When the Band Goes Long...

[W1RKW]

When the band goes long is there a way to keep your signal local and receive local signals and get decent communication?  What antenna configuration would do that?  

There have been times when I've heard the band go long and my nearest (10miles) big gun (K1JJ) signal drops to barely readable.

I remember as a kid listening to the local AM station on 1510KHz and at night when signals would go long I couldn't here the station even though they were 3 miles away.  

[W7TFO]

Maybe set up a NVIS wire?

73DG

[WA3VJB]

I have to check my notes, but about a month ago I think I was talking with W3TIM, Tim, in Culpeper VA, who was describing good results working stations up to around 100 miles with a low height 40M dipole.  

Maybe 10 feet off the ground.

We are within that zone to one another that I plan to try it.  I even have a spare dipole cut and laid out with end insulators ready to go. Just need a hank of coax up to it.

I imagine the effect would replicate on 80M or whatever band you want to keep using when it goes long.

[K5UJ]

You are pretty much SOL with the possible exception of 160 m.  Here's why:

Your skywave propagation involves the ionosphere at different levels.  These are various layers of plasma--ionized gas.  They consist of basic elements in an unbound gaseous state and they are ionized by solar radiation.   When your photon energy excites them they re-radiate your signal (most people find it convenient to think of the radio wave as "bouncing" off the ionosphere).  As the earth rotates away from the sun every night the low layer goes into the shadow and ceases to be ionized and becomes transparent.   Now your high incident radio wave passes through it and the band "goes long" because at the right angle, it arrives at a higher layer that is still in direct sunlight.  But, for close in propagation, your vertical wave on a frequency above the medium wave band has too much energy to reflect back when arriving at the high layer dead on so it passes through it and is not reflected back.   The energy level of RF on 1.8 MHz is low enough to be reflected, though to some extent (these things are not black and white--there's a gradual change in propagation with lower frequency and time of night) even 160 m.  may not support short skip in the winter time late at night.   Technically it can be said that 160 meters is above the layer's critical frequency meaning the frequency below which a radio wave arriving at 90 degrees to the surface of the layer will excite the plasma and be re-radiated back down.  
However,  with a few hundred watts and a decent inverted L and a lot of radials, you may get 20 miles or so decently with groundwave depending on what part of the country you are in.

p.s. Local bc stations will often fade out at night even when the tx site is not far away because they will go to in some cases very low power, or change their antenna pattern, and vanish because of other signals on the same channel coming in via skywave. 

You can have a strong station go to being almost unreadable if you are in a deep night time pattern null and they go to 250 watts or less.

[W2VW]

Another way to lose AM broadcast is when surface wave and sky wave are both present.

[Todd, KA1KAQ]

I have to check my notes, but about a month ago I think I was talking with W3TIM, Tim, in Culpeper VA, who was describing good results working stations up to around 100 miles with a low height 40M dipole.  

Maybe 10 feet off the ground.

7 feet exactly, apparently. Tim was talking with a few of us on 40m back in October and sent along the following link to us:

http://www.hamuniverse.com/supernvis.html

Once I catch up on the remaining aerial projects I plan to give it a go. Would be interesting to see how it works with the local crew. Tim said later that his worked quite well.

Tom/JJ had some ideas as well, as simple as a low dipole for local work if I recall correctly.

I remember all too well 5 years back or so while still up north, when the band would go long early, like 6-7 PM. What a drag!

[ke7trp]

Like others said. A low wire will allow more signal local.  The best would be two verticals. You and the other stations.  The trouble with this is that most people on the low bands use horizontal wire.

[flintstone mop]

I have always wondered about "When the band goes long" Is there ever a situation where your transmitted signal is actually going no where? I understand that 10 miles from your station there would be ground wave reception. But the skip zone or zone of silence could be thousands of miles???

Fred

[K5UJ]

I have always wondered about "When the band goes long" Is there ever a situation where your transmitted signal is actually going no where? I understand that 10 miles from your station there would be ground wave reception. But the skip zone or zone of silence could be thousands of miles???

Fred

By nowhere you mean no skywave?  160 m. at noon in the middle of summer.  Great time to do field strength measurements.

[KX5JT]

Maybe by "nowhere" he means the signal either gets trapped in an ionospheric "duct" or if it does "land" somewhere it is so remote or in the ocean where nobody would be around to receive it?

[Steve - K4HX]

Rob is correct. There really isn't an antenna that can overcome the effect of the skip zone (when the band goes long). Most NVIS antennas produce just a few additional dB gain at the high take-off angles. Even monsters like the Jamaica and Shirley antenna are only good for 6-8 dB. None of these will overcome the multiple 10's of dB drop in signal when the band goes long.

The RF always goes somewhere. When the band is long, it's just not returning to the earth from the ionosphere within the skip zone (actually some is, it's below the noise floor). Sometimes the signal can make it through the ionosphere and out into space. Other times, the D (and sometimes E) layer absorption is large enough that little or no signal makes is back to earth.

[K5UJ]

I was wrong about a few details--there is what looks to be some pretty good information here:

http://en.wikipedia.org/wiki/Ionosphere

I am not sold on Wikipedia as a reliable source in all cases but the entry on Ionosphere didn't look bad.

