Which is why I do my measurements for that kind of sensitivity in the shield room at my University of Maryland office or at our lab in Bowie, Md. In addition, the phase noise leaving the 8640B, especially if you have the "reverse power protection" is pretty ugly.
Bob ARRL SDR Working Group Chair Member: ARRL, AMSAT, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. "And yes I said, yes I will Yes", Molly Bloom -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tayloe Dan-P26412 Sent: Wednesday, December 10, 2008 5:26 PM To: Lux, James P; Jon Maguire; FlexRadio Reflector Subject: Re: [Flexradio] Sensitivity When I make measurements on my homebrew receivers in the -136 dBm range (using an HP8640B), I definitely notice a time of day sensitivity variation. I have chalk this up to external atmospheric noise (20m/30m) bleeding through the coax. I understand coax shielding is only good for ~30 db of attenuation. I just say this to affirm that making sensitivity measurements on very sensitive receivers with out a shielded cage can be a bit difficult. - Dan, N7VE -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Lux, James P Sent: Wednesday, December 10, 2008 11:26 AM To: Jon Maguire; FlexRadio Reflector Subject: Re: [Flexradio] Sensitivity Sensitivity measurements are a canard, anyway, at least for HF. Atmospheric noise is going to dominate receiver noise for the most part. What you REALLY want to know is the instantaneous dynamic range (how big a signal next to my signal can I tolerate). Not only that, but making quality measurements at -140dBm or -150dBm is non-trivial. (we do this at work for space radios) How do you know that you're not getting wideband hash from the computer in the next room leaking into your test set? What's the precision of your attenuator that's giving you your test signal? You might have a precision 0dBm source, and the signal generator has 10dB steps, but I'll bet that the 140dB step has a pretty big uncertainty. (just from packaging issues) (Agilent E8663B which goes down to -135dBm, only has level accuracies to -80dBm, where it's +/-0.8dB) (Agilent E4418B power meter with the 8481D head (which goes down to -70dBm) is good to 1-2%) > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Jon Maguire > Sent: Wednesday, December 10, 2008 9:21 AM > To: FlexRadio Reflector > Subject: [Flexradio] Sensitivity > > Hello fellow Flexers. This was posted on the IC7700 Yahoo group the > other day. Some comments would be interesting. Thank you. > > 73... Jon W1MNK > > > > "Wow, that surprises me.. I thought the IC-7700 would have better > > noise floor figures when signal sensitivy is equal with the Pro 3." > > > > When you're into the -140 dBm MDS range, I would expect > some sampling > > variance from rig-to-rig. The ARRL lab engineers are > testing one unit, > > not a large sample. So, on any given day, they may end up > with a unit > > that measures slightly better or worse than another production unit. > > > > Now compare MDS in the QST Product Reviews at 14 & 50 MHz across a > > range of transceivers from competing manufacturers. Generally, the > > Icom rigs are far and away more sensitive than their > competition. For > > example, look at the MDS for the new SDR product like the > Flex-5000A. > > > > _______________________________________________ > FlexRadio Systems Mailing List > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ > Knowledge Base: http://kc.flex-radio.com/ Homepage: > http://www.flex-radio.com/ > _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
