Extreme NVIS Antenna

(You can click on the pics to enlarge.)

There's more than one way to get on the air ... some good, some bad, and some just get by and there is something to be said for "Makin' do" with what you have.

I knew my neighborhood had antenna restrictions when we bought the house. We liked the house, so we took the bad with the good. I like it that there are restrictions to protect home values and no junk cars in the driveways. So you have to realize that those restrictions cut both ways but hopefully with a common good in mind.

Here is my HF antenna I have used successfully to work 80M and 40M. I am able to check in with the Sooner Traffic Net (3845 khz) on a regular basis as well as the weekly ARES Net (3900 khz). On 40M, I am able to check in with the 7290 Traffic Net on a daily basis.

During the Route 66 Special Event, I was able to make over 200 contacts on 80M to support the club's effort to participate in this fun special event.

Anyway, if you need an antenna for 80M or 40M, a G5RV is a good choice. While the G5RV is designed for 20M, it will work 80M and 40M with a tuner. The full-size G5RV is 102 feet long and fits nicely along my backyard wood fence. I do have a "wrap" on each end of about 10 feet, but the rest of the antenna is pretty much horizontal at about 5 1/2 feet off the ground.

The G5RV has a twin lead section that (ideally) should be vertical when the antenna is mounted 25 to 30 feet high. In my Extreme NVIS Antenna, I have the twin lead vertical for about 5 feet but then curved along the wood fence about a foot off the ground.

All I can say is that it works most of the time and I'm very glad for that!

... AR

IOTA Contest - July 24, 25

This weekend was the IOTA contest and it was fun. A little aggravating at times with pile-ups on some of the more "exotic" calls, but still a good time.

I only made 15 contacts, but these included two Hawaii stations, one New Zealand, and two Australia stations plus several states ranging from TX to MT, MA, NY, and OH. There were also a couple of Canadian stations included.

Most were on 20 meters but I had one HI, MA, and OH on 40 meters. The antenna I used was my G5RV JR mounted about 20 feet high on the roof. I used my Yaesu FT-840 most of the time running about 75 watts.

I should have made more contacts, but time was limited ... come on Sunspot Cycle 24!

...AR

Short Antennas & Automatic Tuners

Or, when do automatic tuners make sense over a manual tuner?

I just found a fascinating article in the May 2008 QST ... actually, it was a short response under Technical Correspondence to an article on automatic tuners. But it answered a question I've had for a long time.

One quote that caught my attention: "...typically, the [automatic] tuners have a tough time when coupling to 'short' antennas whose RR (feedline impedance, if you will) is lower than the prescribed 50 ohms."

The author continues, "...you'll note that in the general instance of the longer -- lower frequency -- antennas, where the feed point (Load) Z is below 50 ohms, the automatic tuners are reticent to couple efficiently, whereas if the feed line Z is above 50 ohms, the tuner is efficient."

A couple of things come to mind ... first, in dealing with short vertical antennas, the antenna Z can be very low, hence the need for radials and/or baluns to match closer to 50 ohms.

Second, if your antenna is "short", whether a shortened 160M dipole or a short vertical, with an impedance of less than 50 ohms, you might want to consider using a manual tuner for better matching range.

If your antenna sports a Z close to or even higher than 50 ohms, the automatic tuners can handle the match easier. The antenna design impedance is affected by a combination of antenna length and height above ground.

This does explain why my auto tuner in my KW TS-440 cranks and cranks to match my NVIS antenna (G5RV at 6 feet high) but quickly tunes on my 40 meter doublet at 20 feet high.

One of these days, I'll have to measure what the impedance is on each of these two antennas.

Something to consider ... AR

What is a Short Vertical Antenna?

I'm quoting from Jerry Sevick's (W2FMI) book "The Short Vertical Antenna and Ground Radial". A short antenna has been defined as one that is small compared to a wavelength.

He gives the following equation on p. 10:
Beta*h less than 0.5
where Beta equals 2*pi / wavelength and h is the height of a ground-mounted vertical.
BTW: the "less than" sign confused the HTML publishing process so had to remove it.

Solving for h gives us the following equation:
h less than 0.5 * wavelength / 6.283

For 40m antenna, the h is less than 3.2 m. If we use 130 feet for the wavelength, then h is less than 10.35 feet. The author uses 11 feet for his purposes.

He maintains that a 40m 1/4 wavelength ground-mounted antenna has a power gain of 1.62 when compared to the mythical isotropic radiator. This antenna is 33 feet high. The 11 foot vertical has a power gain of 1.513! Pretty impressive, don't you think? But HOW?


He further comments that "the very small value of its input resistance" is the important property that makes its capture cross-section nearly equivalent of a full 1/4 wave vertical. A ground mounted 1/4 wavelength vertical has a theoretical input resistance of 35 ohms and a 20 foot has an input resistance of about 8 ohms while the 10 foot antenna has about 2.5 ohms input resistance.

I'm not sure I understand all of this either, but it is very interesting (to me anyway). Well, I have some more to reading to do....AR

Short Wave Listening

Just listening to short wave broadcasts from Vietnam and China. Right now, I am using my 10M vertical - The antenna is 8 feet long and is ground mounted. Receiver is my FT-840 on AM. Times are UTC.

0340 - 0355 on 6175 kHz is the Voice of Vietnam. Signal is s7 to s8 on my s-meter with some QSB. The Listener's Service program is giving reports received from all over the world. This is an English language broadcast!

0355 - 0400 on 6190 kHz is the China Radio International signal. Signal is S9+. They just signed off from their English language broadcast, but the news program that came on at 0400 is also in English. Strange to hear our news from the Chinese perspective.

0430 - 0500 on 6140 kHz is the Radio Havana Cuba. Signal is S9. Had English language news followed by music. Great if you enjoy Cuban rhythm.

40M To Get Better After Mar 29

7100-7200 kHz shortwave broadcasts to cease (Link)

For many years the portion of the band from 7100-7300 kilohertz has been allocated to short wave broadcasters outside the Americas and not available to radio amateurs outside ITU Region 2. At the World Radio Conference WRC-03 in 2003 it was agreed that the broadcast stations would move out of the section 7100–7200 kilohertz on 29 March 2009 and that portion would become a worldwide exclusive amateur allocation afterwards


From Shortwave Central blog ... AR