Bill,

Be careful. I basically made it say what I wanted to by fooling with the gain, filters, and FFT bin size. I could be fooling us both. Let me do one more test. I'll get it back to the configuration I just sent to you and then I'll feed it a 10 MHz signal from my two synthesized signal generators. I'll report back.

(I should have picked a noisier oscillator so I could match it up with the 8566B too).

The oscillator is manufactured by Bulova Electronics. The label says:

Model: PCOXO-HP22

Freq: 10.000 MHz

Osc. Volt: +20V DC

Oven Volt: +30V DC

Part No. 0960-0151

I yanked it out of an HP8660C organ donor.

Juan

-----Original Message----- From: Bill Ress [mailto:bill@hsmicrowave.com] Sent: Wednesday, July 11, 2007 5:25 PM To: juan-rivera@sbcglobal.net Cc: eagle@amsat.org; Dave Black (Home); Dave Black (Work); Dave hartzell; David Smith; Don Ferguson; Juan.Rivera (Work); Samsonoff@Mac. Com Subject: Re: 10 MHz Phase Noise

Hi Juan,

Thanks for collecting the data. Now I'm flat amazed!!!

Assuming, as you say, that the signal is referenced to 0 dBm in the

SDR-IQ then it is essentially repeating the data at 10 Hz and 100Hz that

you got for the 10 MHz oscillator on the HP ES5500. That is really

super! I'm putting an SDR-IQ in the budget. Using clean heterodyne

sources, the SDR-IQ will make a great back end for a VHF-microwave phase

noise test set (unless I'm missing something).

I don't remember the schematic for the SDR-IQ but I think the reference

oscillator is just an ordinary crystal oscillator - right? If so that

accounts for the center frequency drift.

Do you have a HP part number for the 10 MHz oscillator?

Regards...Bill - N6GHz

Juan Rivera wrote:

Bill,

I'm sending you my preliminary phase noise results. As you recall, I

constructed a battery-powered 10 MHz oscillator by grabbing a junked

reference oscillator from an old HP signal generator and mounting it

in a box with two 9-volt batteries, a switch, and a BNC. That allowed

me to bring it into work and use the Agilent ES5500 Phase Noise

Measurement System on it. Then I brought it home as my poor-man's

phase noise source. Here's the test results on the oscillator and the

first look at the SDR-IQ:

*Phase noise of the battery-powered oscillator*

Here's the same oscillator captured with the $400 SDR-IQ. The SDR-IQ

drifts in relation to the device under test so the signal average is

artificially low. It's really at 0db on the scale. With the IF and RF

gain set to their lowest settings I think this lines up pretty well

until the level drops down to the SDR-IQ baseline noise level at about

the 100 kHz point. The 120 Hz bump has to be coupling from the PC via

the USB port where it gets its power. I was able to rid the SDR-14 of

that by tossing the wall wart and using a lab bench supply. For now

I'll just ignore this one.

What do you think?

Juan

-----Original Message-----

From: Bill Ress [mailto:bill@hsmicrowave.com]

Sent: Tuesday, July 10, 2007 7:27 PM

To: Juan Rivera

Subject: 10 MHz Phase Noise

Hi Juan,

Really sorry you couldn't transmit this evening. I always enjoy your

keen comments.

Thanks for the 10 MHz phase noise data. What is the model number for the

HP oscillator? It's probably a version of the one I use.

Now - - - - I'm really interested in what you read on your SDR. On the

8566B you'll just be looking at its internal LO's phase noise floor but

it will be very interesting to see what your SDR phase noise floor is.

Your test results will be the key data point in my decision to buy one.

Again - much thanks for you fine work.

Regards...Bill - N6GHz

Bill,

OK... Here are the results of the latest test. This time I didn't do any averaging. It took some the time to capture the data and do that huge FFT so the relative shift in frequency makes the peak level look lower than it really is. If you reduce the FFT block size back to 8K then it will display correctly.

Here's the crystal oscillator (I know that 120 Hz is not coming from the oscillator)

Here's the HP 8662A - Just slightly noisier. You can see that this oscillator is more stable and the peak is narrower. I feel confident that this is due to less drift during the FFT processing.

And here's the HP 8656B - a much less expensive instrument and fairly nasty, but synced to the same reference. I'm sure that 120 Hz is still there but you can't see it anymore...

Here's the settings you can't see:

Filter Bandwidth: 5 kHz

6620 IF Gain: 0 dB (the lowest)

RF Gain: -20 dB (the lowest)

FFT Window Type: Hanning

Don't feel bad about not understanding these settings. I've been fooling with this for several weeks and I still don't claim to get it. The master oscillator is running at 66 MHz and it's not a straight crystal. You can set it to dial in the frequency if you want to calibrate it. The main spur is always directly in the middle of the display, regardless of frequency. The gain settings have a huge affect on the amplitude.

I hope this helps!

Juan