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Author Topic: VHF Signal Distance?  (Read 3271 times)
WH7DX
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Posts: 1029




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« on: June 16, 2013, 07:58:51 PM »

I don't use VHF much.  Mostly listening in to the WinSystem through a repeater in town about 16 miles away (clear shot), or calling in occasionally to the local emergency net.  I  have a handheld Yaesu and run the Yaesu FT-897 for home use - running a Arrow Antenna OSJ 144/440  on the roof - about 200ft up or so.

http://www.arrowantennas.com/osj/j-pole.html

Starting on Saturday, I was listening to a Big Fishing Tournament off Waianae, Oahu, Hawaii.   It's 36 Miles from my house to the Fishing Home Base.  Didn't compete in it this year..  200 boats trying to catch the largest yellow fin tuna (Ahi), Marlin, Ono or Mahi (Dolphin Fish).  

From Koko Head on the bottom right to Waianae on the upper left.   The signal needs to go over a 2000 ft ridge and then a few smaller hills etc.

I'm surprised that I can hear the Base really clearly in the afternoon (like a phone).   I can also hear boats at sea calling in to base or as relay's for others that are even further out that I can't hear - or can Base.

I could see hearing the boats down south were I would have a clear shot but many are in the Waianae area and West.  

I didn't hear them much in the morning.  I'm wondering if I'm getting some type of temperature or cloud propagation?      

Or signal bending?  Perhaps around the mountain ridge near Kapolei?

https://maps.google.com/maps?q=Honolulu,+HI&hl=en&ll=21.420472,-157.920914&spn=0.478132,0.707245&sll=42.442715,-76.498318&sspn=0.094755,0.176811&oq=honolulu&t=p&hnear=Honolulu,+Hawaii&z=11
« Last Edit: June 16, 2013, 08:05:00 PM by WH7DX » Logged
W8JX
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« Reply #1 on: June 16, 2013, 08:35:09 PM »

What you are seeing is called ducting/air mass bending. It is pretty common this time of year with changing weather patterns. Sometimes it can go several hundred miles.
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WH7DX
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Posts: 1029




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« Reply #2 on: June 16, 2013, 08:54:36 PM »

What you are seeing is called ducting/air mass bending. It is pretty common this time of year with changing weather patterns. Sometimes it can go several hundred miles.

Thank you!   I guess that's why I can hear them much better in the afternoon.   I couldn't hear them much at all in the AM.

I saw the episode on Ham Nation recently with the mountain on the Big Island and West Coast contacts. 

http://arvideonews.com/hrn/HRN_Episode_0076.html

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KA4POL
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Posts: 1978




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« Reply #3 on: June 16, 2013, 09:42:50 PM »

A good explanation of propagation phenomena is at: http://www.dxfm.com/Content/propagation.htm
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WA3SKN
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Posts: 5480




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« Reply #4 on: June 17, 2013, 05:42:41 AM »

There are lots of different propagation modes that can affect 2 meters.  But most common for FM would be a thermal inversion, or "ducting".  And when you notice it, don't be afraid to switch over to SSB/CW with a beam antenna... you will be suprised what you can do!
Hawaii---Mainland 2 meter contacts have been done you know!
Enjoy the opening.
73s.

-Mike.
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WX7G
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« Reply #5 on: June 17, 2013, 06:13:46 AM »

This could be "knife edge diffraction" propagation. That is where a signal will bend around the top of an obstruction.

http://en.wikipedia.org/wiki/Knife-edge_effect
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WH7DX
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« Reply #6 on: June 17, 2013, 11:19:00 AM »

I thought knife edge diffraction was more for buildings etc.. didn't know about mountains.

Thanks guys.   There isn't much VHF/UHF activity on the islands.  Probably a combination of things, and the fact that it is an islands with mountains all over.

I wasn't able to transmit on my Yaesu 897, it said TX Error.  I wasn't sure why.  It didn't really matter so I didn't look it up - more than turning the offset off.

They were using Marine Channel 68 which was 156.425.   I don't know if that's restricted by Yaesu?  I don't believe so.   I would think the power would be auto adjusted as well.   Oh well.   Surprised I could hear them at all.   



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W8JX
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« Reply #7 on: June 17, 2013, 11:25:14 AM »

I wasn't able to transmit on my Yaesu 897, it said TX Error.  I wasn't sure why.  It didn't really matter so I didn't look it up - more than turning the offset off.

They were using Marine Channel 68 which was 156.425.   I don't know if that's restricted by Yaesu?  I don't believe so.   I would think the power would be auto adjusted as well.   Oh well.   Surprised I could hear them at all.  

A stock 897 will not transmit there. I am not surprised you heard them. It is not a rare propagation event.
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WH7DX
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Posts: 1029




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« Reply #8 on: June 17, 2013, 02:02:17 PM »

I wasn't able to transmit on my Yaesu 897, it said TX Error.  I wasn't sure why.  It didn't really matter so I didn't look it up - more than turning the offset off.

They were using Marine Channel 68 which was 156.425.   I don't know if that's restricted by Yaesu?  I don't believe so.   I would think the power would be auto adjusted as well.   Oh well.   Surprised I could hear them at all.  

A stock 897 will not transmit there. I am not surprised you heard them. It is not a rare propagation event.

