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Old 29-07-2012, 13:02   #1
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you guys getting radio skip?

Just curious whether or not VHF radios "skip" in the atmosphere like some other freqs. We've got a VHF at the house, antenna tip about 75 ft. ASL and in the last couple of days we've been hearing transmissions from US Tow Boat in Ft. Lauderdale.
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Old 29-07-2012, 13:17   #2
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Re: you guys getting radio skip?

It can get that high in frequency, though rare. Ducting is a bit more common in VHF. During a peak back in about 1963, I just got my HAM license and heard the 6 meter band was alive, and boy that was an understatement. I quickly built a yagi for TV channel 2, and was receiving TV video and audio from Texas to my home in Northern California.
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Old 29-07-2012, 13:59   #3
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Re: you guys getting radio skip?

On one occasion I spoke to friends who were 100 miles away via vhf. If conditions are good you can hear NOAA weather from Miami in the Berrys and once in a while in Normans Cay in the Exumas.
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Old 29-07-2012, 14:08   #4
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Re: you guys getting radio skip?

We hear USCG helicopters way up in the Bahamas quite often, but they have the altitude. Ft. Lauderdale is 510 nm from here, with a whole lot of Bahamas between us. We've heard US Tow Boat transmissions for several days. Clearly. We don't hear who they are talking to. We've heard them several times on Ch. 16, and yesterday when they told whomever they were talking to to go to Ch.10, we switched to 10 just to see if we could hear them there, and we could.
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Old 29-07-2012, 14:14   #5
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Re: you guys getting radio skip?

Quote:
Originally Posted by Canibul View Post
Ft. Lauderdale is 510 nm from here, with a whole lot of Bahamas between us. We've heard US Tow Boat transmissions for several days. Clearly. .
Well at least you know who to call if you get into trouble.
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Old 29-07-2012, 16:39   #6
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Re: you guys getting radio skip?

Tropospheric ducting.
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Old 29-07-2012, 16:41   #7
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Re: you guys getting radio skip?

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Originally Posted by Auspicious View Post
Tropospheric ducting.
See post #2. Great minds think alike. lol
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Old 29-07-2012, 17:38   #8
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Re: you guys getting radio skip?

We used to routinely see 150 mile line of sight comms from the highsites when I was in the towing business
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Old 29-07-2012, 17:55   #9
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Re: you guys getting radio skip?

Canibul,
As others have posted, this is troposheric ducting (as opposed to a normal "tropo" opening / tropo enhancement...)

You can recognize this by the length of time that it lasts (sometimes days/weeks, depending on weather patterns), and by the almost straight path or tunnel that makes up the effected area....

(I cannot be sure, but I notice that you've not mentioned hearing Ft. Pierce, or Marathon....and maybe not even Miami or West Palm.....and possibly others that are more than 50 miles NE or SW of this duct, are not experiencing much of this effect...
FYI, I'm 70 miles north of Ft. Lauderdale, and have noticed no such ducting at all, this past week...)


Here is a BRIEF explanation of various long distance vhf radio propagation modes....

Simple SSB and CW VHF contacts over thousands of miles (depending on "type of propagation") are not uncommon.....VHF-FM comms over these distances are less common, but do happen more often than most believe...


As an example the first ham radio vhf (144mhz) contacts between California and Hawaii (~ 2400 miles) took place in 1957!!!! Using radios with vacuum tubes!!!! (Tropo-Ducting)


On 144mhz VHF SSB and CW, I've made contacts from FL to Wyoming, Colorado, Nebraska, etc. (~ 2000 - 2300 miles) years ago...(Es-skip).....and regularly make contacts past 700 - 800 miles using tropo-scatter (no enhanced propagation modes)....
As well as bouncing my signal off the moon, and communicating with other hams (~495,000 miles...)....


