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10M Beam
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by ve4mm on December 6, 2003
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What will work better; 2 Hy Gain 5 element 10M beams stacked with a stack match or one Force 12 7 element 10M monobander? Any ideas???? Thanks, Mike.
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RE: 10M Beam
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by N2MG on December 9, 2003
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No question, go with the stack. Try the Terrain Analysis (TA) software (free with the ARRL Antenna Book) to see the effectiveness of stacks.
You can achieve far more useful gain as you change the optimum signal arrival angle by selecting combinations of the antennas. Plus, if one antenna craps out, you have the other.
You don't even have to turn both of them right away (though it IS desirable to do so) - leave the lower one pointed at Europe (or other high-QSO-volume area) and rotate the top one.
If you have two 10m beams, a stack at 60 feet and 30 feet should work great. One could argue that as sunspots decline (as they are - or should be - doing now) a higher stack is desired - say 70' and 40'
Keep the spacing around 25' to 30'.
Mike N2MG
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RE: 10M Beam
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by K1NQ on December 9, 2003
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That really depend on what you are trying to do. If you want to run JA's then the 8 element killer will work just fine. It must be high enough to have good gain at the required take off angles. If you want to run europe or a general purpose contest antenna then go with the stack. You can cover more take off angles with the stack, Switch between upper and lower to optimize, skew the top and bottom antennas to cover a broader area such as N and NE at the same time. You can beam in 2 diffrent directions with the stack.
You will spend less time tweaking a 5 element vs an 8 element when aiming it. An 8 element yagi is very sharp and requires a good deal of care when aiming it.
I am a firm believer in casting the right sized foot print. To run EU the angles are 30 to 60 degrees to cover the area from the east coast. I try to match my antenna 1dB beam widths to cover that zone. I like 4 element 10m yagi antennas on ~.45 WV boom. That gives me about 1db roll off over 40 degrees. A 5 element hygain 10m will give you -1.7 dB roll off over 40 degrees. That also work well. In contesting from the east coast, 80% will be EU so that where I optimize my antennas
K1NQ
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RE: 10M Beam
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by kr6x on December 15, 2003
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You're asking a real complex question. This is about the difference between low angle stuff -- under 6-7 degrees -- and real low angle stuff -- 1, 2, and 3 degrees. Stacking antennas helps at low angles, but doesn't help at real low angles. From New England, some of Europe is at low angles and some of Europe is at real low angles. From New England, New Mexico is at real low angles and California is at medium high angles -- about 10 degrees.
Lets assume for the moment that the top antenna in the stack or the single long boom yagi would be at the same height, but in neither case overly high. At best, at extremely low angles, the gain of the stack can be expected to perform just like the single higher antenna from the stack performs. That's the gain, not the F/B. Yes, this is the first rule of thumb that needs to be understood about stacks. Well, the next three rules of thumb are that
2) for optimum gain, first the separation between the two antennas should be approximately 5/8 wavelength plus half of the yagi boom length
3) for optimum pattern control, the lower antenna should be placed at half of the height of the upper antenna
4) an attempt should be made to place the two antennas at heights that yield approximately the same feedpoint impedences so that the power match delivered to the two antennas can be made accurate for optimum pattern control
With rule of thumb number 4 you have a limitation that can be overcome with careful simulation and slightly unequal feedpoint matching, but the dangers of unequal feedpoint matching are a terrible prospect of introducing phase mismatches that result in really screwing up the stack performance and are probably not worth attempting.
AAAHHHH....
Let's look at this. I'm not sure if this is immediately obvious to you. The truth of the matter is that I prefer the stack, but then again I'm a Californian who places highest priority in domestic contests and not a died in the wool DX contester from New England. Other contesters may make a different decision.
Really you need to know the truth about stacks before you build one and are disappointed. You need to understand rule of thumb number 5.
A single long boom yagi that has been simulated right translates into a real working antenna with positively superior listening performance. From New England you can point one of these at Europe and get vastly superior listening capability. Stations off the back can be truly rejected, making the antenna a real killer for hearing the weak ones in your run. If you hear everyone in the run, you rip through the contacts and everyone hears your clean, crisp QSOs and thinks "I can work this guy easily if I call a couple more times!"
