Date   

Re: FFT possible issue?

prog
 

On Mon, Nov 13, 2017 at 02:57 am, <airspy@...> wrote:
Hi Prog

Very useful. Thanks.
The most important bit is "I understand it so I can fix it". 
My work is done :-)

ps: could the bandwidth on connect be auto-adjusted according to the server bandwidth? e.g if server is 144-146 then a client default of 4.8MHz may not be optimum. The first thing I do when connecting to anything is drop the bandwidth from 4.8
Thanks

Dave GW4GTE
The actual bandwidth depends on the server configuration. Maybe just select the nearest possible value according to the last settings in SDR#. Just an idea.


Re: Airspy HF+ BDR 110dB

prog
 

On Mon, Nov 13, 2017 at 02:33 am, adam9a4qv wrote:
There is nothing wrong in that procedure (with AGC off) and measuring the weak signl 1dB drop, just the math and published figures are not matching to the measured BDR.
Maybe, even better should be to measure the BDR with AGC ingaged and then measure the S/n drop for a 1dB.

I agree, the BDR should be close to 110db but then there is something odd with the P1dB or most probably with the MDS figures?

Adam
Well, I agree. Maybe more tests in different scenarios can be published later. The current testing methodology heavily depends on the underlying architecture because the components that "break" first in a more traditional architecture operate at much relaxed constraints here, and most of the amplification (and hence the biggest contribution to the linearity) happen at narrow baseband.

More background:
The ADC has 113+ dB of dynamic range (with 105 dB SFDR) and there is a spur avoidance mechanism to improve its dynamic behavior (by changing both the sample rate and the RF/IF frequencies). Also, there are tunable N-path filters at RF/IF, plus the passive polyphase mixer. The RF gain is very low - just enough to compensate for the attenuation of the N-path filters. Then the 6 dB stepped AGC controls the operating points for all the stages.


Re: FFT possible issue?

airspy@...
 

Hi Prog

Very useful. Thanks.
The most important bit is "I understand it so I can fix it". 
My work is done :-)

ps: could the bandwidth on connect be auto-adjusted according to the server bandwidth? e.g if server is 144-146 then a client default of 4.8MHz may not be optimum. The first thing I do when connecting to anything is drop the bandwidth from 4.8
Thanks

Dave GW4GTE


Re: Airspy HF+ BDR 110dB

prog
 

On Mon, Nov 13, 2017 at 02:33 am, Mark Jessop wrote:
Well, once I have my AirSpy HF+, i'll post some examples of it in this situation :-)
 
When I was doing something similar with an SDR-IQ on another rig, I'd occasionally see the overload light come on... not sure what level that occurs at though.
 
73
Mark VK5QI
You can see the AGC reaction to strong signals here (actually two of them) :

https://www.rtl-sdr.com/wp-content/uploads/2017/08/hf_pagers.jpg

Note that the pagers themselves are not very clean and have terrible phase noise, hence the rise of the noise floor. Otherwise, the action of the AGC is compensated to avoid any pumping.


Re: FFT possible issue?

prog
 

On Mon, Nov 13, 2017 at 01:39 am, <airspy@...> wrote:
Hi Prog
Sorry, I didn't understand the answer in relation to what I'm seeing. 
It may be something to do with the defined bandwidth at the server end. I was trying to constrain the bandwidth to 144-146 when I noticed the issue.
Widening the bandwidth (as set in the server min and max freq) changes the effect. 
There is also a variable element.
As an example, with server bandwidth set to 143-148 MHz, sample rate at default, I connect from SDR#. Bandwidth always seems to start at 4.8MHz whatever. At this point the FFT is correct.
I now change the bandwidth in the Source panel to say 2.4MHz. again the FFT panel is correct. I then change back to 4.8MHz bandwidth and the FFT is no longer correct.
HOWEVER
If I then make a second connection to the server, the FFT on the first connection immediately jumps to the correct point (ie the red line is now where you are hearing). If I repeat the process for the second connection - to 2.4MHz then back to 4.8, the misalignment happens on this second connection.
THEN
If I make a third connection, upon connecting, the FFT on the second connection immediately corrects.
I could go on but I think you see the pattern here lol
The attached screen shot shows the apparently impossible - three identical connections but the lower one has the incorrect FFT
Dave GW4GTE
Thanks. screenshots work better than generic words like "FFT". This is clearly a frequency synchronization problem at the client.
Short story: The scenario is a bit complex, but the most important thing here is that *I* understand it so I can fix it :-)

Longer version: The center frequency of the device was frozen (existing client, no control), then you zoomed in (using lower bandwidth) to a different region of the spectrum, then the other client disconnected => you gain control. Then another client connects, you lose control. You zoom out (set a higher bandwidth) you see truncated spectrum, but you are no longer in sync with the server - now this is a bug. The sync should be restored. (Please don't ask me to explain more)

I hope this is useful.


