|
Competitive advantage in the terrain The SteppIR yagi is usually at 25 to 30 feet in height (tower cranked down) but can be cranked up to 47 feet. When I point toward Europe, the antenna performs as well as -- and in some cases better than -- an identical antenna on a 120' tower, due to beneficial surrounding terrain that drops off sharply in that direction. Yes, I said 45' here compares favorably to 120' on a flat landscape (say, prairie country), if you believe in terrain advantages. Similar benefits are found when working Africa, Canada, the U.S., and South America. In fact, working Canada and the U.S., I no longer crank up the tower and still get great results due to the higher take-off angle combined with the much lower far-field topography at this QTH. Coax choke for a tribander -- random or solenoid winding? I was plagued by odd SWR issues with my Mosley Classic-33 for a couple of years, ever since installing a randomly-wound coax choke at the feedpoint. Symptoms included working a lot of stations off the back of the beam -- for example, working W4s while beaming Asia, or working W6s while beaming Europe. Also, when using higher power -- say 600 watts or more on RTTY or high-rate CW -- the amplifier would occasionally reduce its output (plate current would rise and output power would fall) and SWR would shift a bit. If I stopped transmitting or lowered power for a while, everything returned to normal. I was using about 8 turns of RG213 taped together in a loop about 6" in diameter. People who know a lot more about these chokes than I do advise using such a bunch-wrapped device only at lower HF frequencies, such as 30M, 40M and below. In my opinion, Ed Gilbert WA2SRQ, has really nailed down the data on which kind of coax coil "air wound" balun or choke to use. Of course, you can use ferrite core baluns, bead baluns and other types of choking devices, but air-wound coax chokes -- in a close-spaced linear coil, not in a scramble-wound bunch -- appear to work as well as any, and they cost only as much as a few extra feet of coax cable. ANYONE can build one. See WA2SRQ's coax choke testing Following WA2SRQ's advice, in Nov. 2008, I replaced the 8-turn randomly wound loop of coax with a solenoid-wound coax choke. The turns are wrapped side-by-side, 7.5 turns on a 4.25" form (made out of an old white plastic canister). Initial testing showed a restored front-to-back performance, but the power-handling problem reappeared during Sweepstakes Phone and CQWW CW later in Nov. 2008. In April 2009, I replaced the Classic-33 antenna with a SteppIR 3-element yagi. I also replaced the coax up the tower. Although the old coax appeared to be fine, I now suspect that it had water inside the jacket, which would have caused problems after running higher power for a while. The new coax and SteppIR antenna handle all the power I have every thrown at it. Info about SWR on the Mosley Classic-33 tribander The Classic-33 is a truly great triband yagi. Yes, it has traps and it's a design from the 1950s, but it has great forward gain thanks to the 18-foot boom and Mosley's little-known balanced capacitive matching system which runs wires inside the radiating driven element. The downside of the Classic-33 is its very narrow SWR bandwidth on 20M. Using the factory-specified CW settings, the antenna offers a very competent 1.5:1 or better SWR over most of 15M and 10M, but on 20M the SWR is 1:1 at the bottom of the band (great) but 2:1 only 150 khz away at 14.150 Mhz. At the top of the Phone band, 14.300, the SWR is beyond 4:1 and totally unusable. I asked Bill K1XT, a former owner of a Classic-33, about his experience tweaking the 20M SWR by adjusting the driver's tips. He confirmed that a small adjustment can move the useful SWR bandwidth to where you need it most. The antenna's sadly narrow bandwidth doesn't change, but you can move the sweetspot around. To more comfortably operate in Sweepstakes Phone 2008, my plan is to tweak the 20M SWR by shortening the tips (outboard from the 10M and 15M traps) by 1.5" -- essentially moving the lowest SWR point up the band by 100 khz. Here's the existing SWR sweep (using the factory's CW settings):
Here's a look at the SWR chart showing before-and-after under-2:1 SWR bandwidths: Here
is the current configuration of the half-squares, my 40M EU raised
vertical array, and the location of my new dual 80M verticals in
the woods.
