#607 Using an External Mixer with a Spectrum Analyzer

Episode 607
Using the IF output and external mixer to increase the frequency range of a spectrum analyzer. Using my HP8558 spectrum analyzer to test a Bluetooth signal at 2.4GHz. Ever wonder why the first LO is on a front panel connector?
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[TestEquipmentAnonymous]

Cool little extension with that external mixer. Regarding the 200 MHz center frequency, your frequency span is 20 MHz, so it's sweeping from 190 - 210 MHz. If the original signal's center is at 2.45 GHz, then the LO must be spanning 2.24 - 2.26 GHz. If you have a frequency counter that goes up that high, set a zero span and see if the LO is operating in that range.

The manual indicates that the low end of the LO on the 8558B is 2.05 GHz, so you might be able to see a part of that span at 400 MHz.

[WAOSH]

It's a clever hack.

From the HP Keysight 9018-05859 user and service manual, the first LO is 2.05 to 3.55 GHz is swept for 0 to 1.5 GHz input frequencies. Under normal operation, the internal mixer brings the signals down to the 2050 MHz first IF.

In your setup, the 1rst LO output and the WIFI/Bluetooth signal at 2.400 to 2.4835 GHz are mixed down to 350 to 433 Mhz and fed into the input. The internal mixer then mixes it down to the 2050 IF.

[egbertgroot]

First time i see the LO output used! Very good

[fredmitchel]

Nice hetrodoyneing...

Thanks IMSAI Guy...

[amirb]

CF=200MHz --> LO=2.2GHz --> RF=2.4GHz---> bluetooth.

[PapasDino]

The old Tek 49X series analyzers had external mixers taking them well beyond the base range they operated at. Nice hack!

[tomeks]

I do understand something about this spectrum analyzer. What does it output to the scope? What is the blue channel set to? Does this analyzer convert frequency sweep to analog amplitude signal with a fixed time base? How do you synchronize the horizontal scale, so that the readings are accurate?

[fredmitchel]

I was hoping the down converted spread frequency signal would of been demodulated...so we could hear that 96 dB S/N audio thru a little newer version LM386 with two channels...

I wonder if there is a chip...?

It sounds like you need to mix again and get to an empty area on FM broadcast ...then listen to your McInTosh receiver tuned and being played thru the JBL 3 ways...

Or send test signal through phone...go through the signal chain...measure the distortion like with you instrument

Maybe if the IC-705...general coverage reciever was turned in...

Its good to see...like how some earlier spectrum analyzer...used to cover like up 1.2 GHz...then go to 21 Gz...without changing the size or appearance that much..

My order S9...had the audio jack...and I would play or listen to the phone YouTube audio or a Playlist by going into the RCA CD port on the Sony reciever heard through Altec Lansings.

I have also (4) CLS-215 Cerwin Vega tower speakers driven by two Crown 2002 XTI class D PA The pa are powerd by 2 12 VDC 8D bus batteries in series running a 3kW perfect sine wave inverter...24VDC to 120 VAC 60 Hz
It's just the little camping Karaoke ..but if someone wants to crank in...we been heard fainty a mile away...lol...
Usually one half playing at 5 watts average a side is plenty..one must not disrupt the animals trying to sleep...
.
Fred don't disrupt IMASI Guy and his teaching

Thanks IMSAI Guy

[johnsantos]

can you please go over how you connected the spec an to the oscope please. I like the way you are using your oscope screen and your spec an hardware to accomplish the video.

[goofypettiger]

Good information. Which is the spectrum analyzer, the HP or the RIGOL sitting above it?

[HelmutTschemernjak]

You have some super cool videos, thank you for educating us. Why not to draw down on a piece of paper the signal flow of this setup and explain some mixer basics, would be easier to understand for most people.
Warm regards from Germany, Helmut
PS: Can you add the Link to the eBay mixer into the description would nee of interest.