Re: Airspy HF+ BDR 110dB

Mark Jessop
 

Well, once I have my AirSpy HF+, i'll post some examples of it in this situation :-)

When I was doing something similar with an SDR-IQ on another rig, I'd occasionally see the overload light come on... not sure what level that occurs at though.

73
Mark VK5QI

On Mon, Nov 13, 2017 at 10:26 AM, prog <info@...> wrote:
On Mon, Nov 13, 2017 at 02:17 am, Mark Jessop wrote:
What kind of response time (time constant?) is the AGC running?
 
I will be using my AirSpy HF+ in the receive loop of a Icom IC-7610, and when I transmit there is likely to be a bit of RF ending up in the AirSpy. (not 100% sure how much yet, will be a function of the TX/RX relay isolation.
Would be good if it didn't take a long time to recover... 
 
73
Mark VK5QI

Good question. The AGC has 4 ms attack and 40 ms decay. Note that the AGC attenuation is compensated digitally to maintain the same signal level.



Re: Airspy HF+ BDR 110dB

adam9a4qv
 

There is nothing wrong in that procedure (with AGC off) and measuring the weak signl 1dB drop, just the math and published figures are not matching to the measured BDR.
Maybe, even better should be to measure the BDR with AGC ingaged and then measure the S/n drop for a 1dB.

I agree, the BDR should be close to 110db but then there is something odd with the P1dB or most probably with the MDS figures?

Adam


Re: Airspy HF+ BDR 110dB

prog
 

On Mon, Nov 13, 2017 at 02:17 am, Mark Jessop wrote:
What kind of response time (time constant?) is the AGC running?
 
I will be using my AirSpy HF+ in the receive loop of a Icom IC-7610, and when I transmit there is likely to be a bit of RF ending up in the AirSpy. (not 100% sure how much yet, will be a function of the TX/RX relay isolation.
Would be good if it didn't take a long time to recover... 
 
73
Mark VK5QI

Good question. The AGC has 4 ms attack and 40 ms decay. Note that the AGC attenuation is compensated digitally to maintain the same signal level.


Re: Airspy HF+ BDR 110dB

prog
 

On Mon, Nov 13, 2017 at 01:32 am, adam9a4qv wrote:
BDR= P1dB - Noise floor

P1dB=IP3-10db
P1dB=15-10 = +5dBm

BDR=+5- (-140)
BDR= 145dB

This is a big difference, 110db or 113dB over to 145dB ?

Adam
Read my reply to Johanne. There's also the action of the AGC which was completely disabled during the tests. The gain was fixed so that the SNR of the weaker tone 3dB.


Re: >> ( Want your radio to be listed here? Contact us.) #spyserver

Meduzi Jellyfish <iain@...>
 

Hi Andrea,

WFM seems to be impossible with stuttering regardless of bandwidth. Increasing buffer size may help. Also there seems to be a lot of possibly Band II imaging throughout VHF. Others will try see what they find on their connection to you.


Re: Airspy HF+ BDR 110dB

Mark Jessop
 

What kind of response time (time constant?) is the AGC running?

I will be using my AirSpy HF+ in the receive loop of a Icom IC-7610, and when I transmit there is likely to be a bit of RF ending up in the AirSpy. (not 100% sure how much yet, will be a function of the TX/RX relay isolation.
Would be good if it didn't take a long time to recover... 

73
Mark VK5QI

On Mon, Nov 13, 2017 at 9:32 AM, adam9a4qv via Groups.Io <adam9a4qv@...> wrote:
How will then the trained professionals explain this:

BDR= P1dB - Noise floor

P1dB=IP3-10db
P1dB=15-10 = +5dBm

BDR=+5- (-140)
BDR= 145dB

This is a big difference, 110db or 113dB over to 145dB ?

Adam



Re: FFT possible issue?

airspy@...
 