But if you read carefully about stacks and their performance and do a whole bunch of antenna simulation with NEC2, NEC4 or MiniNEC you'll learn that the front-to-back ratio of a yagi falls to pieces a bit when you stack two of them. If you do a whole lot more simulation, you'll learn that you can't quite fix the front-to-back of the stack by retuning. Weeks of automated optimizing later, you're still looking at front-to-back ratios that are a couple of dB's down from a single yagi tuned the way you like it.
This translates to a little bit more interference from those W4's and W5's crowding your frequency. Your pile-up hears the trouble you're having getting callsigns right and decides that they don't want to hang around and struggle to work you.
Well, remember the first rule of stacks. At the very low angles, your stack will work like the top antenna in the stack. At slightly higher radiation angles things improve. Yeah, that's right. The real magic of stacks is not the performance at the lowest usable radiation angles. It's really the performance at medium to higher angles.
Don't get me wrong. You can build a stack higher to get superior performance at the low angles. An example of this would be a 10 meter stack at 100 feet and 50 feet. You'd be going beyond the spacing required to get maximum gain. But 100 feet over 50 feet results in some violation of rule number 4, so a better choice would be 140 feet and 70 feet. Ah, even better, 4 stacked yagis at 140/105/70/35.
Well, you asked me, don't complain that some of the things that I suggest sound like pipe dreams. The truth is that a 2 stack at 70 and 35 feet for 10 meters really works great at higher angles, and pretty fair at lower angles. Few will outdo you. But I've operated from somewhere that the capability is greater.
At W6EEN there's a 3 stack at 105/70/56 that has some real superior capabilities. Use the lower two antennas in an SS contest with high sunspot conditions during the middle of the day, then use the upper two antennas or feed all three when twilight approaches. There's a short period when the apparent height of the ionosphere goes really high and skip goes really long that stations in W1 and W2 can be worked in one hop, and the upper two antennas really come into their own. During DX contests Japan and Europe are generally worked on the upper yagi or on the upper 2 yagis stacked, but you never can seem tp predict which combination will work the best to Central America or South America. Hawaii is almost always best on the lower antenna. Couple that with a simple truth -- the upper antenna seems a bit more immune to QRNN type noise sources than the lower and makes a better receiving antenna on almost every DX signal.
Summarizing, W6EEN's stacks on 10 and 15 meters and W6RU's old 20 meter stacked 6 elements at 120 and 60 feet made me a big believer in stacks. But most of the time I wanted to transmit on the stack and receive on the upper yagi alone. If you want to go higher than 70 and 35 feet on 10 meters you'll have to be careful about loss of pattern control. For best utility DXing a longer boom antenna carefully tuned and placed as high as possible will likely give you better performance more of the time, but contesting is about having no holes in your wave angle coverage, and stacks are better at that.
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RE: 10M Beam
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by ve4mm on December 18, 2003
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Thanks for all the GREAT comments guys. Much appreciated. Too bad the Sunspots are on the downside. On the upside I have some time to plan the new array. I do like 10M and would like to have a decent signal from VE4 land. 73 Mike.
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RE: 10M Beam
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by W4ZV on December 19, 2003
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Here's an example of stacking over my actual terrain:
http://users.vnet.net/btippett/terrain_&_toa's.htm
This software is now included with the 20th edition of the ARRL Antenna Book. Antennas are 3 modified KLM 610's at 35/70/105' using K6STI's Yagi Optimizer...see before and after data here:
http://users.vnet.net/btippett/yagi_optimizer_7_0.htm
This system holds the current SOSB10 USA records in both modes for CQ WW, ARRL DX and CQ WPX, i.e. it works as expected.
73, Bill W4ZV
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RE: 10M Beam
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by vk2cz on January 13, 2004
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While I've never used a stack on HF, I now use a 65' (19m) long 8 ele yagi on 10m, and I can knock out local S9 stations down to a 3by1, and follow skew propagation paths easily.
8 element designs seem to be able to maintain constant and good F/B over the full band too for some reason - after carefull messing with the yagi programs. My earlier smaller 5 and 7 ele yagis had F/B that was very frequency dependant, and more noise pickup too.
I have local governemnt laws keeping antenna height down.. but having a nice long boom yagi keeps everything manageable, simple to erect, simple to feed and rotate. The end director of the yagi whips around at ~20mph, making it quite a sight when turning it.
Put up the biggest antenna you can ! I want to do an 80' yagi next..
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