I tried receiving the hydrogen line in the direction of M31 but I can't solve the signal, evidently the s / n ratio is still low.

The first image in the frequency domain, the second in the speed domain.

That signal will be somewhere around 1422.5MHz--right off the edge of your chart.

This update has been pending for quite some time. Now the application can detect and adapt to the DPI of the attached monitor with support for High DPI.
A few other tweaks for the RAW mode when streaming digital data.
Note that this will require .NET 4.8 to work, but the application can still run just as before with .NET 4.6.
The downloads are available as usual at: https://airspy.com/download

Enjoy!

OK. This is garbage. Wes, you seem to be completely confused by how the AGC works. Your signals are much weaker than what the Discovery can handle.
First thing to do is to watch Leif videos to learn about how to test receivers. You can discuss the methodology here if you have any questions.
Then, do your homework and try to reproduce the dynamic range tests using real testing equipment.

On 10/17/2019 9:45 AM, Wes Stewart via Groups.Io wrote:

Of course it's moderated.  It says so every time I post.

I read/post via email, rarely look at the web interface and just learned
that posts are moderated. I've never noticed that; I learned something
today, thanks.

Whatever, they could just identify themselves.

Sure, they could, but how would that change the discussion? Physics
doesn't care who we are :-)

Youssef has described his goals in the design of the HF+ Discovery,
it's not intended as a well-defined 50-ohm match. If someone needs
that, something like a narrow-band matching network or the trusty
stand-by, a resistor pad, is called for.

Joanne has "helped out" as she often does :-).

In all the discussion, I think I missed what your goal is - is there
something specific or general investigation?

73,
Dana  K6JQ

On Thu, Oct 17, 2019 at 07:45 AM, prog wrote:

Let's be more pragmatic. What is the real world performance using an antenna?

Thank you for asking.  Let me preface the following by explaining the environment.  The antenna is a 55 foot vertical over ground radials,  For the results that follow, the antenna is connected to the Airspy through a Telonic Industries Model TG-950 stepped attenuator.  Although not a traceable device I have verified its performance with my DG8SAQ VNWA. I have several plots, all taken during the same session, which are screen grabs of the SDR# program.  The model, serial number, firmware and software versions are all obvious.  This unit is as received a few days ago. 

I'm not sure I can intersperse comments between the attachments so I will summarize them here.  The image "Airspy_1_40db" is of a local MW station with the inline attenuator set to 40dB.  The image  "Airspy_2_20db" is the same as before except the attenuation has been reduced to 20 dB.  It was pointless to go to 0 dB.  Images "Airspy_3_40dB" and "Airspy_4_20db" are similar but of a different station.

The next set, "Airspy_5_20db", "Airspy_6_10db" and "Airspy_7_0db" show station WWV being received on 10 MHz with 20, 10 and 0 dB attenuation respectively.  Note that with 0 dB attenuation, the Airspy is essentially useless.  The next set,  "Airspy_8_10db" and "Airspy_9_0db" show station WWV being received on 15 MHz with 10 and 0 dB attenuation respectively.  Same situation.  Now you might understand my interest in knowing the performance of the input filtering because obviously it isn't up to the task.

But it gets worse.  Image "Airspy_10_Spurious_of_88_1_0db" shows an FM broadcast signal, fully readable so I could identify it, that doesn't exist.  Image "Airspy_11_Spurious_of_88_1_20db" shows the same spectrum with 20 dB of attenuation inline. The non-existent station disappears.

On Thu, Oct 17, 2019 at 07:59 AM, Dana Myers wrote:

On 10/17/2019 7:40 AM, Wes Stewart via Groups.Io wrote:

Well, let me be blunt and see if my comments get past the moderator.

Is this list moderated? I didn't think so.

First, I feel a distinct disadvantage because I don't know who I'm discussing this with.  Two of you hide behind screen names
but I assume that you are the principals in Airspy.

If you're not keen on asking them, the slightest bit of search engine use reveals
full names for both Youssef and Joanne, if that helps at all. I do not believe Joanne
is a principal in Airspy, and I'm not sure anyone other than Youssef is :-)

Of course it's moderated.  It says so every time I post.  Whatever, they could just identify themselves.

Yes, the visible signal is certainly generated by interstellar material belonging to our galaxy.

On 10/17/2019 7:40 AM, Wes Stewart via Groups.Io wrote:

Well, let me be blunt and see if my comments get past the moderator.

Is this list moderated? I didn't think so.

First, I feel a distinct disadvantage because I don't know who I'm discussing this with.  Two of you hide behind screen names but I assume that you are the principals in Airspy.

If you're not keen on asking them, the slightest bit of search engine use reveals
full names for both Youssef and Joanne, if that helps at all. I do not believe Joanne
is a principal in Airspy, and I'm not sure anyone other than Youssef is :-)

Let's be more pragmatic. What is the real world performance using an antenna?

