Beacon Images on waterfall displays

[VK2KRR]

For those of you looking for weak signals on Spectran, this is what to look for. As these dont appear to show up full size in the normal window, I think best idea is to Right Click on them and press 'Open Link In New Window' then this page will remain open. I listen in CW mode with IC910 unless indicated.

Mildura 2m 27.08.08.jpg

Esperance 2m 23.06.08.jpg

Geelong 2m 28.08.08.jpg

[VK2KRR]

More..

Geelong 70cm 27.08.08.jpg

Note Geelong 70cm TXs to NE and West alternating each time

Mt Gambier 2m 27.08.08.jpg

[VK2OMD]

I listen in CW mode with IC910 unless indicated.

Leigh,

Receivers with a narrow CW filter might not capture both mark and space frequencies of FSK beacons as shown in your displays. No big problem, just it will look more like regular A1 in a narrower bandwidth, either normal or inverted depending on whether the mark or space freq is in-band.

Owen

[VK2JDS]

Yeh Matt, i can definately confirm is lost the plot. Signal strength from the beacon from the mountaintop over the 180km path was quite good on the 3 metre dish, but its got a chirping oscillation as seen on your spectran signal there. I emailed vk2wi about it earlier
73's

[VK2JDS]

Now the 1296.420 beacon at Dural is fixed we can get down to some antenna/feed/preamp experiments and aeroplane path logging.
The captures so far have been a single line from the beacon with a doppler shifted single line crossing the beacon line and then fading out about 10 seconds afterwards. 2 days ago I captured these 2 shots.
I reduced the signal from the dural beacon to near zero by aiming the dish south a bit.
They show a faint dural beacon at 600hz with this amazing multifrequency doppler shifted signal array.
What causes this?
there is a gap in between the 2 screen grabs due to me opening a file and saving the dump into it, then getting the next one and they should be the other way around.

[VK2JDS]

Well, I have had one email with a possible solution , but its not interference.
The sound was multifrequency, i could hear it quite clearly and it had the dural beacon ident on it !
73's de Dave vk2jds

[VK2OMD]

...
What causes this?
...

It is an interesting chart.

Again, the waterfall display makes it impossible to accurately gauge the relative strength of the components.

I note the licence is for F1(FSK telegraphy) modulation type, and the WIA beacon list shows it as "CW" which in their terms probably means A1 telegraphy.

The spectral distribution hints FM. It could be from sine wave modulation with a frequency of around 66Hz and m~=3 which would result in significant power in the carrier and first three sidebands. It begs the question whether there is some residual FM or spurious modulating signal.

It would be interesting to see a normal spectrum display from a local station, a display that allows measurement of the relative levels of the components.

Owen

[VK2OMD]

...
Is this what you want Owen?...

Hi Matt,

If I interpret the first graph correctly, it shows a single carrier amplitude modulated with telegraphy. If it was FSK as per its licence, then the MARK and SPACE frequencies should be within the 850Hz assigned bandwidth, and should be visible on the display?

Your report of the signal now doesn't show the effects that Dave reported a few days ago. If Dave's effect is a result of purely of propagation, it is an interesting one, and I am at a bit of a loss to propose a plausible explanation for several components that are evenly spaced from the carrier, suggesting 1st, 2nd, 3rd sidebands, and doppler shifted by the same amount as the carrier. As I said, interesting.

Thanks for taking the trouble to report your obs.

Owen

BTW, PNG is a better format for displaying screenshots like these, GIF is ok, but a more limited palette of 256 colours max, but both formats are lossless compression as opposed to JPG which creates artifacts because of its FFT based compression strategy.

[VK2OMD]

Thinking aloud some more on Dave's interesting observation...

A sine wave amplitude modulated carrier has only one pair of sidebands. Multiple sidebands suggests FM/PM or a complex modulating wave (eg a square wave).

Dave's wave had the appearance of multiple sidebands.

If we can assume that the transmitted carrier was unmodulated, then the modulation must have been caused in the propagation path.

There is clearly a low frequency variation that would be likely to be caused by some kind of doppler mechanism. That doppler mechanism being movement of the common area.

The sidebands spaced at ~66Hz aren't as obvious an explanation.

The path is long enough to include tropospheric propagation.

I have noticed a kind of rapid flutter or rumbling on tropo scatter signals. Presumably it is some amplitude modulation of the signal by the turbulence in the troposphere, and the multi path nature of reflection from the troposphere. If the amplitude variation tended to have a central frequency, but was not simply sinusoidal, it could result in the type of spectral distribution reported. If that is the case, it suggests that the central frequency has something to do with the natural frequency of the turbulence in the troposphere. It would be interesting to capture observations over time and over differing path lengths.

Owen

[VK3HZ]

I've seen this sort of thing when playing with PLL Loop Filter time constants. It also looks like the VK5RSE beacon when they were having troubles with the PLL.

According to Mark VK2XOF, the signal for VK2RSY is generated from a cavity oscillator locked to a 0.1 ppm oven. Locked = PLL (generally).

My initial reaction was to check if the sidebands are a multiple of 50/100 Hz, indicating hum getting in to the oscillator freq control line somewhere, but they appear to be an odd frequency - 66 Hz or so.

I would guess there's a problem with the loop filter - either a component has fallen off or the filter has not been set up properly. However, it is a bit odd that there seem to be two modulating frequencies superimposed - the 66Hz and a very slow variation - something like 0.5 cycle per minute.

BTW, is the beacon FSK or simply keyed on-off?

Regards,
Dave.

[VK2JDS]

Might have just been a meteor, it didnt sound like what i normally hear on 6 and 2 metres,but thinking outside the square here , what about if it was the space shuttle? its very high up, do you think enough turbulence could be created? the exact local time i save the best of the 2 pics was 7:40pm local dst 4 -11-08. I will run orbitron up later and backtrack the shuttle's movements... the doppler was quite wide, so it was something moving fast

from the mountaintop the beacon is very strong and shows no sign of any sidebands like in the AE event .
73's de Dave

[VK2JDS]

Yes the ISS was passing at the time and within coverage area, but it was to the south and is quite a long way off the beam heading of where the dish was pointed until 4 minutes after the event. Thats when it was directly behind the beacon.
So I think that rules that out unless there is a clock problem or ephemeris data error.
Back to meteors again..

[VK2KRR]

Here is a capture of Mt Gambier VK5RSE beacon this evening, received at my station. Ive got it on Spectrum Lab and also the WSPR screen as a longer time period capture.

You can see on the longer WSPR graphs that there had been two aeroplanes on the path at one stage, and also at the beginning the beacon was running the High Temp beeps rather than the usual key down, and then it changed to key down, I guess the temp had cooled enough and you can see the drift then start to fall rather than rise.

VK5RSE 2m

[VK2KRR]

Capture of VK6REP Esperance beacon this morning 14.12.13 about 9.15am on 144.568 MHz +- @ 2312 km.
Seen both on Spectrum Lab and WSPR-X waterfall. Drifting lower after sunrise in Esperance.

VK6REP morning 14.12.13

[VK2KRR]

A new pre-amp sorted out on 1296 MHz over the past 24 hrs!

Anyway, captured a bit of VK3RXX 1296 MHz beacon from Melbourne. Looks much straighter than usual, maybe GPS locked now ? Have run it up on Spectrum Lab and also WSPR X waterfall. Couple of aircraft reflections in there also. Its good to be able to hear again.
Its around 335 km from here. Using my 3.8m dish at about 35 ft.

VK3RXX 1296