Author Topic: NVIS Antenna  (Read 9044 times)

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ClovisMan

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NVIS Antenna
« on: September 20, 2013, 07:52:43 AM »
So I gathered the parts and assembled the 40/80 NVIS antenna using the instructions from DX Engineering.
http://static.dxengineering.com/pdf/WP-NVIS-Rev2.pdf
I sourced a set of MilSurp fiberglass antenna masts and base from eBay for 25 bucks(score!). All that is left is to attach the antenna to the mast and test. What frequencies on the 40m and 80m bands will I likely find someone? I'm a new General class which means I'm new to HF.
(This antenna will be going through my LDG Antenna Tuner to my Yaesu FT857d).
Wouxun KG-UV6D HT Dual Band
Yaesu FT-857D all band transceiver
Yaesu FTM-400DR connected to a Comet 2x4SR

AD

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Re: NVIS Antenna
« Reply #1 on: September 20, 2013, 11:29:29 AM »
Your best bet is to check your usuable freqs http://www.arrl.org/graphical-frequency-allocations where you can operate and start by scanning the bands listening. If you here someone call back. 

It that does not work call "insert call here" CQ, CQ, CQ 40 Meters NVIS & repeat.  Call in the blind for 3-5 minutes then move up or down the band qnd do it again.

What state are you located in?
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Tevin

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Re: NVIS Antenna
« Reply #2 on: September 20, 2013, 06:50:42 PM »
You need NATA Net:

http://www.natanet.info/index.php?option=com_content&view=article&id=205&Itemid=102 

The net runs every evening (including weekends) on 7.185 LSB and exists for the purpose of giving hams a venue for testing their systems and making contacts for awards. Hams from all over the country participate. They are super-nice and it's a perfect chance to give and receive signal reports from all over the place and see how well your setup works. It took me several months of checking in during all seasons and band conditions, but thanks to NATA Net I have a very accurate picture of what my station can and can't do. Be patient; sometimes they have thirty or more check-ins and it can take a while for your turn to come up. They also have nets on other bands but I don't know how busy they are.

By the way, NVIS is not a particular type of antenna design or technology. NVIS refers to to the way radio waves propagate in the atmosphere. In theory, any antenna can be used for NVIS, although some adapt better than others. The .pdf you link to does a pretty good job of explaining what NVIS is but is not clear that you don't necessarily need a special antenna to run NVIS. Maybe it's because they are in the business of selling antennas?  ;)




ghrit

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Re: NVIS Antenna
« Reply #3 on: September 20, 2013, 07:04:56 PM »
There are two kinds of ships.  Submarines and targets.
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Quiet1

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Re: NVIS Antenna
« Reply #4 on: September 21, 2013, 07:44:40 PM »
And more scoop...

This presentation has a lot of modeling with and without reflector wires.
http://www.w5jck.com/nvis/W5JCK-NVIS-Antenna-Presentation.pdf
His bottom line is that a single reflector wire hurts more than it helps.  I can say that when I took up the three reflector wires under my inverted-V, the usable bandwidth on 80 meters opened up by about 50%.  If there was any performance hit, it wasn't noticeable.

Another good presentation:
https://www.txarmymars.org/downloads/NVIS-Theory-and-Practice.pdf
It has some interesting results for quiet parts of the solar cycle on page 5.  (Maybe a 160 meter inverted V isn't so crazy after all....)

NVIS is interesting stuff.  For people like me who just want a solid 0-300 miles range of coverage from an economical wire antenna, it is darned near perfect.
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Captain Crunch

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Re: NVIS Antenna
« Reply #5 on: October 17, 2013, 12:14:31 AM »
For NVIS I'm either going to use something like the CHA EMCOMM II from Chameleon Antenna if I can add some radials: http://chameleonantenna.com/CHA%20EMCOMM%20II/CHA%20EMCOMM%20II.html

or

If I can't use radials (for any reason) the I'll use the CHA ZEPP still from Chameleon Antenna: http://chameleonantenna.com/Chameleon%20ZEPP%20ANTENNA/Chameleon%20ZEPP%20ANTENNA.html

I'll usually try to keep the antenna as horizontal as possible like the following:
http://chameleonantenna.com/resources/EMCOMM_II_Installation_NVIS.png

If I could I would definitively install one of their SKYLOOP around the yard but I don't have the room for it. For what I heard the SKYLOOP is pretty fantastic!