[KX5JT]

As mentioned before too, when using a NVIS sometimes you have some groundwave arriving with the bounced signal and therefore some selective fading (maybe cancelling would be a better term)

[The Slab Bacon]

When the band goes long and conditions get crappy,
It's time to head for the kitchen and make your belly happy.

      

[KB2WIG]

get yer selv a cube refrigerator and ya dont havta go to the kitchen.


klc

[Steve - K4HX]

You would only have groundwave if the other station was within 20-50 miles (and running a vertical) on 160 meters, 10-20 miles on 80 meters and progressively less distance as you go up in frequency. Groundwave is rarely a propagation factor on HF.

As mentioned before too, when using a NVIS sometimes you have some groundwave arriving with the bounced signal and therefore some selective fading (maybe cancelling would be a better term)

[The Slab Bacon]

You would only have groundwave if the other station was within 20-50 miles (and running a vertical) on 160 meters, 10-20 miles on 80 meters and progressively less distance as you go up in frequency. Groundwave is rarely a propagation factor on HF.

When you still lived here in B-more, we were prolly no more than 10-12 miles from each other (as the crow flys). Remember back, how many times we couldn't hear each other. That was a good example.

Ground wave..........hooey, it basically doesnt exist on the lower bands if you are running horizontal antennas. I remember when Rick (N3HIA) was playing with 75m stuff
(or at least trying to) I was listening to him while working at the bench. His house was no more than 4 miles away from mine and I was hearing QSB on his signal.

Without a vertical antenna and a lot of horsepower, "ground wave" is not a reliable mode of propagation on the lower bands.

Another good example was the BCB oldies station IIRC, their call was WYST. They used a vertical (tower) here in the lower bowels of South Baltimore. They ran something like 1000w daytime and 25w night time. (or maybe it was 100w daytime) They were piss weak during the day, and I couldn't even tell they were there at night.
(From my house less than 10 miles away) Basically, if you weren't in the industrial part of South Baltimore, you could not hear them at night. I dont know why they even bothered.

[WD8BIL]

Another good example was the BCB oldies station IIRC, their call was WYST. They used a vertical (tower) here in the lower bowels of South Baltimore. They ran something like 1000w daytime and 25w night time. (or maybe it was 100w daytime) They were piss weak during the day, and I couldn't even tell they were there at night.

The oldies here in Lorain on 1380khz runs 57 watts at night till sunrise. I'll listened to them the first week of the new job as I drove the turnpike east. At 57 watts I'd loose'em 12 miles down the road. Recently, I've been in transit during their daytime power up at sunrise and can enjoy them for another 15 miles.

Their antenna is a 79 degree vertical stick, insulated bottem fed.

Groundwave 160M is a local mode. The more Eimac you gots the more local you can be.

[The Slab Bacon]

The more Eimac you gots the more local you can be.

Ah, yes..................There is nothing like "Antennas by Eimac"     

[Pete, WA2CWA]

The RF always goes somewhere. When the band is long, it's just not returning to the earth from the ionosphere within the skip zone (actually some is, it's below the noise floor). Sometimes the signal can make it through the ionosphere and out into space. Other times, the D (and sometimes E) layer absorption is large enough that little or no signal makes is back to earth.

You said: "Sometimes the signal can make it through the ionosphere and out into space."

If you're at the International Space Station, I often wonder what an HF receiver would sound like when tuning across the dial. It's roughly about 250 miles out in space from earth. The top most layer (F) is roughly about 150 to 300 miles up depending upon ionization. Once the RF energy enters space, does it get weaker as it travels further away from earth?

[W1RKW]

I wonder if that science experiment has ever been done on the ISS.  It would be interesting to know if HF freq. make it out of the ionospheric boundary and to what degree especially when the band goes long and we don't know where our signals endup.  Since humans have been producing RF for over 100 years and most has been in the lower HF region or lower, I wonder if there are any extra terrestrial HF hams, QSL?

[K5UJ]

You must have missed the HAARP 7 MHz moonbounce experiment.   You can google it to find out more.  I heard the echo at my QTH.  Yep at the right angle 7 MHz makes it past the ionosphere and returns.

100 years of RF.   so, the first spark transmissions are 100 light years out there now.  That's not too far.  You have to wrap your head around the size of Universe.  By the time any RF reaches anything if there is anything to detect it, we won't be around, not to mention being around long enough to copy the reply.   All the stuff about ET, SETI, Roswell etc. makes for great science fiction and Hollywood screen plays but the hard reality is that physics intrudes with limits involving vast space, really long travel time and mass to energy speed limit. 

[W1AEX]

By the time any RF reaches anything if there is anything to detect it, we won't be around, not to mention being around long enough to copy the reply.

Yeah, but Rob, think about this. When they tune in ancient slopbucket signals the aliens will be totally confused, however, when they tune in an ancient 75 or 40 meter AM signal they'll no doubt smile and say, "Whoaaaa, those guys had great audio!"

[K5UJ]

Then they'll want to visit.