Hi Prog
Sorry, I didn't understand the answer in relation to what I'm seeing. 
It may be something to do with the defined bandwidth at the server end. I was trying to constrain the bandwidth to 144-146 when I noticed the issue.
Widening the bandwidth (as set in the server min and max freq) changes the effect. 
There is also a variable element.
As an example, with server bandwidth set to 143-148 MHz, sample rate at default, I connect from SDR#. Bandwidth always seems to start at 4.8MHz whatever. At this point the FFT is correct.
I now change the bandwidth in the Source panel to say 2.4MHz. again the FFT panel is correct. I then change back to 4.8MHz bandwidth and the FFT is no longer correct.
HOWEVER
If I then make a second connection to the server, the FFT on the first connection immediately jumps to the correct point (ie the red line is now where you are hearing). If I repeat the process for the second connection - to 2.4MHz then back to 4.8, the misalignment happens on this second connection.
THEN
If I make a third connection, upon connecting, the FFT on the second connection immediately corrects.
I could go on but I think you see the pattern here lol
The attached screen shot shows the apparently impossible - three identical connections but the lower one has the incorrect FFT
Dave GW4GTE
 


Re: Airspy HF+ BDR 110dB

adam9a4qv
 

How will then the trained professionals explain this:

BDR= P1dB - Noise floor

P1dB=IP3-10db
P1dB=15-10 = +5dBm

BDR=+5- (-140)
BDR= 145dB

This is a big difference, 110db or 113dB over to 145dB ?

Adam


Re: Airspy HF+ BDR 110dB

jdow
 

On 2017-11-13 01:19, prog wrote:
On Mon, Nov 13, 2017 at 01:12 am, jdow wrote:
Is their feedback to the program running it for the current AGC setting so
that metering can be accurate in a spectrum analyzer application?
{^_^}
The AGC's are disabled for the BDR tests. You don't want to disable them in real world use.
accurate
These stunts were done by trained professionals, don't try this at home ;-)
I have my trained professional hat and aged tattered and torn tee-shirt among the clothing I am metaphorically wearing at the moment.
{^_-}


Re: Airspy HF+ BDR 110dB

prog
 

On Mon, Nov 13, 2017 at 01:12 am, jdow wrote:
Is their feedback to the program running it for the current AGC setting so that metering can be accurate in a spectrum analyzer application?

{^_^}
The AGC's are disabled for the BDR tests. You don't want to disable them in real world use.

accurate
These stunts were done by trained professionals, don't try this at home ;-)


Re: Airspy HF+ BDR 110dB

jdow
 

On 2017-11-13 00:52, prog wrote:
On Mon, Nov 13, 2017 at 12:29 am, adam9a4qv wrote:
Can somebody explain how this number is calculated or measured?
BDR 110dB?
The method used ?
thanks
Adam
Measured with a weak signal at -115 dBm and a blocker 20kHz away. The blocker is increased until the weak signal decreased by 1 dB - and we are still conservative here. The datasheet says 113 dBm typ.
Also, given all the AGC loops involved, the whole gain distribution is optimized for best sensitivity while all the stages are continuously operating in a comfortable region.
Is their feedback to the program running it for the current AGC setting so that metering can be accurate in a spectrum analyzer application?

{^_^}


Re: Airspy HF+ BDR 110dB

prog
 

On Mon, Nov 13, 2017 at 12:29 am, adam9a4qv wrote:
Can somebody explain how this number is calculated or measured?
BDR 110dB?
The method used ?

thanks
Adam
Measured with a weak signal at -115 dBm and a blocker 20kHz away. The blocker is increased until the weak signal decreased by 1 dB - and we are still conservative here. The datasheet says 113 dBm typ.
Also, given all the AGC loops involved, the whole gain distribution is optimized for best sensitivity while all the stages are continuously operating in a comfortable region.


Re: Spy Server update #spyserver

Evariste Courjaud
 


One question though. Spyserver of course plays very nice with sdr# but
are there other client libraries floating around (python preferred)?
Failed to find one or concrete documentation of the protocol.

Anybody tried this?

Seems that protocol is not public but will be implemented in Gqrx. As it is an opensource project we could inspect the client implementation to use it to other projetcs.

73's Evariste 


Airspy HF+ BDR 110dB

adam9a4qv
 

Can somebody explain how this number is calculated or measured?
BDR 110dB?
The method used ?

thanks
Adam


>> ( Want your radio to be listed here? Contact us.) #spyserver

andrea ottaviani
 

Good morning, can I put my server in the list at this address? https://airspy.com/spy-servers/ Owner: Andrea OTTAVIANI IK0MMI Location: Perugia URL: sdr://ik0mmi.ddns.net/ Radio: Airspy R2 Band. VHF/UHF vertical antenna

thank. you. best 73 de IK0MMI andrea

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