70 cm Receiver on external reference
Bob,
Before our minor crisis I think I owed you a .wav file of the receiver. I set up as follows:
* RF Input: 435.000 from HP 8662A on GSP external reference
* 70 cm Receiver: Also on 10 MHz GPS external reference
* IF out: to SDR-IQ
I demodulated the receiver in CW mode and recorded the wav file using the SDR-IQ SpectraVue program. I can also send you an RF wav file that you can use with a new SpectraVue application that they have on their web. The file is attached.
This screen shot shows the IF output on 10.700 MHz (in green) and the CW detector shape in orange with the red bar at the top showing the passband.
Will this work for you?
73,
Juan - WA6HTP
Guys,
While you wait for the USRP files here's some background info using the SDR-IQ:
The screen shot above is the IF output of the 70 cm Receiver with an RF input of -60 dBm. FFT averaging is set to 100 and the span is 200 Hz.
I then matched the level of the Receiver's IF output using a step attenuator and fed a signal from a battery-powered HP reference oscillator I salvaged from an old signal generator into the SDR-IQ. The SDR-IQ settings remain exactly the same. You can see the difference.
Since the reference oscillator runs on batteries I was able to take it to work last month and test the phase noise using a hugely expensive Agilent E5500 phase noise measurement subsystem. The shot above is the results of the phase noise test on the oscillator so you can correlate the SDR-IQ against the Agilent. So for example, the battery-powered oscillator phase noise is down -130 dBc/Hz at an offset of 100 Hz. The SDR-IQ says it's down about -115 dBc. That's not bad since we're comparing a $400 box against something that probably cost over $100,000. If we assume that adding another -15 dB to the SDR-IQ brings it into line with the Agilent then the 70 cm Receiver has a phase noise of about -85 dBc/Hz at 200 Hz offset. I'll be curious to see what the USRP has to say about this.
There are some external sources of phase noise that need to be considered - The SDR-IQ has its own issues of course, and the Receiver was using my GPS disciplined clock as an external reference. The clock is very clean but nothing is perfect. I can't use the internal reference since it jumps all over the place and will be changed out in the next rev anyway.
IMPORTANT - Last night I think I noticed that the receiver phase noise was greatly affected by the quality of the external reference. If this is true then we need to consider how that external reference will be generated and distributed on Eagle and what sort of quality we can expect - or the Receiver needs to be designed so it can function with a dirty external reference. I'll look into this as time permits. We hope to get the USRP over here this weekend and rerun these tests with it.
73,
Juan
We need a clean reference as it is used to reduce close-in phase noise for the text-mode uplinks.
73,
John KD6OZH ----- Original Message ----- From: Juan Rivera To: K3IO@verizon.net Cc: 'Robert McGwier' ; eagle@amsat.org Sent: Tuesday, September 18, 2007 01:42 UTC Subject: [eagle] 70 cm Receiver Phase Noise
Guys,
While you wait for the USRP files here's some background info using the SDR-IQ:
The screen shot above is the IF output of the 70 cm Receiver with an RF input of -60 dBm. FFT averaging is set to 100 and the span is 200 Hz.
I then matched the level of the Receiver's IF output using a step attenuator and fed a signal from a battery-powered HP reference oscillator I salvaged from an old signal generator into the SDR-IQ. The SDR-IQ settings remain exactly the same. You can see the difference.
Since the reference oscillator runs on batteries I was able to take it to work last month and test the phase noise using a hugely expensive Agilent E5500 phase noise measurement subsystem. The shot above is the results of the phase noise test on the oscillator so you can correlate the SDR-IQ against the Agilent. So for example, the battery-powered oscillator phase noise is down -130 dBc/Hz at an offset of 100 Hz. The SDR-IQ says it's down about -115 dBc. That's not bad since we're comparing a $400 box against something that probably cost over $100,000. If we assume that adding another -15 dB to the SDR-IQ brings it into line with the Agilent then the 70 cm Receiver has a phase noise of about -85 dBc/Hz at 200 Hz offset. I'll be curious to see what the USRP has to say about this.
