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Using two tinySA, one as spectrum analyzer in low input mode and the other as tracking generator with external modulation input
The tracking generator can be set to a small offset so it is possible to do some tests on mixers.
The metal can is a 110MHz BPF

On Mon, Apr 27, 2020 at 10:45 AM, <erik@...> wrote:

Using two tinySA, one as spectrum analyzer in low input mode and the other as tracking generator ...

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Erik,
? How does the tracking feature work?? From the picture you provided, there is no usb-usb connection so it is not a stepped sweep with one spectrum analyzer acting as the host and the other as the controller.? So how does the generator frequency in the first spectrum analyzer stay in sync with the sweep of the second for tracking purposes?

- Herb

Herb,
Asynchronous mode
independent transmitter, independent receiver

73, Gyula

The SA outputs its first LO from the high connector.
The tracking generator mixes the LO with a signal at the first IF and after an LPF you get the tracking signal

On Mon, Apr 27, 2020 at 11:39 PM, <erik@...> wrote:

The SA outputs its first LO from the high connector.
The tracking generator mixes the LO with a signal at the first IF and after an LPF you get the tracking signal

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That's pretty nifty.? Sort of like the old HP8445/HP8568 set-up.? The synchronous tracking should allow for additional depth when sweeping filters. I purchased a rf explorer and rf explorer? generator a couple of years back and the tracking feature could only be evoked by computer control, no stand-alone mode.? I can already envision a future tinysa model which includes the tracking generator inside the case rather than as a separate unit.

- Herb

- Herb

Erik,
? ? Can a tracking generator be created using an external mixer and LPF driven by the tinySA LO?? I have a WJ 0.2-500MHz mixer and 300MHz LPF?on hand. I'm not clear what I.F.? is normally used to drive the mixer, and whether a preamplifier is necessary after the LPF.?

? ? Just wondering if a set-up like that would be an alternative to purchasing two tinySA's to enable the tracking option.??

- Herb

Yes, that was the intention.

You may use this setup:
The external tracking mixer has three ports, LO, RF and IF. I'm assuming the IF port is connected to the diodes in the mixer so it can go down to zero Hz
TinySA in low input mode with tracking output enabled.
The external tracking mixer LO port is connected to the high output of the tinySA.
The mixer drive of the tinySA normally is set to +9dBm but if needed for the tracking mixer you can increase the drive to +15dBm.
You have an external generator that is set to the IF of the tinySA (433.8MHz normally) and is connected to the RF port of the external mixer.
The IF port of the external mixer will now output (amongst other) the signal tracking the scan frequency of the tinySA.
You may clean up the IF output by using a LPF connected to the IF port. With a 300MHz LPF you will also reduce the leakage from the RF port thus increase the dynamic range.
Make sure your external generator output is below mixer drive minus 10dB to avoid overloading the external mixer.
The output signal of you tracking generator will be at external generator output level minus 7-9dB. You may add a amplifier after your LPF but it is not needed as the tinySA is sensitive enough.
?

Here is a picture of the most simple setup



The tinySA at the bottom right is doing the sweeping. Its tracking output from the high connector is connected to the LO port of a mixer.
A generator at 433.8MHz at 1dBm (I used a tinySA at the top right as I do not have a generator) is connected to the RF port and tracking output is coming from the IF port where is goes into a DUT. output of the DUT goes into the low input port of the tinySA.
Instead of a generator at 433.8MHz you may also use a generator with square wave output at 144.6MHz and use the 3rd overtone.

With this setup you can measure the transfer function of a frequency translating device by offsetting the generator.

On Tue, Jul 28, 2020 at 11:13 AM, Igor Jobim wrote:

Would nanoVNA as a tracking generator be an option?

See first post on this subject

So far as I can see, the given examples show a tracking generator operating over the low range. Is it also possible to sweep the high range?

Additionally, how much offset does the current approach permit?

Currently impossible for high range.
Without an extra mixer, so only two tinySA the offset is max about 700kHz
If you add in an extra mixer any offset is possible

On Tue, Jul 28, 2020 at 03:17 PM, Erik Kaashoek wrote:

See first post on this subject

The two links made me understand how it works.

https://tinysa.org/wiki/pmwiki.php?n=Main.MODULATION

On Tue, Jul 28, 2020 at 12:58 PM, Erik Kaashoek wrote:

Currently impossible for high range.
Without an extra mixer, so only two tinySA the offset is max about 700kHz
If you add in an extra mixer any offset is possible

Erik,
? I think the topic deserves its own Wiki entry with specific details for the two tinySA with offset set-up, and using two tinySA's (or one tinySA & external 433.8MHz source) with external mixer and attenuator/preamp for isolation.

? A third option is to put one tinySA in max hold and step a second tinySA/rf generator 290 points using the same step-size as the first tinySA.? I get a pretty clean trace that way, but haven't figured out how to normalize a max-hold trace.

? Most modern specans offer a tracking generator option, so the topic will address those user's looking for a similar feature on the tinySA.? With the availability of the nanoVNA for s21 measurements, the tracking option is not a must have feature for me - unless it can do >70dB down from 100kHz - 350MHz.

- Herb

On Tue, Jul 28, 2020 at 01:26 PM, hwalker wrote:

?A third option is to put one tinySA in max hold and step a second tinySA/rf generator 290 points using the same step-size as the first tinySA.? I get a pretty clean trace that way, but haven't figured out how to normalize a max-hold trace.

? I swept a filter using the proposed third option and realized that a limitation is that harmonics of the tinySA output are 40dB down.? That's actually pretty good for a $50.00 device, but in MAX-HOLD it also means you can't see more than 40dB down because the harmonics lead the sweep.

? The alternative is not to do MAX-HOLD and instead read the peak carrier level at each 290 point generator step, and plot the accumulated data in an external program.? That should get you 70dB or more of dynamic range.??

- Herb