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Using TinySA and NanoVNA in RF

 

Good day All.
I'm trying to restore/align an old FRG7 Com-radio, have a TinySA that have been using as an RF sig gen and a Zeewiie DSO1151g scope that 'should' run past 100Mhz, well lets just say 30Mhz is about its limit, this means I'm unable to look at signals in RF range.
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My question, attached are sample alignment procedures for the RFG-7.
Given that I dont have a fit-for-purpose scope (have three scope probes) but do have a TinySA and a NanoVNA (on the way) how should I then perform the alignements that require use of a scope, so what modifications do I make to testing and how should I review the results.
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Scopes, Im happy with using. SA and VNA interpretation, I'm not familiar with and no option to buy a higher bandwidth scope.
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Thank you.
Br John.
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It is difficult to tell because part of the procedure is missing, and the resolution of the scanned page is not that good (Groups IO scales it).
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At first glance, it looks like a voltage output, or some other trigger, from the swept oscillator time base, needs to be driving the scope X axis, to produce a frequency (X) vs amplitude (Y) display.
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You should be able to achieve a similar function using a VNA to produce the swept signal, and the SA to see the resultant frequency response, without having to trigger one from the other. But you will have to be careful to set appropriate sweep times on each device.
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You will probably have to use separate devices because the RF and IF frequencies will be different from each other, but if you are trying to measure the IF response, around the same centre frequency, then it should be possible to do that just using a VNA.
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Regards,
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Martin
 

Manual uploaded, 9&10 circuit description, 11&12 alignment.

Yaesu FRG7 hi res manual.pdf
Yaesu FRG7 hi res manual.pdf

 

Thank you martin, just uploaded the original PDF to the thread.
 

The VNA by itself should be suitable foe sweep alignment. But it is not plug and play. A method needs to be worked out that is safe for both the radio and the VNA and produces reaonable results.

On Fri, 14 Feb 2025 08:59:52 -0800
"Martin via groups.io" <martin_ehrenfried@...> wrote:

It is difficult to tell because part of the procedure is missing, and the resolution of the scanned page is not that good (Groups IO scales it).

At first glance, it looks like a voltage output, or some other trigger, from the swept oscillator time base, needs to be driving the scope X axis, to produce a frequency (X) vs amplitude (Y) display.

You should be able to achieve a similar function using a VNA to produce the swept signal, and the SA to see the resultant frequency response, without having to trigger one from the other. But you will have to be careful to set appropriate sweep times on each device.

You will probably have to use separate devices because the RF and IF frequencies will be different from each other, but if you are trying to measure the IF response, around the same centre frequency, then it should be possible to do that just using a VNA.

Regards,

Martin
--

73

-Jim
NU0C
 

From what I read in the service manual, all swept measurement are with RF in and measurement out at the same frequency. That's work that should be easy to do with a VNA as there is no frequency translation. Issue is perhaps the loading of the circuit. The VNA is 50 Ohm input. You can put a series resistor in series with the VNA input to increase the impedance. It depends on the circuit output impedance what is acceptable. Perhaps even add AC decoupling if needed. 1K series resistance attenuates the measured signal by 26.4dB but the passband shape should still be clearly visible.
All IF measurement seem to be done maximizing the S-meter reading. One measurement needs a frequency counter. That can be done with the scope as it's a digital one.
Although the VNA will generate a square wave, for this radio it should not matter.
I also saw an absolute measurement with at 100 dB input to adjust the S-meter. That's a huge level, depending what the unit is :-).

 

Hi folks,
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I haven't read through this thread in detail - just skimmed it quickly.? Thought I'd mention that a spectrum analyzer set to zero span can be used as a makeshift oscilloscope.? I don't recall if the TinySA has a zero span.? I haven't had to use mine in awhile.? I think it does, though.?
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Anyway, I'm sure others can offer more advice on the topic.? I just thought I'd mention it in case it helps.
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Basically, when you set the SA to zero span, the SA's sweep time becomes the time base for your "oscilloscope".? In other words, suppose your sweep time is 10 ms, and there are 10 horizontal divisions on screen, then your oscilloscope time base is 1 ms/div.??
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Thanks,
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Steve
 

I just found this interesting using the Tiny SA as a sweep generator.?
Good luck?
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The high output can give a "start of sweep" pulse so no need to modify the HW
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Designer of the tinySA
For more info go to

 

On Mon, Feb 17, 2025 at 12:28 PM, <svkirk@...> wrote:
when you set the SA to zero span, the SA's sweep time becomes the time base for your "oscilloscope".
The "'scope" bandwidth is limited by the RBW and VBW filters, set them as wide as possible.
Best regards, Don Brant

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