Tech Net Notes May 29, 2009

On this evening's net the topic was NVIS. After a brief description of Near-Vertical Incident Skywave (much like the post below this one), we opened the net for check-ins.

ke5okt, Jim, checked in with a question. He has a KendeCom, model KRP-5000 repeater and can't find much information on it. He asked if anyone has information on this brand, such as how to find parts and documentation. kb5vdb, Ron, mentioned that aa5v, Steve, may have a repeater of that brand in his garage, and may know something more about them. Steve is a member of TRO and may be contacted through the club. If anyone has information they think Jim might be able to use about the KendeCom repeaters, he can be contacted at jim@mounds.org.

n5tda, Rex, mentioned that he has a G5RV up at about 25 ft., which would be less than 1/4 wavelength and would fall into the NVIS category. He mentioned that he was not able to get within the 500 mile skip zone at that height.

ke5lnn, Dave, asked if NVIS is in wide use by any particular amateur radio groups. In addition, Dave has a TE Systems 1412G, 2 meter amplifier. He says it works fine on two meter but doesn't work on 70cm. He has heard of a mod that can be done to allow it to work on 70 cm and wants to know if anyone knows how to install that mod. w5ydl, Dan, says he also has one of those amplifiers and that he too would like it to work on 70 cm, but doesn't know how to install the mod. Dave mentioned that he may be able to reach someone at TE tech support who can help.

ka0oxn, Rich, said that he had a 160M installed at about .o4 wavelength height that was good out to about 400 miles. He also had a 40M installed at 10 ft. that was good to about 300 miles.

na5dw, Dan, said that he would like to find a way to get his HF signal from Fairplay, CO to Denver, CO, about 90 miles. He tried a dipole hooked up to his truck's tailgate, on one end, and to a signpost on the other end, about 3 ft. high, 20M or 40M, and couldn't quite make the trip.

ae5ft, Gene, said that n5fem, Steve, was talking into the Dallas, Texas area on 40M, on the NVIS dipole mounted at 5 ft. at the last Route 66 event in Chandler Park. He also mentioned that he uses an NVIS antenna every day to check into the Oklahoma Sooner Traffic Net, which is a part of the National Traffic system Net. His antenna, he calls an "extreme" NVIS antenna, which is a G5RV mounted along the top of his wooden fence at about 6 ft, with about 10 ft. of wrap on each end, fed with about 30ft. of twin-lead and a short piece of coax. He says that he is about 90% effective getting into the net on 80M. He says he's worked both coasts during the Route 66 Contest where folks were trying to make contact with him as a Route 66 station. So it may not be all that good of a test, coast to coast.

ae5mn, Hank, mentioned that this might be an HF solution to his problem of finding something that would fit in with his neighborhood covenants.

kk5edd, Ed, said that he's in the process of building an NVIS antenna, from plans of Dr. Carl Gellenik, n6vng, with two 38ft. elements and then at 90 degrees from them, two 25 ft. elements. The design calls for a threaded center conductor on a SO-239 plug, which Ed is having trouble finding/fabricating. Ed would appreciate hearing back from anyone who might have information on how to find a threaded SO-239 center connector such as this.

ae5ft, Gene, mentioned also that in NVIS applications, we have to look at the maximum usable frequency. That is the maximum frequency that will bounce of (versus penetrating) the ionosphere. That "maximum frequency" can depend a lot on conditions, sunspot activity, and etc. Gene mentioned that 40 M is "iffy" on NVIS, which may explain na5dw's, problem making a 90 mile trip in Colorado. The other thing Gene mentioned, is that when you're looking at 80M NVIS, that's what most dipole installations are, to at least some degree. Few of us can afford to construct 120 ft towers for your dipole!

ke5und, Travis, checked in and mentioned that he's used NVIS technology inadvertently. He understands the principle but now knows what to call it. Travis asked if NVIS relates more to angle of take off. ae5ft, Gene, answered that yes, angle of take off is one of the parameters that NVIS defines. Travis mentioned also that this is probably why he can make it in to Albuquerque, NM but can't quite make the trip into Arizona.

NVIS (Near-Vertical Incident Skywave)

What is NVIS?

Near-Vertical (meaning somewhere around straight up) Incident (an event, something that happens) Skywave (the reflecting of a signal, usually RF, off the ionosphere). Think of it as pointing your antenna straight up and having the signal "shower" down all around you.

NVIS - compared to what?

Think of the two modes of antenna orientation with which we are most familiar: vertical and horizontal.

Vertical - line of sight, groundwave propagation

Horizontal - long-distance, skip

'Splain yourself!

