eHam
eHam Forums => Propagation => Topic started by: W4AEG on September 09, 2022, 02:46:22 PM
-
Why ia 17 meters totally dead after dark even when propagation forecast predict good propagation?
-
Forecast... Predict.... Its kind of like the weather. ;)
-
Why ia 17 meters totally dead after dark even when propagation forecast predict good propagation?
must be something to do with propagation forecasts.
-
Predicting a good forecast for where? Dr. Skov has an excellent talk about how the forecasts for propagation are location specific. What's good in California won't be true in Maine. I'm simple minded.... 10mhz and above during the day... 10mhz and below at night. So...
-
I think --- not to be confused with I know -- that the QRZ forecast for example (a common popular one) is based on the center of the USA. Kansas? That's about 1150 miles from me in north central Florida. Some days when propagation is overall good what I experience is close to what they forecast. But many days it is quite different -- some days even the opposite for good or poor propagation forecast. In the first place it's a forecast. In the second place it will vary from where it was based and where you are. With two variables involved there will be differences between what you read and who you work. Conventional wisdom is 20 is a "daytime band" Yet for months now it has been already open before dawn and still wide open at midnight here. Also people tend to congregate around "watering holes" So if the propagation is declining -- like in the evening -- there will be more on popular modes and frequencies. 17 may actually be open but it's a less popular band than 20 or 40 so at night they are on 20 or 40 and no one is on 17 to hear you call or for you to hear and realize it's open. Not sure if it's my antenna -- a marginal one in a HOA environment -- or the MUF just hasn't risen but I am not finding much above 15 meters at any time.
-
To talk to anyone much beyond the horizon, you need your signal to be reflected off the ionosphere - to go round to the other side of the world, you need multiple reflections from both the ionosphere and the surface of the earth. It is the effect of solar radiation that makes the ionosphere reflective to radio waves - this is why propagation is so much better at solar maxima than at solar minima. The level of ionization - and hence reflectivity - will also vary throughout the day. In darkness, the level of ionization will fall and the ionosphere will become less reflective - but this is also frequency dependent. The propagation forecasts are based on the predicted values of several metrics of which the most relevant to us is usually the MUF - Maximum Usable Frequency. The MUF is related to the propagation path - the figure for you to Europe will not be the same as it is to South America - and it increases during the day as solar radiation ionizes the atmosphere above you and falls over night as the ionization level decays away. I've just run the prediction between my QTH near London and a point somewhere round the west coast of the USA and the figure ranges from something like 7MHz at 6am this morning and 16MHz at 3:30pm this afternoon.
Martin (G8FXC)
-
Its called reality.
17M is known as a "daytime band", however you can usually make contacts after dusk for about 2-3 hrs if you have a LOW angle radiating antenna. (also 2-3 hrs before dawn).
So what antenna are you using?
-Mike.
-
My antenna is an EFHW 80-10 inv. l at 50 feet
-
Correction. Antenna is an inverted L
-
Try this: https://www.voacap.com/hf/ (https://www.voacap.com/hf/)
73
-
Your antenna is radiating at 27-25 degrees.
Try a vertical dipole.
-Mike.
-
What I'm decoding on 17m FT8 at 0Z from my QTH just west of Boston MA, about an hour after local sunset:
(https://www.dxlabsuite.com/dxview/17m.jpg)
antenna: Force 12 4BA at 90 feet, aimed due west
SFI: 140
A-index: 7
K-index: 1
-
I run wires in the half dozen trees around my 0.3 acres in the suburbs of Hartford CT.
Confirmed LoTW contacts
Details W1VT 3D2RRR 2022-06-02 02:37:26 17M SSB 18.15000 ROTUMA
Details W1VT K4BH 2022-05-30 04:25:30 17M FT8 18.10082 UNITED STATES OF AMERICA
Details W1VT WP4BRI 2022-05-30 04:19:45 17M FT8 18.10225 PUERTO RICO
Details W1VT LZ2VQ 2022-05-25 03:27:15 17M FT8 18.10217 BULGARIA
Details W1VT UD8S 2022-05-25 03:26:00 17M FT8 18.10217 ASIATIC RUSSIA
Nothing recently as it is now golfing season for me. I also have three hundred roses that need a lot of attention.
-
There are forecasts and then there is the reality. Also, as another member here said, conditions might be great in some regions of the US and not so great in other regions. Although I've SWLed and DXed MW and SW for several decades, I've never paid much attention to any forecasts. I turn on the radio and tune around. That usually tells me all I need to know.
-
There are forecasts and then there is the reality. Also, as another member here said, conditions might be great in some regions of the US and not so great in other regions. Although I've SWLed and DXed MW and SW for several decades, I've never paid much attention to any forecasts. I turn on the radio and tune around. That usually tells me all I need to know.
Tuning around to look for propagation openings on all possibly active bands takes time - time during which a station you'd like to work might go QRT before you find it.
Propagation forecasts are occasionally wrong, but on average are better than nothing when it comes to determining which bands are likely open to what locations.
DX Cluster spots are also occasionally wrong, but on average are better than propagation forecasts because they reveal actual openings.
-
I have been letting this run for a few days. it seems to be fairly accurate
https://prop.kc2g.com/
-
May I suggest
https://prop.kc2g.com/fof2/
as from foF2 data you can check whatever path length.
And yes, I agree with K0UA: to see ACTUAL conditions is much more meaningful than reading what a STATISTICAL PREDICTION states for... now!
Same for weather...
-
The accuracy of VOCAP can be improved by using the now free EZNC to model the antenna you are using as best you can, and then importing the results into VOACAP.
If you want a simple rule of thumb, low angle radiation typically results in more band openings.
You can see this in a DX contest, like the upcoming CQ WW DX contest.
Stations with beams on towers will work stuff on 15 and 20 meters at night that most ordinary stations can't even hear.
If you are relying on the vertical radiation of an Inverted L, it may help to characterize ground conductivity as accurately as you can.
-
or try 40
-
Why ia 17 meters totally dead after dark even when propagation forecast predict good propagation?
To see if a band is open I take a look at the FT8 band segment on the radio's spectrum display. From my QTH 17 meters will show FT8 signals for over 20 hours out of every 24. I sometimes make 17m CW QSOs to the west as late as 3 AM local time.