Tropo-scatter is the basic "beyond-line-of-sight" mode of vhf communications, and is NOT a propagation mode that requires ANY enhanced conditions at all....it is "always there".....you just need to have the ERP to overcome the path losses...
Tropo-scatter is a VERY reliable (24/7) communication modes, assuming there is adequate transmit power/ERP/antenna gains, to overcome the path loss, which is easily calcuable....



Normal troposheric enhancement aka "Tropo" (what most laypersons wrongly refer to as ducting) allows vhf comms thru 250 - 400 miles...
This usually occurs with a troposhperic temperature inversion....



Tropo-ducting (over water), can occur for long periods of time (sometimes weeks), depending on weather patterns....and Es-skip (anywhere), which depends on E-layer density of the ionosphere.....
Both allow vhf comms from ~600-700 miles out to 2200-2500 miles.....



There are other long distance vhf comms propagation modes, such as auroral, meteor-scatter, auroral-Es, Field Aligned Irregularites, non-TE F2 (VERY RARE), moonbounce (EME), and Trans-Equatorial Propagation....



The longest terrestrial vhf contacts are to/from the N. hemisphere / S. hemisphere, using Trans-Equatorial (TE) Propagation (F2-skip).....with disatnces of 4000 - 5500 miles....


And, with modern low-speed data comm techniques (using computers) these disatnces have continued to grow....


If you wish to see some documentation...have a look at some records...
http://www.arrl.org/distance-records
http://www.ham.se/vhf/dxrecord/dxrec.htm#C
EA6VQ - TEP propagation on 144 MHz.


I hope you find the above helpful...

John
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Old 29-07-2012, 18:58   #10
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Re: you guys getting radio skip?

Is VHF skip different then CB skip ?? I have had both and they seemed to work the same way !! altho the CB (at least mine) got out a lot further like Louisiana to Nor Cal and Washinton State. no reason just askin
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Old 29-07-2012, 19:17   #11
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Re: you guys getting radio skip?

Bob,

CB is right next to the 10 meter HAM band. When propagation allows, those frequencies are the easiest to work world wide on minimal power, like 10 watts. The reason you might of had problems on CB being heard during those conditions are too many stations sharing a single CB channel, plus while you might be running a legal 5 watts, some of the bad boys are running our HAM amps, cranking out 1500 watts.
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Old 29-07-2012, 19:52   #12
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Re: you guys getting radio skip?

Na Bob just a 25 watt SSB with a chip changed !! I had no prob being heard!! LOL Still don't with an Antron 99 65ft high !! right next to the Bayou so no ground plane needed. sorts fun to talk to fellas I know out west!!
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Old 29-07-2012, 20:00   #13
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Re: you guys getting radio skip?

Then you could roam the frequencies between 27.255 to 28.000 mhz, thus you could get a clear frequency. Been there, done that with my HAM gear in the '70's at CB's popularity peak that coincided with great propagation. I forget all the silly assed numbers we used out there, but on AM my handle was Primo, and I was running around 700 watts AM with a pair of 3-400Z Eimac tubes.
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Old 29-07-2012, 22:48   #14
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Re: you guys getting radio skip?

Got in the Habit of useing SSB CBs for talking between boats out west ! if ya had the right radios ya could guide others to the Fish !! LOL without bringing the whole fleet LOL
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Old 30-07-2012, 09:55   #15
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Re: you guys getting radio skip?

While cruising in Mexico and talking on the Manana Net one day, I got a contact from a friend about 400 miles away. He asked me to try using my VHF after the net to call him. Sure enough, we easily made contact on channel 16. After switching to a working channel, he asked me to go to low power ( 1 watt ). I called him and he said, "Go back to high power". When I did, he said he could hear me and tell it was me, but couldn't understand what I was saying.

One more "skip" happened back in the '60's.
I was flipping channels on my parent's old B/W TV and picked up a station on channel 6 (only a bit of snow in the pic), but perfectly viewable. It came and went with snowy fading, and lasted nearly 5 minutes. The station was in Kansas, and we lived in Seattle !
Later, I wrote a snailmail to the station and received a response profusely apologizing for any inconvenience, lol !
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