Message from gypsy at Wednesday, 10-Jun-09 05:19:09 GMT

Something I think we all needed to know about Tim.
Nice article

Message from VK4DGM at Thursday, 11-Jun-09 05:52:20 GMT

Thanks Tim Good Information

Message from Calico at Thursday, 11-Jun-09 09:16:32 GMT

Cheers Daryl, Rohit, and all GT-ers!

It would be fantastic if us folks find some time to add our findings in the Forum theoretical, own research or practical experience!

With people here knowing stuff on Sporadic E, Meteo and Lightning scatter etc, it is an ideal context for learning from one another and then just tuning GT goodies!

Es and ducting this time of the year are big reasons for radio-partying !

73 es gd GT-ing
Tim
PS GT-ing must of course stand for Global Tuning ;)

Message from Calico at Friday, 12-Jun-09 08:02:17 GMT

Propagation indices? What's that?

We come across A, K, S.F.I. while using Global Tuners or elsewhere. But what do these indices tell us about radio propagation?

In a nutshell and as far as HF are concerned...

*Solar Flux Index (SFI): Solar activity determines the amount of radiation we get from the sun. SFI is measured in Solar Flux Units, and varies between 50 and 300.
In general (and NOT locally) SFI around 50 shows Maximum Useable Frequency (MUF) will be low maybe about 12 MHz, whereas SFI around 300 shows MUF will be pretty high, well into VHF frequencies. Expect low SFI values around bottom of sunspot cycle and high SFI values around peak of (+/- 11 year) sunspot cycle.

*Geomagnetic activity indices, K and A

As the number of sunspots rises, more solar particles hit the geomagnetic field of the Earth. This causes the Earth’s magnetic field to behave differently. As the solar stream disrupts the geomagnetic field, HF conditions degrade and M.U.F. gets suppressed. Hence the need to monitor and measure the geomagnetic state.

K-index-> local index of magnetic activity relative to an assumed quiet-day curve for a single geomagnetic observatory site.

Ranges from 0 through to 9 and largest value is recorded at a 3-hour interval of UTC time.

Kp-Index-> Planetary average of all the K indices around the world.

Values about 0 to 1 represent quiet magnetic conditions and this would indicate good HF conditions, whereas 7 to 9 represent a very major storm that could result in a blackout of HF communications.

A-index is for daily average of local geomagnetic activity, and is generated by the 3-hour K index. (We need it as K index is quasi-logarithmic, not suitable for daily averages.)

ap-index -> a measure of the general geomagnetic activity over the planet for any given day.

Ap-index-> a daily, planetary index, calculated from 8 ap indices
Ranges from 0 to 400.

Values from 0 to 3 represent quiet conditions, whereas anything over 80 indicates a storm.

At sunspot peak, the level of the geomagnetic activity rises as a result of the increased level of particles emitted by the sun hitting the Earth's magnetic field. The ionosphere can also be badly affected, as in the case of ionospheric storms. So high Solar Flux Index values, not always good news.

***Did you know?***
- It is the plage, the bright area around the sunspots that emits most of the solar radiation.


-Sunspots were first noticed by Theophrastus around 325 B.C. ! Ionospheric storms can cause total HF blackout

-This is not just a sunspot., is it? Starts with an “I” and ends in an “S” ! http://www.astropix.com/HTML/SHOW_DIG/055.HTM

-Stars, like our sun, have spots too, and quite predictably, are called starspots.

-Sunspots are “only” about 4500 ºC compared to about 5500 ºC of the surrounding areas of the sun.

Sources:
-Ionospheric Radio, Davies K., Institution of Electrical Engineers
-Your guide to propagation, Poole, I.
-Internet: www.radio-electronics.com


(Created for Global Tuners by Dorset Radio)
(Tabulated 12-06-'09)

Message from Calico at Wednesday, 02-Mar-11 10:37:24 GMT

From theory to every day practical communications.
Nicely presented as Power Point Slides:

http://www.infotechcomms.net/ionospheric_sounding.pdf

Message from nickstr1 at Thursday, 03-Mar-11 09:46:19 GMT

I can indeed say that when a high S.F.I is observed that the MUF for F2 skip will be into low VHF given a couple examples. A famous one was in 1938 when techs at an RCA facility in New Jersey or New York managed to receive the 41 MHz video signal from the BBC TV Alexandra Palace transmitter. A more recent example is that in December of 2001 a TV DX enthusiast in Kentucky reported getting NTSC TV channel 2 from Trinidad and Tobago along with Venezuela both audio AND video which meant an MUF of 60 MHz. Some of the VHF DXers here I am sure have tales about these F2 openings in the winter months during periods of high solar activity. This is about all I can think of to add to the discussion because the information stated is for the purposes here complete.

Last edited by nickstr1 at Thursday, 03-Mar-11 09:47:35 UTC

Message from Calico at Friday, 04-Mar-11 12:23:32 GMT

BBC VHF in New York!
WOW !

Message from nickstr1 at Friday, 04-Mar-11 23:42:52 GMT

Not just in New York but also Australia in 1981. VHF F2 propagation can be incredible in terms of distances.

Message from Calico at Saturday, 05-Mar-11 14:57:28 GMT

Incredible, indeed ! Still though...

The 1938 New York reception is for me more significant and impressive than the Australian reception in 1981.

In the 1930's they hardly knew of Appleton layers and the possible range of F2, let alone tropospheric and ducting propagation. History and Science was being in the making.

In the 1980's it was not as challenging anymore. Most of all this (i.e. VHF properties) was well and widely known. Yagis, Arrays, Log-periodics, phasing techniques were commonplace. Optimized low loss lines and waveguides, super sensitive solid state radios, pre-amplifiers, dx-ing recommended times, barometric pressure issues, practices, etc were widely available to anyone.

And as early as 1958 we already had satellites using VHF. Who could ever forget the sensation Sputnik created using e.g. 40 MHz !

I too, like you, wholeheartedly admire the achievements of these VHF radio pioneers and/or enthusiasts.

And on a lighter note, Nick:
Imagine what VHF dx one could catch if they recorded the I/Q data of an SDR VHF RX 24/7. ;-)

Message from nickstr1 at Thursday, 10-Mar-11 09:24:28 GMT

Perhaps but it would be expensive to have such a receiver. It would be a VHF DX enthusiast's best friend because skywave propagation is highly sporadic and unpredictable. Some attempts have been made to predict and understand E-skip but the predictions have been off and there is still quite a bit we don't understand about it yet.