But the secret for GOOD NVIS performance is that ALL operators must use a NVIS configuration.


Tempstar

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Re: NVIS Antenna
« Reply #6 on: October 17, 2013, 05:02:08 AM »
I have a friend who bought the EMCOMM II and gets really good results with it. He uses a 50' piece of 1/16" stainless cable laid on the ground underneath as his ground plane. For NVIS it gets strung at 5' high horizontally, longer distance it goes at 30'. We found with it at 1' and no radial we get pretty effective ground wave out to about 3 miles.
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ClovisMan

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Re: NVIS Antenna
« Reply #7 on: October 21, 2013, 08:22:05 AM »
Update: I've tested this antenna and on 40m during the day, I have made contacts as close as 28 miles away (San Antonio, TX) and as far away 418 miles (Pineville, LA). I would say that it works better than advertised in the "skip zone".  Being located centrally in the state, I would say this is the ideal set-up for me. It allows communication coverage all throughout Texas.

Next I am going to make a OCF Dipole for more long distance comms. I'll post once I have that one going.
Wouxun KG-UV6D HT Dual Band
Yaesu FT-857D all band transceiver
Yaesu FTM-400DR connected to a Comet 2x4SR

jnr0104

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Re: NVIS Antenna
« Reply #8 on: October 21, 2013, 09:24:29 AM »
Clovis, send Tyler an email and set up a time ,freq . Lets see if we can get comms locked in between this AO and yours.

ClovisMan

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Re: NVIS Antenna
« Reply #9 on: October 21, 2013, 12:09:50 PM »
Clovis, send Tyler an email and set up a time ,freq . Lets see if we can get comms locked in between this AO and yours.
We are all supposedly doing that today at 7pm.
Wouxun KG-UV6D HT Dual Band
Yaesu FT-857D all band transceiver
Yaesu FTM-400DR connected to a Comet 2x4SR

unseenone

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Re: NVIS Antenna
« Reply #10 on: October 21, 2013, 01:01:17 PM »
Post your freqs, I would like to try and monitor...

BTPost

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Re: NVIS Antenna
« Reply #11 on: October 21, 2013, 06:59:09 PM »
Just a NOTE, here: If you put the Reflector Element under the Dipole to make your NVIS Antenna, and it is of a FIXED Design and Installed to be a Permanent part of your Station, you might want to consider, how to make it non-Resonant so that you no longer get the NVIS Effect, when you do NOT want it.  Here in Alaska We had a Fellow, KL7BB, (Crazy Bill) who did a lot of work in making a 40 Meter NVIS Antenna, to use during the Iditrod DogSled Race Comms during the Winters. He used the NVIS Version during the Days and the switched to the non-NVIS version after the Band changed, in the evenings. It was a real Pain to go put up the Reflector Element, and the take it down, when the Band Changed.  What he came up with is a Pair of small Hi-Voltage Relays, that were DC Controlled, from the Operating Position, and broke the Element into three shorter non-Resonant sections, which then negated the NVIS Effect of the Element.  Just Say'en.... YMMV....
« Last Edit: October 21, 2013, 07:01:56 PM by BTPost »
Bruce in alaska AL7AQ

Captain Crunch

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Re: NVIS Antenna
« Reply #12 on: November 04, 2013, 11:51:11 AM »
Hi everyone,

for those interested, chameleon just released some youtube about their NVIS EMCOMM II antenna here:

CHA EMCOMM II 40M & 15M Horizontal
Chameleon Antenna - EMCOMM II - 80M NVIS


Lamewolf

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Re: NVIS Antenna
« Reply #13 on: October 18, 2014, 10:11:22 AM »
I know this is an old thread, but I looked at the file from DX Engineering and the lengths of the dipoles are all wrong for the bands stated.  They are listed as 25' per leg for 40 meters and 38' per leg for 80 meters when they should be around 33' per leg for 40 meters and around 65' for 80 meters.  You could use a tuner with the lengths they stated but the efficiency wouldn't be the greatest !  Their long dipole should be resonant somewhere around 6 Mhz, not 3.5, and their short one would be resonant somewhere around 9.3 Mhz, not 7 Mhz.  SO this leaves me wondering why they choose these lengths ?