you have some appropriate rf cable) 
high in the room

- increase the if_gain to 40; use a QT GUI slider to decrease it once you 
acquire a signal

- set the center frequency to an even multiple of MHz; then set your offset to 
hit the desired channel

It takes some patience, but eventually you will get the frequency visible on 
the chart.


Also, be careful not to hit PTT on your handheld, at any time, at any 
frequency, in the vicinity of the hackrf; any moderately strong rf can damage 
the front end of the hackrf. So, I suggest starting with the APRS frequency (in 
North America 144.39 MHz); you get steady traffic, you can hear it on your 
handheld, but you don't have to transmit anything.


Unfortunately, my flowgraphs are 2000 km away right now, but we can probably 
help you get going.


Jake






From: HackRF-dev  on behalf of David 
Hubbard 
Sent: November 9, 2016 7:23:31 AM
To: John Ostrander; hackrf-dev@greatscottgadgets.com
Subject: Re: [Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

On Wed, Nov 9, 2016 at 6:10 AM, John Ostrander 
mailto:j...@crackroot.org>> wrote:
David,

You're likely receiving it, but 70cm is nbfm not wbfm so you're probably
getting loads of noise around the signal you're trying to get at. Try a
flowgraph like the one attached, but with the osmocom source of course.

regards,


Thanks, John! I ran your flowgraph tuned to 443.000 and looked for a 443.700 
signal that was coming in at S9 on my handheld ham radio.

I have attached the flowgraph with my modifications and the screenshot. I 
believe there's no signal. What do you think?


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[Hackrf-dev] FM 96.5MHz rx works but 70cm 441.1MHz rx does not?

[David Hubbard]

I just purchased a HackRF, so there's a good chance I overlooked something.
I followed http://greatscottgadgets.com/sdr/1/ and am able to receive FM
but not 70cm Ham Radio transmissions.

Here is how I tested it:

1. Received 96.5MHz fine on the HackRF. center_freq = 97.9e6,
channel_freq=96.5e6, channel_width=200e3, samp_rate=10e6

2. Tuned to 441.1MHz on a handheld ham radio close by, received ham
transmissions on it

3. Changed the flow graph center_freq to 440.0MHz and channel_freq to
441.1MHz, did not see any visible bumps in the FFT plot, and just a quiet
hiss on the audio.

4. Swapped antennas from the handheld ham radio and the HackRF. The ham
radio received transmissions at S9 with its antenna and S5 with the HackRF
antenna. But the HackRF did not receive anything with either antenna.

5. Swapped antennas back, double checked the ham radio was still receiving
transmissions.

6. Changed the flow graph center_freq back to 97.9e6, channel_freq back to
96.5e6, and double checked the HackRF could still receive 96.5MHz ok.

I can send the flow graph and a screen shot of the FFT but it's just the
flow graph from Lesson 1.

Cheers,
David
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