hf transmissions

Spooky - there is a warning current - see www.ips.gov.au/
Also on the main front view at vks737.on.net, I've got an indicator that mirrors aspects of the above IPS site - red blocks indicates a warning current (valid for IBM compats only it seems).

Phil, what a nifty little idea. Does it work reliably at any time of the sunspot cycle ? Does the MUF always follow that rule ?

Footy,
Yep, its a useful rule of thumb which was taught to me by Phil Pullem from Electric Bug in Adelaide. And the maths is pretty easy. I find it useful for predicting the frequency I should try for a telcall. And beacon calls tells me how close I was. So for a HF mug like me, it works.

I wouldn't have a clue about the sunspot cycle or the MUF!! Hadn't heard of them before, so you got me googling! I'd appreciate if you could fill me in on how they relate to HF transmission.

I looked up the sunspot cycle, so I guess the graph below is what you're talking about.


And as for Maximum Usable Frequency
" This is a statistical prediction of the highest frequency for HF sky wave propagation. If the prediction is correct, this frequency should be refracted by the ionosphere 50% of the time. See Optimum Working Frequency and Upper Decile MUF. "

ok thanks thats what i was looking for simple maths stuff, not to much thinking thanks. o by the way did a beacon call from darwin to hobart today , not bad distance !

Phil, yes its an excellent easy way of thinking about which chan to try, but mostly applicable under say 12 meg and relatively short distances. If you look at your IPS charts you should be able to agree. I hope :))
Yep, sunspot cycle means that around every 11 years or so HF conditions get better as the sunspot count increases until they decrease and HF basically goes down the tube. This is more noticeable on the higher (greater than say 12 meg) frequencies.
MUF varies daily and is shown on the IPS chart you've chosen. It's obviously the maximum useable frequency for a given path, time of day yadda yadda. The trick is to use an upper point towards the MUF rather than working at the point (at which conditions can vary widely and quickly).
To simplify, thats pretty much what the IPS predictions do by using sounders to record the frequency at which signals on a given path go through the ionesphere rather than reflect. Or something like that, it's been a lot of years since I taught this stuff.
In short, use the IPS charts. They aren't infallable but an excellent guide.
PS. Even the US military has some *technical* personel who have zero knowledge of the above, with some startling results. Sat data stuff no worries, but HF radio was a bit beyond some of them.
.

some marine radios are set up to recieve fax/ data for weather conditions. it always amazes me how they can recieve data via a relatively ' crude' transmission wave without any information going missing on the way or getting miss-interpretated by the recieving radio. or am i under estimating the 'powers' of hf transmissions ?

Footy, Thanks again for sharing your HF knowledge.
So, given that the sunspot count is low at present, then HF transmission is not as good as it will be when it peaks again in 5 years time..... I also found out that the sunspots are the "cold" spots on the sun - only about 4000degrees Kelvin :-)))

Those IPS charts have still got me confused - I'll need to look a bit harder and get the brain into gear - it was a long day at work, so brain is in neutral at present.

Cheers
Phil

Yep, weather fax has been around for a long time. The earliest crude data transmission syatem, and remarkably effecient , was Morse Code. These days there are many exotic data over radio systems. There are even frequency hopping and high security encoded syatems in use by the military.
Despite the advent of wide spread satellite comms, HF still has its place. Especially in poorer countries where it is still used extensively.

Oops I meant that Morse was ONE of the early systems, there were others of course, even before WW1. And radio teletypes were the white bread of the data transmission systems for a long time.

Sam,
I have a friend who likes his gadgets, and HF is one of them. He came away with us for 3 weeks in the WA deserts and used his HF for email, weather faxes, and even very slow internet. He had a server set up back in Adelaide which emailed him weather charts every day. It all happened, but you could have a couple of beers while watching a weather chart evolve :-))

I like the telephone calls thru HF ........ I can call people easily..... but its pretty hard for them to call me ........ great system!

Phil, I always recommend ham radio to anyone interested ...and I know you're well past the interested stage.
The reason I do is that there is so much to learn and try that it becomes a life long addiction. Just look at the IPS site :) Wonderful stuff that can compliment the offocial networks. Data transmission, propogation experiments, building modifying and testing gear, aerials, moon bounce and extremly small signal detection techniques are but a few of the aereas you can become involved in.
Now that I've done todays ad I'll shut up for a while :)))

I am not sure about Phil's From electric bug sums

His formula would appear to suggest a a day time frequency of 34mhz Adelaide to Darwin.
Perhaps he knows more than IPS.

ASAPS V5 FREQUENCY PLAN PREDICTIONS ---------------------------- 4 Dec 2006
===============================================================================
Circuit 1: Darwin-Adelaide Distance: 2620km Date: October 2006
Tx: Darwin -12.46 130.85 Bearings: 164 341 T-index: 10
Rx: Adelaide -34.95 138.63 Path: Short Path
Selected frequency set: VKS-737 Network
3.995 5.455 8.022 11.612 14.977
===============================================================================
Mode: 1F TakeOff Angle: 4- 7 | Mode: 1E NONE
Probability > 90% | Probability 50-90% |
===============================================================================
Time Frequency | Time Frequency | Time Frequency
UT MHz | UT MHz | UT MHz
0000-0900 14.977 | 0000-0900 None
0900-1000 11.612 | 0900-1100 14.977
1000-1700 8.022 | 1100-1700 11.612
1700-2100 5.455 | 1700-2100 8.022
2100-2200 8.022 | 2100-2200 11.612
2200-2400 14.977 | 2200-2400 None
===============================================================================
Mode: 2F TakeOff Angle:17-22 | Mode: 2E TakeOff Angle:4
Probability > 90% | Probability 50-90% |
===============================================================================
Time Frequency | Time Frequency | Time Frequency
UT MHz | UT MHz | UT MHz
0000-1100 8.022 | 0000-1100 11.612 | 0000-0800 11.612
1100-1900 5.455 | 1100-1700 8.022 | 0800-0900 8.022
1900-2000 3.995 | 1700-1900 None | 0900-1000 5.455
2000-2100 5.455 | 1900-2000 5.455 | 1000-2200 None
2100-2400 8.022 | 2000-2200 None | 2200-2300 8.022
| 2200-2400 11.612 | 2300-2400 11.612
===============================================================================

Yes, good rule of thumb on single hops, but ....as I said, above around 12 meg where multiple hops are necessary, it doesn't seem to work too well. I'd imagine the MUF etc comes into play. (What I should have said is that its not valid for longer distances)
So in daytime over say 500K, 7meg is about right, nightime 3meg is about right.
But make that 3000k and we have 32 meg daytime frequency and 30 meg nightime, neither one very practical.
So for reliable relatively short paths it seems to work , but not in other situations.

The IPS figures in your post confirm my own observations btw. (of course :)