[Hackrf-dev] FW: FW: deaf HackRF

Wed Jan 21 06:03:49 EST 2015

Hi Karl & Paul,

Thanks for the comments.

Karl – for both tests the gain details were max gain on both devices. VGA gain on hackrf to 14db (but adjusting VGA gain makes little improvement to S/N)

HackRF AMP was OFF for first test.

I don’t think a half duplex TX capability is going to significantly affect receive performance. Conventional 2 way radios use a diode switch to select / isolate RX while TX is active & this does not prevent RF performance of <0.35uv gating sensitivity.

Paul,

I have rerun the test –with HackRF sample rate 2MSPS & 0.25MSPS as you suggested.

I ran the test in a simpler way, RF level required for carrier to show above noise floor.

The performance gap closed to 28dB from 32-36db with the amp off & about 16db with the amp on.

Also, to expand on the NOAA RX test I did previously, I tried a variety of sample rates & amp settings to receive a NOAA satellite – the best being fractionally above the noise floor. Under same test conditions, the RTL was able to receive NOAA APT easily.

I think my intent has been misunderstood here – I am interested to establish if my HackRF is faulty or if this the normal RF sensitivity.

Below is  a previous reference to a deaf HackRF, related to a manufacturing issue:

http://nine.pairlist.net/pipermail/hackrf-dev/2013-August/000236.html

Is anyone able to provide more details on the fault listed in the link above (I.E. is it common, measured effect, resolution etc)? 

Thanks

Stephen

From: HackRF-dev [mailto:hackrf-dev-bounces at greatscottgadgets.com] On Behalf Of Karl Koscher
Sent: Tuesday, 20 January 2015 3:10 PM
To: Paul Connolly
Cc: hackrf-dev at greatscottgadgets.com
Subject: Re: [Hackrf-dev] FW: deaf HackRF

There are also multiple gain settings for the HackRF. I'm not sure what the gain settings are for an RTL device, but I believe both the rtl and the tuner have their own gain settings as well.

Keep in mind that there are engineering tradeoffs when designing any device. The HackRF is designed to be a low-cost TX/RX SDR peripheral with a large frequency range and high bandwidth. RTL devices are RX-only, have a smaller frequency range, and significantly less bandwidth.

On Mon, Jan 19, 2015 at 12:51 PM, Paul Connolly <eeipcy at gmail.com> wrote:

As the sample rate increases, so does the the noise floor. Or with more bandwidth comes more noise. So giving the numbers without the sample rates used is not useful. In SDR# for the HackRF you can type in a sample rate in the sample rate pull down box, try using 2 MSPS. And for the RTL2832 try dropping the sample rate to 0.25MHz. And repeat your experiment again.

On 19/01/2015 20:25, Stephen wrote:

Hi Tom,

Thanks for the reply.

The RX sensitivity figure I quoted is dBm – ‘Decibels above a MilliWatt’. -95dBm is 95 db below a MilliWatt, wheras -127dBm is 127 db below a MilliWatt.

This test was conducted with an RF signal generator.

Regarding the test, to register minimum scale on the SDR# spectrum, the HackRF required -95dBm , the RTL2832 required only -127dBm.

Expressing this as microvolts instead of dBm, the equivalent level in microvolts (to register the same scale on SDR#) are:

0.1uV  for the RTL2832 

3.5uV for the hack RF

Accordingly, The HackRF requires considerably more signal to register the same scale on SDR#.

I discovered this performance limitation when  I attempted to try to receive NOAA weather satellites, I found HackRF barely registered, wheras the RTL2832 registered a strong signal for the same satellite pass  on the same antenna.

I appreciate you are trying to help & I don’t mean to be rude by contradicting you,  but the HackRF I have is definitely ‘deaf’.

Regards,

Stephen

From: Tom Buelens [mailto:tom.buelens at gmail.com] 
Sent: Monday, 19 January 2015 8:23 PM
To: Stephen
Subject: Re: [Hackrf-dev] deaf HackRF

Hi Stephen,

I might be mistaken but I actually think the numbers you mention show that the HackRF is better at receiving the signal.

You see, an attenuation of -105 dBm is resulting in a smaller signal then -69dBm. Please also see here:

http://en.wikipedia.org/wiki/DBm

Cheers,

Tom

On Mon, Jan 19, 2015 at 2:36 AM, Stephen  <mailto:refsmmat at gmail.com> <refsmmat at gmail.com> wrote:

Hi,

Ive just bought a HackRF, but I have found  RF performance is poor. Compared to a $12 USB RTL2832 SDR, it is deaf by about 32-36dB.

The tests were done with an HP 8922 test set & an unmodulated carrier at 137.5MHz. The test was the generated RF signal required for both devices to achieve the same scale level in SDR#.

RTL SDR                  HackRF     Difference

Scale1   -127dBm              -95dBm               32dB

Scale2   -115dBm              -79dBm               36dB

Scale3  -105dBm               -69dBm                36dB

The tests were done with max gain on both devices, but with the HackRF AMP off.

I have seen from posts that others have had this problem – related soldering of RF switches in the manufacturing process.

Can anyone provide further details on the fix  or suggest a resolution please?

Thanks,

Stephen

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