We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: Question about the ionosonde charts  (Read 568 times)

Offline MDK2

  • DX Legend
  • ******
  • Posts: 2813
    • View Profile
    • My radio reception videos
Question about the ionosonde charts
« on: May 11, 2018, 1523 UTC »
I've been using the ionosonde charts a bit more frequently, now that we're getting into sporadic E season, but I've referred to them a bit over the past couple of years since they're on the propagation page, and thankfully I live very close to Boulder and can take their readings as essentially identical for my local conditions.

I have wondered about the spikes you see that don't follow the general line of the MUF. Earlier today there was a single reading on the foF2 chart that looks like it might have actually been higher than the chart can illustrate, since it tops out at 12 MHz. (Also, 1100 UTC is 5:00am here, about 50-55 minutes prior to sunrise. Just in case that matters.) But there are periodic spikes every day, maybe just not that high. My question is, are those readings some kind of outliers, or perhaps false readings? Or do they indicate very brief moments of sporadic E? (Or something else?)

Denver, CO.
SDRPlay RSP2pro, Icom IC-7100, Grundig Satellit 750, Tecsun PL-600.
W6LVP active loop, homebrewed mag loops.
eQSLs appreciated wickerjennie at gmail

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 20215
    • View Profile
    • Black Cat Systems
Re: Question about the ionosonde charts
« Reply #1 on: May 11, 2018, 1816 UTC »
Quote
I have wondered about the spikes you see that don't follow the general line of the MUF. Earlier today there was a single reading on the foF2 chart that looks like it might have actually been higher than the chart can illustrate, since it tops out at 12 MHz. (Also, 1100 UTC is 5:00am here, about 50-55 minutes prior to sunrise. Just in case that matters.) But there are periodic spikes every day, maybe just not that high. My question is, are those readings some kind of outliers, or perhaps false readings? Or do they indicate very brief moments of sporadic E? (Or something else?)

That's a good question. I have always interpreted the spikes to be false readings. I did a quick search, and found this potential answer (search for spikes): https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007RS003742  "Nighttime above-the-MUF HF propagation on a midlatitude circuit"

Quote
The spikes in power that rise above  70 dBW, such as at 06 UT in Figure 1, are probably the result of reflection by sporadic E (Es) layers at the circuit mid- point, although there is no one-to-one correspondence between their occurrence and the occurrence of Es on the ionograms. This lack of correspondence is not surprising, because the correlation distance for Es layers is  100 km, and the ionosonde is  240 km from the circuit midpoint. The blanketing frequency for the Es layer would need to be  3.0 MHz for the layer to reflect 7.335 MHz signals. The levels reached by these spikes tend to be higher for longer durations, suggesting that the Es clouds then have larger horizontal sizes.

The section in the paper in question is not about ionosondes, but measurement of signal strengths from CHU. The paper is titled NIGHTTIME ABOVE-THE-MUF HF PROPAGATION, and looks like a fascinating read, I'll be studying it later. I don't know that this confirms the ionosonde spikes are real (sporadic E) vs glitches, but it sounds possible.

« Last Edit: May 14, 2018, 1057 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline MDK2

  • DX Legend
  • ******
  • Posts: 2813
    • View Profile
    • My radio reception videos
Re: Question about the ionosonde charts
« Reply #2 on: May 12, 2018, 0159 UTC »
Cheers Chris. Food for thought for sure.
Denver, CO.
SDRPlay RSP2pro, Icom IC-7100, Grundig Satellit 750, Tecsun PL-600.
W6LVP active loop, homebrewed mag loops.
eQSLs appreciated wickerjennie at gmail

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 20215
    • View Profile
    • Black Cat Systems
Re: Question about the ionosonde charts
« Reply #3 on: May 12, 2018, 1441 UTC »
It was an interesting paper. To summarize, they propose the propagation mode when foF2 is too low is via ground side scatter.  "In the ground side-scatter mode, the transmitted signals are scattered from the ground at a range exceeding the skip distance, and thence to the receiver. "

We do receive stations (on 43 meter for example) when it should not be possible via normal propagation, based on the real time foF2 values, so this could be one way we're hearing them. Another mechanism is sporadic E, of course.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 20215
    • View Profile
    • Black Cat Systems
Re: Question about the ionosonde charts
« Reply #4 on: May 14, 2018, 1106 UTC »
Speaking of propagation above the MUF... my logging of The Relay Station the other night: https://www.hfunderground.com/board/index.php/topic,42507.0.html

Based on foF2 values I shouldn't have heard anything. But I was actually getting a fairly decent signal at times. He said he was running 500 watts, so significantly more than the typical 20 plus/minus watts of a MOSFET type transmitter. Several S units right there, plus a decent antenna on each side of the circuit.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline TheRelayStation

  • Sr. Member
  • ****
  • Posts: 319
  • 6880 Khz AM 50W/500W - shortwavepirate@aol.com
    • View Profile
    • Email
Re: Question about the ionosonde charts
« Reply #5 on: May 14, 2018, 1606 UTC »
Speaking of propagation above the MUF... my logging of The Relay Station the other night: https://www.hfunderground.com/board/index.php/topic,42507.0.html

Based on foF2 values I shouldn't have heard anything. But I was actually getting a fairly decent signal at times. He said he was running 500 watts, so significantly more than the typical 20 plus/minus watts of a MOSFET type transmitter. Several S units right there, plus a decent antenna on each side of the circuit.
so this would be considered "ground wave scatter" ?
i suspect this type of ground wave propagation would only occur with a certain amount of TX power ?
because i was receiving my signal on many SDR's in the US-west and abroad quite well actually.
6880 Khz AM 50W/500W - shortwavepirate@aol.com

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 20215
    • View Profile
    • Black Cat Systems
Re: Question about the ionosonde charts
« Reply #6 on: May 14, 2018, 1933 UTC »
Speaking of propagation above the MUF... my logging of The Relay Station the other night: https://www.hfunderground.com/board/index.php/topic,42507.0.html

Based on foF2 values I shouldn't have heard anything. But I was actually getting a fairly decent signal at times. He said he was running 500 watts, so significantly more than the typical 20 plus/minus watts of a MOSFET type transmitter. Several S units right there, plus a decent antenna on each side of the circuit.
so this would be considered "ground wave scatter" ?
i suspect this type of ground wave propagation would only occur with a certain amount of TX power ?
because i was receiving my signal on many SDR's in the US-west and abroad quite well actually.

It's possible that is the mechanism for my reception. For the more distant receiving sites, normal propagation would suffice, as foF2 was high enough so the MUF was above 6880.  As the incident angle becomes more shallow, higher frequencies can propagate, for a given foF2 value. Once you get out of the skip zone, the signal can be heard (via normal propagation).

If it was ground wave scatter in my case, the signal was hitting the Earth some distance away from me, then getting scattered/reflected back to me. Think of it as another hop, where that hop is more distant, vs being between the transmitter and receiver sites. I guess you could even think of it along the lines of multipath reception for VHF/UHF? Not quite the same thing, but maybe that helps to visualize it?

The more I learn about propagation, the less I feel I know  ;D
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Josh

  • DX Legend
  • ******
  • Posts: 1726
    • View Profile
Re: Question about the ionosonde charts
« Reply #7 on: May 15, 2018, 1925 UTC »
There's also the old method of simply pointing the beam at a region of propagation a few hops away and using that, very common on 10m. I suppose sans beams at both ends it just becomes luck if one can hear a given signal that "shouldn't" be there.