On Wed, Oct 16, 2019 at 10:43 PM, jdow wrote:

Well, for what it is worth I will reiterate what Youssef said. In general the
input match on the receiver does not matter.

In specific, however, there is an issue with filters attached to the input of
the receiver. Their passband shape will be distorted. If this is a problem for
you then put up a little more wire and add an attenuator to the receiver front
end. The attenuation won't matter and the attenuator will make the filter happy.

For what it is worth for most circuit configurations (Leif appears to have
exception) an input match gives you an absolute minimum noise figure of 3 dB.
However, if you mismatch the inputs creatively you can get a noise figure well
below 3 dB. All devices have an input noise current in shunt with the input and
an input noise voltage in series with the input. The optimum match is
(obviously) En/In, which isn't a neat 1:1 SWR at any impedance. You can,
however, do startling things with extreme mismatches so that En or In are
immaterial. You do not get the optimum possible noise figure. But, you do get a
very very good one.

All that said, what matters in the end is the signal to noise power ratio at the
demodulator. And at HF the single largest source of noise is external to your
system. This is why you can put in a 30 dB attenuator from a 160 meter dipole
and still copy all the weak signals you can find. That is why I declare if input
match is critical to a filter you have designed, then put in a 10 dB pad to make
it happy. I learned this the expensive way as a teenager. I was on 15 meters at
the time in about 1960. I was displeased with SNR on received signals. DowKey
made a super low noise preamp. I scraped up the money (never smoking helped me
save the money) and bought it. If anything the results were worse due to
increased IMD. In college some extra-curricular reading led me to an excellent
book, long out of print, on noise figure. And the old Terman handbook/textbook I
found used filled in the galactic and other noise sources picture for HF through
2 meters where it becomes nearly negligible. Noise figure cannot be reduced from
what your antenna presents your radio. It's something about thermodynamics, the
"you can't win" law. It was some years later that I learned about IMD, the other
slab of bread surrounding the signal sandwich. Gain can help front end noise
mask noise from succeeding stages; gain also puts you closer to overload. (And
the really stinky part of this is that AGC systems may reduce signal level; but,
most ways you can do it also reduce the large signal handling ability.)

So, Wes, at the risk of being overly blunt, for the most part your excellent
efforts were a misinformed waste of time. Sorry for hammering the so many nails
in this coffin; but, this ex-cathedral pontificating finally got to me.

{^_^} Joanne

Well, let me be blunt and see if my comments get past the moderator.  First, I feel a distinct disadvantage because I don't know who I'm discussing this with.  Two of you hide behind screen names but I assume that you are the principals in Airspy.  My name, and amateur callsign, is in the clear and you can look me up on QRZ.com if you wish and get a clue about my capabilities.  Note that I was communicating via moonbounce way back in the 1970s and was building my own equipment.  I know a bit about noise figure, so don't need any lessons.  I also did this stuff professionally but I won't go into that here.

The reason that I chose to measure input matching is because that is the only thing readily accessible to me; I have one coax connector to look at.  If I'm allowed, I can post screenshots of my unit operating in my local environment which would make evident my concern about the performance of the input filtering.

On Thu, Oct 17, 2019 at 04:35 PM, Wes Stewart wrote:

I didn't state any reasons, I asked a question that you, as I anticipated, didn't care to answer.

SWR.

On Wed, Oct 16, 2019 at 10:59 PM, prog wrote:

On Thu, Oct 17, 2019 at 07:44 AM, Wes Stewart wrote:

Since it doesn't appear to me that there is enough room in this package for many Ls and Cs how (if you care to say) do you build these elaborate filters?  Are these active inductors?

Better filters are always better, of course, but definitely not for the reasons you are stating. I would again oprimize for the MDS and the rejection.
Yes, designing receivers is not as intuitive as it seems.

I didn't state any reasons, I asked a question that you, as I anticipated, didn't care to answer.

{^_-}

With antennas suitable for efficient transmitting 10 dB is generally safe through 15 MHz maybe 28 MHz. With poor antennas - well - if you install an attenuator and the noise still rises when you replace a dummy load with the antenna, you're good to go. You won't be able to improve things more than a dB or so. That is the bottom line test for what you have.

{^_-}

On Thu, Oct 17, 2019 at 07:44 AM, Wes Stewart wrote:

Since it doesn't appear to me that there is enough room in this package for many Ls and Cs how (if you care to say) do you build these elaborate filters?  Are these active inductors?

Better filters are always better, of course, but definitely not for the reasons you are stating. I would again oprimize for the MDS and the rejection.
Yes, designing receivers is not as intuitive as it seems.

If a perfectly resistive load is required for something else other than reception, just add attenuators. This will cost you the valuable MDS we fought to get you here, but I'd assume at this point you know what you are doing.
Spectrum analyzers do not make for good receivers for the same reasons.