Bob,
I'm only simulating a clean CW signal of the amplitude predicted by John as worst case. I've been thinking of a field trip up to Marysville to try to capture actual PAVE PAWS using the Matt Ettus USRP board. That might give us some real world signals to work with. But until then I have no idea what PAVE PAWS phase noise would look like, or if the data in the ATP adendum is correct or not. It's derived from open source information released during environmental impact proceedings for a proposed PAVE PAWS upgrade.
Have you looked at the PAVE PAWS addendum in the ATP? Do you think is is accurate? I want to make sure I'm on the same page with you. Pages 50 through 53 spell out the bandplan, pulse duration for both modes, repetition rates, etc. The tracking mode pulses are 16 milliseconds in duraction and chirp 1 MHz. Yes, that's a pulse, but it's extrememly long. There are four channels that look like they will have the most impact - 434.4, 435.6, and 436.8 and 438.0 MHz.
Assuming that this information is accurate, and assuming that the uplinked data decoder dies when the receiver phase noise I'm seeing buries the uplink signal, then my thinking goes like this:
Based on the test results I posted the other night, a clean signal at -43 dBm (PAVE PAWS) will bury a clean adjacent signal at -112 dBm (ham uplink) when it gets within about 7 kHz. So if we do the math - 16 mSec to move 1 MHz = 0.24 milliseconds to move 15 kHz (the distance required to move from one side of the uplink to the other) The rep rate for tracking mode is 54 milliseconds so I would expect to see a .24 mSec drop out every 54 mSec when illuminated with PAVE PAWS tracking mode EMI, under worst case conditions. I would think that if you bulit in enough forward error correction to deal with that then you could uplink right through PAVE PAWS, assuming that my simple test produced accurate results.
Something else to consider is the recovery time when the receiver is hit by a strong pulse. I haven't looked into that yet but it could add some time to the .24 mSec drop out.
Bottom line - Yes, I know my test is simpistic but it's the best I can do with what I have available now. If we can capture actual PAVE PAWS using the USRP board then we can conduct much more sophisticated tests using that digitized PAVE PAWS signal as the EMI source.
73,
Juan
-----Original Message----- From: Robert McGwier [mailto:rwmcgwier@gmail.com] Sent: Thursday, June 28, 2007 5:01 AM To: juan-rivera@sbcglobal.net Cc: eagle@amsat.org; Bill Ress; Dave Black (Home); Dave Black (Work); Dave hartzell; David Smith; Don Ferguson; Rivera, Juan A.; Samsonoff@Mac. Com Subject: Re: [eagle] IMD, Phase Noise, a New Spur, and EMI suggestions
Juan:
If we have had this discussion before, forgive me. I have misplaced both the interaction and my memory.
What is the generator for the "Pave Paws" source? I ask this because the phase noise for the "Pave Paws" source does not seem to be included in your consideration.
Pave Paws is a pulsed instrument. It will not have its energy concentrated at a single frequency. Its energy will be spread considerably and much of that energy will fall outside of the front end filter of the 70 cm RX. A more realistic test would compute that a -70.2 dBm Pave Paw signal will put (say) -90 dBm inside our passband and further, it will be on/off. Since it is on/off, there will be gaps where the amateur signal is not drastically impacted. A receive system on the ground, necessarily narrow band, will provide processing gain. If we do a good job of writing code, and we do not run out of processing cycles, it would be nice to do pave paws pulse detection and subtraction.
My point here is, the pave paws situation is a great deal more complex than your test is capable of revealing.
Bob
-- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "If you're going to be crazy, you have to get paid for it or else you're going to be locked up." Hunter S. Thompson