HF Comms during sunrise & sunset?

[Massey1Bravo]

Are there any 'rules of thumb' when selecting a HF comms frequency in eastbound and westbound flights during sunrise and sunset? I know it's related to the reduced MUF during the night but how do you choose which frequencies to use to communicate ahead and behind?

e.g. An a/c is flying westbound during sunset, which HF frequencies would be most suitable for communicating ahead and behind?
13261,8867,5643,3467

Thanks in advance!

[Intruder]

How far ahead/behind? I usually try a freq suitable to the time of day at the ground station...

If I'm over the pacific, talking with San Francisco behind and Tokyo ahead, and it is local sunset where I am (and will be so for quite a while...), I'd try San Francisco on 56 and Tokyo on 88 if I didn't have any other guidance.

[Massey1Bravo]

How far ahead/behind?.

Around 500nm ahead and 500nm behind. (At the half way point)

[OzExpat]

My general "rule of thumb" for HF comms is :-
Low frequencies for low hours of the day.
High frequencies for high hours of the day.
Works for me.

[Intruder]

OzExpat:

Actually, your rule of thumb should be that the high/low freqs match the height of the sun in the sky: highest freqs at noon, lowest freqs at midnight (based on local time at the ground station).

Massie:

On what 1000 mi route do you use HF? On the NATracks HF freqs are normally assigned, so no guesswork is required.

[AerocatS2A]

My general "rule of thumb" for HF comms is :-
Low frequencies for low hours of the day.
High frequencies for high hours of the day.
Works for me.

Or "always go down at night" :).

Massey1Bravo,

The only HF airspace I fly in, the preferred frequency is stipulated by ATC. So you try that first, and if you have no luck getting through, you try one of the other ones.

[OzExpat]

Thanks Intruder, I did word my post rather poorly didn't I! :eek:

S2A... even simpler, ta!
Get UP by day.
Go DOWN by night!
Too easy! :E

[Self Loading Freight]

Thanks Intruder, I did word my post rather poorly didn't I! :eek:
S2A... even simpler, ta!
Get UP by day.
Go DOWN by night!
Too easy! :E

Students of HF propagation and the effect of the Maximum Usable Frequency (http://hfradio.org/muf_basics.html) on communication after dark know this as the MUF dive.

R

[ionagh]

For those interested, there is a site offering more or less real-time MUF charts.

http://solar.spacew.com/www/realtime.php

[green granite]

A more indepth article on the subject

Cycles that Affect Propagation
Propagation is affected by cyclical environmental conditions. The shortest of these conditions is the day/night cycle. In general, the transmitting and receiving conditions are by far the best in the nighttime hours. During the daytime, the MUF and LUF both rise -- in order to talk across great distances, less reliable (because of the very long skip) higher frequencies must be used. The season of the year also affects propagation The winter/summer cycles are somewhat like the day/night cycles, except having a lesser influence. In general, the MUF and LUF will both be higher in the summer and lower in the winter. Also, the noise from thunder storms and other natural phenomena is much higher during the summer. In fact, except for local transmissions, communications in the 1700- to 3000 kHz range during the summertime are of limited regular use.

The longest environmental cycle that affects propagation is the sunspot cycle. Before the age of radio, it was noticed that the number of solar storms (sun spots) varies from year to year. Also, the number of sunspots per year was not entirely random. The number of solar storms during a good propagational month exceeds 150 and the number during a weak month is often fewer than 30. The sunspot cycle reaches its peak approximately every 11 years, cycles that have a great impact on radio propagation.

Between these peaks are several years with very low sunspot activity. During years with high sunspot activity, the MUF dramatically increases and long-distance communications across much of the HF band is possible. During the peak of the last sunspot cycle, in 1989, the MUF was often above 30 MHz! When the cycle is at its low point, the MUF decreases and much less of the HF band is usable for long-range communications. Generally, the frequencies above 10,000 kHz dramatically improve during the peak years of the sunspot cycle, and the frequencies below 10,000 kHz are much less affected

@ dawn and dusk there is also a phenomina called GREY LINE propagation which enhances the north / south line range significantly
hope this helps :8

[ionagh]

......and not forgeting those days in summer when MUF can reach nearly 200MHz (sporadic-E).

500nm in each direction? VHF will do nicely!:eek:

[HOMER SIMPSONS LOVECHILD]

After a few years of diligent study,here's the method I've had the most success with on the nattracs.
Try 5598,then 8906,then 13336.If you are still feeling keen choose another frequency completely at random from the chart(forget all that "nat A,B,C,," stuff,prop forcasts etc,just stick a pin in).If it's a line check and you've still had no joy try a for a relay.If that fails,do the crossword and repeat the cycle at the next waypoint.;)

[Spodman]

"the high/low freqs match the height of the sun in the sky: highest freqs at noon, lowest freqs at midnight"

HF works by bouncing signals (refracting anyhow) off the ozone layer, activity within which is driven by the sun. It lags the actual position of the sun though, MUF's are at their max mid afternoon, at a min before dawn. It is the activity between you and the station you need to consider, not just overhead the ground station.

I used to do International HF many moons ago in Perth, West Australia. Our transmitters were in Perth, but our recievers were miles away near Pearce. If you transmitted while disabling the reciever mute you got a nice squeal to tell you the radio worked. Near the end of a long winter night the higher freq recievers couldn't 'hear' their transmitters! On the other hand an aircraft checking the radio on 3 MHz on the ground at Perth in the afternoon could sometimes not be heard.

[FE Hoppy]

"around the world on eights"
Having spent far too many hours flogging up and down the atlantic north and south. Having taken part in many equipment tests at all times of year, month and day I can honestly say that the best option is eights regardles of local/station time of day.

Often it's as much use not keying the mike and shouting at the windshield.

[ionagh]

I can honestly say that the best option is eights regardles of local/station time of day.


:ok:

This is supported by the maritime HF service where distress alerts from ships have a default selection of the 8MHz band. Experience has shown that it usually works.

[blueplume]

Sun up - Frequency up
Sun down - Frequency down