Real On-Air Spectrum Analyzer Test Videos - Put 'em on the table mate!

[Steve - WB3HUZ]

Yea, that was great when you banged it while we were listening for weak west coast signals.   

I'd liked to have seen what that insulator of mine looked like in a spectrum analyzer when i kept beating it with a screwdriver. I tuned around and could hear it as far up as 3885 but it just happened to be strongest on 3878. Actually wonder what 3870 looked like tonight to someone looking with an sdr or something like that that could see the signals, especially when everyone was banging on something, i guess i kinda got everyone started on that with the infamous ceramic insulator.
Shelby

[K1JJ]

Dan and the guys -

Thanks again for the waveforms, Dan. I also used SigJenny, Rob - tnx, OM!

I ran some triangle waveforms thru Fabio today. (Plate modulated 4X1 with a quality LS driver transformer and BC mod transformer.)  I went directly into the audio driver with no processing of any kind.

When I run sinewaves thru the audio, they look great from about 25 hz up to about 8khz or so.


Triangle results as shown below:

The 1khz wave looked near perfect. (not pictured)  The 600hz triangle looked OK. The 400hz started to show sloping.   The 200hz started to turn into a semi-sinewave with rounded edges.

Just what are we measuring with a triangle?  Does the sloping show phase shift, frequency response or something else?  What does it mean when we move the frequency lower and the sloping gets worse?

I know some guys don't use triangles below 1khz, though I think Steve/QIX uses them near 200hz with the E rigs.

T

* These pics were taken with the digital low pass filter INLINE at about 6500 hz.  Notice the rounded tops compared to the pics I took in a later post with sharper peaks. I think the filter is inadvertantly rolling off the lows too, as shown in the 200hz pic.

#1 = 600hz triangle
#2 = 400hz
#3 = 200hz

 

[ke7trp]

I would like to know also.. Here is mine at 200HZ.  No EQ.. Just straight into the box.

C

[ke7trp]

And dan.. I cant get Sigeny to work since I have a new PC.  Can you please make clips of Triangle at other FReqs so we can all compare?

C

[Steve - WB3HUZ]

A triangle wave is composed of odd-harmonics of the fundamental. The same is true for a square wave. But the amplitude of the harmonics drops off more quickly in a triangle wave - at the rate of 1/x² as compared or 1/x for a square wave (where x is the harmonic number).

So, the rounding off shows loss of the higher numbered harmonics or high frequency loss. The curvature of the sides shows low frequency loss or phase shift.

[WA1GFZ]

In a DC coupled PDM rig faster is harder to do then slower. You are usually looking at the points to see how sharp they are when they reverse direction. Your LF plots show the transformers and coupling between stages falling apart.

[W1DAN]

Tom:

The rounding of the tip of the triangle wave at 400hz shows clipping or saturation. I believe the angling of the slope is showing a frequency or phase change (not shure).

This is a difficult test and I bet your modulator shounds fine, however negative clipping will get tilted a bit through your modulator.

Glad to help...wish I had time to get on the air and listen.

Yes I can get other frequencies made and posted...sometime this week.

Dan

[ke7trp]

Dan.. I realized Spectra view has Triangle in it..  So dont bother with the Files unless someone else wants them to try.

I ran Triangle tests from 100 to 1K.  I dont get that Shark fin.  My Transmitter just shows a peak like the Scope shot shows above.  If I run more gain, I just get the Tips cut as the carrier closes.

C

[K1JJ]

A triangle wave is composed of odd-harmonics of the fundamental. The same is true for a square wave. But the amplitude of the harmonics drops off more quickly in a triangle wave - at the rate of 1/x² as compared or 1/x for a square wave (where x is the harmonic number).

So, the rounding off shows loss of the higher numbered harmonics or high frequency loss. The curvature of the sides shows low frequency loss or phase shift.

Yes, the sinewave below 25hz  starts to fall apart in form . ... maybe the 3db point is around 50hz, so this makes sense.

The highs also drop off and actually show some distortion above 8khz, so guess thats the rounding off. If I use the LP filter or keep the 8khz highs below  ~80% modulation, they are clean.

So, the triangle is very revealing in just one single waveform, whereas the sinewave takes more time to analyze.


** So, as the triangle frequency is moved lower, is the form deterioration ALL from low frequency problems and the highs are not affected? ie, If the 1khz triangle looks perfect does this mean the highs look FB?  I don't understand why moving the frequency from 600 to 200hz has such a big effect on the highs, if it does. (waveform rounding off as you said)

Interesting.
T

[W1DAN]

Clark:

I bet the rounding on the tip of your scope image is HF rolloff. The LF rolloff shows in the rounded sides.

Tom: Remember that a sinewave tests only one frequency. This is good for level and distortion at that frequency. A triangle (and square) wave tests the fundamental and harmonics. With this signal, amplitude, phase and distortion can be determined.

A square wave is even harder to pass. If it is fully square and not modified, we have flat frequency and phase response...I know even my PDM transmitter will mess with a square wave!

Dan

[K1JJ]

Dan,

Steve said that curvature of the sides means "low frequency loss OR phase shift."