If you can talk about 50 miles on a vertical antenna predictably, and on the horizontal plane you can pretty much count on shooting over most stations that are closer than 500 miles away, NVIS is a method that you can use to fill the gap (skip zone). NVIS allows you to have more reliable communications with stations within a 100-200 mile range.

Great! How do I do it?

You do this by directing your signal straight up. Rather than pointing your beam directly overhead, you can do it the easy way. Cut a dipole to the desired frequency, and install it less than 1/4 wave above ground. Last September at the Route 66 event in Chandler Park, N5FEM, Steve, installed one at about 5 feet and did very well with it. By installing it closer to the ground, you are using the ground as a reflector. In a sense, it becomes an upward pointed beam.


Putting One On Top of a Hill

Well...yes you can...but...with valleys generally containing more moisture than hilltops, often-times you get a better reflection in a valley. And, after all, you're directing your signal upward, so a valley may be more advantageous, especially if you're trying to avoid detection (military applications).


What Bands?

Generally speaking, 160M, 80/75M, 60M, & 40M is where you can use this system most effectively. As we have learned, the higher frequencies will tend to penetrate the ionosphere more, and reflect off the ionosphere less.


Why bother?

In an emergency or if you have friends within the dreaded skip zone (200 miles), this allows us to have fairly predictable communications. Skipping on the horizontal plane is not that predictable, and where it is predictable, may not be that useful. On the vertical plane, line-of-sight may not cut it. You often need more. NVIS fills the gap between the two.

You can read more about this at: athensarc.org/nvis.asp

Tech Net Notes May 13, 2009

Without much of a topic, the net began with a string of check-ins from Ron's, kb5vdb, group. There were storms looming around Oklahoma and Ron kept an eye on things for us with regular updates.

ke5yoo, Mike, started off with a question regarding a problem he was having with RFI. On 10 meters, Mike has been getting into his (and worse yet, his neighbors') wireless phones. Mike wanted to know if that was a common problem (on 10 meters) and if anyone had experience with fixes for that kind of problem. ke5omv, Don, stated that he had a similar problem on 10 meters, on with his computer, when he keyed up the computer locked up.

w2csl, Bob, asked what frequency the phones were on and mentioned that (older) 50 Mhz phones are near a harmonic of 10 meters. ke5yoo, Mike, responded that the phones were in the 2 Ghz range.

kb5vdb, Ron, suggested that K-COM makes a line of telephone filters that are sold through AES and can probably be found in AES's online catalog. In addition, the higher he could get his 10 meter antenna, the better for reducing chances of nearby RFI.

ae5mn, Hank, checked in and mentioned that his Fong Dual-Band Twin-Lead J-poles are doing well. He mentioned that he was surprised at how well his smaller Fong antenna was doing mounted in the attic. He said he enclosed it in a protective sleeve normally used around fluorescent tubes. It's a thin, clear tube of plastic with caps. Hank has it installed near a gable in the attic. Though he normally has problems getting into the 910 repeater, with that set-up, he seems to be doing fine.

ke5wga, Ray, checked in and gave a report on his GP9 look-alike, the Tram WP 1481. Ray just installed it last week and has it about 25 ft. in the air. Ray mentioned that he felt he did fairly well moderating the Saturday Night Simplex Net with it. He said he was able to talk to all that he heard.

ke5yoo, Mike, was asked what kind of antenna he was using that caused the RFI with wireless phones. Mike responded that it's a G5RV junior.

wb5uuw, Earl, cautioned to make sure that the coax, where you hook up to the balun is 35 ft. long. The ladder line should be about 17 ft. long with a 4:1 balun.

ke5uiu, James, said that he has a G5RV (full size) with 45 ft. of ladder line, a 1:1 balun, a 100 ft. of coax and can talk well on it. He would like to be more directional and is planning on a rotating dipole for sometime in the future. Being in Porum, he can hit the 910 repeater with his 4-element beam on low power. To get to Bartlesville on 2-meter he has to bump the power up to 25 watts.

kk5edd, Ed, questioned if anyone had built an NVIS, 4 radial, antenna. ae5pb, Paul, came back and mentioned some positive experience he had with it, through the military and that two legs are cut for 80 (moderator: I think!) and the other two are cut for 60 meters.

ke5icx, Tom, checked in from a Broken Arrow motel room. He is visiting the area and heard the net.

End of Tech Net

(Note: If you have any corrections or additions to these notes please leave them in the comments section. I did not take as good of notes as I would have liked, so if there are other cogent points that were made (or that you would like to now make)that I missed, please let me know.