End-fed angle and NVIS, observations.

[gil]

I have noticed an interesting and expected effect when using my PAR 10/20/40 end fed either vertical or at 45 degrees. Hung vertically I always made DX contacts thousands of miles away with very little power. With the antenna at 45 degrees it seems my range is of a few hundred miles. I get lots of contacts on 40m from the North of France to England. 150 miles seems common (Lille to London). No local contacts though, the antenna would have to be horizontal for that.

I expect my 80m Windom will be great for NVIS mounted at 20ft above ground, but not for DX. I need a fiberglass pole to mount my end fed vertically... Ether a 17ft or 33ft mast. 33 would be much better of course.

Gil

[NWARadio]

How do you plan to mount your NVIS that high? Will this be on your boat or on land?

[gil]

On land, I lost my boat. 20ft. isn't very high, as dipoles should be a half wavelength from the ground..

Gil.

[NWARadio]

I knew you'd lost your boat (sorry about that, btw) but I wasn't sure if you were planning on getting another one.

[K7JLJ]

For NVIS I thought the 15Ft was the upper limit?


- Jim

[cockpitbob]

I just refreshed my reading on NVIS.  The rule of thumb is to have the antenna 1/8 to 1/4 wavelengths above the ground.

There's lots of good reading out there, but much of it seems like excessive fussing to me.  Use 10MHz and below.  Use a horizontal antenna 1/8 to 1/4 wave above the ground.  Done.

Here's a 40 page NVIS Theory and Design from the Texas Army MARS orginaztion.  It seems pretty good though at 40pgs a bit long.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjinuz2xq_NAhUsyoMKHQFOBv4QFggqMAI&url=https%3A%2F%2Fwww.txarmymars.org%2Fdownloads%2FNVIS-Antenna-Theory-and-Design.pdf&usg=AFQjCNEU9J8XhMfNst7Eu82jp07xvck7aA&sig2=_aoIW3j6Dz95DYfOtikjxg

[RichardSinFWTX]

From my time in MARS I seem to remember our antennae were to be 12 - 16' up...or 3 to 4 camo poles at the apex.

[Quietguy]

Another thing to remember is there is not a sharp break between NVIS to not-NVIS.  There is a radiation pattern transition that goes from favoring an upward radiation pattern (NVIS) down to a radiation pattern that favors the horizon (not-NVIS).  Reality says that most ham 80 m dipoles have at least some NVIS characteristics because it is really hard to get them high enough in the air to avoid it.  As Bob mentioned, 1/8 to 1/4 wavelength above ground works for NVIS, and at 80 meters that is roughly 30 to 60 ft.  Lobes can come and go depending on height above ground and nearby objects.

A few years ago I had a fan dipole up about 50 feet that included 80 meters and it worked extremely well for daytime SSB contacts with friends out to about 200 miles.  Then at night I had reliable peer to peer 80m Pactor 3 links with friends in Virginia, Louisiana and Southern California from my more or less rural location in SW Washington state.  The limiting factor was really local QRM/QRN on their end.  That simple 80/40/20 fan dipole between trees at about 50 feet was pretty much a great all-purpose solution.  Nationwide daytime 20 meter Pactor 3 was a slam dunk and 80 meter daytime NVIS was a piece of cake.  Either 40 or 80 worked well for distance links at night, depending on conditions.

At the time I used WL2K as backup email and my routine was to hit an 80 m station about 100 miles away during the day and the San Diego Yacht Club station (about 1000ish air miles) on 80m at night.  If for some reason the "local" 80m station wasn't available during the day, 20 m would usually get me the San Diego station if it's frequency was clear (which was usually not the case during RTTY contests).

Wally

[K7JLJ]

I have found my 80M in sloper tends to reach 100-600 miles so there is definitely a mix going  on even with that non-traditional NVIS config.

If I ever get whisper working I'd like to play with this a lot more


- Jim

[Lamewolf]

For NVIS I thought the 15Ft was the upper limit?


- Jim

Anything under a quarter wave high will work for NVIS to a point.  My OCFD is 35' at the center and 20' on the ends and works great for NVIS and I've also worked a lot of DX with it.

[Lamewolf]

For NVIS I thought the 15Ft was the upper limit?


- Jim

Actually you can vary the distance of your communications somewhat by adjusting the height of the antenna.  As you go up higher, the upward pattern broadens and is broader when it arrives back to earth, but go too high and it radiates more toward the horizon for DX type operation.  But for short range comms, the military did use a maypole type antenna with a center feed point at about 15' and crossed dipoles cut to different frequencies called the AS 2259.  I think one was cut for around 5.9 MHz and the other around 9.1 mhz.