There are some external sources of phase noise that need to be considered - The SDR-IQ has its own issues of course, and the Receiver was using my GPS disciplined clock as an external reference. The clock is very clean but nothing is perfect. I can't use the internal reference since it jumps all over the place and will be changed out in the next rev anyway.
IMPORTANT - Last night I think I noticed that the receiver phase noise was greatly affected by the quality of the external reference. If this is true then we need to consider how that external reference will be generated and distributed on Eagle and what sort of quality we can expect - or the Receiver needs to be designed so it can function with a dirty external reference. I'll look into this as time permits. We hope to get the USRP over here this weekend and rerun these tests with it.
73,
Juan
------------------------------------------------------------------------------
_______________________________________________ Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
John,
Does your proposed receiver specification spell out the quality of the external reference (other than levels)? We should get whoever is going to be generating that reference signal on Eagle in the loop on this, don't you think?
Juan
On 9/18/07, John B. Stephensen kd6ozh@comcast.net wrote:
We need a clean reference as it is used to reduce close-in phase noise for the text-mode uplinks.
73,
John KD6OZH
----- Original Message ----- *From:* Juan Rivera juan-rivera@sbcglobal.net *To:* K3IO@verizon.net *Cc:* 'Robert McGwier' rwmcgwier@comcast.net ; eagle@amsat.org *Sent:* Tuesday, September 18, 2007 01:42 UTC *Subject:* [eagle] 70 cm Receiver Phase Noise
Guys,
While you wait for the USRP files here's some background info using the SDR-IQ:
The screen shot above is the IF output of the 70 cm Receiver with an RF input of -60 dBm. FFT averaging is set to 100 and the span is 200 Hz.
I then matched the level of the Receiver's IF output using a step attenuator and fed a signal from a battery-powered HP reference oscillator I salvaged from an old signal generator into the SDR-IQ. The SDR-IQ settings remain exactly the same. You can see the difference.
Since the reference oscillator runs on batteries I was able to take it to work last month and test the phase noise using a hugely expensive Agilent E5500 phase noise measurement subsystem. The shot above is the results of the phase noise test on the oscillator so you can correlate the SDR-IQ against the Agilent. So for example, the battery-powered oscillator phase noise is down -130 dBc/Hz at an offset of 100 Hz. The SDR-IQ says it's down about -115 dBc. That's not bad since we're comparing a $400 box against something that probably cost over $100,000. If we assume that adding another -15 dB to the SDR-IQ brings it into line with the Agilent then the 70 cm Receiver has a phase noise of about -85 dBc/Hz at 200 Hz offset. I'll be curious to see what the USRP has to say about this.
There are some external sources of phase noise that need to be considered – The SDR-IQ has its own issues of course, and the Receiver was using my GPS disciplined clock as an external reference. The clock is very clean but nothing is perfect. I can't use the internal reference since it jumps all over the place and will be changed out in the next rev anyway.
IMPORTANT – Last night I think I noticed that the receiver phase noise was greatly affected by the quality of the external reference. If this is true then we need to consider how that external reference will be generated and distributed on Eagle and what sort of quality we can expect - or the Receiver needs to be designed so it can function with a dirty external reference. I'll look into this as time permits. We hope to get the USRP over here this weekend and rerun these tests with it.
73,
Juan
Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle
Juan:
I prefer that we get full I/Q sampling with no processing whatsoever so we can analyzed the raw digitized signal.
THANKS!
Bob
Juan Rivera wrote:
Bob,
Before our minor crisis I think I owed you a .wav file of the receiver. I set up as follows:
· RF Input: 435.000 from HP 8662A on GSP external reference
· 70 cm Receiver: Also on 10 MHz GPS external reference
· IF out: to SDR-IQ
I demodulated the receiver in CW mode and recorded the wav file using the SDR-IQ SpectraVue program. I can also send you an RF wav file that you can use with a new SpectraVue application that they have on their web. The file is attached.
This screen shot shows the IF output on 10.700 MHz (in green) and the CW detector shape in orange with the red bar at the top showing the passband.
Will this work for you?
73,
Juan – WA6HTP
participants (4)
-
John B. Stephensen -
Juan Rivera -
Robert McGwier -
Tom Clark, K3IO