(Click image to view full-size in a new window) April
2008 The 160M inverted-L has been moved. I was feeding the bottom of the wire hanging down in the middle of the back lawn, with an SO-239 feedpoint mounted on the same post that supported my now-dismantled ground-mounted all-band vertical. Now, the 160M coax feedpoint (SO-239) is attached to the top rail of my chainlink fence. Will be pulling up all the old radials on the back lawn, so I can mow properly without constantly stopping to fix or move errant radial wires. Will arrange a few raised 160M 1/4-wave radials for the 160M antenna. 160M SWR is high at over 2:1 right now, but expect to fine-tune over the summer in plenty of time for fall's top-band contesting. March
2008 I recorded a few seconds of VP5/W5CW working stations on 40M around 0340Z on March 26, 2008. Switching between the two half-squares, you can hear his signal rise on one half-square and, at times, almost disappear on the other half-square (about 90 degrees off his bearing in the Turks and Caicos Islands, 3,200 miles away). Listen to audio (MP3, 400kb) I also recorded CM6RCR in Cuba, showing an even more dramatic difference between the two half-squares. Listen to audio (MP3, 727kb) There is one issue with the new EU half-square location -- the horizontal wire runs over part of the house, so if I run high power, the RF gets into one of our TVs (the kids use an old 26" TV to play almost as old classic Nintendo video games in one of their bedrooms... Go figure, they have XBox 360 on a 52" HDTV in the family room. Kids these days, I tell ya). So, I have discovered that the forgotten 40M 2-element raised vertical array I have hanging in the woods (now nicely tucked in between the 80M verticals) works really well for EU paths. It's a passive array, fed at the north element, with the south element cut 5 percent longer and spaced 30 feet or so a bit southwest, so the signal fires a bit northeast, almost perfectly at Europe (a bearing of 30 degrees). May
2007 The current setup is:
Observations about the current antennas: For 40M, I have now put up two half-squares -- one for E-W (slightly south-east facing) and one for N-S (just slightly north-east facing). Broadside patterns are nice and wide, with strong end-nulls. Often, these antennas give me 4 s-units between signals when switching. For example, if listening to a W6 on the antenna facing W6, I can switch to the antenna facing E-W and an S9 signal drops to S-4 or S-5. It's great. The horizontal wires on these are about 70', and the vertical legs about 35' -- just added a bit length to each to get the SWR down. It's 1.1:1 from 7.000 to 7.070 on my EU/W6, and a bit higher on my JA/US-VE-Caribbean half-square. Last summer (August 2006), I installed the 18AVT/WB ground-mounted vertical in the back lawn (see below for details). The update is: aluminum fence wire began disintegrating in the lawn by spring 2007, about nine months after installation, and it all has to be replaced. I continue to scrounge insulated copper wire, most of it very light guage telephone-wire (22ga or so). Sad to think how many days I spent running the 36 radials, all now to be re-done with insulated copper. The hope is this wire will have a much longer lifespan. Many have reported great success with pinning wire on top of the lawn, and I can verify that the lawn does, indeed, grow over and draw the wire into the mulch layer. The aluminum was invisible after a few weeks -- at least, where I could get lawn staples into the hard-packed earth. The radial system also serves the wire 160M inverted-L. This wire is actually clipped into the base of the Hy-Gain trapped vertical, which has allowed me to basically use that vertical on 160M. It's a touchy feed SWR-wise... and has never been as good as when, originally, I fed the 160M L with its own coax (even with a much lesser radial system). Grand plans: Today (took Friday as a vacation day to prep for WPX CW this afternoon) I am adding an SO-239 to the vertical base, to which I will attach the 160M inverted-V wire and a new standalone 80M vertical wire of 67'. Will feed them from a new coax run to the base in the lawn, and run as many replacement radials as I can manage (even temporarily till I can do a proper stapling job). WPX CW doesn't have a lot of 80M activity, so the trap vertical would probably be sufficient, but I want to see what a half-decent radial field and a true 1/4-wave vertical can do at the bottom of the solar cycle. We are smack-dab in the minimum -- today, zero sunspots again. But by the fall contest season, I'll be thankful to have sorted out a useful antenna for this often valuable band in both DX and domestic contests. August
2005 The rope supports:
Because the support rope actually runs above part of my HF yagi, I have decided to re-route it to another tree in the yard -- but it will be just 40' high to the West, and only 70' from the tall pine to the East. I will be able to keep the 160M Inverted-L, though the horizontal portion will slope downward. I may be able to keep the 40M two-element beam, but it will point slightly NE now. The
80M two-elements never really worked as a beam, so I may go back
to a delta loop -- one I had last winter worked very nicely (Worked
Senegal the night before CQWW CW!). At 80' apex, the delta will
fit all right on a slight diagonal NE-SW. As it's only slightly
directional, I should still have good omni coverage and very nice
low-angle (but low-gain) performance. Phased 40M Verticals: In the forest on the slope below our back yard, I used to have two 40M verticals suspended from a rope between two pines. Read about the 40M wire vertical array Mosley Tribander: My primary 10M-20M antenna is a three-element Mosley Classic 33 (CL33) on a 40' tubular crankup, tilt-over tower. The yagi is at about 45' when the tower's fully extended, and the mast continues 10' up to a 40M rotary dipole. All-Band
Vertical: In early August 2006, I took an old HyGain 18AVT/WB
vertical off the chainlink fence where it was useless, and put it
on the ground in the middle of the large back lawn. I spent a couple
of vacation days putting down about 1,500 feet of aluminum fence
wire on the lawn in 36 radials of varying lengths (averaging over
40'). Because the vertical is directly below the rope supporting all my wire antennas, I will be able to tie the 160M Inverted-L base to the same radial field -- have never had any real radials for that antenna and look forward to seeing how it plays this winter. July
2004 The highest wires are the 80m and 40m full-size dipoles at about 65', running from east to west. I have a 20m dipole up there, too, which works very nicely into Europe.
I have a half-size G5RV (52' is the space between available trees) at about 45' in the air, running roughly north to south. This is my primary antenna for working Japan and most of North America. Even tunes on 80m in a pinch. I also use a fence-mounted HyGain 18AVT/wb vertical to fill in on 80m when the high E-W dipole is in the wrong orientation. For the July NAQP RTTY test, I rigged up my old 2-element wire tribander, which slopes from one tree at 45' or so down to 15'. Supposed to work well like that. Will know in an hour or so how it plays in the contest. A couple of weeks after we moved, and my first wires were up, the neighbor asked my father-in-law "how did he get those up so high?" They were astonished to learn that I had used a slingshot and fishing line. 80M
Wire Vertical Phased Array Project 40M
Rotatable Dipole Project My
Hex Beam Project Spider
Beam Group on Yahoo DF4SA
Spider Beam Site
|
