Thank you, the first sentence in the wiki alone is important...transmissions are very short!

On Tue, Sep 29, 2020 at 01:41 PM, Kurt Poulsen wrote:

the NFM has a deviation of 17KHz and pretty high distortion

Hi Kurt,

The NB FM 'spikes' are peaking up to 22KHz according to the graticule on my scope.

If I switch in the 3KHz LPF on the Racal 9008 modulation meter , the results are a bit more sensible, but still not good enough to use.

Erik, is the Narrow and Wide FM modulation produced in the same way ?

Can you reduce the 'size' of the modulation pseudo sine wave 'steps' in FM wide mode (or increase then in FM narrow mode) to see if we can find the point at which the stepped modulation turns into sharp spikes. This may give clue about what's happening.

I also tried modulation in High mode and it's showing the same effect at 300MHz. The RF output level in Low mode is pretty close to the stated value, but in High mode it's good at -30dBm, but varies considerably from the selected value at other settings (typically 6dB out, but sometimes 10dB or more) it doesn't always step up or down by the same amount. If the attenuator is binary switched, I'm wondering if two of the bits have got crossed somewhere.

Regards,

Martin

Erik,
37dBm is 5 Watts. I didn’t think the RX/TX could generate that much power.
Gary
W9TD

开云体育

On Tue, Sep 29, 2020 at 01:22 PM, Martin wrote:

The Racal modulation meter says it's about 100% modulated

Correction 50% modulated.

On Tue, Sep 29, 2020 at 12:48 PM, Erik Kaashoek wrote:

The WFM and AM look correct.

The AM is a bit asymmetric but otherwise OK. The Racal modulation meter says it's about 100% modulated.

I'm not sure if 7 or 9 point approximation would help. It may simply be the loop bandwidth, or something associated with it, that is the issue as you suggest.

If you wish to send me test firmware to see if it makes a difference, that would be OK with me.

Regards,

Martin

On Tue, Sep 29, 2020 at 05:35 AM, Martin wrote:

NB FM 1KHz modulation - not so good, wide excursion spikes.

Many thanks for the measurement.?Indeed, the PLL loop has some severe overshoot. Would a 7 or 9 point approximation help? That should halve the frequency steps

The WFM and AM look correct.

Hi Erik,

Demodulated output from my Racal deviation meter.

AM 1KHz modulation



WB FM 1KHz modulation



NB FM 1KHz modulation - not so good, wide excursion spikes.




I tried a HP signal generator just to check the demod process was OK. 5KH deviation 1KHz modulating frequency.

Note the deviation meter scale is set a bit more sensitive that the previous capture as the peak deviation was much smaller.



Regards,

Martin

Hi EriK,

Ah OK that could explain a lot of things :-)

I hadn't realised you were doing it this way, but it makes sense now that I think of it.

Because of the non-sinusoidal modulation, I get variations between modulation values depending upon what method I use and what filters I apply.

I've dug out my old Racal 9008 modulation meter, and it's giving different readings to my Spectrum Analyser modulation measurement option.

I think this is because of the TinySA modulation wave shape and the type of detector used to measure it.

Regards,

Martin

Depending where in the world you are, these devices may operate on different frequencies.
Weather sensors, security cameras and alarms may operate around 434MHz or 868MHz

The wiki contains some info on capturing these signals:?

The modulation is a rather crude 5 point approximation of a sinus. Yes, there should be harmonics.

As the components in the tinySA do not support FM modulation I change the fractional divider of the PLL to modulate the frequency. As this is done inside the PLL loop the PLL loop has to follow the change in register setting and the speed at which this happens will depend on the loop parameters which are unknown to me.
So I guess the dependence of the? deviation in NFM on the modulation frequency comes from the PLL loop having some problems (overshoot?) following the changes of the fractional dividers.

Any hints for using the Tinysa to find signals from household security cameras, outdoor wireless weather sensors, and driveway alarms?

Just got Tinysa from Aliexpress, version 39 (not even listed in the past updates!). Works fine, still learning.

I have tried to see the signals from outdoor wireless camera and my driveway alarm, but can't readily see them. Maybe I need to know the frequency first and then set the Tinsa to a narrow band? But it seems a spectrum analyzer should find them.

Thanks
Mike
K4QET

Hi Erik,

Is the AF modulation a square wave?

It looks like it could be when observed with a scope on the demodulated output from my deviation meter.

Regards,

Martin

On Tue, Sep 29, 2020 at 10:56 AM, Erik Kaashoek wrote:

Weird you can not set the modulation frequency below 1kHz.

Hi Erik,

I just rechecked and it is OK with modulation frequencies below 400Hz.

For some reason my measurement kit didn't like the low deviation 500Hz RMS (it may have been locking to something else) that is produced with this modulating frequency, but I can confirm that it does indeed work with modulating frequencies down to 100Hz.

My apologies for not spotting this.

Are you using phase or frequency modulation, could this be the reason for the variation in deviation vs modulating frequency ?

Regards,

Martin

https://www.youtube.com/watch?v=Ne6PkxxOhMI

Martin,

Thanks for the feedback.
It should be possible to increase the AM modulation depth, will look into this
Weird you can not set the modulation frequency below 1kHz. Kurt did some testing and he could use till at least 100Hz.
Not sure why the NFM deviation should increase with frequency. Could be PLL overshoot as I am modulating inside the PLL loop. If so there is not much I can do to improve.

The Bessel Nul technique is referred to in the tinySA? wiki measurement examples:?
You are most welcome if you want to provide some better text for the wiki.

Hi Erik,

I just tried the modulation on the Low output.

The modulation frequency is correct from 1KHz up to about 9KHz. When set below 1KHz the modulation frequency is >1KHz

FM Wide produces an RMS deviation of around 42KHz regardless of modulation frequency
FM Narrow produces an RMS deviation of around 2.8 KHz with 1KHz modulation frequency
FM Narrow produces an RMS deviation of around 4.1 KHz with 2KHz modulation frequency
FM Narrow produces an RMS deviation of around 5.0 KHz with 3KHz modulation frequency
AM produces an RMS value of of around 14% regardless of modulation frequency

The FM Narrow deviation increases as the modulation frequency is increased.

For typical receiver testing it may be useful to have some fixed settings in addition to the current adjustable values.

e.g.

AM 30% modulation 400Hz
AM 30% modulation 1000Hz
NBFM +/- 2.5KHz peak 400Hz for 12.5KHz channel spacing
WBFM 50KHz RMS 400Hz
Etc.

400Hz is a particularly useful audio modulation frequency because it's on the flat part of the pre-emphasis curve.

Incidentally it may also be useful to show folks how to measure transmitter deviation with a spectrum analyser using the Bessel Null technique.

We used to use this method to check FM broadcast transmitters for compliance 'back in the day', before we had decent deviation meters.



Regards,

Martin

New FW release
Version v1.1-2

Changes:
- The console command "Marker {number} {value}" now accepts either a index (if below sweep points) or frequency as value

Examples:
>marker 1 100
sets marker 1 to index 100 (if sweep points > 100)
>marker 1 100M
sets marker 1 to 100M (if within sweep range)

If frequency is outside sweep range nothing happens.
Setting the marker to an index or frequency disables tracking

Can you elaborate a bit about the use case?