I poked around a little.   I see some talk about "opening up" the 857 for Marine Frequency (I have the FT-987) but then they said that any transmission on the Marine SSB Frequencies is Illegal if it's not an emergency?    I had to look up Marine SSB.   I'm was at 156.425 FM.....

I just *assumed* that if you had an actual Ham RAdio license and a nice $1000 rig you'd be able to talk to someone who went to WestMarine with $100 and no license?  

Now I'm curious.   I'm sure someone with some marine experience can explain this.   The Fishing tournament was using Channel 68 (156.425mhz)

>>>>Yes it is perfectly usable for HAM bands.
It can be opened up for extension of transmission frequencies to also cover transmission on the marine SSB frequencies, but even with a HAM license transmission ont those marine SSB frequencies is illegal. Only for emergencies.<<<<

Found something on my FT-897

>>>I am using myself the Yaesu FT-897D, it is very compact and ruggedly built. It can easily be 'opened up' to allow transceiving on marine frequencies (oops I did not tell you that...).<<<<

It's not something I plan to do.. and I have a boat and regular marine radio on it.. but I'm curious to what "easily opened up" is.

Can't be as easy as cutting the green wire on the 811H for 10M  Grin
« Last Edit: June 17, 2013, 02:41:37 PM by WH7DX » Logged
K2OWK
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« Reply #9 on: June 17, 2013, 02:49:57 PM »

Hello, The posts about ducting are correct. The temperature inversion layer produces a duct that acts as a wave guide and allows VHF/UHF signals to bend around the curvature of the earth. This duct can be right on the earths service or up to 100 feet in height above the earth. An antenna system set just above ground plane works best. The ducting range (over salt water, ice and land) can be predicted by using the Trans Horizon Path Loss Attenuation Theory. This theory takes into account the two way gain in the direction of transmission (transmit gain, receive gain) including antenna gain. This is what accounts for you hearing the signals over the distance you are experiencing.

Hope this helps,

73s

K2OWK
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WX7G
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« Reply #10 on: June 17, 2013, 03:56:29 PM »

How to tell if this particular path is ducting or knife edge diffraction?

If the path is open 24/7 it is knife edge diffraction. If the path opens and closes it is ducting.
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K0JEG
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« Reply #11 on: June 17, 2013, 07:38:30 PM »

I thought knife edge diffraction was more for buildings etc.. didn't know about mountains.

When I lived in Fraser, Colorado (about 40 miles west of Boulder, but with the continental divide in between) I could regularly hit some Denver/Boulder area repeaters on low power with an HT, and others not at all no matter how much power and antenna. Moving even as little as a block away would make it impossible to hit the same repeater no matter how much power I'd have. Knife edge is interesting stuff.
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W8JX
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« Reply #12 on: June 17, 2013, 07:57:10 PM »

I thought knife edge diffraction was more for buildings etc.. didn't know about mountains.

When I lived in Fraser, Colorado (about 40 miles west of Boulder, but with the continental divide in between) I could regularly hit some Denver/Boulder area repeaters on low power with an HT, and others not at all no matter how much power and antenna. Moving even as little as a block away would make it impossible to hit the same repeater no matter how much power I'd have. Knife edge is interesting stuff.

I suspect you are more likely seeing bounce/reflection of some rock face rather than knife edge. The small movement tends to support this and loss of "focal" point
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KQ6Q
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Posts: 976




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« Reply #13 on: June 17, 2013, 07:58:11 PM »

regarding the non- legality of 'opening up' your radio.
Hams are allowed to build their own radios, and operate ON THE HAM BANDS,
subject to the spurious emissions requirements in the FCC Regs.
Radios used in other services - Aircraft, Marine, Broadcast, Business, must be Type Accepted by the FCC.
Radios built commercially for the amateur service cannot be legally used in other services.
BUT radios Type Accepted for other services CAN be used on the Amateur Bands,
because hams are allowed to build and modify radios, to use ON THEIR AUTHORIZED FREQUENCIES.
You can use an Aircraft or Marine HF radio on amateur HF bands if you have a ham license.
You can modify a business band VHF or UHF radio to use on Amateur VHF or UHF frequencies. Hams have
been doing it for years. But you are NOT allowed to build a radio to use outside the Amateur Bands
without Type Acceptance for the Radio, AND the proper license/authorization to use it.
There are lots of FCC Regulations. Part 97 applies to hams. There are lots of others!
BTW - enjoy the surprises in VHF propagation and ducting, ionosheric reflections, etc.

Fred, KQ6q
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WH7DX
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Posts: 1029




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« Reply #14 on: June 17, 2013, 08:16:32 PM »

Thanks for the input guys.    That makes sense regarding the "make it" part and keeping that out of the other bands.

I think I read that ICOM has a radio or two for HF, VHF/UHF and Marine SSB/FM?  Unless I'm mistaken.   It just seemed odd to have this nice FT-897 and I couldn't TX but my crappy radio in my boat has no problem.   

It would seem like more of these portable radios that do HF, VHF/UHF would want Marine and that the FCC would allow them to if they can't?   If I had a sailboat, I would want a radio for all of that and perhaps a good small water resistant portable for backup.

For a sailboat - the Yaesu FT-897 and 100W could be valuable but you'd still need a regular Marine Radio.
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