Can we determine which one it is by the triangle form or we cannot determine this from the triangle alone?


I'm still confused as to why there is such a big change in waveform from 600hz to 200hz. Is this caused by the lows only or the highs too?  It wud seem that 600 to 200hz is a small increment compared to the distance to the 6-8kc highs.. know what I mean?  Why doesn't the highs deficiency show up in the 600hz waveform too?

T
 

[Steve - WB3HUZ]

I don't understand why moving the frequency from 600 to 200hz has such a big effect on the highs, if it does. (waveform rounding off as you said)

I'd guess possible transformer saturation.


The curvature of the sides may be caused by HF problems too. Think about what a sinewave looks like as it transitions from negative to positive. There is a short section right around the zero crossing where it is almost a straight line (at an angle). As you add more harmonics, the line gets more straight and covers a longer span. At some point you arrive at the triangle wave.

[W1DAN]

Steve:

I too believe Tom's flattening of the triangle at 200hz is saturation (or clipping..eiher way loss of amplitude headroom), however the sides curvinb should be LF frequency response errors.

Dan

[K1JJ]

Steve,

Yeah, I'll bet that 35w LS driver transformer is saturating. It will be good when the MOSFET driver replaces it.  I know the mod iron is not saturating cuz I can go into the high tap and modulate twice the power carrier as shown in the test I did above.  That's a good thang at least...


T

[Steve - WB3HUZ]

Yes in the center of the sides, most definitely would be LF.

Steve:

I too believe Tom's flattening of the triangle at 200hz is saturation (or clipping..eiher way loss of amplitude headroom), however the sides curvinb should be LF frequency response errors.

Dan

[Steve - WB3HUZ]

Your hand might get tired though.

Hear the SBE below.

Anyone happen to see what the Tron's SBE looked like on an analyzer. I bet that was something interesting to watch as it wobbled around.

Yup.

I wouldn't say as much "interesting" as "annoying".

Do the same thing by wiggling the vfo knob back and forth.

[K1JJ]

I like this triangle test. Now I have a good indicator to work with and keep at it until Fabio's triangle looks nearly perfect at 200hz.  The sinewave tests were more opinion and not as easy to see flaws.  

I'd like to see more guys post their 200hz to 600hz triangles. Also, Dan how about posting your class E triangles?

I would also like to see a ricebox using a balanced modulator that has been modified for hi-fi. By right that should look really good, but who knows?  HUZ, how about your FT-102?

We can all learn a lot seeing various rigs on display. (and improvements when made)

T

[K9ACT]

In QSO with N9MS, I learned that I already have the capability to do something of the sort and didn't know it.

The Behringer 2496 has a button called RTA as in Real Time Analyzer which I just ignored for a year because there was already enough I did not understand about this piece of equipment.

I learned that one can plug in a mic, audio chain or receiver audio and get an audio spectrum display.  I plugged my sound card output into it and Voila!... Real On-Air Spectrum Analyzer.

I didn't feel like fussing with video but the snap below of W6PSS calling CQ tonite on 3700 says it all.

Now like so many of these things, I need to find out if it is of any real value.

One thing I have noticed is that there usually is a lot more energy at the very low end than is believable.

Any thoughts?

Jack K9ACT

[K1JJ]

Hi Jack,

Does it sample RF from a pickup, demodulate it and produce the display?  Or is it audio taken from the audio chain and displayed?

T

[K9ACT]

Hi Jack,

Does it sample RF from a pickup, demodulate it and produce the display?  Or is it audio taken from the audio chain and displayed?

T

It's strictly audio but I was thinking more of in bound analyzing.... as in "how's my audio today?"

js

[KF1Z]

Screenshot of the SBE, taken a few minutes ago.....

[WA1GFZ]

I put a 2 KHz triangle through the 160 meter class E rig years ago. The tips were slightly rounded. I have the filter set to start rolling off at about 8 KHz.
Last night I did a FFT display of a 1 KHz triangle and there is harmonic energy way past 10 KHz. It is way down but there. 

[W3RSW]

Here's the SBE with some sort of modulation which I put on the board a few weeks ago when our QSO on 3733 was molested.

Tore 'ZRF a new one, it did, yeah.

[K1JJ]

I put a 2 KHz triangle through the 160 meter class E rig years ago. The tips were slightly rounded. I have the filter set to start rolling off at about 8 KHz.
Last night I did a FFT display of a 1 KHz triangle and there is harmonic energy way past 10 KHz. It is way down but there. 

Interesting.

Frank, In a previous post you suggested it's easy for a class E rig to pass a 200hz triangle but hard for it to pass a 1khz or higher triangle. Is the low triangle easy cuz of DC coupling of the class E modulator?  But why is the higher frequency triangle hard for a class E rig whereas Fabio passed it easily?

So, in summary, a class E rig would have a tendency to show clean, straight triangle sides with rounded tips, whereas a good transformer class C rig would likely show more sloped sides and sharp peaks... is this correct?

T

[WA1GFZ]

Yes DC coupled and low frequency is further away from the PDM filter corner frequency allowing more odd harmonics through. The more odd harmonics the sharper the point.